diff --git a/crates/lingua/src/providers/google/adapter.rs b/crates/lingua/src/providers/google/adapter.rs
index 6133d954..b4113847 100644
--- a/crates/lingua/src/providers/google/adapter.rs
+++ b/crates/lingua/src/providers/google/adapter.rs
@@ -31,6 +31,11 @@ use crate::universal::{
     UniversalStreamChunk, UniversalUsage, UserContent,
 };
 
+/// Internal extras key used to stash generationConfig fields that don't have
+/// universal equivalents (candidateCount, speechConfig, responseModalities, etc.)
+/// so they survive a roundtrip through the universal format.
+const GENERATION_CONFIG_EXTRAS_KEY: &str = "_generationConfigExtras";
+
 /// Adapter for Google AI GenerateContent API.
 pub struct GoogleAdapter;
 
@@ -67,37 +72,49 @@ impl ProviderAdapter for GoogleAdapter {
             .map_err(|e| TransformError::ToUniversalFailed(e.to_string()))?;
 
         // Extract params from generationConfig (now typed in params struct)
-        let (temperature, top_p, top_k, max_tokens, stop, reasoning) =
-            if let Some(config) = &typed_params.generation_config {
-                let max_tokens = config.max_output_tokens;
-                // Convert Google's thinkingConfig to ReasoningConfig
-                // thinkingBudget: 0 means disabled
-                let reasoning = config.thinking_config.as_ref().map(|tc| {
-                    let is_disabled = tc.thinking_budget == Some(0);
-                    let budget_tokens = tc.thinking_budget;
-                    // Derive effort from budget_tokens
-                    let effort = budget_tokens
-                        .map(|b| crate::universal::reasoning::budget_to_effort(b, None));
-                    crate::universal::ReasoningConfig {
-                        enabled: Some(!is_disabled),
-                        effort,
-                        budget_tokens,
-                        canonical: Some(crate::universal::ReasoningCanonical::BudgetTokens),
-                        ..Default::default()
-                    }
-                });
-                let stop = config.stop_sequences.clone().filter(|s| !s.is_empty());
-                (
-                    config.temperature,
-                    config.top_p,
-                    config.top_k,
-                    max_tokens,
-                    stop,
-                    reasoning,
-                )
-            } else {
-                (None, None, None, None, None, None)
-            };
+        let (
+            temperature,
+            top_p,
+            top_k,
+            max_tokens,
+            stop,
+            reasoning,
+            seed,
+            presence_penalty,
+            frequency_penalty,
+        ) = if let Some(config) = &typed_params.generation_config {
+            let max_tokens = config.max_output_tokens;
+            // Convert Google's thinkingConfig to ReasoningConfig
+            // thinkingBudget: 0 means disabled
+            let reasoning = config.thinking_config.as_ref().map(|tc| {
+                let is_disabled = tc.thinking_budget == Some(0);
+                let budget_tokens = tc.thinking_budget;
+                // Derive effort from budget_tokens
+                let effort =
+                    budget_tokens.map(|b| crate::universal::reasoning::budget_to_effort(b, None));
+                crate::universal::ReasoningConfig {
+                    enabled: Some(!is_disabled),
+                    effort,
+                    budget_tokens,
+                    canonical: Some(crate::universal::ReasoningCanonical::BudgetTokens),
+                    ..Default::default()
+                }
+            });
+            let stop = config.stop_sequences.clone().filter(|s| !s.is_empty());
+            (
+                config.temperature,
+                config.top_p,
+                config.top_k,
+                max_tokens,
+                stop,
+                reasoning,
+                config.seed,
+                config.presence_penalty,
+                config.frequency_penalty,
+            )
+        } else {
+            (None, None, None, None, None, None, None, None, None)
+        };
 
         // Convert tools using typed conversions
         let tools = typed_params
@@ -127,9 +144,9 @@ impl ProviderAdapter for GoogleAdapter {
             tools,
             tool_choice,
             response_format,
-            seed: None, // Google doesn't support seed
-            presence_penalty: None,
-            frequency_penalty: None,
+            seed,
+            presence_penalty,
+            frequency_penalty,
             stream: None, // Google uses endpoint-based streaming
             // New canonical fields - Google doesn't support most of these
             parallel_tool_calls: None,
@@ -142,12 +159,50 @@ impl ProviderAdapter for GoogleAdapter {
             extras: Default::default(),
         };
 
-        // Use extras captured automatically via #[serde(flatten)]
-        if !typed_params.extras.is_empty() {
-            params.extras.insert(
-                ProviderFormat::Google,
-                typed_params.extras.into_iter().collect(),
-            );
+        // Collect Google-specific extras: serde-flatten unknowns + known fields
+        // that don't map to universal params.
+        let mut google_extras: Map<String, Value> = typed_params.extras.into_iter().collect();
+
+        if let Some(v) = typed_params.safety_settings {
+            google_extras.insert("safetySettings".into(), v);
+        }
+        if let Some(v) = typed_params.cached_content {
+            google_extras.insert("cachedContent".into(), Value::String(v));
+        }
+
+        // Preserve generationConfig fields that don't have universal equivalents.
+        // Serialize the whole config, strip fields we already handle, keep the rest.
+        if let Some(config) = &typed_params.generation_config {
+            if let Ok(Value::Object(mut config_map)) = serde_json::to_value(config) {
+                // Remove fields handled canonically above
+                for key in &[
+                    "temperature",
+                    "topP",
+                    "topK",
+                    "maxOutputTokens",
+                    "stopSequences",
+                    "thinkingConfig",
+                    "responseMimeType",
+                    "responseSchema",
+                    "seed",
+                    "presencePenalty",
+                    "frequencyPenalty",
+                ] {
+                    config_map.remove(*key);
+                }
+                // Remove null entries
+                config_map.retain(|_, v| !v.is_null());
+                if !config_map.is_empty() {
+                    google_extras.insert(
+                        GENERATION_CONFIG_EXTRAS_KEY.into(),
+                        Value::Object(config_map),
+                    );
+                }
+            }
+        }
+
+        if !google_extras.is_empty() {
+            params.extras.insert(ProviderFormat::Google, google_extras);
         }
 
         Ok(UniversalRequest {
@@ -220,13 +275,23 @@ impl ProviderAdapter for GoogleAdapter {
             .map(|r| !r.is_effectively_disabled())
             .unwrap_or(false);
         let has_response_format = req.params.response_format.is_some();
+        let has_gen_config_extras = req
+            .params
+            .extras
+            .get(&ProviderFormat::Google)
+            .and_then(|e| e.get(GENERATION_CONFIG_EXTRAS_KEY))
+            .is_some();
         let has_params = req.params.temperature.is_some()
             || req.params.top_p.is_some()
             || req.params.top_k.is_some()
             || req.params.output_token_budget().is_some()
             || req.params.stop.is_some()
+            || req.params.seed.is_some()
+            || req.params.presence_penalty.is_some()
+            || req.params.frequency_penalty.is_some()
             || has_reasoning
-            || has_response_format;
+            || has_response_format
+            || has_gen_config_extras;
 
         if has_params {
             // Convert ReasoningConfig to Google's thinkingConfig
@@ -254,6 +319,9 @@ impl ProviderAdapter for GoogleAdapter {
                 max_output_tokens: req.params.output_token_budget(),
                 stop_sequences,
                 thinking_config,
+                seed: req.params.seed,
+                presence_penalty: req.params.presence_penalty,
+                frequency_penalty: req.params.frequency_penalty,
                 ..Default::default()
             };
 
@@ -262,11 +330,30 @@ impl ProviderAdapter for GoogleAdapter {
                 apply_response_format_to_generation_config(&mut config, format);
             }
 
-            obj.insert(
-                "generationConfig".into(),
-                serde_json::to_value(config)
-                    .map_err(|e| TransformError::SerializationFailed(e.to_string()))?,
-            );
+            let mut config_value = serde_json::to_value(config)
+                .map_err(|e| TransformError::SerializationFailed(e.to_string()))?;
+
+            // Strip null entries (e.g. responseSchema which is Box<Option<Schema>>
+            // and always serializes, producing null when None)
+            if let Some(config_map) = config_value.as_object_mut() {
+                config_map.retain(|_, v| !v.is_null());
+            }
+
+            // Merge back generationConfig extras (candidateCount, speechConfig, etc.)
+            if let Some(extras) = req.params.extras.get(&ProviderFormat::Google) {
+                if let Some(Value::Object(config_extras)) = extras.get(GENERATION_CONFIG_EXTRAS_KEY)
+                {
+                    if let Some(config_map) = config_value.as_object_mut() {
+                        for (k, v) in config_extras {
+                            if !config_map.contains_key(k) {
+                                config_map.insert(k.clone(), v.clone());
+                            }
+                        }
+                    }
+                }
+            }
+
+            obj.insert("generationConfig".into(), config_value);
         }
 
         // Add tools if present
@@ -296,6 +383,10 @@ impl ProviderAdapter for GoogleAdapter {
         // Merge back provider-specific extras (only for Google)
         if let Some(extras) = req.params.extras.get(&ProviderFormat::Google) {
             for (k, v) in extras {
+                // _generationConfigExtras is merged into generationConfig above
+                if k == GENERATION_CONFIG_EXTRAS_KEY {
+                    continue;
+                }
                 // Don't overwrite canonical fields we already handled
                 if !obj.contains_key(k) {
                     obj.insert(k.clone(), v.clone());
@@ -526,6 +617,11 @@ mod tests {
     use super::*;
     use crate::serde_json::json;
 
+    /// Parse a reconstructed JSON Value back into typed GoogleParams for assertions.
+    fn parse_params(value: &Value) -> GoogleParams {
+        serde_json::from_value(value.clone()).expect("should parse as GoogleParams")
+    }
+
     #[test]
     fn test_google_detect_request() {
         let adapter = GoogleAdapter;
@@ -553,7 +649,6 @@ mod tests {
         });
 
         let universal = adapter.request_to_universal(payload).unwrap();
-        // Use approximate comparison due to f32->f64 conversion precision
         assert!((universal.params.temperature.unwrap() - 0.7).abs() < 0.001);
         assert_eq!(
             universal.params.token_budget,
@@ -561,8 +656,9 @@ mod tests {
         );
 
         let reconstructed = adapter.request_from_universal(&universal).unwrap();
-        assert!(reconstructed.get("contents").is_some());
-        assert!(reconstructed.get("generationConfig").is_some());
+        let params = parse_params(&reconstructed);
+        assert!(params.contents.is_some());
+        assert!(params.generation_config.is_some());
     }
 
     #[test]
@@ -577,10 +673,113 @@ mod tests {
         });
 
         let universal = adapter.request_to_universal(payload).unwrap();
-        // safetySettings is a known key, so it won't be in extras
-        // but it should be preserved through serialization
+        let reconstructed = adapter.request_from_universal(&universal).unwrap();
+        let params = parse_params(&reconstructed);
+        assert!(params.contents.is_some());
+        assert_eq!(
+            params.safety_settings,
+            Some(json!([{"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_NONE"}]))
+        );
+    }
+
+    #[test]
+    fn test_google_roundtrip_generation_config_extras() {
+        let adapter = GoogleAdapter;
+        let payload = json!({
+            "contents": [{"role": "user", "parts": [{"text": "hi"}]}],
+            "generationConfig": {
+                "temperature": 0.5,
+                "seed": 42,
+                "presencePenalty": 0.3,
+                "frequencyPenalty": 0.7,
+                "candidateCount": 2,
+                "responseLogprobs": true,
+                "responseModalities": ["TEXT"],
+                "mediaResolution": "MEDIA_RESOLUTION_LOW"
+            }
+        });
+
+        let universal = adapter.request_to_universal(payload).unwrap();
+        assert_eq!(universal.params.seed, Some(42));
+        assert!((universal.params.presence_penalty.unwrap() - 0.3).abs() < 0.001);
+        assert!((universal.params.frequency_penalty.unwrap() - 0.7).abs() < 0.001);
 
         let reconstructed = adapter.request_from_universal(&universal).unwrap();
-        assert!(reconstructed.get("contents").is_some());
+        let params = parse_params(&reconstructed);
+        let config = params.generation_config.unwrap();
+        assert_eq!(config.seed, Some(42));
+        assert_eq!(config.candidate_count, Some(2));
+        assert_eq!(config.response_logprobs, Some(true));
+        assert!(config.response_modalities.is_some());
+        assert!(config.media_resolution.is_some());
+    }
+
+    #[test]
+    fn test_google_roundtrip_cached_content() {
+        let adapter = GoogleAdapter;
+        let payload = json!({
+            "contents": [{"role": "user", "parts": [{"text": "hi"}]}],
+            "cachedContent": "cachedContents/abc123"
+        });
+
+        let universal = adapter.request_to_universal(payload).unwrap();
+        let reconstructed = adapter.request_from_universal(&universal).unwrap();
+        let params = parse_params(&reconstructed);
+        assert_eq!(params.cached_content, Some("cachedContents/abc123".into()));
+    }
+
+    #[test]
+    fn test_google_openai_google_roundtrip_seed_and_penalties() {
+        use crate::processing::adapters::adapter_for_format;
+        use crate::providers::openai::params::OpenAIChatParams;
+
+        let google = adapter_for_format(ProviderFormat::Google).unwrap();
+        let openai = adapter_for_format(ProviderFormat::ChatCompletions).unwrap();
+
+        let google_payload = json!({
+            "model": "gemini-2.0-flash",
+            "contents": [{"role": "user", "parts": [{"text": "hello"}]}],
+            "generationConfig": {
+                "seed": 42,
+                "presencePenalty": 0.5,
+                "frequencyPenalty": 0.8,
+                "candidateCount": 2,
+                "responseModalities": ["TEXT"],
+                "temperature": 0.7
+            },
+            "safetySettings": [{"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_ONLY_HIGH"}],
+            "cachedContent": "cachedContents/test123"
+        });
+
+        // Google -> Universal
+        let universal = google.request_to_universal(google_payload.clone()).unwrap();
+        assert_eq!(universal.params.seed, Some(42));
+        assert!((universal.params.presence_penalty.unwrap() - 0.5).abs() < 0.001);
+        assert!((universal.params.frequency_penalty.unwrap() - 0.8).abs() < 0.001);
+
+        // Universal -> OpenAI ChatCompletions
+        let openai_payload = openai.request_from_universal(&universal).unwrap();
+        let openai_params: OpenAIChatParams =
+            serde_json::from_value(openai_payload.clone()).unwrap();
+        assert_eq!(openai_params.seed, Some(42));
+
+        // OpenAI -> Universal (back)
+        let universal_2 = openai.request_to_universal(openai_payload).unwrap();
+        assert_eq!(universal_2.params.seed, Some(42));
+
+        // Universal -> Google (back)
+        let google_out = google.request_from_universal(&universal_2).unwrap();
+        let params = parse_params(&google_out);
+        let config = params.generation_config.unwrap();
+        // Universal params survive cross-provider roundtrip
+        assert_eq!(config.seed, Some(42));
+        assert!(config.presence_penalty.is_some());
+        assert!(config.frequency_penalty.is_some());
+        assert!(config.temperature.is_some());
+
+        // Google-specific extras (candidateCount, responseModalities, safetySettings,
+        // cachedContent) are stored under ProviderFormat::Google in extras, so they
+        // survive a Google->Google roundtrip but NOT a cross-provider trip through OpenAI.
+        // This is expected: OpenAI doesn't know about Google's candidateCount etc.
     }
 }
diff --git a/crates/lingua/src/providers/google/convert.rs b/crates/lingua/src/providers/google/convert.rs
index ca633d88..6792bf0f 100644
--- a/crates/lingua/src/providers/google/convert.rs
+++ b/crates/lingua/src/providers/google/convert.rs
@@ -55,12 +55,7 @@ impl TryFromLLM<GoogleContent> for Message {
     type Error = ConvertError;
 
     fn try_from(content: GoogleContent) -> Result<Self, Self::Error> {
-        let role = content
-            .role
-            .as_deref()
-            .ok_or(ConvertError::MissingRequiredField {
-                field: "role".to_string(),
-            })?;
+        let role = content.role.as_deref().unwrap_or("user");
         let parts = content.parts.ok_or(ConvertError::MissingRequiredField {
             field: "parts".to_string(),
         })?;
@@ -877,6 +872,23 @@ mod tests {
         assert_eq!(fc.name.as_deref(), Some("get_weather"));
     }
 
+    #[test]
+    fn test_google_content_to_message_missing_role_defaults_to_user() {
+        let content = GoogleContent {
+            role: None,
+            parts: Some(vec![text_part("Hello".to_string())]),
+        };
+
+        let message = <Message as TryFromLLM<GoogleContent>>::try_from(content).unwrap();
+        match message {
+            Message::User { content } => match content {
+                UserContent::String(s) => assert_eq!(s, "Hello"),
+                _ => panic!("Expected string content"),
+            },
+            _ => panic!("Expected user message"),
+        }
+    }
+
     #[test]
     fn test_google_to_universal_simple() {
         let request = GenerateContentRequest {
diff --git a/crates/lingua/tests/fuzz/Makefile b/crates/lingua/tests/fuzz/Makefile
index 8eb222d5..9b6e480f 100644
--- a/crates/lingua/tests/fuzz/Makefile
+++ b/crates/lingua/tests/fuzz/Makefile
@@ -1,4 +1,4 @@
-.PHONY: run stats prune run-openai stats-openai prune-openai run-responses stats-responses prune-responses run-anthropic stats-anthropic prune-anthropic run-two-arm stats-two-arm prune-two-arm run-three-arm stats-three-arm prune-three-arm refresh-snapshots
+.PHONY: run stats prune run-openai stats-openai prune-openai run-responses stats-responses prune-responses run-anthropic stats-anthropic prune-anthropic run-google stats-google prune-google run-two-arm stats-two-arm prune-two-arm run-google-two-arm stats-google-two-arm prune-google-two-arm run-three-arm stats-three-arm prune-three-arm refresh-snapshots
 
 run: run-openai
 
@@ -33,6 +33,24 @@ stats-anthropic:
 prune-anthropic:
 	cargo test -p lingua --test fuzz anthropic_roundtrip_prune_snapshots -- --ignored --nocapture --exact
 
+run-google:
+	cargo test -p lingua --test fuzz google_roundtrip -- --ignored --nocapture --exact
+
+stats-google:
+	cargo test -p lingua --test fuzz google_roundtrip_stats -- --ignored --nocapture --exact
+
+prune-google:
+	cargo test -p lingua --test fuzz google_roundtrip_prune_snapshots -- --ignored --nocapture --exact
+
+run-google-two-arm:
+	cargo test -p lingua --test fuzz chat_google_two_arm -- --ignored --nocapture --exact
+
+stats-google-two-arm:
+	cargo test -p lingua --test fuzz chat_google_two_arm_stats -- --ignored --nocapture --exact
+
+prune-google-two-arm:
+	cargo test -p lingua --test fuzz chat_google_two_arm_prune_snapshots -- --ignored --nocapture --exact
+
 run-two-arm:
 	cargo test -p lingua --test fuzz chat_anthropic_two_arm -- --ignored --nocapture --exact
 
@@ -64,8 +82,14 @@ refresh-snapshots:
 	-cargo test -p lingua --test fuzz chat_anthropic_two_arm_stats -- --ignored --nocapture --exact
 	-cargo test -p lingua --test fuzz chat_responses_anthropic_three_arm -- --ignored --nocapture --exact
 	-cargo test -p lingua --test fuzz chat_responses_anthropic_three_arm_stats -- --ignored --nocapture --exact
+	-cargo test -p lingua --test fuzz google_roundtrip -- --ignored --nocapture --exact
+	-cargo test -p lingua --test fuzz google_roundtrip_stats -- --ignored --nocapture --exact
+	-cargo test -p lingua --test fuzz chat_google_two_arm -- --ignored --nocapture --exact
+	-cargo test -p lingua --test fuzz chat_google_two_arm_stats -- --ignored --nocapture --exact
 	cargo test -p lingua --test fuzz openai_roundtrip_prune_snapshots -- --ignored --nocapture --exact
 	cargo test -p lingua --test fuzz responses_roundtrip_prune_snapshots -- --ignored --nocapture --exact
 	cargo test -p lingua --test fuzz anthropic_roundtrip_prune_snapshots -- --ignored --nocapture --exact
 	cargo test -p lingua --test fuzz chat_anthropic_two_arm_prune_snapshots -- --ignored --nocapture --exact
 	cargo test -p lingua --test fuzz chat_responses_anthropic_three_arm_prune_snapshots -- --ignored --nocapture --exact
+	cargo test -p lingua --test fuzz google_roundtrip_prune_snapshots -- --ignored --nocapture --exact
+	cargo test -p lingua --test fuzz chat_google_two_arm_prune_snapshots -- --ignored --nocapture --exact
diff --git a/crates/lingua/tests/fuzz/main.rs b/crates/lingua/tests/fuzz/main.rs
index 37db5d19..1d24e312 100644
--- a/crates/lingua/tests/fuzz/main.rs
+++ b/crates/lingua/tests/fuzz/main.rs
@@ -25,6 +25,8 @@ const SNAPSHOT_SUITE_ANTHROPIC: &str = "anthropic-roundtrip";
 const SNAPSHOT_SUITE_CHAT_ANTHROPIC_TWO_ARM: &str = "chat-anthropic-two-arm";
 const SNAPSHOT_SUITE_CHAT_RESPONSES_ANTHROPIC_THREE_ARM: &str =
     "chat-responses-anthropic-three-arm";
+const SNAPSHOT_SUITE_GOOGLE: &str = "google-roundtrip";
+const SNAPSHOT_SUITE_CHAT_GOOGLE_TWO_ARM: &str = "chat-google-two-arm";
 
 fn workspace_root() -> PathBuf {
     Path::new(env!("CARGO_MANIFEST_DIR"))
@@ -497,6 +499,123 @@ fn assert_responses_roundtrip_verbose(payload: &Value) -> Result<bool, String> {
     assert_provider_roundtrip_verbose(ProviderFormat::Responses, payload)
 }
 
+fn assert_google_roundtrip(payload: &Value) -> Option<Vec<String>> {
+    assert_provider_roundtrip(ProviderFormat::Google, payload)
+}
+
+fn assert_google_roundtrip_verbose(payload: &Value) -> Result<bool, String> {
+    assert_provider_roundtrip_verbose(ProviderFormat::Google, payload)
+}
+
+fn assert_chat_google_two_arm(payload: &Value) -> Option<Vec<String>> {
+    let chat = adapter_for_format(ProviderFormat::ChatCompletions)?;
+    let google = adapter_for_format(ProviderFormat::Google)?;
+
+    let universal_1 = match chat.request_to_universal(payload.clone()) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("chat->universal error: {e}")]),
+    };
+    let google_1 = match google.request_from_universal(&universal_1) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("universal->google(1) error: {e}")]),
+    };
+    let universal_2 = match google.request_to_universal(google_1.clone()) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("google->universal(1) error: {e}")]),
+    };
+    let google_2 = match google.request_from_universal(&universal_2) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("universal->google(2) error: {e}")]),
+    };
+    let universal_3 = match google.request_to_universal(google_2.clone()) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("google->universal(2) error: {e}")]),
+    };
+    let chat_out = match chat.request_from_universal(&universal_3) {
+        Ok(v) => v,
+        Err(e) => return Some(vec![format!("universal->chat error: {e}")]),
+    };
+
+    let mut issues = Vec::new();
+    let universal_1_json = serde_json::to_value(&universal_1).unwrap_or(Value::Null);
+    let universal_2_json = serde_json::to_value(&universal_2).unwrap_or(Value::Null);
+    append_diff_issues(
+        "universal(1->2):",
+        &universal_1_json,
+        &universal_2_json,
+        &mut issues,
+    );
+    append_diff_issues("google(1->2):", &google_1, &google_2, &mut issues);
+    append_diff_issues("chat(final):", payload, &chat_out, &mut issues);
+
+    Some(issues)
+}
+
+fn assert_chat_google_two_arm_verbose(payload: &Value) -> Result<bool, String> {
+    let chat = adapter_for_format(ProviderFormat::ChatCompletions)
+        .ok_or_else(|| "No chat-completions adapter".to_string())?;
+    let google = adapter_for_format(ProviderFormat::Google)
+        .ok_or_else(|| "No google adapter".to_string())?;
+
+    let universal_1 = chat
+        .request_to_universal(payload.clone())
+        .map_err(|e| format!("chat->universal error: {e}"))?;
+    let google_1 = google
+        .request_from_universal(&universal_1)
+        .map_err(|e| format!("universal->google(1) error: {e}"))?;
+    let universal_2 = google
+        .request_to_universal(google_1.clone())
+        .map_err(|e| format!("google->universal(1) error: {e}"))?;
+    let google_2 = google
+        .request_from_universal(&universal_2)
+        .map_err(|e| format!("universal->google(2) error: {e}"))?;
+    let universal_3 = google
+        .request_to_universal(google_2.clone())
+        .map_err(|e| format!("google->universal(2) error: {e}"))?;
+    let chat_out = chat
+        .request_from_universal(&universal_3)
+        .map_err(|e| format!("universal->chat error: {e}"))?;
+
+    let mut issues = Vec::new();
+    let universal_1_json = serde_json::to_value(&universal_1).unwrap_or(Value::Null);
+    let universal_2_json = serde_json::to_value(&universal_2).unwrap_or(Value::Null);
+    append_diff_issues(
+        "universal(1->2):",
+        &universal_1_json,
+        &universal_2_json,
+        &mut issues,
+    );
+    append_diff_issues("google(1->2):", &google_1, &google_2, &mut issues);
+    append_diff_issues("chat(final):", payload, &chat_out, &mut issues);
+
+    if issues.is_empty() {
+        return Ok(true);
+    }
+
+    Err(format!(
+        "chat->universal->google->universal->google->universal->chat mismatch:\n{}\n\n\
+         chat_input: {}\n\
+         universal_1: {}\n\
+         google_1: {}\n\
+         universal_2: {}\n\
+         google_2: {}\n\
+         universal_3: {}\n\
+         chat_output: {}",
+        issues
+            .iter()
+            .map(|i| format!("  {i}"))
+            .collect::<Vec<_>>()
+            .join("\n"),
+        as_pretty_json(payload),
+        as_pretty_json(&universal_1),
+        as_pretty_json(&google_1),
+        as_pretty_json(&universal_2),
+        as_pretty_json(&google_2),
+        as_pretty_json(&universal_3),
+        as_pretty_json(&chat_out),
+    ))
+}
+
 fn assert_chat_responses_anthropic_three_arm(payload: &Value) -> Option<Vec<String>> {
     let chat = adapter_for_format(ProviderFormat::ChatCompletions)?;
     let responses = adapter_for_format(ProviderFormat::Responses)?;
@@ -666,7 +785,9 @@ fn assert_chat_responses_anthropic_three_arm_verbose(payload: &Value) -> Result<
 // ============================================================================
 
 mod strategies {
-    use super::schema_strategy::{load_openapi_definitions, strategy_for_schema_name};
+    use super::schema_strategy::{
+        load_discovery_definitions, load_openapi_definitions, strategy_for_schema_name,
+    };
     use super::*;
 
     fn specs_dir() -> String {
@@ -701,6 +822,50 @@ mod strategies {
             )
             .boxed()
     }
+
+    pub fn arb_google_payload() -> BoxedStrategy<Value> {
+        let defs =
+            load_discovery_definitions(&format!("{}/specs/google/discovery.json", specs_dir()));
+        strategy_for_schema_name("GenerateContentRequest", &defs)
+            .prop_filter("payload must parse as Google params", |payload| {
+                lingua::providers::google::try_parse_google(payload).is_ok()
+            })
+            .prop_filter(
+                "contents must be valid Google API input (valid roles, non-empty parts with data)",
+                |payload| {
+                    let part_has_data = |part: &Value| {
+                        part.get("text").and_then(Value::as_str).is_some()
+                            || part.get("inlineData").and_then(|d| d.get("data")).is_some()
+                            || part
+                                .get("fileData")
+                                .and_then(|d| d.get("fileUri"))
+                                .is_some()
+                            || part
+                                .get("functionCall")
+                                .and_then(|d| d.get("name"))
+                                .is_some()
+                            || part
+                                .get("functionResponse")
+                                .and_then(|d| d.get("name"))
+                                .is_some()
+                    };
+                    payload
+                        .get("contents")
+                        .and_then(|c| c.as_array())
+                        .is_some_and(|contents| {
+                            contents.iter().all(|entry| {
+                                matches!(
+                                    entry.get("role").and_then(Value::as_str),
+                                    Some("user" | "model")
+                                ) && entry.get("parts").and_then(|p| p.as_array()).is_some_and(
+                                    |parts| !parts.is_empty() && parts.iter().all(part_has_data),
+                                )
+                            })
+                        })
+                },
+            )
+            .boxed()
+    }
 }
 
 // ============================================================================
@@ -978,6 +1143,19 @@ fn chat_responses_anthropic_three_arm_saved_snapshots() {
     );
 }
 
+#[test]
+fn google_roundtrip_saved_snapshots() {
+    run_saved_snapshots_suite(SNAPSHOT_SUITE_GOOGLE, assert_google_roundtrip);
+}
+
+#[test]
+fn chat_google_two_arm_saved_snapshots() {
+    run_saved_snapshots_suite(
+        SNAPSHOT_SUITE_CHAT_GOOGLE_TWO_ARM,
+        assert_chat_google_two_arm,
+    );
+}
+
 /// Prune fuzz snapshots in a loop until stable:
 /// - remove malformed request/meta pairs
 /// - remove orphan meta files
@@ -1018,6 +1196,21 @@ fn chat_responses_anthropic_three_arm_prune_snapshots() {
     );
 }
 
+#[test]
+#[ignore]
+fn google_roundtrip_prune_snapshots() {
+    run_prune_snapshots_suite(SNAPSHOT_SUITE_GOOGLE, assert_google_roundtrip);
+}
+
+#[test]
+#[ignore]
+fn chat_google_two_arm_prune_snapshots() {
+    run_prune_snapshots_suite(
+        SNAPSHOT_SUITE_CHAT_GOOGLE_TWO_ARM,
+        assert_chat_google_two_arm,
+    );
+}
+
 /// Fail on the first error with verbose output (input, output, diff).
 /// Use for debugging a specific issue.
 #[test]
@@ -1085,6 +1278,32 @@ fn chat_responses_anthropic_three_arm() {
     );
 }
 
+#[test]
+#[ignore]
+fn google_roundtrip() {
+    run_fail_fast_suite(
+        SNAPSHOT_SUITE_GOOGLE,
+        "google",
+        "request-roundtrip",
+        strategies::arb_google_payload(),
+        assert_google_roundtrip,
+        assert_google_roundtrip_verbose,
+    );
+}
+
+#[test]
+#[ignore]
+fn chat_google_two_arm() {
+    run_fail_fast_suite(
+        SNAPSHOT_SUITE_CHAT_GOOGLE_TWO_ARM,
+        "chat-completions",
+        "chat-google-two-arm",
+        strategies::arb_openai_payload(),
+        assert_chat_google_two_arm,
+        assert_chat_google_two_arm_verbose,
+    );
+}
+
 /// Run all cases and report an aggregated summary of unique issues.
 /// Use for triaging the full scope of failures.
 #[test]
@@ -1151,3 +1370,29 @@ fn chat_responses_anthropic_three_arm_stats() {
         assert_chat_responses_anthropic_three_arm,
     );
 }
+
+#[test]
+#[ignore]
+fn google_roundtrip_stats() {
+    run_stats_suite(
+        SNAPSHOT_SUITE_GOOGLE,
+        "google",
+        "request-roundtrip",
+        "Google roundtrip fuzz",
+        strategies::arb_google_payload(),
+        assert_google_roundtrip,
+    );
+}
+
+#[test]
+#[ignore]
+fn chat_google_two_arm_stats() {
+    run_stats_suite(
+        SNAPSHOT_SUITE_CHAT_GOOGLE_TWO_ARM,
+        "chat-completions",
+        "chat-google-two-arm",
+        "Chat->Google two-arm fuzz",
+        strategies::arb_openai_payload(),
+        assert_chat_google_two_arm,
+    );
+}
diff --git a/crates/lingua/tests/fuzz/schema_strategy.rs b/crates/lingua/tests/fuzz/schema_strategy.rs
index e1f0ff76..67532908 100644
--- a/crates/lingua/tests/fuzz/schema_strategy.rs
+++ b/crates/lingua/tests/fuzz/schema_strategy.rs
@@ -322,6 +322,20 @@ pub fn load_openapi_definitions(spec_path: &str) -> Map<String, Value> {
         .unwrap_or_else(|| panic!("No components.schemas in {}", spec_path))
 }
 
+/// Load a Google Discovery REST spec and extract the top-level `schemas` map.
+pub fn load_discovery_definitions(spec_path: &str) -> Map<String, Value> {
+    let content = std::fs::read_to_string(spec_path)
+        .unwrap_or_else(|e| panic!("Failed to read spec at {}: {}", spec_path, e));
+
+    let spec: Value = serde_json::from_str(&content)
+        .unwrap_or_else(|e| panic!("Failed to parse spec at {}: {}", spec_path, e));
+
+    spec.get("schemas")
+        .and_then(|s| s.as_object())
+        .cloned()
+        .unwrap_or_else(|| panic!("No schemas in {}", spec_path))
+}
+
 /// Build a strategy for a named schema from the definitions map.
 pub fn strategy_for_schema_name(
     name: &str,
diff --git a/mise.toml b/mise.toml
index b646d7dd..804b084f 100644
--- a/mise.toml
+++ b/mise.toml
@@ -1,2 +1,6 @@
+[env]
+_.file = ".env"
+
 [tools]
 pnpm = "10.26.2"
+nodejs = "22.15.0"
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.meta.json
new file mode 100644
index 00000000..e907e6f9
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.meta.json
@@ -0,0 +1,7 @@
+{
+  "issues": [
+    "chat->universal error: Conversion to universal format failed: data did not match any variant of untagged enum ChatCompletionRequestMessageContent"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.request.json
new file mode 100644
index 00000000..5c6b4743
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-00616f16cb8603d4.request.json
@@ -0,0 +1,74 @@
+{
+  "audio": {
+    "format": "flac",
+    "voice": ".!KNF2Zkn5,f h?,Ig"
+  },
+  "function_call": "none",
+  "functions": [
+    {
+      "name": "n5 8w!1.?3,,??W,!v?O.,y?2!,8?i?tF,!..I?2?  .gEt"
+    }
+  ],
+  "logit_bias": {},
+  "logprobs": false,
+  "max_completion_tokens": 652,
+  "messages": [
+    {
+      "content": "?..7?68e  pC?pf? t",
+      "name": "4.Xn..a1,B",
+      "refusal": null,
+      "role": "assistant"
+    },
+    {
+      "content": [
+        {
+          "text": null,
+          "type": null
+        }
+      ],
+      "name": "lOe?mtn3?zrU?,g!,MuKSzAYuG!.6,Q,.7.,Y?T6",
+      "role": "user"
+    }
+  ],
+  "modalities": null,
+  "model": "gpt-5-mini-2025-08-07",
+  "n": -860,
+  "presence_penalty": 54.71461087452379,
+  "reasoning_effort": "minimal",
+  "response_format": {
+    "type": "json_object"
+  },
+  "seed": 374,
+  "store": true,
+  "stream_options": {
+    "include_obfuscation": true
+  },
+  "tool_choice": {
+    "allowed_tools": {
+      "mode": "required",
+      "tools": [
+        {},
+        {}
+      ]
+    },
+    "type": "allowed_tools"
+  },
+  "tools": [
+    {
+      "function": {
+        "name": "D!ZHX,3v,0,IH"
+      },
+      "type": "function"
+    },
+    {
+      "custom": {
+        "format": {
+          "type": "text"
+        },
+        "name": ".,XfS!9GnFE8"
+      },
+      "type": "custom"
+    }
+  ],
+  "web_search_options": {}
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.meta.json
new file mode 100644
index 00000000..d117b649
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.meta.json
@@ -0,0 +1,26 @@
+{
+  "issues": [
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.seed (965 -> null)",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.tools.length (3 -> 1)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "universal(1->2): changed: params.parallel_tool_calls (true -> null)",
+    "universal(1->2): changed: messages.length (2 -> 1)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: seed",
+    "chat(final): lost: n",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: modalities",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: stream",
+    "chat(final): lost: function_call",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: audio",
+    "chat(final): changed: messages.length (2 -> 1)",
+    "chat(final): changed: tools.length (3 -> 1)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.request.json
new file mode 100644
index 00000000..6705ffdf
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-04afc1e70d055310.request.json
@@ -0,0 +1,64 @@
+{
+  "audio": {
+    "format": "wav",
+    "voice": "W!W.s60,.!qRRHBY??AI"
+  },
+  "function_call": "none",
+  "logprobs": false,
+  "max_completion_tokens": 17,
+  "messages": [
+    {
+      "content": null,
+      "name": "hC,2.CDLKTNfe!AUmB2oq83k.0lO?q,lf?13O6.Lk.",
+      "role": "function"
+    },
+    {
+      "content": "9.tf..W?t4a2.5..Na.?,4.Wmo43j,",
+      "name": "??,,0.K3,A. e",
+      "role": "system"
+    }
+  ],
+  "modalities": null,
+  "model": "ns!?6,y!.9.t f",
+  "n": -125,
+  "parallel_tool_calls": true,
+  "reasoning_effort": "low",
+  "seed": 965,
+  "stream": true,
+  "stream_options": null,
+  "tool_choice": {
+    "function": {
+      "name": "!p.Z.Y,7"
+    },
+    "type": "function"
+  },
+  "tools": [
+    {
+      "function": {
+        "description": "n!n8.E9!,A ,3Xs 87?.yx",
+        "name": "IEii ,7tON6r1.zYHzLc? 6hJ!Y.l",
+        "parameters": {}
+      },
+      "type": "function"
+    },
+    {
+      "custom": {
+        "name": "a?Y.!?,pDvp,.m?0,!k"
+      },
+      "type": "custom"
+    },
+    {
+      "custom": {
+        "description": "?B!L ja.S?7m",
+        "name": "? 8mi?9jiV,Gf,4,3X.Rn?,?fL?O.,f34,!8x,!,"
+      },
+      "type": "custom"
+    }
+  ],
+  "web_search_options": {
+    "user_location": {
+      "approximate": {},
+      "type": "approximate"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.meta.json
new file mode 100644
index 00000000..b99df818
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.meta.json
@@ -0,0 +1,30 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (2 -> 1)",
+    "universal(1->2): changed: params.seed (-465 -> null)",
+    "universal(1->2): changed: params.top_logprobs (3 -> null)",
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.parallel_tool_calls (true -> null)",
+    "universal(1->2): changed: params.frequency_penalty (-14.320129888587324 -> null)",
+    "universal(1->2): changed: params.store (true -> null)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "universal(1->2): changed: params.tools.length (3 -> 1)",
+    "chat(final): lost: n",
+    "chat(final): lost: modalities",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: store",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: stream",
+    "chat(final): lost: function_call",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: frequency_penalty",
+    "chat(final): lost: prediction",
+    "chat(final): lost: seed",
+    "chat(final): changed: messages.length (2 -> 1)",
+    "chat(final): changed: tools.length (3 -> 1)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.request.json
new file mode 100644
index 00000000..ce186577
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-05048e3ab95af455.request.json
@@ -0,0 +1,69 @@
+{
+  "frequency_penalty": -14.320129888587324,
+  "function_call": {
+    "name": "X,Qr??v Bx T "
+  },
+  "logprobs": false,
+  "max_completion_tokens": -165,
+  "messages": [
+    {
+      "content": "8!,u0e ???,0.?mVFs",
+      "role": "tool",
+      "tool_call_id": "fX2.xOiU,.Uc.4i..,,Hdg?NqD2,,llBs ,..,d"
+    },
+    {
+      "content": null,
+      "name": ",?w?4?2,",
+      "role": "function"
+    }
+  ],
+  "modalities": [
+    "audio",
+    "audio"
+  ],
+  "model": "gpt-4-0314",
+  "n": 720,
+  "parallel_tool_calls": true,
+  "prediction": {
+    "content": "aX,U6fU,!qHk",
+    "type": "content"
+  },
+  "reasoning_effort": "medium",
+  "seed": -465,
+  "stop": [
+    " .a!Kk8!.. .oHXN?y,v.HJE9. ,7",
+    "5?obn?uA2k.HO!.,g8EE?.3, l,,,?,R,l2su",
+    "ThRiC.41r.,8?lnp9I,qqSJ,?e..eow.l..yV ?dW.hu89t",
+    "1u,!i7 a."
+  ],
+  "store": true,
+  "stream": true,
+  "stream_options": {
+    "include_obfuscation": false,
+    "include_usage": false
+  },
+  "tools": [
+    {
+      "custom": {
+        "description": "?Yp wJ ,T,5!a30m.?L?pLk,5,d,L.MgG7,! ",
+        "name": "R,.!05gtHST??Nf.?v?i.M.o,M,,50C,?C33a,qR"
+      },
+      "type": "custom"
+    },
+    {
+      "function": {
+        "name": "? . TEFt5. .i yoR17!7ZMWro,7.x.!",
+        "parameters": {},
+        "strict": null
+      },
+      "type": "function"
+    },
+    {
+      "custom": {
+        "name": "A.,j5?x.3Fm43O"
+      },
+      "type": "custom"
+    }
+  ],
+  "top_logprobs": 3
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.meta.json
new file mode 100644
index 00000000..548ffd21
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.meta.json
@@ -0,0 +1,24 @@
+{
+  "issues": [
+    "universal(1->2): changed: params.top_logprobs (571 -> null)",
+    "universal(1->2): changed: params.stream (false -> null)",
+    "universal(1->2): changed: messages[0].content[0].output (\"\" -> {\"output\":\"\"})",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: n",
+    "chat(final): lost: prediction",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: stream",
+    "chat(final): lost: reasoning_effort",
+    "chat(final): lost: function_call",
+    "chat(final): lost: modalities",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: messages[0].name",
+    "chat(final): added: messages[0].tool_call_id",
+    "chat(final): changed: messages[0].role (\"function\" -> \"tool\")",
+    "chat(final): changed: messages[0].content (null -> \"{\\\"output\\\":\\\"\\\"}\")",
+    "chat(final): changed: stop (\"qWI.O,G YvnirG?!..6Ne?a?Y ?B?.. Xg..\" -> [\"qWI.O,G YvnirG?!..6Ne?a?Y ?B?.. Xg..\"])"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.request.json
new file mode 100644
index 00000000..a9361a04
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0680230824e2f95c.request.json
@@ -0,0 +1,39 @@
+{
+  "function_call": "auto",
+  "logit_bias": {},
+  "messages": [
+    {
+      "content": null,
+      "name": "rE?nA ..Iaz7,",
+      "role": "function"
+    }
+  ],
+  "modalities": [
+    "audio",
+    "text",
+    "audio"
+  ],
+  "model": "gpt-3.5-turbo-0125",
+  "n": 79,
+  "prediction": {
+    "content": "6F???!I8E3q.?l s!HCJ6r,6ipo,a1,tfnL n?GLD..iI",
+    "type": "content"
+  },
+  "reasoning_effort": null,
+  "stop": "qWI.O,G YvnirG?!..6Ne?a?Y ?B?.. Xg..",
+  "stream": false,
+  "stream_options": {
+    "include_obfuscation": false
+  },
+  "top_logprobs": 571,
+  "web_search_options": {
+    "user_location": {
+      "approximate": {
+        "city": "U1?x4.0vCuuf5758r.92.",
+        "country": "KHvr?1?,.",
+        "region": ".P R.5a,U!j.uH3!?.ZayNP5.???UnH?z.,?s.,xa2ixO.B"
+      },
+      "type": "approximate"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.meta.json
new file mode 100644
index 00000000..b6f8617e
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.meta.json
@@ -0,0 +1,21 @@
+{
+  "issues": [
+    "universal(1->2): changed: params.tools.length (3 -> 2)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: functions",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: stream",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: tool_choice",
+    "chat(final): lost: logprobs",
+    "chat(final): changed: stop (\"f0OdJ.T,\" -> [\"f0OdJ.T,\"])",
+    "chat(final): changed: tools.length (3 -> 2)",
+    "chat(final): changed: messages.length (1 -> 0)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.request.json
new file mode 100644
index 00000000..0906e86d
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-08c80730b339ee0d.request.json
@@ -0,0 +1,74 @@
+{
+  "functions": [
+    {
+      "description": ".u.OqTee1,?",
+      "name": "?,k.z? ?kB8v!E.?,1tIg..4xR2i?",
+      "parameters": {}
+    },
+    {
+      "description": "v,4!S?52L?",
+      "name": "?Vm?0L!,14.HRw?oUn8L!19!.5o.u,. ",
+      "parameters": {}
+    },
+    {
+      "name": "S.911sUGo..,. .DxB,c? .?2  dY8W ?5?e,Q ,s?8li ?.a?",
+      "parameters": {}
+    },
+    {
+      "description": "?44wV1?!Mn.D92z! ?,!iq8 G,r. ,?",
+      "name": ",q.?FT5?",
+      "parameters": {}
+    }
+  ],
+  "logit_bias": {},
+  "logprobs": false,
+  "messages": [
+    {
+      "content": "4 .!3.4D,pb! 0gNe!oyk?R47.jK",
+      "name": ".0?.??!.??i..V.Hi6.c. eLS8v2!x,3",
+      "role": "system"
+    }
+  ],
+  "model": "u1!7B!g.d?wEVv!Pt?CVD?11 2..M",
+  "stop": "f0OdJ.T,",
+  "stream": true,
+  "stream_options": {
+    "include_obfuscation": true,
+    "include_usage": true
+  },
+  "tool_choice": {
+    "allowed_tools": {
+      "mode": "auto",
+      "tools": [
+        {},
+        {}
+      ]
+    },
+    "type": "allowed_tools"
+  },
+  "tools": [
+    {
+      "custom": {
+        "description": "?70,.S?.,O,?3.N43X,L? 6 f",
+        "name": "n,kI,A"
+      },
+      "type": "custom"
+    },
+    {
+      "function": {
+        "name": "GhZ?,!1.j .3?!,.?4.6",
+        "parameters": {}
+      },
+      "type": "function"
+    },
+    {
+      "function": {
+        "name": " ",
+        "parameters": {},
+        "strict": null
+      },
+      "type": "function"
+    }
+  ],
+  "verbosity": "medium"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.meta.json
new file mode 100644
index 00000000..5ec098b8
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.meta.json
@@ -0,0 +1,28 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "universal(1->2): changed: params.top_logprobs (-747 -> null)",
+    "universal(1->2): changed: params.seed (-877 -> null)",
+    "universal(1->2): changed: params.tools.length (2 -> 1)",
+    "universal(1->2): changed: params.presence_penalty (49.989426326552554 -> null)",
+    "universal(1->2): changed: params.store (false -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: n",
+    "chat(final): lost: store",
+    "chat(final): lost: functions",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: audio",
+    "chat(final): lost: modalities",
+    "chat(final): lost: function_call",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: seed",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: web_search_options",
+    "chat(final): changed: messages.length (1 -> 0)",
+    "chat(final): changed: stop (\"O,.1.cI.s\" -> [\"O,.1.cI.s\"])",
+    "chat(final): changed: tools.length (2 -> 1)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.request.json
new file mode 100644
index 00000000..2f5a7332
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-09fa42838b8cfd7b.request.json
@@ -0,0 +1,87 @@
+{
+  "audio": {
+    "format": "aac",
+    "voice": "?PoW!1.,c?0.x!??!!?9,rF!,o??,.!n1 ,W4Sl"
+  },
+  "function_call": {
+    "name": "?,M1 ..,ig??."
+  },
+  "functions": [
+    {
+      "description": "Bb!2G9?!.xE6V5X,C7 3! ZYLib,!. nIC.",
+      "name": ". ,?j.O,, C?"
+    },
+    {
+      "description": ",.oB! Qq,n,?!1y,BQ,G,Ym,! uRE5?",
+      "name": ",7K, 8Uu,r!43?Faoz?.,.,?.Mkgc k,!Us?r?uQ ?j ,44",
+      "parameters": {}
+    },
+    {
+      "name": "?q .?,S .u yo a.!q,?4,h6H.ShnxC?.ONI?",
+      "parameters": {}
+    },
+    {
+      "description": ",h?7?f4gkagr.4e!,cLW3",
+      "name": "?!!?8pSg21?4m 2,j,9y1D"
+    },
+    {
+      "description": ".Z.,?4?,VF0Z,.0,?i,.??V26?tUl9m2Lsdyk,",
+      "name": "ti9,lBD.dU??KubFqF.9?, mub.?u..m0,Hxw4P"
+    }
+  ],
+  "logit_bias": {},
+  "messages": [
+    {
+      "content": [
+        {
+          "text": ".K.SW,!En!oHS??z",
+          "type": "text"
+        },
+        {
+          "text": "6c!lN!?. 6X?p ?QzS ! 6I",
+          "type": "text"
+        },
+        {
+          "text": "5.O",
+          "type": "text"
+        }
+      ],
+      "role": "developer"
+    }
+  ],
+  "modalities": null,
+  "model": "gpt-4-turbo",
+  "n": -841,
+  "presence_penalty": 49.989426326552554,
+  "response_format": {
+    "type": "json_object"
+  },
+  "seed": -877,
+  "stop": "O,.1.cI.s",
+  "store": false,
+  "tools": [
+    {
+      "function": {
+        "name": "E"
+      },
+      "type": "function"
+    },
+    {
+      "custom": {
+        "name": ",0?,0,,?Q!.9Q,9?..9W, oC!????  6.I9M.3bHy?CI0l?ht"
+      },
+      "type": "custom"
+    }
+  ],
+  "top_logprobs": -747,
+  "verbosity": null,
+  "web_search_options": {
+    "search_context_size": "medium",
+    "user_location": {
+      "approximate": {
+        "country": "vD u?,x"
+      },
+      "type": "approximate"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.meta.json
new file mode 100644
index 00000000..4895b408
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.meta.json
@@ -0,0 +1,7 @@
+{
+  "issues": [
+    "chat->universal error: Conversion to universal format failed: invalid type: null, expected a string"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.request.json
new file mode 100644
index 00000000..8947d006
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0af37cb5b59d868b.request.json
@@ -0,0 +1,98 @@
+{
+  "function_call": {
+    "name": "5rg1,OEx.!gn?7cxP4,0dd?Q?,.f?62 X1..6p,8"
+  },
+  "functions": [
+    {
+      "name": ".b.?!0.4qmSKM!!5..  .RYUUY!,64.z.u!IVO"
+    },
+    {
+      "name": "  t!?!,aO,88a E??,3"
+    },
+    {
+      "name": " ,ceGQ?.S!.. V!,.CN0?2?m??6??3?U"
+    },
+    {
+      "name": "F?KE?5KP5NK..Ue.l! ??DxLX!",
+      "parameters": {}
+    }
+  ],
+  "logit_bias": {},
+  "logprobs": true,
+  "messages": [
+    {
+      "audio": {
+        "id": "I???"
+      },
+      "function_call": null,
+      "refusal": "? .4YfA?!w, Q!!?FzK!.O.h.u?qCSu",
+      "role": "assistant",
+      "tool_calls": [
+        {
+          "function": {
+            "arguments": null,
+            "name": null
+          },
+          "id": "h8,Z?,wnL13??x.3?w,m?m54D eU?V!4qNa?cp?",
+          "type": "function"
+        }
+      ]
+    }
+  ],
+  "model": "tDu?!8TeZ.?.!weY!?D!,..AxNjG.",
+  "prediction": {
+    "content": "X?2?.Pj!.vQ,.!J7.zgWZW7 ,RA",
+    "type": "content"
+  },
+  "presence_penalty": 93.829137528793,
+  "reasoning_effort": "high",
+  "response_format": {
+    "type": "json_object"
+  },
+  "seed": 794,
+  "stop": [
+    ".HL.p?b.,b!,!v?",
+    "XE?5X0V6Y4i1N?qI!4?P?Y,Y. .y3,7 9v,I?1,2",
+    "!?4m0s.!F2.?8,,E70!",
+    "1I,.Eu?0r?.?."
+  ],
+  "stream": false,
+  "stream_options": null,
+  "tool_choice": {
+    "allowed_tools": {
+      "mode": "required",
+      "tools": [
+        {},
+        {},
+        {}
+      ]
+    },
+    "type": "allowed_tools"
+  },
+  "tools": [
+    {
+      "custom": {
+        "description": ",. AT,7.ZGQ0vu0Z.? V.MU,Q3.Ht.?M ?6t,",
+        "name": "49CMAK!,"
+      },
+      "type": "custom"
+    },
+    {
+      "custom": {
+        "description": "kD e.o",
+        "format": {
+          "type": "text"
+        },
+        "name": "??q6,HB 2k?v,?!g M"
+      },
+      "type": "custom"
+    },
+    {
+      "custom": {
+        "description": "229y8G4C?.Gx,34s4te7,Fn?? .q.RI",
+        "name": ", "
+      },
+      "type": "custom"
+    }
+  ]
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.meta.json
new file mode 100644
index 00000000..9560e951
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.meta.json
@@ -0,0 +1,30 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "universal(1->2): changed: params.parallel_tool_calls (false -> null)",
+    "universal(1->2): changed: params.logprobs (true -> null)",
+    "universal(1->2): changed: params.store (true -> null)",
+    "universal(1->2): changed: params.top_logprobs (-581 -> null)",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.seed (573 -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: n",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: store",
+    "chat(final): lost: seed",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: max_tokens",
+    "chat(final): lost: stream",
+    "chat(final): lost: modalities",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: function_call",
+    "chat(final): added: max_completion_tokens",
+    "chat(final): changed: messages.length (1 -> 0)",
+    "chat(final): changed: reasoning_effort (\"minimal\" -> \"low\")"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.request.json
new file mode 100644
index 00000000..28cf1575
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f6021d1f374dc8f.request.json
@@ -0,0 +1,32 @@
+{
+  "function_call": {
+    "name": "6."
+  },
+  "logit_bias": {},
+  "logprobs": true,
+  "max_tokens": -780,
+  "messages": [
+    {
+      "content": [
+        {
+          "text": "FnoiN.!,?JL6?1es?5?",
+          "type": "text"
+        }
+      ],
+      "role": "developer"
+    }
+  ],
+  "modalities": null,
+  "model": "gpt-4-turbo-preview",
+  "n": 353,
+  "parallel_tool_calls": false,
+  "reasoning_effort": "minimal",
+  "response_format": {
+    "type": "json_object"
+  },
+  "seed": 573,
+  "store": true,
+  "stream": true,
+  "top_logprobs": -581,
+  "verbosity": null
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.meta.json
new file mode 100644
index 00000000..2ad3f311
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.meta.json
@@ -0,0 +1,25 @@
+{
+  "issues": [
+    "universal(1->2): added: params.tools[1].parameters.items",
+    "universal(1->2): changed: messages.length (3 -> 1)",
+    "universal(1->2): changed: params.presence_penalty (-78.0783387945037 -> null)",
+    "universal(1->2): changed: params.top_logprobs (-218 -> null)",
+    "universal(1->2): changed: params.stream (false -> null)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: audio",
+    "chat(final): lost: stream",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: tools[1].function.strict",
+    "chat(final): added: tools[1].function.parameters.items",
+    "chat(final): changed: messages.length (3 -> 1)",
+    "chat(final): changed: stop (\".?,O,m.zJVSm bFX,.,.Rg.OB,\" -> [\".?,O,m.zJVSm bFX,.,.Rg.OB,\"])"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.request.json
new file mode 100644
index 00000000..49fe0c4b
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-0f9d6200213116a0.request.json
@@ -0,0 +1,48 @@
+{
+  "audio": {
+    "format": "mp3",
+    "voice": "cedar"
+  },
+  "logit_bias": {},
+  "logprobs": false,
+  "max_completion_tokens": -236,
+  "messages": [
+    {
+      "content": "m u.??a.21lI4,!?",
+      "name": "s.Q,..Y 2 UgW9L!.6Zq368,.?quY5O.PH  .s,?V.1",
+      "role": "developer"
+    },
+    {
+      "content": "!. p .?",
+      "name": "z.QMa9 JWyz,m?.Wc?g,I..!! Rl?3?arL?xjkG",
+      "role": "system"
+    },
+    {
+      "content": "?iM..Rc,h2iyR.!!,?xP72.iK!M0,t W! lCgjP!ks,!ex,!, ",
+      "role": "assistant"
+    }
+  ],
+  "model": "n?36xW.,,!!..y?.d3.1NjounY ,F.",
+  "presence_penalty": -78.0783387945037,
+  "stop": ".?,O,m.zJVSm bFX,.,.Rg.OB,",
+  "stream": false,
+  "stream_options": {},
+  "tools": [
+    {
+      "function": {
+        "name": "B.qb?,2x1fK!!S?,V4E!JN?hf.,dU.G.WYDk8.rxI.Y0xuH.!?"
+      },
+      "type": "function"
+    },
+    {
+      "function": {
+        "name": "kcG!yMV ?3qs.3 !?J6,.?LzDX1HZ",
+        "parameters": {},
+        "strict": null
+      },
+      "type": "function"
+    }
+  ],
+  "top_logprobs": -218,
+  "verbosity": "high"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.meta.json
new file mode 100644
index 00000000..15f916c0
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.meta.json
@@ -0,0 +1,25 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "universal(1->2): changed: params.response_format.format_type (\"JsonSchema\" -> \"JsonObject\")",
+    "universal(1->2): changed: params.seed (438 -> null)",
+    "universal(1->2): changed: params.store (false -> null)",
+    "universal(1->2): changed: params.stream (false -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: stream",
+    "chat(final): lost: prediction",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: modalities",
+    "chat(final): lost: seed",
+    "chat(final): lost: store",
+    "chat(final): lost: functions",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: audio",
+    "chat(final): lost: function_call",
+    "chat(final): lost: response_format.json_schema",
+    "chat(final): changed: response_format.type (\"json_schema\" -> \"json_object\")",
+    "chat(final): changed: messages.length (1 -> 0)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.request.json
new file mode 100644
index 00000000..3dbd306c
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-16f47bea5be70dfb.request.json
@@ -0,0 +1,79 @@
+{
+  "audio": {
+    "format": "opus",
+    "voice": "ballad"
+  },
+  "function_call": "none",
+  "functions": [
+    {
+      "description": "l.iLO??Nj?Mg ?,.",
+      "name": "Go?.k!.dNG.,6.64Gg.9cfMP3w, fCdg??lt??,,YpIm .Y.68",
+      "parameters": {}
+    },
+    {
+      "name": "5Zi!tj,"
+    },
+    {
+      "description": "XKu!? z .pA3k,0.2D5za  08a!,,hqJ.5K?,w,.j?!6",
+      "name": "?D,l ,5H9Wb? ",
+      "parameters": {}
+    },
+    {
+      "description": ",!.5??w6z,9qP.pR.i,?R.?,?paRrUJcdB ?OD.?4a5K.,",
+      "name": "g?t,9?G Via?v,",
+      "parameters": {}
+    }
+  ],
+  "logit_bias": {},
+  "messages": [
+    {
+      "content": [
+        {
+          "text": "b..??.d97 ???E7z,b,1.???",
+          "type": "text"
+        }
+      ],
+      "role": "developer"
+    }
+  ],
+  "modalities": null,
+  "model": "gpt-4-turbo-2024-04-09",
+  "prediction": {
+    "content": [
+      {
+        "text": ",fL.?,.O8H?!.Cy6rWC7pK!,e?",
+        "type": "text"
+      }
+    ],
+    "type": "content"
+  },
+  "response_format": {
+    "json_schema": {
+      "description": "bAw Vx,T8z?uT",
+      "name": ".5UiXyS 6ege9yt?4.64.",
+      "strict": null
+    },
+    "type": "json_schema"
+  },
+  "seed": 438,
+  "store": false,
+  "stream": false,
+  "tools": [
+    {
+      "function": {
+        "description": "S.NGOKC.?3,",
+        "name": "S q!gI06 e,w,?l,s??4.SG9W?pZS3,.V?ZE,.FsiZ,.9"
+      },
+      "type": "function"
+    }
+  ],
+  "web_search_options": {
+    "user_location": {
+      "approximate": {
+        "country": "!.6.H  9q6!?Ex??,",
+        "timezone": "0.,"
+      },
+      "type": "approximate"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.meta.json
new file mode 100644
index 00000000..b399dd55
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.meta.json
@@ -0,0 +1,21 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (2 -> 1)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: max_tokens",
+    "chat(final): lost: modalities",
+    "chat(final): lost: audio",
+    "chat(final): lost: functions",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: function_call",
+    "chat(final): lost: reasoning_effort",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: prediction",
+    "chat(final): changed: max_completion_tokens (-256 -> -818)",
+    "chat(final): changed: messages.length (2 -> 1)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.request.json
new file mode 100644
index 00000000..794e7536
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-1e0526fa83578884.request.json
@@ -0,0 +1,59 @@
+{
+  "audio": {
+    "format": "flac",
+    "voice": "cedar"
+  },
+  "function_call": {
+    "name": "8g!O zxpcI1H,?Z!?., ?W!mhI5!!.3.a"
+  },
+  "functions": [
+    {
+      "name": ".3Xd"
+    },
+    {
+      "name": ".49Xv,?E.3!??4,fveEgNO76?Id.IpW.,0.n.OE.?v,.Q 4.",
+      "parameters": {}
+    },
+    {
+      "description": ",nf2,8?7.goi?l",
+      "name": "5 ?u.????,,,.L?.,8d?.",
+      "parameters": {}
+    },
+    {
+      "name": "k39Zt.,kv?.sR 8!rC,",
+      "parameters": {}
+    }
+  ],
+  "logprobs": false,
+  "max_completion_tokens": -256,
+  "max_tokens": -818,
+  "messages": [
+    {
+      "content": "Q.F?,w1 .U,Sr3b??7u0, .D.?i.4y",
+      "name": " 84g4?e?RE,sJ.f?q.8,,w3CgtUE!  ?.Ee",
+      "role": "function"
+    },
+    {
+      "content": ".t?o,.Zy.E.1Ka.,cRz ..6??9?Pj.y,CJB. is2zQ",
+      "role": "system"
+    }
+  ],
+  "modalities": [
+    "audio",
+    "audio"
+  ],
+  "model": "2g C3i",
+  "prediction": {
+    "content": "8,!!u?d,q3K,h?,? !!., ?t?!Xbpx5.,mB4 wI1Gks.,.vZ8",
+    "type": "content"
+  },
+  "reasoning_effort": null,
+  "stream_options": null,
+  "tool_choice": {
+    "function": {
+      "name": "XZ 2Xq   xr,?g9H6!.?7A?ncLt,y,K??"
+    },
+    "type": "function"
+  },
+  "web_search_options": {}
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.meta.json
new file mode 100644
index 00000000..218a8e7f
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.meta.json
@@ -0,0 +1,32 @@
+{
+  "issues": [
+    "universal(1->2): added: params.response_format.json_schema.schema.items",
+    "universal(1->2): changed: params.presence_penalty (42.567216991235036 -> null)",
+    "universal(1->2): changed: params.top_logprobs (778 -> null)",
+    "universal(1->2): changed: params.response_format.json_schema.strict (false -> null)",
+    "universal(1->2): changed: params.response_format.json_schema.name (\"! !c6Z4,a. 7?vRj??.?7,.GoO09Mh\" -> \"response\")",
+    "universal(1->2): changed: params.tools.length (2 -> 1)",
+    "universal(1->2): changed: params.parallel_tool_calls (true -> null)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "universal(1->2): changed: params.seed (476 -> null)",
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: function_call",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: audio",
+    "chat(final): lost: functions",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: seed",
+    "chat(final): lost: response_format.json_schema.strict",
+    "chat(final): added: response_format.json_schema.schema.items",
+    "chat(final): changed: response_format.json_schema.name (\"! !c6Z4,a. 7?vRj??.?7,.GoO09Mh\" -> \"response\")",
+    "chat(final): changed: messages.length (1 -> 0)",
+    "chat(final): changed: tools.length (2 -> 1)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.request.json
new file mode 100644
index 00000000..98d2ca31
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-260034010784dcec.request.json
@@ -0,0 +1,68 @@
+{
+  "audio": {
+    "format": "mp3",
+    "voice": "aNp??T!  .53?zm,q 0O4c!ITUF i?7J..,U.?"
+  },
+  "function_call": {
+    "name": "p5,!,X.E,,! Hi.xfo.uF?!?.?fRKv. .ce!l!!!"
+  },
+  "functions": [
+    {
+      "name": ",.! ,A,7w,",
+      "parameters": {}
+    }
+  ],
+  "logit_bias": {},
+  "logprobs": false,
+  "max_completion_tokens": 39,
+  "messages": [
+    {
+      "content": [
+        {
+          "text": "54MSC!,,?X?5.j,?2n2??,Hh.??.3",
+          "type": "text"
+        },
+        {
+          "text": " p!ox7,!..UBr?6,4 ,I4nG9O0Y?hkM5I Ak2.IS n.f7Cs.",
+          "type": "text"
+        },
+        {
+          "text": "6?.ngc!???,t.333",
+          "type": "text"
+        }
+      ],
+      "name": "NjH?7g,9,r XSfG.XHuuC.P,,.zc?3DYqwz Y56?Wk..O T6H",
+      "role": "developer"
+    }
+  ],
+  "model": "gpt-4-turbo",
+  "parallel_tool_calls": true,
+  "presence_penalty": 42.567216991235036,
+  "response_format": {
+    "json_schema": {
+      "name": "! !c6Z4,a. 7?vRj??.?7,.GoO09Mh",
+      "schema": {},
+      "strict": false
+    },
+    "type": "json_schema"
+  },
+  "seed": 476,
+  "stream_options": null,
+  "tools": [
+    {
+      "function": {
+        "name": "pdU.vXy8bF",
+        "parameters": {},
+        "strict": null
+      },
+      "type": "function"
+    },
+    {
+      "custom": {
+        "name": "n4!?0P?,,t5pIF 2?h,n3UP p3l.B27.?A"
+      },
+      "type": "custom"
+    }
+  ],
+  "top_logprobs": 778
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.meta.json
new file mode 100644
index 00000000..1c1d2c38
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.meta.json
@@ -0,0 +1,25 @@
+{
+  "issues": [
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.logprobs (false -> null)",
+    "universal(1->2): changed: params.parallel_tool_calls (false -> null)",
+    "universal(1->2): changed: params.frequency_penalty (46.10292730424837 -> null)",
+    "universal(1->2): changed: params.tool_choice.disable_parallel (true -> null)",
+    "universal(1->2): changed: messages[0].content[0].output (\"?S?W\" -> {\"output\":\"?S?W\"})",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: functions",
+    "chat(final): lost: frequency_penalty",
+    "chat(final): lost: n",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: stream",
+    "chat(final): lost: modalities",
+    "chat(final): changed: messages[0].content (\"?S?W\" -> \"{\\\"output\\\":\\\"?S?W\\\"}\")"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.request.json
new file mode 100644
index 00000000..8c9f090a
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-2ee666392a1d7d74.request.json
@@ -0,0 +1,37 @@
+{
+  "frequency_penalty": 46.10292730424837,
+  "functions": [
+    {
+      "name": "vDrB3? ",
+      "parameters": {}
+    },
+    {
+      "description": "8oiu?.G,yt28!o?,",
+      "name": "WDz,7Wr0,Tqu.VRWfyE."
+    }
+  ],
+  "logit_bias": {},
+  "logprobs": false,
+  "messages": [
+    {
+      "content": "?S?W",
+      "role": "tool",
+      "tool_call_id": "4.?,W!3 z e,.?, 8a.S .3C.t"
+    }
+  ],
+  "modalities": null,
+  "model": "3!4. .5..T?!!IkJ5wDX?9 ?V.?tg?8",
+  "n": 913,
+  "parallel_tool_calls": false,
+  "reasoning_effort": "high",
+  "response_format": {
+    "type": "text"
+  },
+  "stream": true,
+  "stream_options": null,
+  "tool_choice": "none",
+  "verbosity": "low",
+  "web_search_options": {
+    "search_context_size": "high"
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.meta.json
new file mode 100644
index 00000000..0d3dfa58
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.meta.json
@@ -0,0 +1,21 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages[0].content (\"\" -> [{\"text\":\"\",\"type\":\"text\"}])",
+    "universal(1->2): changed: messages[1].content[0].output (\"\" -> {\"output\":\"\"})",
+    "universal(1->2): changed: params.store (false -> null)",
+    "chat(final): lost: reasoning_effort",
+    "chat(final): lost: prediction",
+    "chat(final): lost: function_call",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: store",
+    "chat(final): lost: n",
+    "chat(final): lost: messages[0].audio",
+    "chat(final): lost: messages[1].name",
+    "chat(final): added: messages[0].content",
+    "chat(final): added: messages[1].tool_call_id",
+    "chat(final): changed: messages[1].content (null -> \"{\\\"output\\\":\\\"\\\"}\")",
+    "chat(final): changed: messages[1].role (\"function\" -> \"tool\")"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.request.json
new file mode 100644
index 00000000..adf092c2
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-310ed34a7ad861b4.request.json
@@ -0,0 +1,29 @@
+{
+  "function_call": "auto",
+  "messages": [
+    {
+      "audio": {
+        "id": "mjK.?,NZp..6. N0? 8.?TUh.?r cvG!o.v!8xIa1k 7MpF6q5"
+      },
+      "role": "assistant"
+    },
+    {
+      "content": null,
+      "name": "Q,ovM?",
+      "role": "function"
+    }
+  ],
+  "model": ",YaO?5!H?z?x.4!SH F?,.X0TDS?.Px,!8A,,p",
+  "n": 673,
+  "prediction": {
+    "content": "c..o,T?x7D.?.m!?6!Q ?i? ",
+    "type": "content"
+  },
+  "reasoning_effort": null,
+  "response_format": {
+    "type": "json_object"
+  },
+  "store": false,
+  "stream_options": null,
+  "tool_choice": "none"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.meta.json
new file mode 100644
index 00000000..3ebacff3
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.meta.json
@@ -0,0 +1,28 @@
+{
+  "issues": [
+    "universal(1->2): changed: messages.length (3 -> 1)",
+    "universal(1->2): changed: params.seed (-695 -> null)",
+    "universal(1->2): changed: params.tools ([{\"description\":\" .?!BQ.,1S!83?.vy4\",\"kind\":\"custom\",\"name\":\"V3.Zj.hB?nc.L?Ql.,c4?f?x1uPsO.,,,.?ya?,4?e\"},{\"format\":{\"grammar\":{\"definition\":\"6.2xx?Wt,!c?A?f,2Za?O, L J3Jy.8,yp.\",\"syntax\":\"lark\"},\"type\":\"grammar\"},\"kind\":\"custom\",\"name\":\"264!F?j8F\"}] -> null)",
+    "universal(1->2): changed: params.top_logprobs (328 -> null)",
+    "universal(1->2): changed: params.parallel_tool_calls (true -> null)",
+    "universal(1->2): changed: params.presence_penalty (-17.30499605635964 -> null)",
+    "universal(1->2): changed: params.frequency_penalty (8.40294665126246 -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: prediction",
+    "chat(final): lost: n",
+    "chat(final): lost: frequency_penalty",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: seed",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: max_tokens",
+    "chat(final): lost: tools",
+    "chat(final): lost: functions",
+    "chat(final): lost: audio",
+    "chat(final): changed: messages.length (3 -> 1)",
+    "chat(final): changed: max_completion_tokens (-902 -> 586)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.request.json
new file mode 100644
index 00000000..c4da079d
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-33d13b18d488f747.request.json
@@ -0,0 +1,98 @@
+{
+  "audio": {
+    "format": "opus",
+    "voice": "?,R.l..YBo?,j.!1a.CT!3es.P?W893?,Mjli"
+  },
+  "frequency_penalty": 8.40294665126246,
+  "functions": [
+    {
+      "description": "?e4W,DB?.?4VO??T?4e.EZ6.?D,5?5.v5j.D,pG5.uX ",
+      "name": "N,O?.,9,.d,.4 75fh,wl?04!.9 4e ..?4A",
+      "parameters": {}
+    },
+    {
+      "name": "Dbjw??"
+    },
+    {
+      "name": "!O,??",
+      "parameters": {}
+    },
+    {
+      "name": "NXf.?S, 1OO2??R.o!vC,x.7?bS ku,,R?EigRM ?yUx,Y?SJz",
+      "parameters": {}
+    }
+  ],
+  "max_completion_tokens": -902,
+  "max_tokens": 586,
+  "messages": [
+    {
+      "function_call": null,
+      "role": "assistant"
+    },
+    {
+      "content": [
+        {
+          "text": ",S!?6!s,AyB.Wn3T,us.g.3",
+          "type": "text"
+        }
+      ],
+      "name": "?S.3Y.?3?55Q.71Ot5RoF1,P60?.?bjE.?8??XM4?P?m,,?",
+      "role": "developer"
+    },
+    {
+      "audio": null,
+      "content": ".A4.1.a,,4L.ni,8.ve,?qnsu6?P",
+      "name": "b5,!O!k l.HQJI!Bi0c!!,",
+      "role": "assistant"
+    }
+  ],
+  "model": "a,1?0?.7,BTr57g?W.N7 ,h3IJr S4 nc",
+  "n": 159,
+  "parallel_tool_calls": true,
+  "prediction": {
+    "content": [
+      {
+        "text": ",6?Q ",
+        "type": "text"
+      },
+      {
+        "text": "8x?x?9..N. !..Lm.? ?4.,??LuO.A5Uj",
+        "type": "text"
+      },
+      {
+        "text": "DZBe .7 .?,J6Q?Qcy!.il52., ,!",
+        "type": "text"
+      }
+    ],
+    "type": "content"
+  },
+  "presence_penalty": -17.30499605635964,
+  "seed": -695,
+  "tool_choice": "required",
+  "tools": [
+    {
+      "custom": {
+        "description": " .?!BQ.,1S!83?.vy4",
+        "name": "V3.Zj.hB?nc.L?Ql.,c4?f?x1uPsO.,,,.?ya?,4?e"
+      },
+      "type": "custom"
+    },
+    {
+      "custom": {
+        "format": {
+          "grammar": {
+            "definition": "6.2xx?Wt,!c?A?f,2Za?O, L J3Jy.8,yp.",
+            "syntax": "lark"
+          },
+          "type": "grammar"
+        },
+        "name": "264!F?j8F"
+      },
+      "type": "custom"
+    }
+  ],
+  "top_logprobs": 328,
+  "web_search_options": {
+    "search_context_size": "medium"
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.meta.json
new file mode 100644
index 00000000..81f807b8
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.meta.json
@@ -0,0 +1,28 @@
+{
+  "issues": [
+    "universal(1->2): added: params.tools[0].parameters.items",
+    "universal(1->2): changed: messages[0].content[0].output (\"\" -> {\"output\":\"\"})",
+    "universal(1->2): changed: messages[1].content (\"F.sO.G!g?ba?8bDF F,Dd.Dg,.,Z?0,xA,5i?!!?..9oZecMc\" -> [{\"text\":\"F.sO.G!g?ba?8bDF F,Dd.Dg,.,Z?0,xA,5i?!!?..9oZecMc\",\"type\":\"text\"}])",
+    "universal(1->2): changed: params.presence_penalty (17.299183099790024 -> null)",
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.top_logprobs (672 -> null)",
+    "universal(1->2): changed: params.parallel_tool_calls (true -> null)",
+    "chat(final): lost: parallel_tool_calls",
+    "chat(final): lost: n",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: prediction",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: messages[0].name",
+    "chat(final): lost: messages[1].audio",
+    "chat(final): lost: messages[1].function_call",
+    "chat(final): lost: messages[1].refusal",
+    "chat(final): added: tools[0].function.parameters.items",
+    "chat(final): added: messages[0].tool_call_id",
+    "chat(final): changed: stop (\"!D.k?R?p L!N,qnWi,s 8.5,l L. k!h\" -> [\"!D.k?R?p L!N,qnWi,s 8.5,l L. k!h\"])",
+    "chat(final): changed: messages[0].content (null -> \"{\\\"output\\\":\\\"\\\"}\")",
+    "chat(final): changed: messages[0].role (\"function\" -> \"tool\")"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.request.json
new file mode 100644
index 00000000..a4a10759
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-34ba485a1406f69c.request.json
@@ -0,0 +1,60 @@
+{
+  "messages": [
+    {
+      "content": null,
+      "name": "??.p m,!6?00w.?..CQ8.!...uZ...s?g.A",
+      "role": "function"
+    },
+    {
+      "audio": null,
+      "content": "F.sO.G!g?ba?8bDF F,Dd.Dg,.,Z?0,xA,5i?!!?..9oZecMc",
+      "function_call": {
+        "arguments": "D,e uLG3v A6XQ,5m",
+        "name": ",Pm?,,,BAg!N.khza.XW.jV?,5.Rp51,."
+      },
+      "refusal": null,
+      "role": "assistant"
+    }
+  ],
+  "model": "7oKl,XCq8,fE,35,VV!,..?s.2 3kn.!I.Un.gWoI1",
+  "n": 905,
+  "parallel_tool_calls": true,
+  "prediction": {
+    "content": [
+      {
+        "text": "  vIfvB.l0.U?i",
+        "type": "text"
+      },
+      {
+        "text": "..?l.!20eC..?Om0q!9?b.51lt,??m,.. .F,e,a",
+        "type": "text"
+      }
+    ],
+    "type": "content"
+  },
+  "presence_penalty": 17.299183099790024,
+  "reasoning_effort": "low",
+  "response_format": {
+    "type": "json_object"
+  },
+  "stop": "!D.k?R?p L!N,qnWi,s 8.5,l L. k!h",
+  "tool_choice": {
+    "function": {
+      "name": "5,?F,2x?Frh1 .Uq5!.m"
+    },
+    "type": "function"
+  },
+  "tools": [
+    {
+      "function": {
+        "name": "CNl.bI.?D?WW,.af,?!QY.?.? ?.z85Pp?! oZ",
+        "parameters": {}
+      },
+      "type": "function"
+    }
+  ],
+  "top_logprobs": 672,
+  "web_search_options": {
+    "search_context_size": "high"
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.meta.json
new file mode 100644
index 00000000..a2a2ac47
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.meta.json
@@ -0,0 +1,23 @@
+{
+  "issues": [
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.store (true -> null)",
+    "universal(1->2): changed: params.logprobs (true -> null)",
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.reasoning.effort (\"medium\" -> \"low\")",
+    "universal(1->2): changed: params.presence_penalty (90.809479429592 -> null)",
+    "universal(1->2): changed: messages.length (1 -> 0)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: presence_penalty",
+    "chat(final): lost: stream",
+    "chat(final): lost: functions",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: store",
+    "chat(final): lost: n",
+    "chat(final): lost: logprobs",
+    "chat(final): changed: reasoning_effort (\"medium\" -> \"low\")",
+    "chat(final): changed: messages.length (1 -> 0)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.request.json
new file mode 100644
index 00000000..86176579
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-4ec638697bbccbe3.request.json
@@ -0,0 +1,56 @@
+{
+  "functions": [
+    {
+      "name": ".?Hw.?,!..w",
+      "parameters": {}
+    },
+    {
+      "description": "fv 0gAo?Ez6,Hr,.W?,M ZtY,  7n21nS?fH.W?,c",
+      "name": "? L?g?,E?!.?.A?80R8.dqY,UScyT8134?.Z8W!?.,,?8"
+    },
+    {
+      "description": "bB ,, .9.l.,Y?P.???e5",
+      "name": "iv?!"
+    }
+  ],
+  "logprobs": true,
+  "max_completion_tokens": 160,
+  "messages": [
+    {
+      "content": [
+        {
+          "text": "3Oqp,..",
+          "type": "text"
+        },
+        {
+          "text": "??cGz!,5y8",
+          "type": "text"
+        },
+        {
+          "text": "BSs E?k6?6,..?!fC?5A,",
+          "type": "text"
+        }
+      ],
+      "name": "!u,?Nl?,O2 0 ag!6. rw..!?,LMp!L?!VWf,.av!",
+      "role": "developer"
+    }
+  ],
+  "model": "RJ",
+  "n": -396,
+  "presence_penalty": 90.809479429592,
+  "reasoning_effort": "medium",
+  "response_format": {
+    "type": "json_object"
+  },
+  "store": true,
+  "stream": true,
+  "web_search_options": {
+    "search_context_size": "low",
+    "user_location": {
+      "approximate": {
+        "region": "1?x?zH7z,.,27Doe?C."
+      },
+      "type": "approximate"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.meta.json
new file mode 100644
index 00000000..10c4129d
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.meta.json
@@ -0,0 +1,37 @@
+{
+  "issues": [
+    "universal(1->2): added: params.response_format.json_schema.schema.items",
+    "universal(1->2): changed: messages.length (3 -> 1)",
+    "universal(1->2): changed: params.tools ([{\"description\":\"Owd5Y!XouwrA4x..qh11U !?74 m ?VFbY,k ce!.k eE\",\"kind\":\"custom\",\"name\":\".XDT!ckr9,,?wXL?.,.x u !2,.1?  5b!9o!HAF.?7\"},{\"format\":{\"type\":\"text\"},\"kind\":\"custom\",\"name\":\"Y,,o.uPG6,cEg!f.fA83B4.6umV?N ?uZJ!,vi\"}] -> null)",
+    "universal(1->2): changed: params.reasoning.effort (\"high\" -> \"low\")",
+    "universal(1->2): changed: params.reasoning.canonical (\"effort\" -> \"budget_tokens\")",
+    "universal(1->2): changed: params.store (false -> null)",
+    "universal(1->2): changed: params.top_logprobs (-941 -> null)",
+    "universal(1->2): changed: params.response_format.json_schema.name (\"i?.Bn.S?eF.K!.9v rPD,?,.1R.LY92i,,?..OY8,?,!W.\" -> \"response\")",
+    "universal(1->2): changed: params.response_format.json_schema.description (\",?N !u3d?Z0?F  \" -> null)",
+    "universal(1->2): changed: params.seed (-566 -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: seed",
+    "chat(final): lost: functions",
+    "chat(final): lost: verbosity",
+    "chat(final): lost: function_call",
+    "chat(final): lost: tools",
+    "chat(final): lost: top_logprobs",
+    "chat(final): lost: max_tokens",
+    "chat(final): lost: logit_bias",
+    "chat(final): lost: audio",
+    "chat(final): lost: prediction",
+    "chat(final): lost: store",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: response_format.json_schema.strict",
+    "chat(final): lost: response_format.json_schema.description",
+    "chat(final): added: response_format.json_schema.schema.items",
+    "chat(final): changed: messages.length (3 -> 1)",
+    "chat(final): changed: stop (\"7QY,1D c,.9K.n,,,k!,1?fcO\" -> [\"7QY,1D c,.9K.n,,,k!,1?fcO\"])",
+    "chat(final): changed: max_completion_tokens (416 -> 357)",
+    "chat(final): changed: response_format.json_schema.name (\"i?.Bn.S?eF.K!.9v rPD,?,.1R.LY92i,,?..OY8,?,!W.\" -> \"response\")",
+    "chat(final): changed: reasoning_effort (\"high\" -> \"low\")"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.request.json
new file mode 100644
index 00000000..db7bb721
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-64011eae99c883f4.request.json
@@ -0,0 +1,99 @@
+{
+  "audio": {
+    "format": "wav",
+    "voice": "w?!L"
+  },
+  "function_call": "auto",
+  "functions": [
+    {
+      "description": ".Zw?E",
+      "name": "d",
+      "parameters": {}
+    },
+    {
+      "description": "7Qb?,!As ? 4JdK !!!2! D,?xo l",
+      "name": "NJW.N.z0u9!aP,lI4,k.2,M2U0K"
+    },
+    {
+      "description": ". ,nGTl.d..yZBuF.,b5lgE  .EIkP.L",
+      "name": "!"
+    }
+  ],
+  "logit_bias": {},
+  "max_completion_tokens": 416,
+  "max_tokens": 357,
+  "messages": [
+    {
+      "content": null,
+      "name": "B,.?!N7iTxUU9P,v,!q!75? E.TB 0!j.GVvD.C2",
+      "role": "function"
+    },
+    {
+      "content": "MJ1.a,kg6!?.HDr,e0,.s.Kx02",
+      "role": "system"
+    },
+    {
+      "content": ",V.i7x,rD,..a?p5 0?Z",
+      "role": "tool",
+      "tool_call_id": "BW "
+    }
+  ],
+  "model": "gpt-4-turbo-preview",
+  "prediction": {
+    "content": [
+      {
+        "text": "h?92fv9z3G, ?,?c..?P,,0,Y.R,?.NEK,OGe?",
+        "type": "text"
+      },
+      {
+        "text": " .?gAD.gXaD?.r,GJ?.",
+        "type": "text"
+      },
+      {
+        "text": ".!.!.6?J1,.7gO?j3v? W.s,,?2O,.? QG,b4m?o.",
+        "type": "text"
+      }
+    ],
+    "type": "content"
+  },
+  "reasoning_effort": "high",
+  "response_format": {
+    "json_schema": {
+      "description": ",?N !u3d?Z0?F  ",
+      "name": "i?.Bn.S?eF.K!.9v rPD,?,.1R.LY92i,,?..OY8,?,!W.",
+      "schema": {},
+      "strict": null
+    },
+    "type": "json_schema"
+  },
+  "seed": -566,
+  "stop": "7QY,1D c,.9K.n,,,k!,1?fcO",
+  "store": false,
+  "stream_options": null,
+  "tool_choice": {
+    "function": {
+      "name": "9d.o!.GQZ,? ??A O?s,"
+    },
+    "type": "function"
+  },
+  "tools": [
+    {
+      "custom": {
+        "description": "Owd5Y!XouwrA4x..qh11U !?74 m ?VFbY,k ce!.k eE",
+        "name": ".XDT!ckr9,,?wXL?.,.x u !2,.1?  5b!9o!HAF.?7"
+      },
+      "type": "custom"
+    },
+    {
+      "custom": {
+        "format": {
+          "type": "text"
+        },
+        "name": "Y,,o.uPG6,cEg!f.fA83B4.6umV?N ?uZJ!,vi"
+      },
+      "type": "custom"
+    }
+  ],
+  "top_logprobs": -941,
+  "verbosity": null
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.meta.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.meta.json
new file mode 100644
index 00000000..776c55da
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.meta.json
@@ -0,0 +1,28 @@
+{
+  "issues": [
+    "universal(1->2): lost: params.tools[0].strict",
+    "universal(1->2): changed: messages.length (3 -> 0)",
+    "universal(1->2): changed: params.logprobs (true -> null)",
+    "universal(1->2): changed: params.frequency_penalty (-70.06246855099464 -> null)",
+    "universal(1->2): changed: params.stream (true -> null)",
+    "universal(1->2): changed: params.store (false -> null)",
+    "google(1->2): lost: systemInstruction",
+    "chat(final): lost: store",
+    "chat(final): lost: reasoning_effort",
+    "chat(final): lost: audio",
+    "chat(final): lost: modalities",
+    "chat(final): lost: prediction",
+    "chat(final): lost: stream",
+    "chat(final): lost: frequency_penalty",
+    "chat(final): lost: web_search_options",
+    "chat(final): lost: function_call",
+    "chat(final): lost: stream_options",
+    "chat(final): lost: functions",
+    "chat(final): lost: logprobs",
+    "chat(final): lost: tools[0].function.strict",
+    "chat(final): changed: stop (\".9.h?,!3X cix?R7?b.mP7x4p6H??6!?7pC,?k?U\" -> [\".9.h?,!3X cix?R7?b.mP7x4p6H??6!?7pC,?k?U\"])",
+    "chat(final): changed: messages.length (3 -> 0)"
+  ],
+  "kind": "chat-google-two-arm",
+  "provider": "chat-completions"
+}
diff --git a/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.request.json b/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.request.json
new file mode 100644
index 00000000..f5261471
--- /dev/null
+++ b/payloads/fuzz-snapshots/chat-google-two-arm/case-a3ec1907e0d629d5.request.json
@@ -0,0 +1,80 @@
+{
+  "audio": {
+    "format": "pcm16",
+    "voice": "ash"
+  },
+  "frequency_penalty": -70.06246855099464,
+  "function_call": "auto",
+  "functions": [
+    {
+      "name": "E 1qQ KmZ? "
+    }
+  ],
+  "logprobs": true,
+  "max_completion_tokens": 443,
+  "messages": [
+    {
+      "content": [
+        {
+          "text": ",f  .wX ?",
+          "type": "text"
+        }
+      ],
+      "role": "developer"
+    },
+    {
+      "content": " 5xPcy?qc ,Q?.,?!.?10KMn.,F?V,h?9?Y",
+      "name": " Lof..WP56s i!9Xw",
+      "role": "system"
+    },
+    {
+      "content": [
+        {
+          "text": "8yt!w",
+          "type": "text"
+        },
+        {
+          "text": ".!wX?",
+          "type": "text"
+        }
+      ],
+      "name": "A,8.d.p., ??k..2h8  9 HI.t!u8.1s?t,OV!?H! !?E5W!y",
+      "role": "developer"
+    }
+  ],
+  "modalities": null,
+  "model": "o3-2025-04-16",
+  "prediction": {
+    "content": [
+      {
+        "text": "??j.,.E1 f,.?d.50QswHW.!5S.2?h?oLnJi?z5.T,tg.",
+        "type": "text"
+      },
+      {
+        "text": ".?n?6,N.t8I!?!qy?hu.A88!?vU2vj.t.2?AxUG ,XhPh",
+        "type": "text"
+      }
+    ],
+    "type": "content"
+  },
+  "reasoning_effort": null,
+  "stop": ".9.h?,!3X cix?R7?b.mP7x4p6H??6!?7pC,?k?U",
+  "store": false,
+  "stream": true,
+  "stream_options": {
+    "include_obfuscation": false
+  },
+  "tools": [
+    {
+      "function": {
+        "description": "r.7.?J!3x",
+        "name": "?,Z",
+        "strict": true
+      },
+      "type": "function"
+    }
+  ],
+  "web_search_options": {
+    "search_context_size": "medium"
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.meta.json
new file mode 100644
index 00000000..c77444fe
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.meta.json
@@ -0,0 +1,7 @@
+{
+  "issues": [
+    "request_to_universal error: Conversion to universal format failed: Missing required field: parts"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.request.json
new file mode 100644
index 00000000..8a5b052d
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-00015db5103bca8c.request.json
@@ -0,0 +1,53 @@
+{
+  "cachedContent": "Zx.yEkOd0",
+  "contents": [
+    {
+      "role": ".,i?0"
+    },
+    {
+      "role": "?kV.k ,,LMM.3f,1?,mlxb6I3IG"
+    }
+  ],
+  "generationConfig": {
+    "_responseJsonSchema": null,
+    "frequencyPenalty": -60.42419908836965,
+    "imageConfig": {},
+    "logprobs": -825,
+    "maxOutputTokens": -266,
+    "presencePenalty": 62.34146184198899,
+    "responseMimeType": "S",
+    "responseModalities": [
+      "IMAGE"
+    ],
+    "speechConfig": {
+      "multiSpeakerVoiceConfig": {
+        "speakerVoiceConfigs": [
+          {
+            "voiceConfig": {
+              "prebuiltVoiceConfig": null
+            }
+          }
+        ]
+      }
+    },
+    "stopSequences": [
+      "zA!,2.xB,TLcC. jfvuE.,k!xy S.?5I?2c.o"
+    ],
+    "thinkingConfig": {
+      "includeThoughts": true,
+      "thinkingBudget": -573,
+      "thinkingLevel": "MINIMAL"
+    }
+  },
+  "safetySettings": [
+    {},
+    {}
+  ],
+  "systemInstruction": {},
+  "toolConfig": {
+    "functionCallingConfig": {
+      "mode": "AUTO"
+    },
+    "retrievalConfig": {}
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.meta.json
new file mode 100644
index 00000000..033e4af0
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.meta.json
@@ -0,0 +1,15 @@
+{
+  "issues": [
+    "lost: systemInstruction",
+    "lost: toolConfig",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "lost: contents[0].parts[0].videoMetadata",
+    "lost: contents[0].parts[0].partMetadata",
+    "lost: contents[0].parts[0].functionResponse",
+    "lost: contents[0].parts[0].thought",
+    "lost: contents[0].parts[0].functionCall",
+    "added: contents[0].role"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.request.json
new file mode 100644
index 00000000..92e9f4d2
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-0005d480caf84338.request.json
@@ -0,0 +1,97 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "functionCall": {
+            "id": "xJ9iB"
+          },
+          "functionResponse": {
+            "id": ".qM?",
+            "name": ",W?zH.p??d 3!",
+            "willContinue": true
+          },
+          "partMetadata": {},
+          "text": "52, .X?,!Z 1L s!,GH!!!aFdv.mKl,l?,.?Dq",
+          "thought": true,
+          "thoughtSignature": " Kl,6?",
+          "videoMetadata": {
+            "endOffset": "Bpv?? !,,Jr,giuk!n. EZe66,1!buc?",
+            "fps": 11.271011959752407,
+            "startOffset": "5P3Q,w,n,3e,x"
+          }
+        }
+      ]
+    }
+  ],
+  "systemInstruction": {
+    "parts": [
+      {
+        "codeExecutionResult": {
+          "output": "?I.,?jJ!f. .DuF1374!.Ahv2q7,9j22T3zHbO.Rn4?A"
+        },
+        "executableCode": {
+          "code": "!?B?D.N!U??us1?.x??,,S4f2b6.L",
+          "language": "LANGUAGE_UNSPECIFIED"
+        },
+        "fileData": {
+          "fileUri": "?!.jj?!,PC8. 6.??,x8,?s?pw33A,R?L L",
+          "mimeType": ",,.?.!w1w0 3i.9!?...yQ.x,FVL!.."
+        },
+        "functionCall": {
+          "args": {},
+          "id": "7?. 5.sjWl9 2Qc 5,! z. ??Qo H.q47. OPvJuB.,!iNi v",
+          "name": ".3A?.?4g?IO!?Ymdx!a??s!,p?.fOGE?.e,Vg?"
+        },
+        "functionResponse": {
+          "id": "!,cd,fy.. hA?82S9Fhp 4m.h?!DJ!u8?j.?N9g1,",
+          "parts": [
+            {
+              "inlineData": {
+                "mimeType": null
+              }
+            },
+            {},
+            {
+              "inlineData": {
+                "data": null
+              }
+            }
+          ]
+        },
+        "partMetadata": {},
+        "text": "S"
+      },
+      {
+        "codeExecutionResult": {
+          "outcome": "OUTCOME_DEADLINE_EXCEEDED",
+          "output": "a.MGjQ4"
+        },
+        "fileData": {
+          "mimeType": "7.Q8 NZ..D..Q?yNAc?KVNg,?p8.??,"
+        },
+        "functionResponse": {
+          "parts": [
+            {
+              "inlineData": {}
+            },
+            {
+              "inlineData": {
+                "data": null
+              }
+            }
+          ],
+          "response": {},
+          "scheduling": "INTERRUPT"
+        },
+        "inlineData": {},
+        "videoMetadata": {
+          "endOffset": " .,.?g9.,j,Ly2O,47.XqVw.p?Oe?0?ZA",
+          "fps": 69.29815115247787,
+          "startOffset": "i ?x?71He,si?1.?.IW,B?!I!0"
+        }
+      }
+    ]
+  },
+  "toolConfig": {}
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.meta.json
new file mode 100644
index 00000000..6432821c
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.meta.json
@@ -0,0 +1,9 @@
+{
+  "issues": [
+    "changed: contents[0].role (\"a\" -> \"user\")",
+    "changed: contents[0].parts.length (1 -> 0)",
+    "changed: tools.length (1 -> 2)"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.request.json
new file mode 100644
index 00000000..e0ea4523
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-007bd4500a682a93.request.json
@@ -0,0 +1,27 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "inlineData": {}
+        }
+      ],
+      "role": "a"
+    }
+  ],
+  "tools": [
+    {
+      "computerUse": {
+        "excludedPredefinedFunctions": [
+          "?.bi.?,p"
+        ]
+      },
+      "googleSearch": {
+        "timeRangeFilter": {
+          "startTime": "QDBDMGS.?lxG,,?.X?9?j.k?TA.!x.R,?9,"
+        }
+      },
+      "googleSearchRetrieval": {}
+    }
+  ]
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.meta.json
new file mode 100644
index 00000000..0bc93dfa
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.meta.json
@@ -0,0 +1,10 @@
+{
+  "issues": [
+    "lost: toolConfig",
+    "lost: contents[0].parts[0].inlineData",
+    "lost: contents[0].parts[0].videoMetadata",
+    "changed: contents[0].role (\"j.,.kD8c,v! ?\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.request.json
new file mode 100644
index 00000000..abd0ac60
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-051ebd07ca42b0d6.request.json
@@ -0,0 +1,23 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "inlineData": {},
+          "text": "?lsKj.a? ??R6?,uO3q?p2j?? .h ",
+          "videoMetadata": {
+            "fps": 70.04902652071755
+          }
+        }
+      ],
+      "role": "j.,.kD8c,v! ?"
+    }
+  ],
+  "toolConfig": {
+    "retrievalConfig": {
+      "latLng": {
+        "longitude": 42.35899714596116
+      }
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.meta.json
new file mode 100644
index 00000000..1ecb131c
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.meta.json
@@ -0,0 +1,13 @@
+{
+  "issues": [
+    "lost: toolConfig",
+    "lost: systemInstruction",
+    "lost: contents[0].parts[0].videoMetadata",
+    "lost: contents[0].parts[0].mediaResolution",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "added: contents[0].role",
+    "added: contents[0].parts[0].inlineData.mimeType"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.request.json
new file mode 100644
index 00000000..642d91b6
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-066263d9b371b047.request.json
@@ -0,0 +1,50 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "inlineData": {
+            "data": ".vW1 v?,Nx6mq?a?A?8,5E"
+          },
+          "mediaResolution": {},
+          "thoughtSignature": "AVJlL,u.?Y?PN Tsr",
+          "videoMetadata": {
+            "fps": 65.50903686895178,
+            "startOffset": "?Z?R,.Fu d. ,"
+          }
+        }
+      ]
+    }
+  ],
+  "model": "D ",
+  "safetySettings": [
+    {}
+  ],
+  "systemInstruction": {
+    "parts": [
+      {
+        "codeExecutionResult": {
+          "outcome": "OUTCOME_UNSPECIFIED"
+        },
+        "executableCode": {
+          "code": " 9.!?..t3VA.2?",
+          "language": "LANGUAGE_UNSPECIFIED"
+        },
+        "functionResponse": {
+          "response": {},
+          "willContinue": false
+        },
+        "text": "z,f 7,IZlg, N!W,u?a f5,4U!.2!,d,.",
+        "thought": true,
+        "thoughtSignature": ",KheB??KQqCP,M1!.c.e.,2gzDKYJ.?,FBt,Pk8"
+      }
+    ]
+  },
+  "toolConfig": {
+    "retrievalConfig": {
+      "latLng": {
+        "longitude": -49.83756195325235
+      }
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.meta.json
new file mode 100644
index 00000000..b6e22213
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.meta.json
@@ -0,0 +1,14 @@
+{
+  "issues": [
+    "lost: contents[0].parts[0].partMetadata",
+    "lost: contents[0].parts[0].thought",
+    "lost: contents[0].parts[0].mediaResolution",
+    "lost: contents[0].parts[0].videoMetadata",
+    "lost: contents[0].parts[0].codeExecutionResult",
+    "lost: contents[0].parts[0].functionCall",
+    "lost: contents[0].parts[0].fileData",
+    "changed: contents[0].role (\"L,???b3M?!vZ!y,.3Q..FL0!.5 e.,?\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.request.json
new file mode 100644
index 00000000..ac7ef8f6
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-08e697e9ba45fe3e.request.json
@@ -0,0 +1,28 @@
+{
+  "cachedContent": "W02F.q!.GGcS.qm.,3..M!mn!8H? .9bSyHSf?UVER",
+  "contents": [
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {
+            "outcome": "OUTCOME_OK",
+            "output": "32iaPm,psYi,u1JR"
+          },
+          "fileData": {
+            "fileUri": "G?.ua?tx64Ri?,??z.3Zk5T?Y8????I,Pd79sa.?XX?, ,"
+          },
+          "functionCall": {},
+          "mediaResolution": {},
+          "partMetadata": {},
+          "text": "GnQ,!2?,Zx2.4 Z.?  ,H 0a0Qd?,8Z2M.3u.!.L.dm?pN",
+          "thought": false,
+          "videoMetadata": {
+            "endOffset": "MOKAT ,a,V,v,?ng.i KP.17ZK,,,k,i.o?kQ?,,4xWx,.p.3t",
+            "startOffset": "77?!d. ?!j "
+          }
+        }
+      ],
+      "role": "L,???b3M?!vZ!y,.3Q..FL0!.5 e.,?"
+    }
+  ]
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.meta.json
new file mode 100644
index 00000000..0c95c2ae
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.meta.json
@@ -0,0 +1,14 @@
+{
+  "issues": [
+    "lost: systemInstruction",
+    "lost: toolConfig.functionCallingConfig.allowedFunctionNames",
+    "lost: generationConfig.responseMimeType",
+    "lost: generationConfig.speechConfig.multiSpeakerVoiceConfig.speakerVoiceConfigs[0].voiceConfig.prebuiltVoiceConfig",
+    "added: generationConfig.responseSchema",
+    "changed: toolConfig.functionCallingConfig.mode (\"VALIDATED\" -> \"AUTO\")",
+    "changed: contents[0].parts.length (1 -> 0)",
+    "changed: contents[0].role (\"092,?JS.,02,N4 ..xQ3X..d6!p8u?l.aq73k,FK!tG?5I\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.request.json
new file mode 100644
index 00000000..12a39020
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-0bde07b217c86337.request.json
@@ -0,0 +1,94 @@
+{
+  "cachedContent": "1FfW7eP9!!!wV!c?4?758Z2i?8a1.B?8b,6X.M.?5?,",
+  "contents": [
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {
+            "output": "ql.H,?Ewf973 g.I,XZ?bqw7,nZ? kGi !S?1ia?k"
+          },
+          "executableCode": {
+            "code": ",A.. Q.J?TD",
+            "language": "LANGUAGE_UNSPECIFIED"
+          },
+          "fileData": {
+            "mimeType": "?. 2?77o.3,krV00 am6,z"
+          },
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_HIGH"
+          },
+          "partMetadata": {},
+          "thought": true,
+          "videoMetadata": {}
+        }
+      ],
+      "role": "092,?JS.,02,N4 ..xQ3X..d6!p8u?l.aq73k,FK!tG?5I"
+    }
+  ],
+  "generationConfig": {
+    "candidateCount": -720,
+    "frequencyPenalty": -2.548798129137723,
+    "logprobs": -608,
+    "mediaResolution": "MEDIA_RESOLUTION_HIGH",
+    "presencePenalty": -81.12346234355222,
+    "responseJsonSchema": " 4c09s BvUzow4y6G3UV7w1 qqs2",
+    "responseLogprobs": true,
+    "responseMimeType": "M,Q.,NU.,N",
+    "responseModalities": [
+      "AUDIO",
+      "MODALITY_UNSPECIFIED",
+      "IMAGE"
+    ],
+    "seed": 562,
+    "speechConfig": {
+      "languageCode": "!VH,",
+      "multiSpeakerVoiceConfig": {
+        "speakerVoiceConfigs": [
+          {
+            "voiceConfig": {
+              "prebuiltVoiceConfig": null
+            }
+          },
+          {
+            "voiceConfig": {}
+          },
+          {
+            "speaker": "N,?K0wu.R!o.,E hVT,!,O,38v 5"
+          }
+        ]
+      }
+    },
+    "topP": 30.900514366320234
+  },
+  "model": "IerC,???XA,Iy7N1n4,..y! ?.KO ",
+  "systemInstruction": {
+    "parts": [
+      {
+        "executableCode": {
+          "code": "e!CfUzN.i? .... 55r.Z3LQf41",
+          "language": "PYTHON"
+        },
+        "functionCall": {
+          "args": {}
+        },
+        "functionResponse": {
+          "id": ". .X",
+          "name": "oat09o.n3RQ4.E ?3ZEJp?t!E9,P ,wms",
+          "response": {}
+        },
+        "mediaResolution": {},
+        "thought": false,
+        "thoughtSignature": "L9p5"
+      }
+    ],
+    "role": "Z,?WUq?M,Dm9MY 2.4mA8,0 ,XD7M?,, 1.7fE6!! XNb9"
+  },
+  "toolConfig": {
+    "functionCallingConfig": {
+      "allowedFunctionNames": [
+        ",??0X.7x?MJ.8XD!,T27t?hQJ"
+      ],
+      "mode": "VALIDATED"
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.meta.json
new file mode 100644
index 00000000..2da9bb91
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.meta.json
@@ -0,0 +1,9 @@
+{
+  "issues": [
+    "lost: toolConfig",
+    "lost: systemInstruction",
+    "changed: contents.length (3 -> 1)"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.request.json
new file mode 100644
index 00000000..218004eb
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-117472f2bf6ae259.request.json
@@ -0,0 +1,157 @@
+{
+  "cachedContent": "?j.JUM04?.k3rAjkY ,?R! 25J.?,8M3MkbN7?6, ,a.ZHe",
+  "contents": [
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {
+            "outcome": "OUTCOME_UNSPECIFIED"
+          },
+          "fileData": {},
+          "functionResponse": {
+            "id": "Zi aFh?a6aG2H?.pMlo,P.m,Py .gj",
+            "parts": [
+              {
+                "inlineData": null
+              }
+            ],
+            "scheduling": "INTERRUPT",
+            "willContinue": true
+          },
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_HIGH"
+          },
+          "partMetadata": {},
+          "text": "e?T.3z0P,7a8  ,m8!.e.? ..,N.n,zaN2Ez!hoydi",
+          "thought": true
+        },
+        {
+          "functionCall": {
+            "args": {},
+            "id": ". .?2T jy!..yx.Sy1? .6P"
+          },
+          "functionResponse": {
+            "id": "wC?0 ,ha jvdb!,.,n,9?E!.O fn.wOgAc,26",
+            "response": {},
+            "willContinue": true
+          },
+          "inlineData": {},
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_UNSPECIFIED"
+          },
+          "partMetadata": {},
+          "text": "yu?9MLHSL",
+          "thought": true
+        }
+      ]
+    },
+    {
+      "parts": [
+        {
+          "executableCode": {
+            "code": "Wt, 1?OVQqtM0V2?,fd1IX?.o,?.144uE",
+            "language": "LANGUAGE_UNSPECIFIED"
+          },
+          "fileData": {
+            "mimeType": "SrZB3J,.!"
+          },
+          "functionCall": {
+            "args": {},
+            "name": "DyN!?,,,.Li8?d,Al9u7M,,L5,xXm M"
+          },
+          "functionResponse": {
+            "id": ",??,ec. j4WkMARA?8y,!.?gXTqo..3s?H jnR,.er8?g!,",
+            "name": ".L!.URw.,en!",
+            "response": {},
+            "scheduling": "WHEN_IDLE"
+          },
+          "inlineData": {
+            "data": "4.?7,Z?Z!R.,,3A .v2,rQ,?,!.lo.?!1i,Mm G2w eI0j0"
+          },
+          "text": "?2.I!1QnE,q?9u.E.S.!W.T,4..26.!3?p.z..gO",
+          "thought": false,
+          "thoughtSignature": "OAl!w8R L?, e0 !?v.w? 6",
+          "videoMetadata": {
+            "endOffset": "?.?dimZDh.?6VgY.!D?7S.. Q.A3a.,?!n",
+            "fps": 31.80004873880053,
+            "startOffset": ".56.1I.,,"
+          }
+        },
+        {
+          "codeExecutionResult": {
+            "outcome": "OUTCOME_FAILED",
+            "output": "ov2."
+          },
+          "executableCode": {
+            "language": "LANGUAGE_UNSPECIFIED"
+          },
+          "fileData": {
+            "fileUri": ".8Kp oG.P.8?u Uc",
+            "mimeType": "?t?0.r?Y.."
+          },
+          "inlineData": {
+            "mimeType": " Z .?l.,.V8UOK"
+          },
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_LOW"
+          },
+          "text": " nQ7UhFf9,cJ5dO3,8?2??1b",
+          "thought": true,
+          "videoMetadata": {
+            "fps": -87.21323262709994,
+            "startOffset": "5Ps.Q,s!??Y84.,bh??G??!! "
+          }
+        }
+      ]
+    },
+    {
+      "parts": [
+        {
+          "functionCall": {
+            "args": {}
+          },
+          "inlineData": {
+            "data": "?ijMBl4H,,w..?.vW1 v?,Nx6mq?a?A?8,5E"
+          },
+          "mediaResolution": {},
+          "thoughtSignature": "AVJlL,u.?Y?PN Tsr",
+          "videoMetadata": {
+            "fps": 65.50903686895178,
+            "startOffset": "?Z?R,.Fu d. ,"
+          }
+        }
+      ]
+    }
+  ],
+  "model": "D ",
+  "safetySettings": [
+    {}
+  ],
+  "systemInstruction": {
+    "parts": [
+      {
+        "codeExecutionResult": {
+          "outcome": "OUTCOME_UNSPECIFIED"
+        },
+        "executableCode": {
+          "code": " 9.!?..t3VA.2?",
+          "language": "LANGUAGE_UNSPECIFIED"
+        },
+        "functionResponse": {
+          "response": {},
+          "willContinue": false
+        },
+        "text": "z,f 7,IZlg, N!W,u?a f5,4U!.2!,d,.",
+        "thought": true,
+        "thoughtSignature": ",KheB??KQqCP,M1!.c.e.,2gzDKYJ.?,FBt,Pk8"
+      }
+    ]
+  },
+  "toolConfig": {
+    "retrievalConfig": {
+      "latLng": {
+        "longitude": -49.83756195325235
+      }
+    }
+  }
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.meta.json
new file mode 100644
index 00000000..c62ede6e
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.meta.json
@@ -0,0 +1,21 @@
+{
+  "issues": [
+    "lost: contents[0].parts[0].inlineData",
+    "lost: contents[0].parts[0].codeExecutionResult",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "lost: contents[0].parts[0].executableCode",
+    "lost: contents[0].parts[1].videoMetadata",
+    "lost: contents[0].parts[1].mediaResolution",
+    "lost: contents[0].parts[1].executableCode",
+    "lost: contents[0].parts[2].codeExecutionResult",
+    "lost: contents[0].parts[2].functionCall",
+    "lost: contents[0].parts[2].inlineData",
+    "lost: contents[0].parts[2].videoMetadata",
+    "lost: generationConfig.responseJsonSchema",
+    "added: generationConfig.responseSchema",
+    "changed: contents[0].role (\"7oF,.m6,L?OK,7?0JW\" -> \"user\")",
+    "changed: tools.length (1 -> 3)"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.request.json
new file mode 100644
index 00000000..8fd35f37
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-138766d1b5d34371.request.json
@@ -0,0 +1,69 @@
+{
+  "cachedContent": " xQ.PP?",
+  "contents": [
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {},
+          "executableCode": {},
+          "inlineData": {
+            "mimeType": ".e?9rOs40B!,F,.JEv,Q6j9!,,?Ad"
+          },
+          "text": " nI?G m,sy?a.?JB..!,,8rnc4R7DmvKT,,K",
+          "thoughtSignature": "z1.Tf ,4fQ..,o.Tf4w?2 F9?!N 3"
+        },
+        {
+          "executableCode": {
+            "code": "Ph.G Qw5n4r.8,Z5,.xWd!?.. o?z.a!?7B6 Aj"
+          },
+          "mediaResolution": {},
+          "text": "N.,n6a,94?II.?X?6bn.zE F R.?,c??X1 BKf2J0U 6,..",
+          "videoMetadata": {
+            "fps": -90.9113865558719
+          }
+        },
+        {
+          "codeExecutionResult": {},
+          "functionCall": {},
+          "inlineData": {
+            "data": "31A.,",
+            "mimeType": "2k.s05,Z,.e 81.?5r.bsC."
+          },
+          "text": ".,7.??JU9,.,y?!F.Dr?0,Mb,Tyc,REg,.r ,hy!PR2FhB",
+          "videoMetadata": {
+            "endOffset": "?  J!?w!w,.n ?jg.9?",
+            "startOffset": ",8C.MP!,"
+          }
+        }
+      ],
+      "role": "7oF,.m6,L?OK,7?0JW"
+    }
+  ],
+  "generationConfig": {
+    "_responseJsonSchema": "NF ",
+    "candidateCount": 861,
+    "mediaResolution": "MEDIA_RESOLUTION_HIGH",
+    "presencePenalty": -24.74147361495701,
+    "responseJsonSchema": null,
+    "seed": 764
+  },
+  "model": ",!Ji,1X.,2R5I2ME!P r7?OuIO",
+  "safetySettings": [
+    {
+      "threshold": "BLOCK_ONLY_HIGH"
+    },
+    {}
+  ],
+  "tools": [
+    {
+      "codeExecution": {},
+      "googleSearch": {},
+      "googleSearchRetrieval": {
+        "dynamicRetrievalConfig": {
+          "mode": "MODE_DYNAMIC"
+        }
+      },
+      "urlContext": {}
+    }
+  ]
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.meta.json
new file mode 100644
index 00000000..25df2d8a
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.meta.json
@@ -0,0 +1,16 @@
+{
+  "issues": [
+    "lost: toolConfig",
+    "lost: generationConfig.responseMimeType",
+    "lost: generationConfig.responseJsonSchema",
+    "lost: contents[0].parts[0].executableCode",
+    "lost: contents[0].parts[0].mediaResolution",
+    "lost: contents[0].parts[0].videoMetadata",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "added: generationConfig.thinkingConfig.includeThoughts",
+    "changed: generationConfig.responseSchema ({\"default\":\"u U712X\",\"description\":\"1!?mw!9,T??NU.9E321?92.ySf 1UXL5.!,Lf.b?l87ZJ3V.D,\",\"enum\":[\"4N,?c?.??p?.EJ5vq..UOc4,,?s1H,ZHt.D3,? \",\".dROe b.53\",\"a D?1vG.vQ.,,Kk?Pq.A8.R,\"],\"format\":\",p..E , .Zv\",\"items\":{\"description\":\",j,.!,Ng!c.chY\",\"example\":null,\"format\":\"7i8KLWM!,r6.J  !j?Q0.t???,N?.!?.!9?B,v6z6,?MN!Qt\",\"maxLength\":\" \",\"minItems\":\"?? ,?HzCp8,G?..? qr Fwj\",\"minProperties\":\",..sN.U O VN?LjP,,Z?? dhpK.d1v7.Z1,l\",\"nullable\":true,\"properties\":{},\"propertyOrdering\":[\"K !.?N,!y!!,29yTXWe?,,21 ?,.\",\"t 69\",\". z,t??2\"],\"type\":\"NULL\"},\"maxLength\":\"bpL!zlx Lbu?z,Wym.g3P!,. UE,RGT!c!64y7p?hOpTOh.\",\"maxProperties\":\"4 .,\",\"maximum\":19.61703789371374,\"minProperties\":\"!,Y.!s.?UW o,Q??!.f6!?o i\",\"required\":[\"?,? ?G,? nW.mg2e?02 R5M a6E0IP?!.,035M,,86?.\",\"PFq?L\",\".k,,?.BB6j6J\"],\"title\":\"0..QG7D,u.P?pJqM?f1?x?D,?xu0SKP,\",\"type\":\"ARRAY\"} -> null)",
+    "changed: contents[0].role (\"? ,gbww6.kgJ7Pi.6P7z.K?,J8!2?f.N.!0?\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.request.json
new file mode 100644
index 00000000..4976c63d
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-375c9df694c3d0a3.request.json
@@ -0,0 +1,95 @@
+{
+  "cachedContent": "MIL?l v.,! Y??m?j?a.,.?vzX,c3K m.DGjy.!",
+  "contents": [
+    {
+      "parts": [
+        {
+          "executableCode": {
+            "language": "LANGUAGE_UNSPECIFIED"
+          },
+          "inlineData": {
+            "data": "i?9O,2.,.H0rl7.,5.?Q,f?,n67aVy?dP",
+            "mimeType": "99bn9.?jx9?5Xu?F.6t.Q,q.V3.7ER."
+          },
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_ULTRA_HIGH"
+          },
+          "thoughtSignature": "?u!eIug..9C? soB0.8sTxo.q.k?65W??,p4 g.i3mX6 u7??",
+          "videoMetadata": {
+            "fps": 51.698216934714644
+          }
+        }
+      ],
+      "role": "? ,gbww6.kgJ7Pi.6P7z.K?,J8!2?f.N.!0?"
+    }
+  ],
+  "generationConfig": {
+    "_responseJsonSchema": "Z aX5ge66 6D 59xXsGnF",
+    "frequencyPenalty": 2.6697296059110456,
+    "imageConfig": {
+      "imageSize": "BZw,!JpI?T?CHAOT4?w .8!?P MMuh ?2S,?."
+    },
+    "logprobs": -41,
+    "maxOutputTokens": -889,
+    "mediaResolution": "MEDIA_RESOLUTION_UNSPECIFIED",
+    "responseJsonSchema": null,
+    "responseMimeType": "yH? .rM!6 .",
+    "responseModalities": [
+      "AUDIO",
+      "AUDIO"
+    ],
+    "responseSchema": {
+      "default": "u U712X",
+      "description": "1!?mw!9,T??NU.9E321?92.ySf 1UXL5.!,Lf.b?l87ZJ3V.D,",
+      "enum": [
+        "4N,?c?.??p?.EJ5vq..UOc4,,?s1H,ZHt.D3,? ",
+        ".dROe b.53",
+        "a D?1vG.vQ.,,Kk?Pq.A8.R,"
+      ],
+      "format": ",p..E , .Zv",
+      "items": {
+        "description": ",j,.!,Ng!c.chY",
+        "example": null,
+        "format": "7i8KLWM!,r6.J  !j?Q0.t???,N?.!?.!9?B,v6z6,?MN!Qt",
+        "maxLength": " ",
+        "minItems": "?? ,?HzCp8,G?..? qr Fwj",
+        "minProperties": ",..sN.U O VN?LjP,,Z?? dhpK.d1v7.Z1,l",
+        "nullable": true,
+        "properties": {},
+        "propertyOrdering": [
+          "K !.?N,!y!!,29yTXWe?,,21 ?,.",
+          "t 69",
+          ". z,t??2"
+        ],
+        "type": "NULL"
+      },
+      "maxLength": "bpL!zlx Lbu?z,Wym.g3P!,. UE,RGT!c!64y7p?hOpTOh.",
+      "maxProperties": "4 .,",
+      "maximum": 19.61703789371374,
+      "minProperties": "!,Y.!s.?UW o,Q??!.f6!?o i",
+      "required": [
+        "?,? ?G,? nW.mg2e?02 R5M a6E0IP?!.,035M,,86?.",
+        "PFq?L",
+        ".k,,?.BB6j6J"
+      ],
+      "title": "0..QG7D,u.P?pJqM?f1?x?D,?xu0SKP,",
+      "type": "ARRAY"
+    },
+    "speechConfig": {
+      "languageCode": "9avd?RZ?9hs.,n?6?!HX?.",
+      "voiceConfig": {
+        "prebuiltVoiceConfig": {}
+      }
+    },
+    "stopSequences": [
+      ",9BK hokEj Y9zD?,k!,??KLXuP?7l,,5y"
+    ],
+    "thinkingConfig": {
+      "thinkingBudget": 763
+    },
+    "topK": 207,
+    "topP": -3.3063070170643147
+  },
+  "model": "4 .,,9I4xTh,1  w?,.3rYaJMR!?? Vq.H.!.kiKyp0,?!h?D9",
+  "toolConfig": {}
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.meta.json
new file mode 100644
index 00000000..b8e47420
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.meta.json
@@ -0,0 +1,9 @@
+{
+  "issues": [
+    "lost: tools",
+    "changed: contents[0].parts.length (1 -> 0)",
+    "changed: contents[0].role (\"a\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.request.json
new file mode 100644
index 00000000..17c74e9e
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-65163e2b3d0cab80.request.json
@@ -0,0 +1,15 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "inlineData": {}
+        }
+      ],
+      "role": "a"
+    }
+  ],
+  "tools": [
+    {}
+  ]
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.meta.json
new file mode 100644
index 00000000..fa0d81b8
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.meta.json
@@ -0,0 +1,14 @@
+{
+  "issues": [
+    "lost: systemInstruction",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "lost: contents[0].parts[0].thought",
+    "lost: contents[0].parts[0].fileData",
+    "lost: contents[0].parts[0].videoMetadata",
+    "lost: contents[0].parts[0].functionCall",
+    "added: contents[0].parts[0].inlineData",
+    "changed: contents[0].role (\"N,L770L K,H,?,.l4n ,\" -> \"user\")"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.request.json
new file mode 100644
index 00000000..70069d2d
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-97dcb376a3bad1c9.request.json
@@ -0,0 +1,24 @@
+{
+  "contents": [
+    {
+      "parts": [
+        {
+          "fileData": {
+            "fileUri": "f,T?W.46R?.?!i.?",
+            "mimeType": "!?SN.U?oo8.u,.!LJ!?,,??5nY? P?e,IN57N.,4Hw,9 "
+          },
+          "functionCall": {
+            "args": {}
+          },
+          "thought": true,
+          "thoughtSignature": ",?U!bl.87n?e.q34Um,? ",
+          "videoMetadata": {
+            "startOffset": "Hfb5..I4?6iQ.bN1.se23,,4,J5,7?, ."
+          }
+        }
+      ],
+      "role": "N,L770L K,H,?,.l4n ,"
+    }
+  ],
+  "systemInstruction": {}
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.meta.json
new file mode 100644
index 00000000..6f2af3d2
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.meta.json
@@ -0,0 +1,16 @@
+{
+  "issues": [
+    "lost: toolConfig",
+    "lost: contents[0].parts[0].partMetadata",
+    "lost: contents[0].parts[0].thoughtSignature",
+    "lost: contents[0].parts[0].codeExecutionResult",
+    "lost: contents[0].parts[0].executableCode",
+    "lost: contents[0].parts[0].functionCall",
+    "added: generationConfig.responseSchema",
+    "added: generationConfig.thinkingConfig.thinkingBudget",
+    "changed: contents[0].role (\"!,B?.p,.J9H\" -> \"user\")",
+    "changed: generationConfig.thinkingConfig.includeThoughts (false -> true)"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.request.json
new file mode 100644
index 00000000..73f6e249
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-a2d3e2321403c3b4.request.json
@@ -0,0 +1,50 @@
+{
+  "cachedContent": "..? !?3?!?U4,F!H7.B,!,?,t,?zP !F,.Z?,?XGJa",
+  "contents": [
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {
+            "outcome": "OUTCOME_DEADLINE_EXCEEDED",
+            "output": "NSO?6?r,T !.8Y kfN.!"
+          },
+          "executableCode": {},
+          "functionCall": {
+            "args": {},
+            "id": "b!V!qCx?Ov?Qm?9FKKY,t,?8",
+            "name": "?AX4??PUX.m.9ZJ.w.o,o7XVJJ.?y?.!Bt 4!.2.0,?,l ,2,"
+          },
+          "inlineData": {
+            "data": "ARCQ?3tWv!?Ss.aA!1XUZ!6G?,6e.2D??,D?!5TA",
+            "mimeType": "p.b,28!m?k,Zz20td.83n,.WiazGM?lB!,.I2GIy,"
+          },
+          "partMetadata": {},
+          "thoughtSignature": "y.Rb?? .,??V?7...,O.!!?pXEh,b?.?,?Pg!?!!F91.c ,xd."
+        }
+      ],
+      "role": "!,B?.p,.J9H"
+    }
+  ],
+  "generationConfig": {
+    "_responseJsonSchema": "o8  2Wo hA3MC q 8v  A0nfE",
+    "enableEnhancedCivicAnswers": false,
+    "imageConfig": {},
+    "logprobs": 397,
+    "maxOutputTokens": 650,
+    "presencePenalty": -24.12705797021374,
+    "responseModalities": [
+      "TEXT",
+      "MODALITY_UNSPECIFIED"
+    ],
+    "speechConfig": {
+      "voiceConfig": {}
+    },
+    "temperature": -85.88575612520403,
+    "thinkingConfig": {
+      "includeThoughts": false
+    },
+    "topP": -20.02183526273265
+  },
+  "model": "!PB!YL,lai...XDJ,x??e,L0.3?3..w?C905?",
+  "toolConfig": {}
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.meta.json b/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.meta.json
new file mode 100644
index 00000000..f7ca4327
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.meta.json
@@ -0,0 +1,13 @@
+{
+  "issues": [
+    "lost: systemInstruction",
+    "lost: toolConfig",
+    "lost: tools[0].urlContext",
+    "lost: tools[0].fileSearch",
+    "lost: tools[0].computerUse",
+    "lost: tools[0].googleMaps",
+    "changed: contents.length (3 -> 1)"
+  ],
+  "kind": "request-roundtrip",
+  "provider": "google"
+}
diff --git a/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.request.json b/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.request.json
new file mode 100644
index 00000000..f29d206e
--- /dev/null
+++ b/payloads/fuzz-snapshots/google-roundtrip/case-c18e28e85b79bba8.request.json
@@ -0,0 +1,116 @@
+{
+  "cachedContent": " , oQC,?,,q,, p5?.94nKlh?1X?,S,W",
+  "contents": [
+    {
+      "parts": [
+        {
+          "functionCall": {
+            "args": {}
+          },
+          "functionResponse": {
+            "id": "XZo.5,Co. P",
+            "scheduling": "SCHEDULING_UNSPECIFIED"
+          },
+          "mediaResolution": {
+            "level": "MEDIA_RESOLUTION_LOW"
+          },
+          "partMetadata": {},
+          "videoMetadata": {
+            "endOffset": "Z?!g!rE,53E,2Z?9YAmEOJK.Mx.31?V,4 !3 !Z,"
+          }
+        }
+      ],
+      "role": ",B.?!8??,y!?"
+    },
+    {
+      "parts": [
+        {
+          "executableCode": {
+            "code": ",q3gj8!T,.Dg.?!k8d?C,F!J7?q?!Pwb.."
+          },
+          "text": "!,? ? ! ",
+          "thoughtSignature": "O.Vla, !"
+        },
+        {
+          "codeExecutionResult": {},
+          "fileData": {
+            "fileUri": "Bbv..,!gr6c3.,,,,!6.p!Hkg.Cx11 ,.Fx"
+          },
+          "inlineData": {
+            "data": ".4??,Kyu 4?S?c?.,9HXyV,,1F.RN.,8gx,,P?",
+            "mimeType": "?G?,.!?,?? Vg.s7Y,gb,hV?1.?Tz0Vg2"
+          },
+          "mediaResolution": {},
+          "partMetadata": {},
+          "videoMetadata": {
+            "endOffset": "A.,!H5.3?TuvHw!lM"
+          }
+        },
+        {
+          "inlineData": {},
+          "mediaResolution": {},
+          "partMetadata": {},
+          "text": "8U?,Xlzb?.,I!6R?.Q9Zi???Uf0E",
+          "thoughtSignature": "?b7?hP,7?Zau F!.Pxw.b",
+          "videoMetadata": {
+            "startOffset": "!?B..S ,e.,..?.ox50o.?4.,.?Tf!Ig A"
+          }
+        }
+      ],
+      "role": ",,,!"
+    },
+    {
+      "parts": [
+        {
+          "codeExecutionResult": {
+            "outcome": "OUTCOME_UNSPECIFIED",
+            "output": "F?.?D2"
+          },
+          "partMetadata": {},
+          "text": ",,w?,aq2pq",
+          "thought": true,
+          "thoughtSignature": "5?0doC"
+        }
+      ],
+      "role": "?!?z..FPc.6 !??en?1!T?.,sq9zWp"
+    }
+  ],
+  "systemInstruction": {
+    "parts": [
+      {
+        "codeExecutionResult": {
+          "output": "o?oKV,X.gyZ?.?C?7..rJG Ci?o?,QIO9N51M8,IjEF"
+        },
+        "fileData": {
+          "mimeType": "K1.A .?w8!"
+        },
+        "functionResponse": {
+          "parts": [
+            {}
+          ],
+          "scheduling": "WHEN_IDLE",
+          "willContinue": true
+        },
+        "partMetadata": {},
+        "text": ".,. ,??68F?wZtr WCfmVZ.!.,F0z,!zA.v"
+      }
+    ]
+  },
+  "toolConfig": {},
+  "tools": [
+    {
+      "computerUse": {
+        "environment": "ENVIRONMENT_BROWSER"
+      },
+      "fileSearch": {
+        "metadataFilter": ",4W L.ApfF?a,3m! ? ?fb. 4SIgm8",
+        "topK": 382
+      },
+      "googleMaps": {
+        "enableWidget": false
+      },
+      "googleSearch": {},
+      "urlContext": {}
+    }
+  ]
+}
diff --git a/payloads/scripts/transforms/__snapshots__/transforms.test.ts.snap b/payloads/scripts/transforms/__snapshots__/transforms.test.ts.snap
index e5309657..fba6ae81 100644
--- a/payloads/scripts/transforms/__snapshots__/transforms.test.ts.snap
+++ b/payloads/scripts/transforms/__snapshots__/transforms.test.ts.snap
@@ -2499,7 +2499,6 @@ exports[`chat-completions → google > complexReasoningRequest > request 1`] = `
   ],
   "generationConfig": {
     "maxOutputTokens": 20000,
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -2616,6 +2615,9 @@ exports[`chat-completions → google > frequencyPenaltyParam > request 1`] = `
       "role": "user",
     },
   ],
+  "generationConfig": {
+    "frequencyPenalty": 0.5,
+  },
   "model": "gemini-2.5-flash",
 }
 `;
@@ -2798,7 +2800,6 @@ exports[`chat-completions → google > maxCompletionTokensParam > request 1`] =
   ],
   "generationConfig": {
     "maxOutputTokens": 500,
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -2895,7 +2896,6 @@ exports[`chat-completions → google > multimodalRequest > request 1`] = `
   ],
   "generationConfig": {
     "maxOutputTokens": 300,
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -3279,6 +3279,9 @@ exports[`chat-completions → google > presencePenaltyParam > request 1`] = `
       "role": "user",
     },
   ],
+  "generationConfig": {
+    "presencePenalty": 0.5,
+  },
   "model": "gemini-2.5-flash",
 }
 `;
@@ -3368,7 +3371,6 @@ exports[`chat-completions → google > reasoningEffortLowParam > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "thinkingConfig": {
       "includeThoughts": true,
       "thinkingBudget": 1024,
@@ -3500,7 +3502,6 @@ exports[`chat-completions → google > reasoningRequestTruncated > request 1`] =
   ],
   "generationConfig": {
     "maxOutputTokens": 100,
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -3547,7 +3548,6 @@ exports[`chat-completions → google > reasoningSummaryParam > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "thinkingConfig": {
       "includeThoughts": true,
       "thinkingBudget": 2048,
@@ -3704,6 +3704,9 @@ exports[`chat-completions → google > seedParam > request 1`] = `
       "role": "user",
     },
   ],
+  "generationConfig": {
+    "seed": 12345,
+  },
   "model": "gemini-2.5-flash",
 }
 `;
@@ -3793,7 +3796,6 @@ exports[`chat-completions → google > simpleRequest > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "thinkingConfig": {
       "includeThoughts": true,
       "thinkingBudget": 1024,
@@ -3849,7 +3851,6 @@ exports[`chat-completions → google > stopSequencesParam > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "stopSequences": [
       "10",
       "ten",
@@ -3945,7 +3946,6 @@ exports[`chat-completions → google > systemMessageArrayContent > request 1`] =
   ],
   "generationConfig": {
     "maxOutputTokens": 300,
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
   "systemInstruction": {
@@ -4017,7 +4017,6 @@ exports[`chat-completions → google > temperatureParam > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "temperature": 0.7,
   },
   "model": "gemini-2.5-flash",
@@ -4066,7 +4065,6 @@ exports[`chat-completions → google > textFormatJsonObjectParam > request 1`] =
   ],
   "generationConfig": {
     "responseMimeType": "application/json",
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -4244,7 +4242,6 @@ exports[`chat-completions → google > textFormatTextParam > request 1`] = `
   ],
   "generationConfig": {
     "responseMimeType": "text/plain",
-    "responseSchema": null,
   },
   "model": "gemini-2.5-flash",
 }
@@ -4459,7 +4456,6 @@ exports[`chat-completions → google > topPParam > request 1`] = `
     },
   ],
   "generationConfig": {
-    "responseSchema": null,
     "topP": 0.9,
   },
   "model": "gemini-2.5-flash",
diff --git a/scripts/validate_google_payload.py b/scripts/validate_google_payload.py
new file mode 100755
index 00000000..44ac4e5a
--- /dev/null
+++ b/scripts/validate_google_payload.py
@@ -0,0 +1,116 @@
+#!/usr/bin/env python3
+"""Send a Google Gemini payload to the real API and report whether it's accepted.
+
+Usage:
+    # Validate the minimal fuzz case:
+    python scripts/validate_google_payload.py '{"contents": [{}]}'
+
+    # Validate from a snapshot file:
+    python scripts/validate_google_payload.py payloads/fuzz-snapshots/google-roundtrip/case-XYZ.request.json
+
+    # Validate all snapshots in a directory:
+    python scripts/validate_google_payload.py payloads/fuzz-snapshots/google-roundtrip/
+
+Requires GEMINI_API_KEY (or GOOGLE_API_KEY) in the environment.
+"""
+
+import json
+import os
+import sys
+from pathlib import Path
+from urllib.error import HTTPError
+from urllib.request import Request, urlopen
+
+MODEL = os.environ.get("GEMINI_MODEL", "gemini-2.0-flash")
+API_KEY = os.environ.get("GEMINI_API_KEY") or os.environ.get("GOOGLE_API_KEY")
+BASE_URL = "https://generativelanguage.googleapis.com/v1beta"
+
+
+def validate_payload(payload: dict, label: str = "") -> bool:
+    url = f"{BASE_URL}/models/{MODEL}:generateContent?key={API_KEY}"
+    data = json.dumps(payload).encode()
+    req = Request(url, data=data, headers={"Content-Type": "application/json"})
+
+    prefix = f"[{label}] " if label else ""
+    try:
+        resp = urlopen(req)
+        body = json.loads(resp.read())
+        print(f"{prefix}ACCEPTED (200) -- API processed the payload")
+        if "candidates" in body:
+            text = (
+                body["candidates"][0]
+                .get("content", {})
+                .get("parts", [{}])[0]
+                .get("text", "")[:80]
+            )
+            if text:
+                print(f"  response: {text!r}")
+        return True
+    except HTTPError as e:
+        body = e.read().decode()
+        try:
+            err = json.loads(body)
+            msg = err.get("error", {}).get("message", body[:200])
+            status = err.get("error", {}).get("status", e.code)
+        except json.JSONDecodeError:
+            msg = body[:200]
+            status = e.code
+        print(f"{prefix}REJECTED ({status}) -- {msg}")
+        return False
+
+
+def load_payload(arg: str) -> list[tuple[str, dict]]:
+    """Return list of (label, payload) from a JSON string, file, or directory."""
+    path = Path(arg)
+
+    # Directory: load all .request.json files
+    if path.is_dir():
+        results = []
+        for f in sorted(path.glob("*.request.json")):
+            with open(f) as fh:
+                results.append((f.name, json.load(fh)))
+        return results
+
+    # File
+    if path.is_file():
+        with open(path) as fh:
+            return [(path.name, json.load(fh))]
+
+    # Inline JSON string
+    try:
+        return [("inline", json.loads(arg))]
+    except json.JSONDecodeError:
+        print(f"Error: not a valid JSON string, file, or directory: {arg}", file=sys.stderr)
+        sys.exit(1)
+
+
+def main():
+    if not API_KEY:
+        print("Set GEMINI_API_KEY or GOOGLE_API_KEY environment variable.", file=sys.stderr)
+        sys.exit(1)
+
+    if len(sys.argv) < 2:
+        print(__doc__.strip())
+        sys.exit(1)
+
+    payloads = load_payload(sys.argv[1])
+    if not payloads:
+        print("No payloads found.", file=sys.stderr)
+        sys.exit(1)
+
+    accepted = 0
+    rejected = 0
+    for label, payload in payloads:
+        if validate_payload(payload, label):
+            accepted += 1
+        else:
+            rejected += 1
+
+    if len(payloads) > 1:
+        print(f"\n--- {accepted} accepted, {rejected} rejected (of {len(payloads)}) ---")
+
+    sys.exit(0 if rejected == 0 else 1)
+
+
+if __name__ == "__main__":
+    main()