diff --git a/docs/developers-guide.md b/docs/developers-guide.md
index 9b17d2476..8e462e911 100644
--- a/docs/developers-guide.md
+++ b/docs/developers-guide.md
@@ -1434,12 +1434,12 @@ ordinary bare-word exceptions.
 
 Apart from the inline-code span, which the overlay masks until the shared
 dictionary does so itself, use one exact documented pattern per exception
-rather than disabling a whole syntax class. The remaining exceptions are
-limited to the `PoolServerBehavior` test-server fixture, the former
-`BackoffConfig::normalised` public method, exact generic-bound fragments in RFC
-0001, immutable en-GB diagnostic fixtures, and Tokio test attributes. Add a new
-pattern only when a narrower correction or wording change would alter a public
-API, external-tool key, formal name, or deliberately fixed diagnostic.
+rather than disabling a whole syntax class. The remaining exceptions cover the
+published `PoolServerBehavior` and `start_with_behavior` test-server names, the
+former `BackoffConfig::normalised` public method, exact generic-bound fragments
+in RFC 0001, and fixed external tool, CI and Tokio syntax. Add a new pattern
+only when a narrower correction or wording change would alter a public API,
+external-tool key, formal name, or deliberately fixed diagnostic.
 
 Eligible tracked files must remain readable UTF-8 text so the gate cannot
 silently omit them. Continuous integration installs Nixie 1.1.0 with Python
diff --git a/docs/rstest-bdd-users-guide.md b/docs/rstest-bdd-users-guide.md
index e97ead7a0..130308a79 100644
--- a/docs/rstest-bdd-users-guide.md
+++ b/docs/rstest-bdd-users-guide.md
@@ -762,7 +762,7 @@ fn counter() -> Counter {
     Counter::default()
 }
 
-#[given("a counter initialised to 0")]
+#[given("a counter initialized to 0")]
 fn init(counter: &mut Counter) {
     counter.value = 0;
 }
diff --git a/docs/users-guide.md b/docs/users-guide.md
index 2065e8c1e..8084b4fc5 100644
--- a/docs/users-guide.md
+++ b/docs/users-guide.md
@@ -208,7 +208,11 @@ through `on_connection_setup`, not in a rebuilt application graph.
 Serialization helpers `send_response` and `send_response_framed` (or
 `send_response_framed_with_codec` for custom codecs) return typed `SendError`
 variants when encoding or I/O fails, and the connection closes after ten
-consecutive deserialization errors.[^6][^7]
+consecutive deserialization errors.[^6][^7] Each `SendError` variant's
+`Display` output starts with a fixed prefix: `serialization error:` for
+`Serialize`, `I/O error:` for `Io`, and `codec error:` for `Codec`. Those
+prefixes are stable and form the public diagnostic contract that callers may
+match on; the source error text after them is not part of that contract.
 
 ### Custom frame codecs
 
diff --git a/src/app/error.rs b/src/app/error.rs
index 481fc43b0..c9b5298eb 100644
--- a/src/app/error.rs
+++ b/src/app/error.rs
@@ -11,7 +11,7 @@ use crate::codec::CodecError;
 #[non_exhaustive]
 pub enum SendError {
     /// Serialization failed.
-    #[error("serialisation error: {0}")]
+    #[error("serialization error: {0}")]
     Serialize(#[source] Box<dyn std::error::Error + Send + Sync>),
     /// Writing to the stream failed.
     #[error("I/O error: {0}")]
diff --git a/src/test_helpers/pool_client.rs b/src/test_helpers/pool_client.rs
index 688316910..af0c4b57e 100644
--- a/src/test_helpers/pool_client.rs
+++ b/src/test_helpers/pool_client.rs
@@ -75,7 +75,7 @@ struct PoolServerState {
     /// One-shot flag controlling malformed-response coverage.
     malformed_response_sent: Arc<AtomicBool>,
     /// Response mode selected by the test case.
-    behavior: PoolServerBehavior,
+    behaviour: PoolServerBehavior,
 }
 
 impl PoolTestServer {
@@ -93,7 +93,7 @@ impl PoolTestServer {
     /// # Errors
     ///
     /// Returns an error if the test listener cannot bind to a local port.
-    pub async fn start_with_behavior(behavior: PoolServerBehavior) -> std::io::Result<Self> {
+    pub async fn start_with_behavior(behaviour: PoolServerBehavior) -> std::io::Result<Self> {
         let listener = TcpListener::bind("127.0.0.1:0").await?;
         let addr = listener.local_addr()?;
         let preamble_count = Arc::new(AtomicUsize::new(0));
@@ -102,7 +102,7 @@ impl PoolTestServer {
             preamble_count: preamble_count.clone(),
             connection_count: connection_count.clone(),
             malformed_response_sent: Arc::new(AtomicBool::new(false)),
-            behavior,
+            behaviour,
         };
 
         let handle = tokio::spawn(run_pool_test_accept_loop(listener, state));
@@ -192,7 +192,7 @@ async fn run_pool_test_accept_loop(listener: TcpListener, state: PoolServerState
             preamble_count: state.preamble_count.clone(),
             connection_count: state.connection_count.clone(),
             malformed_response_sent: state.malformed_response_sent.clone(),
-            behavior: state.behavior,
+            behaviour: state.behaviour,
         };
         tokio::spawn(handle_pool_test_connection(stream, state));
     }
@@ -224,7 +224,7 @@ async fn handle_pool_test_connection(mut stream: tokio::net::TcpStream, state: P
             break;
         };
 
-        let payload = if state.behavior == PoolServerBehavior::MalformedFirstResponse
+        let payload = if state.behaviour == PoolServerBehavior::MalformedFirstResponse
             && !state.malformed_response_sent.swap(true, Ordering::SeqCst)
         {
             Vec::new()
diff --git a/tests/extractor.rs b/tests/extractor.rs
index b82bf7222..084c3044d 100644
--- a/tests/extractor.rs
+++ b/tests/extractor.rs
@@ -34,7 +34,7 @@ struct TestMsg(u8);
 #[rstest]
 fn message_extractor_parses_and_advances(request: MessageRequest) {
     let msg = TestMsg(42);
-    let bytes = msg.to_bytes().expect("failed to serialise message");
+    let bytes = msg.to_bytes().expect("failed to serialize message");
     let mut payload = Payload::new(bytes.as_slice());
 
     let extracted = Message::<TestMsg>::from_message_request(&request, &mut payload)
diff --git a/tests/fixtures/fragment/mod.rs b/tests/fixtures/fragment/mod.rs
index 6b8c20638..6443dcb42 100644
--- a/tests/fixtures/fragment/mod.rs
+++ b/tests/fixtures/fragment/mod.rs
@@ -184,13 +184,13 @@ impl FragmentWorld {
     fn series(&self) -> TestResult<&FragmentSeries> {
         self.series
             .as_ref()
-            .ok_or_else(|| "fragment series not initialised".into())
+            .ok_or_else(|| "fragment series not initialized".into())
     }
 
     fn series_mut(&mut self) -> TestResult<&mut FragmentSeries> {
         self.series
             .as_mut()
-            .ok_or_else(|| "fragment series not initialised".into())
+            .ok_or_else(|| "fragment series not initialized".into())
     }
 
     /// Assert that the latest fragment failed due to an index mismatch.
diff --git a/tests/fixtures/message_assembly.rs b/tests/fixtures/message_assembly.rs
index a01232715..ffeae4609 100644
--- a/tests/fixtures/message_assembly.rs
+++ b/tests/fixtures/message_assembly.rs
@@ -158,7 +158,7 @@ impl MessageAssemblyWorld {
             return Err("no pending first frame".into());
         };
         let Some(state) = self.state.as_mut() else {
-            return Err("state not initialised".into());
+            return Err("state not initialized".into());
         };
         let Some(now) = self.current_time else {
             return Err("time not set".into());
@@ -184,7 +184,7 @@ impl MessageAssemblyWorld {
     /// Returns an error if state not initialized or time not set.
     pub fn accept_all_first_frames(&mut self) -> TestResult {
         let Some(state) = self.state.as_mut() else {
-            return Err("state not initialised".into());
+            return Err("state not initialized".into());
         };
         let Some(now) = self.current_time else {
             return Err("time not set".into());
@@ -218,7 +218,7 @@ impl MessageAssemblyWorld {
     )]
     pub fn accept_continuation(&mut self, params: ContinuationFrameParams) -> TestResult {
         let Some(state) = self.state.as_mut() else {
-            return Err("state not initialised".into());
+            return Err("state not initialized".into());
         };
         let Some(now) = self.current_time else {
             return Err("time not set".into());
@@ -257,7 +257,7 @@ impl MessageAssemblyWorld {
     /// Returns an error if state not initialized or time not set.
     pub fn purge_expired(&mut self) -> TestResult {
         let Some(state) = self.state.as_mut() else {
-            return Err("state not initialised".into());
+            return Err("state not initialized".into());
         };
         let Some(now) = self.current_time else {
             return Err("time not set".into());
diff --git a/tests/response/response_errors.rs b/tests/response/response_errors.rs
index ee7a08354..fba4a4a63 100644
--- a/tests/response/response_errors.rs
+++ b/tests/response/response_errors.rs
@@ -208,6 +208,7 @@ async fn send_response_returns_encode_error() {
         .await
         .expect_err("send_response should fail when encode errors");
     assert_serialize_error(&err);
+    assert_eq!(err.to_string(), "serialization error: Other(\"fail\")");
 }
 
 #[tokio::test]
diff --git a/typos.local.toml b/typos.local.toml
index 5f42f2228..5ae3b451f 100644
--- a/typos.local.toml
+++ b/typos.local.toml
@@ -11,37 +11,21 @@ accepted = []
 [patterns]
 ignore = [
   # Inline code spans are masked; the shared dictionary does not mask them yet.
+  '`[^`\n]+`',
   # Preserve the external Linux linker name only in its command and flag forms.
   "-Clink-arg=-fuse-ld=mold",
   "sudo apt-get install -y mold",
   "mold --version",
   # setup-rust's input that installs the linker.
   "install-mold",
-  '`[^`\n]+`',
-  # Public test-server fixture identifier. This preserves the externally
-  # visible helper name without accepting a bare word.
+  # Published test-server identifiers retain their public spellings.
   "\\bPoolServerBehavior\\b",
-  # Pool-test-server Rust fixtures. These exact source fragments preserve the
-  # public test helper's identifier and deliberately malformed response names.
-  "\\ \\ \\ \\ PoolServerBehavior,",
+  "\\bstart_with_behavior\\b",
+  # Fixed CI and Tokio identifiers keep their external spellings.
   "\\ \\ \\ \\ \\ \\ CARGO_TERM_COLOR:\\ always",
-  "\\ \\ \\ \\ \\ \\ \\ Self::start_with_behavior\\(PoolServerBehavior::Ech",
-  "\\ \\ \\ \\ \\ \\ \\ \\ PoolServerBehavior,",
-  "\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ behavior,",
-  "\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ behavior:\\ state\\.behavior,",
-  "\\ \\ \\ \\ \\ \\ \\ \\ behavior:\\ state\\.behavior,",
-  "\\ \\ \\ \\ \\ format!\\(\"failed\\ to\\ deserialise\\ envelope:\\ \\{error\\}\"\\),",
-  "\\ \\ \\ \\ \\#\\[error\\(\"serialisation\\ error:\\ \\{0\\}\"\\)\\]",
-  "\\ \\ \\ \\ behavior:\\ PoolServerBehavior,",
-  # Rust diagnostic fixtures use established en-GB messages that Typos must
-  # not reinterpret as prose corrections.
-  "\\ \\ return\\ Err\\(\"state\\ not\\ initialised\"\\.into\\(\\)\\);",
-  "\\ fn\\ start_with_behavior\\(behavior:\\ PoolServerBehavior\\)\\ \\->",
-  "\\ let\\ payload\\ =\\ if\\ state\\.behavior\\ ==\\ PoolServerBehavior::",
   "\\ reopened,\\ synchronize,\\ labeled,\\ ready_for_review\\]",
   "\\#\\[tokio::test\\(flavor\\ =\\ \"current_thread\",\\ sta",
   "\\#\\[tokio::test\\(flavor\\ =\\ \"current_thread\"\\)\\]",
-  "\\|\\|\\ \"fragment\\ series\\ not\\ initialised\"\\.into\\(\\)\\)",
   # Migration documentation records the immutable former public method name.
   "BackoffConfig::normalised",
   # RFC generic-bound examples use the declared `Ser` parameter only in these
@@ -50,15 +34,7 @@ ignore = [
   "Ser: Serializer",
   "DecodeWith<Ser>",
   "EncodeWith<Ser>",
-  "e\\.behavior\\ ==\\ PoolServerBehavior::MalformedFirstResponse",
-  "ior\\(behavior:\\ PoolServerBehavior\\)\\ \\->\\ std::io::Result<Sel",
-  "lTestServer::start_with_behavior\\(PoolServerBehavior::Mal",
-  "pub\\ async\\ fn\\ start_with_behavior\\(behavior:\\ PoolServerBeh",
-  "pub\\ enum\\ PoolServerBehavior\\ \\{",
   "st\\(start_paused\\ =\\ true,\\ flavor\\ =\\ \"current_thread\"\\)\\]",
-  "tes\\(\\)\\.expect\\(\"failed\\ to\\ serialise\\ message\"\\);",
-  "with_behavior\\(PoolServerBehavior::EchoPong\\)\\.await",
-  "with_behavior\\(PoolServerBehavior::MalformedFirstResponse",
 ]
 
 [files]
diff --git a/typos.toml b/typos.toml
index 8a734bfa6..794559960 100644
--- a/typos.toml
+++ b/typos.toml
@@ -42,19 +42,7 @@ extend-ignore-re = [
     "HashiCorp",
     "How to organise your Rust tests",
     "Ser: Serializer",
-    "\\ \\ \\ \\ PoolServerBehavior,",
     "\\ \\ \\ \\ \\ \\ CARGO_TERM_COLOR:\\ always",
-    "\\ \\ \\ \\ \\ \\ \\ Self::start_with_behavior\\(PoolServerBehavior::Ech",
-    "\\ \\ \\ \\ \\ \\ \\ \\ PoolServerBehavior,",
-    "\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ behavior,",
-    "\\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ behavior:\\ state\\.behavior,",
-    "\\ \\ \\ \\ \\ \\ \\ \\ behavior:\\ state\\.behavior,",
-    "\\ \\ \\ \\ \\ format!\\(\"failed\\ to\\ deserialise\\ envelope:\\ \\{error\\}\"\\),",
-    "\\ \\ \\ \\ \\#\\[error\\(\"serialisation\\ error:\\ \\{0\\}\"\\)\\]",
-    "\\ \\ \\ \\ behavior:\\ PoolServerBehavior,",
-    "\\ \\ return\\ Err\\(\"state\\ not\\ initialised\"\\.into\\(\\)\\);",
-    "\\ fn\\ start_with_behavior\\(behavior:\\ PoolServerBehavior\\)\\ \\->",
-    "\\ let\\ payload\\ =\\ if\\ state\\.behavior\\ ==\\ PoolServerBehavior::",
     "\\ reopened,\\ synchronize,\\ labeled,\\ ready_for_review\\]",
     "\\#\\[tokio::test\\(flavor\\ =\\ \"current_thread\",\\ sta",
     "\\#\\[tokio::test\\(flavor\\ =\\ \"current_thread\"\\)\\]",
@@ -66,25 +54,17 @@ extend-ignore-re = [
     "\\bcolor-(?:mix|contrast)\\b",
     "\\bflavor = ",
     "\\brust-analyzer\\b",
+    "\\bstart_with_behavior\\b",
     "\\{COLOR\\}",
     "\\{color\\}",
-    "\\|\\|\\ \"fragment\\ series\\ not\\ initialised\"\\.into\\(\\)\\)",
     "`[^`\\n]+`",
     "`color`",
     "`var\\.iamge_id` instead of `var\\.image_id`",
     "currentColor",
-    "e\\.behavior\\ ==\\ PoolServerBehavior::MalformedFirstResponse",
     "install-mold",
-    "ior\\(behavior:\\ PoolServerBehavior\\)\\ \\->\\ std::io::Result<Sel",
-    "lTestServer::start_with_behavior\\(PoolServerBehavior::Mal",
     "mold --version",
-    "pub\\ async\\ fn\\ start_with_behavior\\(behavior:\\ PoolServerBeh",
-    "pub\\ enum\\ PoolServerBehavior\\ \\{",
     "st\\(start_paused\\ =\\ true,\\ flavor\\ =\\ \"current_thread\"\\)\\]",
     "sudo apt-get install -y mold",
-    "tes\\(\\)\\.expect\\(\"failed\\ to\\ serialise\\ message\"\\);",
-    "with_behavior\\(PoolServerBehavior::EchoPong\\)\\.await",
-    "with_behavior\\(PoolServerBehavior::MalformedFirstResponse",
 ]
 
 [default.extend-words]
diff --git a/wireframe_testing/README.md b/wireframe_testing/README.md
index 7b49d22df..f7903f6a3 100644
--- a/wireframe_testing/README.md
+++ b/wireframe_testing/README.md
@@ -21,7 +21,7 @@ use wireframe_testing::{decode_frames, drive_with_bincode, logger};
 #[tokio::test]
 async fn drives_app() -> std::io::Result<()> {
     let _log_guard = logger();
-    let app = WireframeApp::new().expect("failed to initialise app");
+    let app = WireframeApp::new().expect("failed to initialize app");
 
     let raw = drive_with_bincode(app, 42u8).await?;
     let frames = decode_frames(&raw)?;
diff --git a/wireframe_testing/src/helpers/tests/helper_tests.rs b/wireframe_testing/src/helpers/tests/helper_tests.rs
index 9f5fa9f9c..3042f7ba1 100644
--- a/wireframe_testing/src/helpers/tests/helper_tests.rs
+++ b/wireframe_testing/src/helpers/tests/helper_tests.rs
@@ -81,7 +81,7 @@ async fn drive_with_payloads_wraps_frames() -> io::Result<()> {
     let (decoded, _) = serializer.deserialize::<Envelope>(first).map_err(|error| {
         io::Error::new(
             io::ErrorKind::InvalidData,
-            format!("failed to deserialise envelope: {error}"),
+            format!("failed to deserialize envelope: {error}"),
         )
     })?;
     if decoded.payload_bytes() != payload.as_slice() {