diff --git a/docs-site/src/content/docs/fr/guides/claude-code.md b/docs-site/src/content/docs/fr/guides/claude-code.md
index 5c13e041b6..ffc3ad6e88 100644
--- a/docs-site/src/content/docs/fr/guides/claude-code.md
+++ b/docs-site/src/content/docs/fr/guides/claude-code.md
@@ -500,7 +500,7 @@ Le proxy traduit chaque requête Anthropic Messages API au format Codex Response
 | Texte assistant | `output_text` |
 | Assistant `tool_use` | `function_call` (`input` → JSON-stringifié `arguments`) |
 | Utilisateur `tool_result` | `function_call_output` (`is_error` → préfixe `[tool error]`) |
-| Relecture de `thinking` / `redacted_thinking` | Ignorée |
+| Relecture de `thinking` / `redacted_thinking` | Éléments `reasoning` avec enveloppes `ocxr1` bornées pour les signatures et les contenus masqués |
 | Outils fonctionnels | `{type: "function"}` (`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`, `none`→`none`, `any`→`required`, fonction nommée→`{type:"function",name}`, hébergée WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -516,7 +516,7 @@ Le proxy traduit chaque requête Anthropic Messages API au format Codex Response
 | `response.created` | `message_start` + `ping` |
 | Battement de coeur | `ping` |
 | Deltas de texte | `content_block_start` → `content_block_delta` (texte) → `content_block_stop` |
-| Résumé ou texte de raisonnement | Bloc `thinking` avec signature synthétique |
+| Résumé ou texte de raisonnement | Bloc `thinking` avec la signature relue, ou une enveloppe de secours `ocxr1` bornée |
 | Trames d'appel de fonction | Bloc `tool_use` avec `input_json_delta` |
 | Événement terminal | `message_delta` → `message_stop` |
 | EOF avant la borne | style 502 `api_error` |
diff --git a/docs-site/src/content/docs/guides/claude-code.md b/docs-site/src/content/docs/guides/claude-code.md
index 5ed946c72a..b237955adb 100644
--- a/docs-site/src/content/docs/guides/claude-code.md
+++ b/docs-site/src/content/docs/guides/claude-code.md
@@ -513,7 +513,7 @@ The proxy translates every Anthropic Messages API request into the Codex Respons
 | Assistant text | `output_text` |
 | Assistant `tool_use` | `function_call` (`input` → JSON-stringified `arguments`) |
 | User `tool_result` | `function_call_output` (`is_error` → `[tool error]` prefix) |
-| `thinking` / `redacted_thinking` replay | Dropped |
+| `thinking` / `redacted_thinking` replay | `reasoning` items with bounded `ocxr1` envelopes for signatures and redacted payloads |
 | Function tools | `{type: "function"}` (`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`, `none`→`none`, `any`→`required`, named function→`{type:"function",name}`, hosted WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -530,7 +530,7 @@ name.
 | `response.created` | `message_start` + `ping` |
 | Heartbeat | `ping` |
 | Text deltas | `content_block_start` → `content_block_delta` (text) → `content_block_stop` |
-| Reasoning summary/text | `thinking` block with synthetic signature |
+| Reasoning summary/text | `thinking` block with the replayed signature, or a bounded `ocxr1` fallback envelope |
 | Function-call frames | `tool_use` block with `input_json_delta` |
 | Terminal event | `message_delta` → `message_stop` |
 | EOF before terminal | 502-style `api_error` |
diff --git a/docs-site/src/content/docs/ja/guides/claude-code.md b/docs-site/src/content/docs/ja/guides/claude-code.md
index 8c9f433956..43b8bcee24 100644
--- a/docs-site/src/content/docs/ja/guides/claude-code.md
+++ b/docs-site/src/content/docs/ja/guides/claude-code.md
@@ -368,7 +368,7 @@ Claude Code の `/effort` 設定はアダプターでも維持されます。
 | Assistant テキスト | `output_text` |
 | Assistant `tool_use` | `function_call`(`input` → JSON 文字列に変換した `arguments`) |
 | ユーザー `tool_result` | `function_call_output`(`is_error` → `[tool error]` 接頭辞) |
-| `thinking` / `redacted_thinking` 再生 | 破棄 |
+| `thinking` / `redacted_thinking` 再生 | シグネチャと秘匿ペイロードを境界付き `ocxr1` エンベロープに保持した `reasoning` 項目 |
 | Function ツール | `{type: "function"}`(`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`、`none`→`none`、`any`→`required`、名前指定関数→`{type:"function",name}`、ホスト型 WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -384,7 +384,7 @@ role、`tool_use_id` のない `tool_result`、id/name のない `tool_use`、na
 | `response.created` | `message_start` + `ping` |
 | Heartbeat | `ping` |
 | テキスト delta | `content_block_start` → `content_block_delta`(text) → `content_block_stop` |
-| 推論要約/テキスト | 合成シグネチャ付きの `thinking` ブロック |
+| 推論要約/テキスト | 再生されたシグネチャ、または境界付き `ocxr1` フォールバックを持つ `thinking` ブロック |
 | Function-call フレーム | `input_json_delta` を持つ `tool_use` ブロック |
 | 終了イベント | `message_delta` → `message_stop` |
 | 終了前に EOF | 502 形式 `api_error` |
diff --git a/docs-site/src/content/docs/ko/guides/claude-code.md b/docs-site/src/content/docs/ko/guides/claude-code.md
index 1368cf5698..0964f2ff49 100644
--- a/docs-site/src/content/docs/ko/guides/claude-code.md
+++ b/docs-site/src/content/docs/ko/guides/claude-code.md
@@ -406,7 +406,7 @@ Claude Code의 `/effort` 설정은 어댑터에서도 유지돼요.
 | Assistant 텍스트 | `output_text` |
 | Assistant `tool_use` | `function_call`(`input` → JSON 문자열로 변환한 `arguments`) |
 | 사용자 `tool_result` | `function_call_output`(`is_error` → `[tool error]` 접두사) |
-| `thinking` / `redacted_thinking` 재생 | 버려요 |
+| `thinking` / `redacted_thinking` 재생 | 서명과 비공개 페이로드를 제한된 `ocxr1` 봉투에 담은 `reasoning` 항목 |
 | Function 도구 | `{type: "function"}`(`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`, `none`→`none`, `any`→`required`, 이름 지정 함수→`{type:"function",name}`, 호스팅 WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -422,7 +422,7 @@ role, `tool_use_id` 없는 `tool_result`, id/name 없는 `tool_use`, name 없는
 | `response.created` | `message_start` + `ping` |
 | Heartbeat | `ping` |
 | 텍스트 delta | `content_block_start` → `content_block_delta`(text) → `content_block_stop` |
-| 추론 요약/텍스트 | 합성 signature가 있는 `thinking` 블록 |
+| 추론 요약/텍스트 | 재생된 서명 또는 제한된 `ocxr1` 폴백이 있는 `thinking` 블록 |
 | Function-call 프레임 | `input_json_delta`가 있는 `tool_use` 블록 |
 | 종료 이벤트 | `message_delta` → `message_stop` |
 | 종료 전에 EOF | 502 형식 `api_error` |
diff --git a/docs-site/src/content/docs/ru/guides/claude-code.md b/docs-site/src/content/docs/ru/guides/claude-code.md
index 3f6c07a4aa..1769642bd7 100644
--- a/docs-site/src/content/docs/ru/guides/claude-code.md
+++ b/docs-site/src/content/docs/ru/guides/claude-code.md
@@ -393,7 +393,7 @@ Claude Code — это лишь учётные данные для доступ
 | Текст ассистента | `output_text` |
 | `tool_use` ассистента | `function_call` (`input` → `arguments` в виде JSON-строки) |
 | `tool_result` пользователя | `function_call_output` (`is_error` → префикс `[tool error]`) |
-| Повтор `thinking` / `redacted_thinking` | Отбрасывается |
+| Повтор `thinking` / `redacted_thinking` | Элементы `reasoning` с ограниченными конвертами `ocxr1` для подписей и скрытых данных |
 | Function-инструменты | `{type: "function"}` (`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`, `none`→`none`, `any`→`required`, именованная функция→`{type:"function",name}`, размещённый WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -410,7 +410,7 @@ id/name; именованный `tool_choice` без имени.
 | `response.created` | `message_start` + `ping` |
 | Heartbeat | `ping` |
 | Текстовые дельты | `content_block_start` → `content_block_delta` (text) → `content_block_stop` |
-| Резюме/текст рассуждений | Блок `thinking` с синтетической подписью |
+| Резюме/текст рассуждений | Блок `thinking` с повторно переданной подписью или ограниченным резервным конвертом `ocxr1` |
 | Кадры function-call | Блок `tool_use` с `input_json_delta` |
 | Завершающее событие | `message_delta` → `message_stop` |
 | EOF до завершающего события | `api_error` в стиле 502 |
diff --git a/docs-site/src/content/docs/tr/guides/claude-code.md b/docs-site/src/content/docs/tr/guides/claude-code.md
index 5450d6b748..29d96506ac 100644
--- a/docs-site/src/content/docs/tr/guides/claude-code.md
+++ b/docs-site/src/content/docs/tr/guides/claude-code.md
@@ -582,7 +582,7 @@ dönüştürür:
 | Asistan metni | `output_text` |
 | Asistan `tool_use` | `function_call` (`input` → JSON dizgeleştirilmiş `arguments`) |
 | Kullanıcı `tool_result` | `function_call_output` (`is_error` → `[tool error]` öneki) |
-| `thinking` / `redacted_thinking` tekrarı | Bırakılır |
+| `thinking` / `redacted_thinking` tekrarı | İmzaları ve gizli yükleri sınırlı `ocxr1` zarflarında taşıyan `reasoning` öğeleri |
 | Fonksiyon araçları | `{type: "function"}` (`web_search*` → `{type: "web_search"}`) |
 | `tool_choice` | `auto`→`auto`, `none`→`none`, `any`→`required`, adlandırılmış fonksiyon→`{type:"function",name}`, barındırılan WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -599,7 +599,7 @@ kimlik/ad içermeyen `tool_use`; ad içermeyen adlandırılmış `tool_choice`.
 | `response.created` | `message_start` + `ping` |
 | Kalp atışı (Heartbeat) | `ping` |
 | Metin farkları | `content_block_start` → `content_block_delta` (metin) → `content_block_stop` |
-| Akıl yürütme özeti/metni | Sentetik imzalı `thinking` bloğu |
+| Akıl yürütme özeti/metni | Tekrarlanan imzayı veya sınırlı bir `ocxr1` yedeğini taşıyan `thinking` bloğu |
 | Fonksiyon çağrısı çerçeveleri | `input_json_delta` ile `tool_use` bloğu |
 | Terminal olayı | `message_delta` → `message_stop` |
 | Terminalden önce EOF | 502 tarzı `api_error` |
diff --git a/docs-site/src/content/docs/zh-cn/guides/claude-code.md b/docs-site/src/content/docs/zh-cn/guides/claude-code.md
index 3bbe49646b..3e2824d3e9 100644
--- a/docs-site/src/content/docs/zh-cn/guides/claude-code.md
+++ b/docs-site/src/content/docs/zh-cn/guides/claude-code.md
@@ -344,7 +344,7 @@ Claude Code 的 `/effort` 设置会完整保留并传递给适配器：
 | Assistant 文本 | `output_text` |
 | Assistant `tool_use` | `function_call`（`input` → JSON 字符串化的 `arguments`） |
 | 用户 `tool_result` | `function_call_output`（`is_error` → `[tool error]` 前缀） |
-| 重放 `thinking` / `redacted_thinking` | 丢弃 |
+| 重放 `thinking` / `redacted_thinking` | `reasoning` 项；签名和脱敏载荷保存在有界 `ocxr1` 信封中 |
 | Function 工具 | `{type: "function"}`（`web_search*` → `{type: "web_search"}`） |
 | `tool_choice` | `auto`→`auto`，`none`→`none`，`any`→`required`，指定函数→`{type:"function",name}`，托管 WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -361,7 +361,7 @@ role；`tool_result` 缺少 `tool_use_id`；`tool_use` 缺少 id/name；指定
 | `response.created` | `message_start` + `ping` |
 | 心跳 | `ping` |
 | 文本增量 | `content_block_start` → `content_block_delta`（文本）→ `content_block_stop` |
-| 推理摘要/文本 | 带合成签名的 `thinking` 块 |
+| 推理摘要/文本 | 带重放签名或有界 `ocxr1` 回退信封的 `thinking` 块 |
 | Function-call 帧 | 带 `input_json_delta` 的 `tool_use` 块 |
 | 终止事件 | `message_delta` → `message_stop` |
 | 在终止事件前 EOF | 502 风格的 `api_error` |
diff --git a/docs-site/src/content/docs/zh-tw/guides/claude-code.md b/docs-site/src/content/docs/zh-tw/guides/claude-code.md
index ccfb3b9ddd..5a6fbf3a86 100644
--- a/docs-site/src/content/docs/zh-tw/guides/claude-code.md
+++ b/docs-site/src/content/docs/zh-tw/guides/claude-code.md
@@ -420,7 +420,7 @@ Claude Code 的 `/effort` 設定會完整保留並傳遞給適配器：
 | Assistant 文字 | `output_text` |
 | Assistant `tool_use` | `function_call`（`input` → JSON 字串化的 `arguments`） |
 | 使用者 `tool_result` | `function_call_output`（`is_error` → `[tool error]` 字首） |
-| 重放 `thinking` / `redacted_thinking` | 丟棄 |
+| 重放 `thinking` / `redacted_thinking` | `reasoning` 項目；簽名與遮蔽載荷保存在有界 `ocxr1` 信封中 |
 | Function 工具 | `{type: "function"}`（`web_search*` → `{type: "web_search"}`） |
 | `tool_choice` | `auto`→`auto`，`none`→`none`，`any`→`required`，指定名稱 function→`{type:"function",name}`，hosted WebSearch/web_search→`{type:"web_search"}` |
 | `max_tokens` | `max_output_tokens` |
@@ -437,7 +437,7 @@ role；`tool_result` 缺少 `tool_use_id`；`tool_use` 缺少 id/name；指定
 | `response.created` | `message_start` + `ping` |
 | 心跳 | `ping` |
 | 文字增量 | `content_block_start` → `content_block_delta`（文字）→ `content_block_stop` |
-| 推理摘要/文字 | 帶合成簽名的 `thinking` 塊 |
+| 推理摘要/文字 | 帶重播簽名或有界 `ocxr1` 備援信封的 `thinking` 塊 |
 | Function-call 幀 | 帶 `input_json_delta` 的 `tool_use` 塊 |
 | 終止事件 | `message_delta` → `message_stop` |
 | 在終止事件前 EOF | 502 風格的 `api_error` |
diff --git a/scripts/test-layout/layout.json b/scripts/test-layout/layout.json
index d309073a3f..255c78e916 100644
--- a/scripts/test-layout/layout.json
+++ b/scripts/test-layout/layout.json
@@ -312,6 +312,7 @@
     "claude-outbound.test.ts": "claude-integration",
     "claude-shell-hook.test.ts": "claude-integration",
     "claude-sidecar-override.test.ts": "claude-integration",
+    "claude-source-envelope.test.ts": "claude-integration",
     "claude-system-env-auto.test.ts": "claude-integration",
     "cleanup-orphaned-workflows.test.ts": "ci-workflows",
     "clearable-deadline.test.ts": "lib",
@@ -999,6 +1000,7 @@
     "rate-limit-reset-credits.test.ts": "gui",
     "rate-limit-retry.test.ts": "providers",
     "reasoning-effort.test.ts": "codex-integration",
+    "reasoning-envelope.test.ts": "responses",
     "reasoning-replay-identity.test.ts": "adapters",
     "reasoning-replay-robustness.test.ts": "adapters",
     "reasoning-replay-scope-source.test.ts": "lib",
diff --git a/src/claude/inbound.ts b/src/claude/inbound.ts
index 3ac4731385..5e876ca6cb 100644
--- a/src/claude/inbound.ts
+++ b/src/claude/inbound.ts
@@ -4,8 +4,8 @@
  * Design (devlog/260711_claude_inbound/010, 003_evidence.md):
  *  - translate-and-replay: the produced body MUST pass the real responsesRequestSchema
  *    parse so routing/OAuth/pool/failover are inherited unchanged.
- *  - thinking/redacted_thinking blocks on replay are DROPPED (v1 policy) — routed
- *    providers carry reasoning in Responses items/ocxr1 envelopes instead.
+ *  - thinking/redacted_thinking replay is preserved in Responses reasoning items;
+ *    signatures and redacted payloads travel in bounded ocxr1 envelopes.
  *  - thinking.budget_tokens is NEVER forwarded raw; it maps to an effort tier.
  *  - top_k is accepted and silently dropped (no Responses equivalent, CCR parity).
  */
@@ -17,6 +17,7 @@ export { resolveInboundModel, effortForThinkingBudget, effortFromOutputConfig, e
 import { AnthropicRequestError, isRec, type Rec } from "./inbound-records";
 import { resolveInboundModel, effortForThinkingBudget, effortFromOutputConfig, formatFromOutputConfig } from "./inbound-model-options";
 import { systemToInstructions, toolsToResponses, toolChoiceToResponses } from "./inbound-content-options";
+import { decodeReasoningEnvelope, encodeReasoningEnvelope, OCX_REASONING_PREFIX } from "../responses/reasoning-envelope";
 
 
 
@@ -234,9 +235,26 @@ function assistantMessageToItems(content: unknown, input: Rec[]): void {
         input.push({ type: "function_call", call_id: raw.id, name: raw.name, arguments: JSON.stringify(raw.input ?? {}) });
         break;
       }
-      case "thinking":
-      case "redacted_thinking":
-        break; // v1 policy: dropped on replay (003 evidence — safe for routed providers)
+      case "thinking": {
+        flush();
+        const thinking = typeof raw.thinking === "string" ? raw.thinking : "";
+        const signature = typeof raw.signature === "string" ? raw.signature : "";
+        if (signature.startsWith(OCX_REASONING_PREFIX)) {
+          const owned = decodeReasoningEnvelope(signature);
+          if (!owned) throw new AnthropicRequestError("malformed ocxr1 reasoning signature");
+          if (Object.hasOwn(owned, "sig")) throw new AnthropicRequestError("OpenCodex reasoning continuity cannot be replayed as an Anthropic signature");
+        }
+        const encrypted = signature.length === 0 ? undefined : signature.startsWith(OCX_REASONING_PREFIX) ? signature : encodeReasoningEnvelope({ sig: signature });
+        if (thinking.length === 0 && !encrypted) break;
+        input.push({ type: "reasoning", id: `rs_${crypto.randomUUID().replace(/-/g, "")}`, summary: thinking.length > 0 ? [{ type: "summary_text", text: thinking }] : [], ...(encrypted ? { encrypted_content: encrypted } : {}) });
+        break;
+      }
+      case "redacted_thinking": {
+        flush();
+        const data = typeof raw.data === "string" ? raw.data : "";
+        if (data.length > 0) input.push({ type: "reasoning", id: `rs_${crypto.randomUUID().replace(/-/g, "")}`, summary: [], encrypted_content: encodeReasoningEnvelope({ red: [data] }) });
+        break;
+      }
       default:
         break;
     }
diff --git a/src/claude/outbound.ts b/src/claude/outbound.ts
index 48bb06c15a..8c0db5b7b8 100644
--- a/src/claude/outbound.ts
+++ b/src/claude/outbound.ts
@@ -5,8 +5,8 @@
  *  - Transport-only `ping` events may appear at any point, including before
  *    message_start. Semantic framing stays message_start ->
  *    (content_block_start -> deltas -> content_block_stop)* -> message_delta -> message_stop.
- *  - thinking blocks get thinking_delta(s) then ONE synthetic signature_delta just
- *    before content_block_stop (CCR precedent: Claude Code does not verify signatures).
+ *  - thinking blocks get thinking_delta(s), then one signature_delta containing the
+ *    genuine replay signature or a bounded ocxr1 fallback envelope.
  *  - message_delta.usage is cumulative; message_start embeds a full message snapshot.
  *  - errors: {type:"error", error:{type,message}}; may arrive mid-stream after HTTP 200.
  */
@@ -20,6 +20,7 @@ import {
   type TranslatorBudget,
 } from "../lib/translator-budget";
 import { sseFieldOffset, sseFieldValue } from "../lib/sse-decoder";
+import { decodeReasoningEnvelope, encodeReasoningEnvelope } from "../responses/reasoning-envelope";
 
 type Rec = Record<string, unknown>;
 
@@ -214,6 +215,9 @@ interface OpenBlock {
   callId?: string;
   /** Last fixed-size reasoning identity (item + summary/content index) seen by this block. */
   reasoningPartKey?: string;
+  thinkingBuf?: string;
+  thinkingBufBytes?: number;
+  reasoningSig?: string;
 }
 
 /** Streaming: Responses SSE bytes -> Anthropic Messages SSE bytes. */
@@ -253,6 +257,11 @@ export function responsesSseToAnthropicSse(
     const bytes = queuedLiveFrameBytes.shift();
     if (bytes !== undefined) translatorBudget.releaseRetained(bytes, { kind: "live_transient" });
   };
+  const releaseThinkingBuffer = (block: OpenBlock | null | undefined) => {
+    if (block?.kind !== "thinking") return;
+    translatorBudget.releaseRetained(block.thinkingBufBytes ?? 0, { kind: "reasoning" });
+    block.thinkingBufBytes = 0;
+  };
 
   return new ReadableStream<Uint8Array>({
     start(controller) {
@@ -296,13 +305,14 @@ export function responsesSseToAnthropicSse(
           open.webSearchArgsEmitted = true;
         }
         if (open.kind === "thinking") {
-          // Synthetic signature: Claude Code accepts it (003 E6); inbound drops replays anyway.
+          const signature = open.reasoningSig ?? encodeReasoningEnvelope({ txt: open.thinkingBuf ?? "" });
           emit("content_block_delta", {
             type: "content_block_delta", index: open.index,
-            delta: { type: "signature_delta", signature: `ocx${Date.now()}` },
+            delta: { type: "signature_delta", signature },
           });
         }
         emit("content_block_stop", { type: "content_block_stop", index: open.index });
+        releaseThinkingBuffer(open);
         if (open.callId) translatorBudget.closeCall(open.callId);
         open = null;
       };
@@ -315,7 +325,7 @@ export function responsesSseToAnthropicSse(
           ? { type: "text", text: "" }
           : { type: "thinking", thinking: "", signature: "" };
         emit("content_block_start", { type: "content_block_start", index, content_block: contentBlock });
-        open = { kind, index };
+        open = { kind, index, thinkingBuf: "", thinkingBufBytes: 0 };
       };
       const finish = (stopReason: string, usage: unknown) => {
         if (terminated) return;
@@ -339,6 +349,7 @@ export function responsesSseToAnthropicSse(
         if (terminated) return;
         terminated = true;
         if (code === "translation_buffer_limit") {
+          releaseThinkingBuffer(open);
           if (open?.callId) translatorBudget.closeCall(open.callId);
           open = null;
           // No normal close frames are valid after overflow. Emit exactly one bounded
@@ -374,8 +385,10 @@ export function responsesSseToAnthropicSse(
           case "response.output_text.delta": {
             if (typeof data.delta !== "string" || data.delta.length === 0) break;
             ensureBlock("text");
+            const active = open;
+            if (!active || active.kind !== "text") break;
             emit("content_block_delta", {
-              type: "content_block_delta", index: open!.index,
+              type: "content_block_delta", index: active.index,
               delta: { type: "text_delta", text: data.delta },
             });
             break;
@@ -384,6 +397,8 @@ export function responsesSseToAnthropicSse(
           case "response.reasoning_text.delta": {
             if (typeof data.delta !== "string" || data.delta.length === 0) break;
             ensureBlock("thinking");
+            const active = open;
+            if (!active || active.kind !== "thinking") break;
             // The JSON path joins reasoning summary/content parts with "\n\n"
             // (responsesJsonToAnthropicMessage); mirror that at part and item boundaries
             // so multi-part summaries do not glue into one run-on paragraph. Frames
@@ -395,15 +410,32 @@ export function responsesSseToAnthropicSse(
             // components while retaining item and part equality, rather than dropping item_id and
             // accidentally joining distinct malformed reasoning items.
             const partKey = `${boundedReasoningIdentity(data.item_id)}:${slot}`;
-            if (open!.reasoningPartKey !== undefined && open!.reasoningPartKey !== partKey) {
+            const needsPartSeparator = active.reasoningPartKey !== undefined
+              && active.reasoningPartKey !== partKey;
+            const appended = `${needsPartSeparator ? "\n\n" : ""}${data.delta}`;
+            const previous = active.thinkingBuf ?? "";
+            const previousBytes = active.thinkingBufBytes ?? 0;
+            const nextBytes = appendedUtf8Bytes(previous, previousBytes, appended);
+            const scope = { kind: "reasoning" } as const;
+            const reservation = translatorBudget.reserveTransient(nextBytes, scope);
+            try {
+              active.thinkingBuf = previous + appended;
+              active.thinkingBufBytes = nextBytes;
+              reservation.commitRetained();
+              translatorBudget.releaseRetained(previousBytes, scope);
+            } catch (error) {
+              reservation.release();
+              throw error;
+            }
+            if (needsPartSeparator) {
               emit("content_block_delta", {
-                type: "content_block_delta", index: open!.index,
+                type: "content_block_delta", index: active.index,
                 delta: { type: "thinking_delta", thinking: "\n\n" },
               });
             }
-            open!.reasoningPartKey = partKey;
+            active.reasoningPartKey = partKey;
             emit("content_block_delta", {
-              type: "content_block_delta", index: open!.index,
+              type: "content_block_delta", index: active.index,
               delta: { type: "thinking_delta", thinking: data.delta },
             });
             break;
@@ -499,10 +531,9 @@ export function responsesSseToAnthropicSse(
               if (pair.completed) webSearchRequests++;
               break;
             }
-            if (!open) break;
             // Close the matching open block (message/reasoning items close implicitly on
             // the next block; function_call items must close here so tool input parses).
-            if (open.kind === "tool_use" && item.type === "function_call") {
+            if (open && open.kind === "tool_use" && item.type === "function_call") {
               if (open.bufferWebSearchArgs && !open.webSearchArgsEmitted) {
                 const rawArgs = typeof item.arguments === "string" && item.arguments.length > 0
                   ? item.arguments
@@ -518,8 +549,23 @@ export function responsesSseToAnthropicSse(
               }
               closeOpenBlock();
             }
-            else if (open.kind === "text" && item.type === "message") closeOpenBlock();
-            else if (open.kind === "thinking" && item.type === "reasoning") closeOpenBlock();
+            else if (open && open.kind === "text" && item.type === "message") closeOpenBlock();
+            else if (item.type === "reasoning") {
+              const encrypted = typeof item.encrypted_content === "string" ? item.encrypted_content : "";
+              const env = encrypted ? decodeReasoningEnvelope(encrypted) : null;
+              const red = env?.red ?? [];
+              if (env?.sig && open?.kind !== "thinking") ensureBlock("thinking");
+              if (open?.kind === "thinking") {
+                if (env?.sig) open.reasoningSig = env.sig;
+                closeOpenBlock();
+              }
+              if (red.length > 0) ensureStarted();
+              for (const data of red) {
+                const idx = blockIndex++;
+                emit("content_block_start", { type: "content_block_start", index: idx, content_block: { type: "redacted_thinking", data } });
+                emit("content_block_stop", { type: "content_block_stop", index: idx });
+              }
+            }
             break;
           }
           case "response.completed": {
@@ -704,6 +750,7 @@ export function responsesSseToAnthropicSse(
             fail(413, "upstream translation buffer exceeded the safe limit", false, "translation_buffer_limit");
           } else fail(500, err instanceof Error ? err.message : String(err));
         } finally {
+          releaseThinkingBuffer(open);
           translatorBudget.releaseRetained(bufferBytes, { kind: "live_transient" });
           if (pingTimer !== undefined) clearInterval(pingTimer);
           reader.releaseLock();
@@ -717,6 +764,7 @@ export function responsesSseToAnthropicSse(
     cancel(reason) {
       cancelled = true;
       while (queuedLiveFrameBytes.length > 0) releaseDeliveredFrame();
+      releaseThinkingBuffer(open);
       if (open?.callId) translatorBudget.closeCall(open.callId);
       if (pingTimer !== undefined) clearInterval(pingTimer);
       return reader?.cancel(reason);
@@ -756,9 +804,12 @@ export function responsesJsonToAnthropicMessage(json: unknown, model: string): R
             if (isRec(s) && typeof s.text === "string" && s.text.length > 0) parts.push(s.text);
           }
         }
-        if (parts.length > 0) {
-          content.push({ type: "thinking", thinking: parts.join("\n\n"), signature: `ocx${Date.now()}` });
+        const encrypted = typeof raw.encrypted_content === "string" ? raw.encrypted_content : "";
+        const env = encrypted ? decodeReasoningEnvelope(encrypted) : null;
+        if (parts.length > 0 || env?.sig) {
+          content.push({ type: "thinking", thinking: parts.join("\n\n"), signature: env?.sig ?? encodeReasoningEnvelope({ txt: parts.join("\n\n") }) });
         }
+        for (const data of env?.red ?? []) content.push({ type: "redacted_thinking", data });
         break;
       }
       case "function_call": {
diff --git a/src/responses/reasoning-envelope.ts b/src/responses/reasoning-envelope.ts
index 1735f775fb..2a56563578 100644
--- a/src/responses/reasoning-envelope.ts
+++ b/src/responses/reasoning-envelope.ts
@@ -50,10 +50,11 @@ export function decodeReasoningEnvelope(encryptedContent: string): ReasoningEnve
       if (red.length > 0) envelope.red = red;
     }
     const txt = (parsed as { txt?: unknown }).txt;
-    if (typeof txt === "string" && txt.length > 0) envelope.txt = txt;
+    const hasTxt = typeof txt === "string";
+    if (hasTxt) envelope.txt = txt;
     const krc = (parsed as { krc?: unknown }).krc;
     if (typeof krc === "string" && krc.length > 0) envelope.krc = krc;
-    return envelope.sig || envelope.red || envelope.txt || envelope.krc ? envelope : null;
+    return envelope.sig || envelope.red || hasTxt || envelope.krc ? envelope : null;
   } catch {
     return null;
   }
diff --git a/tests/claude-integration/claude-code-thought-signature-scope.test.ts b/tests/claude-integration/claude-code-thought-signature-scope.test.ts
index eb544dce97..b3d981c327 100644
--- a/tests/claude-integration/claude-code-thought-signature-scope.test.ts
+++ b/tests/claude-integration/claude-code-thought-signature-scope.test.ts
@@ -125,4 +125,16 @@ describe("Claude Code Anthropic inbound reasoning-replay scope", () => {
     const parsed = await drive({ promptCacheKey: "   ", promptCacheKeyIsSharedCohort: false });
     expect(parsed._reasoningReplayScope).toBeUndefined();
   });
+
+  test("distinct session identities remain distinct and bounded", async () => {
+    const first = await drive({ promptCacheKey: "session-a", promptCacheKeyIsSharedCohort: false });
+    const second = await drive({ promptCacheKey: "session-b", promptCacheKeyIsSharedCohort: false });
+    const a = first._reasoningReplayScope?.clientThreadId;
+    const b = second._reasoningReplayScope?.clientThreadId;
+    expect(a).toBeDefined();
+    expect(b).toBeDefined();
+    expect(a).not.toBe(b);
+    expect(a).toBe("session-a");
+    expect(b).toBe("session-b");
+  });
 });
diff --git a/tests/claude-integration/claude-inbound.test.ts b/tests/claude-integration/claude-inbound.test.ts
index 32207c9019..7227bbf2f1 100644
--- a/tests/claude-integration/claude-inbound.test.ts
+++ b/tests/claude-integration/claude-inbound.test.ts
@@ -84,12 +84,12 @@ describe("claude inbound translation", () => {
     expect(tools[1]).toEqual({ type: "web_search" });
 
     const input = body.input as Record<string, any>[];
-    // user text, assistant text (thinking dropped), function_call, function_call_output, user tail
-    expect(input.map(i => i.type ?? i.role)).toEqual(["message", "message", "function_call", "function_call_output", "message"]);
-    expect(input[1].content).toEqual([{ type: "output_text", text: "Reading it now." }]);
-    expect(input[2]).toMatchObject({ call_id: "toolu_01", name: "Read", arguments: JSON.stringify({ file_path: "/README.md" }) });
-    expect(input[3]).toMatchObject({ call_id: "toolu_01", output: [{ type: "input_text", text: "# hello" }] });
-    const tail = input[4].content as Record<string, any>[];
+    // user text, reasoning, assistant text, function_call, function_call_output, user tail
+    expect(input.map(i => i.type ?? i.role)).toEqual(["message", "reasoning", "message", "function_call", "function_call_output", "message"]);
+    expect(input[2].content).toEqual([{ type: "output_text", text: "Reading it now." }]);
+    expect(input[3]).toMatchObject({ call_id: "toolu_01", name: "Read", arguments: JSON.stringify({ file_path: "/README.md" }) });
+    expect(input[4]).toMatchObject({ call_id: "toolu_01", output: [{ type: "input_text", text: "# hello" }] });
+    const tail = input[5].content as Record<string, any>[];
     expect(tail[0]).toEqual({ type: "input_text", text: "now summarize" });
     expect(tail[1]).toEqual({ type: "input_image", image_url: "data:image/png;base64,aWc=" });
   });
diff --git a/tests/claude-integration/claude-outbound.test.ts b/tests/claude-integration/claude-outbound.test.ts
index 299ce5135d..e78cc529d3 100644
--- a/tests/claude-integration/claude-outbound.test.ts
+++ b/tests/claude-integration/claude-outbound.test.ts
@@ -13,6 +13,7 @@ import {
   TRANSLATOR_MAX_CALL_ARGUMENT_BYTES,
   type TranslatorBudget,
 } from "../../src/lib/translator-budget";
+import { decodeReasoningEnvelope, encodeReasoningEnvelope } from "../../src/responses/reasoning-envelope";
 
 const streamBudgets = new WeakMap<ReadableStream<Uint8Array>, TranslatorBudget>();
 
@@ -274,6 +275,8 @@ describe("claude outbound SSE", () => {
       "**A**\n\nOne.\n\n**B**\n\nTwo.",
       "Three.",
     ]);
+    expect(decodeReasoningEnvelope(thinkingBlocks[0].signature)?.txt)
+      .toBe("**A**\n\nOne.\n\n**B**\n\nTwo.");
 
     // Parity: the non-streaming translator joins the same summary parts identically.
     const json = responsesJsonToAnthropicMessage({
@@ -286,6 +289,59 @@ describe("claude outbound SSE", () => {
     expect(jsonThinking.thinking).toBe("**A**\n\nOne.\n\n**B**\n\nTwo.");
   });
 
+  test("reasoning fallback buffering is bounded and releases its retained budget", async () => {
+    const budget = createTestTranslatorBudget({ maxTurnBytes: 8 * 1024 });
+    let reasoningCommitted = 0;
+    let reasoningReleased = 0;
+    const trackedBudget: TranslatorBudget = {
+      openCall: id => budget.openCall(id),
+      closeCall: id => budget.closeCall(id),
+      reserveTransient(bytes, scope) {
+        const reservation = budget.reserveTransient(bytes, scope);
+        return {
+          commitRetained() {
+            reservation.commitRetained();
+            if (scope.kind === "reasoning") reasoningCommitted += bytes;
+          },
+          release: () => reservation.release(),
+        };
+      },
+      chargeRetained(bytes, scope) {
+        budget.chargeRetained(bytes, scope);
+        if (scope.kind === "reasoning") reasoningCommitted += bytes;
+      },
+      releaseRetained(bytes, scope) {
+        budget.releaseRetained(bytes, scope);
+        if (scope.kind === "reasoning") reasoningReleased += bytes;
+      },
+      observeAcceptedRequestCopy: bytes => budget.observeAcceptedRequestCopy(bytes),
+      observeExternallyCapped: (kind, bytes) => budget.observeExternallyCapped(kind, bytes),
+      snapshot: () => budget.snapshot(),
+      dispose: () => budget.dispose(),
+    };
+    const frames = [
+      sse("response.created", { response: { id: "resp_1", status: "in_progress" } }),
+      ...Array.from({ length: 32 }, (_, index) => sse("response.reasoning_text.delta", {
+        item_id: "rs_1",
+        content_index: 0,
+        delta: `${index}:` + "x".repeat(512),
+      })),
+    ];
+    const events = await collectEvents(responsesSseToAnthropicSse(
+      streamFromChunks(frames),
+      "m",
+      { translatorBudget: trackedBudget },
+    ));
+
+    expect(events.at(-1)).toMatchObject({
+      name: "error",
+      data: { error: { type: "request_too_large", code: "translation_buffer_limit" } },
+    });
+    expect(budget.snapshot().overflows).toBe(1);
+    expect(reasoningCommitted).toBeGreaterThan(0);
+    expect(reasoningReleased).toBe(reasoningCommitted);
+  });
+
   test("same-part deltas and index-free reasoning frames never get a separator", async () => {
     const samePart = [
       sse("response.created", { response: { id: "resp_1", status: "in_progress" } }),
@@ -1109,4 +1165,32 @@ describe("sanitizeWebSearchInput (#381)", () => {
       data: { error: { type: "request_too_large", code: "translation_buffer_limit" } },
     });
   }, 60_000);
+
+  test("redacted-only reasoning emits a standalone redacted_thinking block", async () => {
+    const events = await collectEvents(responsesSseToAnthropicSse(streamFrom([
+      sse("response.output_item.done", {
+        item: { type: "reasoning", id: "rs_red", encrypted_content: encodeReasoningEnvelope({ red: ["opaque"] }) },
+      }),
+      sse("response.completed", { response: { status: "completed", usage: {} } }),
+    ].join("")), "m"));
+    expect(events.map(event => event.name)).toEqual([
+      "message_start", "ping", "content_block_start", "content_block_stop", "message_delta", "message_stop",
+    ]);
+    expect(events[2].data.content_block).toEqual({ type: "redacted_thinking", data: "opaque" });
+  });
+
+  test("signature-only reasoning emits an empty thinking block with the genuine signature", async () => {
+    const events = await collectEvents(responsesSseToAnthropicSse(streamFrom([
+      sse("response.output_item.done", {
+        item: { type: "reasoning", id: "rs_sig", encrypted_content: encodeReasoningEnvelope({ sig: "sig-only" }) },
+      }),
+      sse("response.completed", { response: { status: "completed", usage: {} } }),
+    ].join("")), "m"));
+    expect(events.map(event => event.name)).toEqual([
+      "message_start", "ping", "content_block_start", "content_block_delta", "content_block_stop",
+      "message_delta", "message_stop",
+    ]);
+    expect(events[2].data.content_block).toEqual({ type: "thinking", thinking: "", signature: "" });
+    expect(events[3].data.delta).toEqual({ type: "signature_delta", signature: "sig-only" });
+  });
 });
diff --git a/tests/claude-integration/claude-source-envelope.test.ts b/tests/claude-integration/claude-source-envelope.test.ts
new file mode 100644
index 0000000000..a78c9f1a15
--- /dev/null
+++ b/tests/claude-integration/claude-source-envelope.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, test } from "bun:test";
+import { anthropicToResponsesBody } from "../../src/claude/inbound";
+
+describe("Claude source envelope boundaries", () => {
+  test("nested tool results retain only bounded structured content", () => {
+    const body = anthropicToResponsesBody({
+      model: "m",
+      messages: [
+        { role: "assistant", content: [{ type: "tool_use", id: "call-1", name: "lookup", input: { q: "x" } }] },
+        { role: "user", content: [{ type: "tool_result", tool_use_id: "call-1", content: [
+          { type: "text", text: "ok" },
+          { type: "document", title: "report" },
+          { type: "future_block", payload: "secret-payload" },
+        ] }] },
+      ],
+    }) as any;
+    expect(body.input.map((item: any) => item.type)).toEqual(["function_call", "function_call_output"]);
+    expect(body.input[1].output).toEqual([
+      { type: "input_text", text: "ok" },
+      { type: "input_text", text: "[document: report]" },
+    ]);
+    expect(JSON.stringify(body)).not.toContain("secret-payload");
+  });
+
+  test("malformed tool results fail closed instead of becoming an unpaired output", () => {
+    expect(() => anthropicToResponsesBody({
+      model: "m", messages: [{ role: "user", content: [{ type: "tool_result", content: "secret-payload" }] }],
+    })).toThrow(/unknown|unpaired|tool/i);
+  });
+});
diff --git a/tests/fixtures/test-layout-expected.json b/tests/fixtures/test-layout-expected.json
index 6565f12821..928752d213 100644
--- a/tests/fixtures/test-layout-expected.json
+++ b/tests/fixtures/test-layout-expected.json
@@ -125,6 +125,7 @@
   "claude-authmode-migration.test.ts": "claude-integration",
   "claude-cli.test.ts": "claude-integration",
   "claude-code-thought-signature-scope.test.ts": "claude-integration",
+  "claude-source-envelope.test.ts": "claude-integration",
   "claude-compatibility.test.ts": "claude-integration",
   "claude-context-windows.test.ts": "claude-integration",
   "claude-desktop-1m.test.ts": "claude-integration",
@@ -1020,6 +1021,7 @@
   "test-home-guard.test.ts": "ci-workflows",
   "test-runner.test.ts": "ci-workflows",
   "thought-signature-credential-scope.test.ts": "responses",
+  "reasoning-envelope.test.ts": "responses",
   "token-estimate.test.ts": "lib",
   "token-guardian.test.ts": "codex-integration",
   "tool-argument-integers.test.ts": "adapters",
diff --git a/tests/responses/reasoning-envelope.test.ts b/tests/responses/reasoning-envelope.test.ts
new file mode 100644
index 0000000000..75c51994f2
--- /dev/null
+++ b/tests/responses/reasoning-envelope.test.ts
@@ -0,0 +1,79 @@
+import { describe, expect, test } from "bun:test";
+import { anthropicToResponsesBody } from "../../src/claude/inbound";
+import { decodeReasoningEnvelope, encodeReasoningEnvelope } from "../../src/responses/reasoning-envelope";
+import { responsesJsonToAnthropicMessage } from "../../src/claude/outbound";
+
+describe("reasoning and tool/result envelopes", () => {
+  test("preserves ordered thinking blocks and genuine signatures", () => {
+    const body = anthropicToResponsesBody({
+      model: "m", messages: [{ role: "assistant", content: [
+        { type: "thinking", thinking: "first", signature: "sig-first" },
+        { type: "tool_use", id: "call-1", name: "Read", input: {} },
+        { type: "thinking", thinking: "second", signature: "sig-second" },
+      ] }],
+    }) as any;
+    expect(body.input.map((item: any) => item.type)).toEqual(["reasoning", "function_call", "reasoning"]);
+    expect(body.input[0].encrypted_content).toBe(encodeReasoningEnvelope({ sig: "sig-first" }));
+    expect(body.input[2].encrypted_content).toBe(encodeReasoningEnvelope({ sig: "sig-second" }));
+  });
+
+  test("rejects malformed or nested OpenCodex signatures", () => {
+    for (const signature of [
+      "ocxr1:not-base64!!!",
+      encodeReasoningEnvelope({ sig: "nested" }),
+      encodeReasoningEnvelope({ sig: "", txt: "nested-empty-signature" }),
+    ]) {
+      expect(() => anthropicToResponsesBody({
+        model: "m", messages: [{ role: "assistant", content: [{ type: "thinking", thinking: "x", signature }] }],
+      })).toThrow();
+    }
+  });
+
+  test("round-trips redacted thinking without exposing it as a genuine signature", () => {
+    const encoded = encodeReasoningEnvelope({ sig: "sig", red: ["red-a", "red-b"] });
+    const message = responsesJsonToAnthropicMessage({
+      output: [{ type: "reasoning", summary: [{ type: "summary_text", text: "visible" }], encrypted_content: encoded }],
+    }, "m") as any;
+    expect(message.content[0]).toMatchObject({ type: "thinking", signature: "sig" });
+    expect(message.content.slice(1)).toEqual([
+      { type: "redacted_thinking", data: "red-a" },
+      { type: "redacted_thinking", data: "red-b" },
+    ]);
+  });
+
+  test("owned fallback is bounded and decodable", () => {
+    const message = responsesJsonToAnthropicMessage({
+      output: [{ type: "reasoning", summary: [{ type: "summary_text", text: "think" }] }],
+    }, "m") as any;
+    const signature = message.content[0].signature as string;
+    expect(signature.startsWith("ocxr1:")).toBe(true);
+    expect(decodeReasoningEnvelope(signature)).toEqual({ txt: "think" });
+  });
+
+  test("preserves an explicitly empty fallback text", () => {
+    expect(decodeReasoningEnvelope(encodeReasoningEnvelope({ txt: "" }))).toEqual({ txt: "" });
+  });
+
+  test("inbound preserves redacted-only reasoning when visible text is empty", () => {
+    const body = anthropicToResponsesBody({
+      model: "m", messages: [{ role: "assistant", content: [{ type: "redacted_thinking", data: "opaque" }] }],
+    }) as any;
+    expect(body.input).toHaveLength(1);
+    expect(body.input[0].type).toBe("reasoning");
+    expect(decodeReasoningEnvelope(body.input[0].encrypted_content)?.red).toEqual(["opaque"]);
+  });
+
+  test("drops an empty unsigned thinking block", () => {
+    const body = anthropicToResponsesBody({
+      model: "m", messages: [{ role: "assistant", content: [{ type: "thinking", thinking: "", signature: "" }] }],
+    }) as any;
+    expect(body.input).toEqual([]);
+  });
+
+  test("preserves signature-only reasoning in JSON output", () => {
+    const message = responsesJsonToAnthropicMessage({
+      output: [{ type: "reasoning", summary: [], encrypted_content: encodeReasoningEnvelope({ sig: "sig-only" }) }],
+    }, "m") as any;
+    expect(message.content).toEqual([{ type: "thinking", thinking: "", signature: "sig-only" }]);
+  });
+});