diff --git a/README.md b/README.md
index 9f4873a..b3cb468 100644
--- a/README.md
+++ b/README.md
@@ -108,7 +108,8 @@ doctor` as a blocking failure) — the durable abuse-control prerequisites do no
 development/test composition may enable it. Every public body-consuming route — Better Auth,
 Core's grant-mutation endpoint, and every module route (via a new, required `maxBodyBytes` field on
 the executable route contract) — now has an explicit, platform-enforced byte ceiling with one
-sanitized `413` contract. The Node HTTP server now has finite header/request timeouts. See
+sanitized `413` contract. The Node HTTP server now has finite header/request timeouts, whose real
+transport-level failures are observed and logged in sanitized form. See
 [API](docs/development/api.md), [Module development](docs/module-development/README.md#http-routes),
 and [ADR 0017](docs/architecture/decisions/0017-public-request-perimeter-hardening.md). **This pass
 does not add distributed rate limiting, durable public-signup abuse control, or any deployment/TLS
diff --git a/apps/api/src/server.ts b/apps/api/src/server.ts
index 3141ab6..9c85247 100644
--- a/apps/api/src/server.ts
+++ b/apps/api/src/server.ts
@@ -1,3 +1,4 @@
+import type { Socket } from "node:net";
 import path from "node:path";
 import { pathToFileURL } from "node:url";
 import type { ModuleRuntimeServices } from "@ekklesia/contracts";
@@ -64,9 +65,48 @@ const PRODUCTION_NODE_SERVER_TIMEOUTS: NodeServerTimeouts = Object.freeze({
   requestTimeoutMs: 30_000,
 });
 
-/** Never carries the remote address, request path, headers, or any other connection detail. */
+/**
+ * The two fixed operational lines a transport-level client failure may produce. Neither ever
+ * carries the remote address, request path, query, headers, cookies, body, forwarding chain, the
+ * caught error's own message, or the malformed bytes that caused it — an attacker controls all of
+ * those, and a parse failure's message in particular is derived directly from the rejected input.
+ */
 const NODE_SERVER_TIMEOUT_LOG_MESSAGE =
   "[server] A connection was closed for exceeding a configured header/request timeout.";
+const NODE_SERVER_CLIENT_ERROR_LOG_MESSAGE =
+  "[server] A connection was closed after a malformed or oversized client request.";
+
+/**
+ * Node's own documented default `clientError` responses, reproduced byte-for-byte (verified
+ * directly against the pinned Node 24 runtime by driving each case through a real socket with no
+ * listener attached). Registering *any* `clientError` listener suppresses that default entirely —
+ * `_http_server.js` only falls back when `server.emit("clientError", ...)` returns `false` — so a
+ * listener that merely observes would silently turn every 408/400/431 into a bare connection reset.
+ * Reproducing the exact bytes is what lets the platform log the event without changing what a
+ * caller actually receives.
+ */
+const NODE_CLIENT_ERROR_RESPONSES: Readonly<Record<string, string>> = Object.freeze({
+  ERR_HTTP_REQUEST_TIMEOUT: "HTTP/1.1 408 Request Timeout\r\nConnection: close\r\n\r\n",
+  HPE_HEADER_OVERFLOW: "HTTP/1.1 431 Request Header Fields Too Large\r\nConnection: close\r\n\r\n",
+});
+const NODE_CLIENT_ERROR_DEFAULT_RESPONSE = "HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n";
+
+/**
+ * Mirrors Node's own `socketOnError` fallback exactly: write the code-appropriate response only
+ * when the socket is still writable *and* no response has already begun for the in-flight request,
+ * then destroy the socket. The `_httpMessage` guard is what prevents a second, corrupting status
+ * line when a handler already responded and only the (unread) request body subsequently timed out.
+ */
+function writeNodeClientErrorResponse(error: NodeJS.ErrnoException, socket: Socket): void {
+  const inFlightResponse = (socket as Socket & { _httpMessage?: { headersSent?: boolean } })
+    ._httpMessage;
+  const alreadyResponding = inFlightResponse?.headersSent === true;
+  if (socket.writable && !alreadyResponding) {
+    const code = typeof error.code === "string" ? error.code : "";
+    socket.write(NODE_CLIENT_ERROR_RESPONSES[code] ?? NODE_CLIENT_ERROR_DEFAULT_RESPONSE);
+  }
+  socket.destroy();
+}
 
 export interface RunningApi {
   readonly app: Hono;
@@ -150,12 +190,20 @@ function bindServer(
         }
       },
     );
-    // A sanitized operational observation only — Node's own headersTimeout/requestTimeout
-    // enforcement already closes the connection (and, for requestTimeout, sends a 408) regardless
-    // of whether anything is listening here; this never carries the remote address, headers, or any
-    // other request detail.
-    server.on("timeout", () => {
-      console.error(NODE_SERVER_TIMEOUT_LOG_MESSAGE);
+    // `headersTimeout`/`requestTimeout` do NOT surface as the server's general `'timeout'` event —
+    // that event only fires for `server.setTimeout()`'s idle-socket timer, which this server never
+    // arms. Verified directly against the pinned Node 24 runtime by driving a real slow-header and
+    // slow-body connection through a real socket: the only server-level event either produces is
+    // `'clientError'`, carrying `err.code === "ERR_HTTP_REQUEST_TIMEOUT"`. Observing the failure
+    // therefore has to happen here, and — because registering a listener suppresses Node's own
+    // default response — this handler must reproduce that default itself.
+    server.on("clientError", (error: NodeJS.ErrnoException, socket: Socket) => {
+      console.error(
+        error.code === "ERR_HTTP_REQUEST_TIMEOUT"
+          ? NODE_SERVER_TIMEOUT_LOG_MESSAGE
+          : NODE_SERVER_CLIENT_ERROR_LOG_MESSAGE,
+      );
+      writeNodeClientErrorResponse(error, socket);
     });
     server.once("error", () => {
       if (!settled) {
diff --git a/apps/api/tests/api-http.integration.ts b/apps/api/tests/api-http.integration.ts
index 0bbf2ef..28c1231 100644
--- a/apps/api/tests/api-http.integration.ts
+++ b/apps/api/tests/api-http.integration.ts
@@ -1948,69 +1948,29 @@ describe.sequential("live API — client-address resolution and auth rate-limit
   });
 });
 
-describe.sequential("live API — Node header/request timeouts", () => {
-  it("closes a connection whose headers never complete within the configured headersTimeout, never invoking a handler", async () => {
-    const database = await createDisposableDatabase("node_timeouts");
-    await applyCoreMigrations(database.url);
-    const config = createApiRuntimeConfig(
-      {
-        databaseUrl: database.url,
-        host: "127.0.0.1",
-        identity: {
-          baseUrl: identityBaseUrl,
-          publicSignupEnabled: false,
-          secret: "integration-test-secret-0123456789abcdefgh",
-          trustedOrigins: [identityBaseUrl],
-        },
-        port: 0,
-      },
-      { environment: "production" },
-    );
-    // Deliberately tiny, test-only timeouts — production composition (server.ts's `main`) never
-    // sets this override — so this test observes the real transport-event close deterministically,
-    // in well under a second, rather than waiting out the production values.
-    const running = await startApi(config, {
-      nodeServerTimeoutOverride: {
-        connectionsCheckingIntervalMs: 100,
-        headersTimeoutMs: 200,
-        keepAliveTimeoutMs: 200,
-        requestTimeoutMs: 300,
-      },
-    });
-    try {
-      const address = running.server.address();
-      if (!address || typeof address !== "object") {
-        throw harnessError("The API integration server has no bound address.");
-      }
-
-      const socket = net.connect({ host: "127.0.0.1", port: address.port });
-      await new Promise<void>((resolve, reject) => {
-        socket.once("connect", () => resolve());
-        socket.once("error", reject);
-      });
-      const receivedChunks: Buffer[] = [];
-      // A `net.Socket` stays paused (and never surfaces the peer's eventual FIN as `close`) until
-      // something actively consumes its readable side — attaching this listener is what makes the
-      // socket start flowing, not merely a way to capture the response for the assertion below.
-      socket.on("data", (chunk) => receivedChunks.push(chunk as Buffer));
-      const closed = new Promise<void>((resolve) => socket.once("close", resolve));
-
-      // An incomplete request: a request line and one header, deliberately never terminated by the
-      // blank line that would mark the end of the headers, and no further data ever sent.
-      socket.write("GET /api/v1/principal HTTP/1.1\r\nHost: 127.0.0.1\r\n");
-
-      await closed;
-      expect(socket.destroyed).toBe(true);
-      const received = Buffer.concat(receivedChunks).toString("utf8");
-      expect(received).toContain("408");
-    } finally {
-      await running.shutdown().catch(() => undefined);
-      await dropDatabase(database.name);
-    }
-  });
-
-  it("closes a connection whose body never completes within the configured requestTimeout, never invoking a handler or writing a second response", async () => {
-    const database = await createDisposableDatabase("node_timeouts_body");
+describe.sequential("live API — Node header/request timeouts and client errors", () => {
+  /**
+   * Drives one raw, deliberately-malformed or deliberately-slow byte sequence through a real
+   * listening API and returns everything observable at the transport boundary, plus everything the
+   * *real* production logging seam (`console.error`, which `apps/api/src/server.ts` writes its
+   * sanitized operational line through) actually emitted while it happened.
+   *
+   * This is the only shape of proof that counts for the timeout-observability claim: no event is
+   * manually emitted, no logger is called directly, and nothing asserts merely that a listener was
+   * registered — a real socket is opened against a real server, real bytes are written, and the
+   * real Node transport is left to do whatever it genuinely does.
+   */
+  async function driveRawConnection(
+    label: string,
+    write: (socket: net.Socket) => void,
+    timeouts: Partial<NodeServerTimeouts> = {
+      connectionsCheckingIntervalMs: 100,
+      headersTimeoutMs: 200,
+      keepAliveTimeoutMs: 200,
+      requestTimeoutMs: 300,
+    },
+  ): Promise<{ destroyed: boolean; logs: string[]; received: string }> {
+    const database = await createDisposableDatabase(label);
     await applyCoreMigrations(database.url);
     const config = createApiRuntimeConfig(
       {
@@ -2026,14 +1986,11 @@ describe.sequential("live API — Node header/request timeouts", () => {
       },
       { environment: "production" },
     );
-    const running = await startApi(config, {
-      nodeServerTimeoutOverride: {
-        connectionsCheckingIntervalMs: 100,
-        headersTimeoutMs: 300,
-        keepAliveTimeoutMs: 200,
-        requestTimeoutMs: 400,
-      },
-    });
+    // Deliberately tiny, test-only timeouts — production composition (server.ts's `main`) never
+    // sets this override — so a real timeout is observed deterministically in well under a second
+    // rather than by waiting out the production values.
+    const running = await startApi(config, { nodeServerTimeoutOverride: timeouts });
+    const errorSpy = vi.spyOn(console, "error").mockImplementation(() => undefined);
     try {
       const address = running.server.address();
       if (!address || typeof address !== "object") {
@@ -2046,29 +2003,134 @@ describe.sequential("live API — Node header/request timeouts", () => {
         socket.once("error", reject);
       });
       const receivedChunks: Buffer[] = [];
+      // A `net.Socket` stays paused (and never surfaces the peer's eventual FIN as `close`) until
+      // something actively consumes its readable side — attaching this listener is what makes the
+      // socket start flowing, not merely a way to capture the response for the assertions below.
       socket.on("data", (chunk) => receivedChunks.push(chunk as Buffer));
+      socket.on("error", () => undefined);
       const closed = new Promise<void>((resolve) => socket.once("close", resolve));
 
-      // Complete, well-formed headers declaring a body that never actually arrives.
-      socket.write(
-        "POST /api/auth/sign-in/email HTTP/1.1\r\n" +
-          "Host: 127.0.0.1\r\n" +
-          "Content-Type: application/json\r\n" +
-          "Content-Length: 1000\r\n" +
-          "\r\n" +
-          '{"partial":',
-      );
-
+      write(socket);
       await closed;
-      const received = Buffer.concat(receivedChunks).toString("utf8");
-      // Node's own documented requestTimeout behavior: a 408, never a real sign-in attempt (which
-      // would need the complete body to ever reach Better Auth), and never a second response.
-      expect(received).toContain("408");
-      expect(received).not.toContain("Set-Cookie");
-      expect(received.match(/^HTTP\/1\.1 \d{3}/gmu)?.length ?? 0).toBeLessThanOrEqual(1);
+
+      const logs = errorSpy.mock.calls.flat().map((value) => String(value));
+      return {
+        destroyed: socket.destroyed,
+        logs,
+        received: Buffer.concat(receivedChunks).toString("utf8"),
+      };
     } finally {
+      errorSpy.mockRestore();
       await running.shutdown().catch(() => undefined);
       await dropDatabase(database.name);
     }
+  }
+
+  /** Every status line in a response stream — more than one would mean the platform corrupted the
+   * connection by writing a second response after Node (or a handler) already wrote one. */
+  function statusLines(received: string): readonly string[] {
+    return received.match(/^HTTP\/1\.1 \d{3}[^\r\n]*/gmu) ?? [];
+  }
+
+  /** The exact operational line `apps/api/src/server.ts` promises for a transport-level client
+   * failure — no request path, query, body, cookie, authorization value, client-address header,
+   * forwarding chain, raw peer address, stack, or parser payload may appear anywhere in the logs. */
+  function expectSanitizedTransportLog(logs: readonly string[]): void {
+    expect(logs).toHaveLength(1);
+    const emitted = logs.join("\n");
+    for (const forbidden of [
+      "/api/v1/principal",
+      "/api/auth",
+      "127.0.0.1",
+      "Cookie",
+      "cookie",
+      "Authorization",
+      "authorization",
+      "x-forwarded-for",
+      "x-ekklesia-client-address",
+      "partial",
+      "Parse Error",
+      "HPE_",
+      "ERR_HTTP_REQUEST_TIMEOUT",
+      "at ",
+    ]) {
+      expect(emitted).not.toContain(forbidden);
+    }
+  }
+
+  it("answers a never-completed header sequence with exactly one 408, closes the socket, invokes no handler, and emits exactly one sanitized operational log", async () => {
+    const { destroyed, logs, received } = await driveRawConnection(
+      "node_timeouts",
+      // An incomplete request: a request line and one header, deliberately never terminated by the
+      // blank line that would mark the end of the headers, and no further data ever sent.
+      (socket) => socket.write("GET /api/v1/principal HTTP/1.1\r\nHost: 127.0.0.1\r\n"),
+    );
+
+    expect(received).toBe("HTTP/1.1 408 Request Timeout\r\nConnection: close\r\n\r\n");
+    expect(statusLines(received)).toHaveLength(1);
+    // A handler would have produced a JSON principal body; Node answered before routing.
+    expect(received).not.toContain("anonymous");
+    expect(destroyed).toBe(true);
+    expectSanitizedTransportLog(logs);
+  });
+
+  it("answers a never-completed body with exactly one 408, closes the socket, invokes no auth logic, and emits exactly one sanitized operational log", async () => {
+    const { destroyed, logs, received } = await driveRawConnection(
+      "node_timeouts_body",
+      // Complete, well-formed headers declaring a body that never actually arrives.
+      (socket) =>
+        socket.write(
+          "POST /api/auth/sign-in/email HTTP/1.1\r\n" +
+            "Host: 127.0.0.1\r\n" +
+            "Content-Type: application/json\r\n" +
+            "Content-Length: 1000\r\n" +
+            "\r\n" +
+            '{"partial":',
+        ),
+      {
+        connectionsCheckingIntervalMs: 100,
+        headersTimeoutMs: 300,
+        keepAliveTimeoutMs: 200,
+        requestTimeoutMs: 400,
+      },
+    );
+
+    expect(received).toBe("HTTP/1.1 408 Request Timeout\r\nConnection: close\r\n\r\n");
+    expect(statusLines(received)).toHaveLength(1);
+    expect(received).not.toContain("Set-Cookie");
+    expect(destroyed).toBe(true);
+    expectSanitizedTransportLog(logs);
+  });
+
+  it("preserves Node's own 400 for a malformed request line, without logging the malformed bytes", async () => {
+    const { destroyed, logs, received } = await driveRawConnection("node_bad_request", (socket) =>
+      socket.write("!!!!NOT-HTTP-AT-ALL!!!! /secret-path\r\n\r\n"),
+    );
+
+    expect(received).toBe("HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n");
+    expect(statusLines(received)).toHaveLength(1);
+    expect(destroyed).toBe(true);
+    expectSanitizedTransportLog(logs);
+    // The attacker-controlled bytes must never reach the log.
+    expect(logs.join("\n")).not.toContain("NOT-HTTP-AT-ALL");
+    expect(logs.join("\n")).not.toContain("secret-path");
+  });
+
+  it("preserves Node's own 431 for an oversized header block, without logging the header contents", async () => {
+    const { destroyed, logs, received } = await driveRawConnection(
+      "node_header_overflow",
+      (socket) =>
+        socket.write(
+          `GET /api/v1/principal HTTP/1.1\r\nHost: 127.0.0.1\r\nX-Overflow: ${"z".repeat(20_000)}\r\n\r\n`,
+        ),
+    );
+
+    expect(received).toBe(
+      "HTTP/1.1 431 Request Header Fields Too Large\r\nConnection: close\r\n\r\n",
+    );
+    expect(statusLines(received)).toHaveLength(1);
+    expect(destroyed).toBe(true);
+    expectSanitizedTransportLog(logs);
+    expect(logs.join("\n")).not.toContain("zzz");
   });
 });
diff --git a/apps/api/tests/lifecycle.test.ts b/apps/api/tests/lifecycle.test.ts
index fc5d71c..f4b14e2 100644
--- a/apps/api/tests/lifecycle.test.ts
+++ b/apps/api/tests/lifecycle.test.ts
@@ -213,9 +213,11 @@ function fakeDiscoveredModule(
 /** A minimal fake `ServerType`: enough of Node's `http.Server` shape for `bindServer`/`shutdown`
  * to drive without a real socket. `close` and `once` are spies so tests can assert call counts;
  * `triggerError` simulates the server's own `'error'` event (e.g. a bind failure). */
+type ClientErrorHandler = (error: NodeJS.ErrnoException, socket: import("node:net").Socket) => void;
+
 function fakeServer() {
   let errorHandler: ((error: Error) => void) | undefined;
-  let timeoutHandler: (() => void) | undefined;
+  let clientErrorHandler: ClientErrorHandler | undefined;
   const server = {
     address: () => ({ address: "127.0.0.1", family: "IPv4", port: 4_000 }),
     close: vi.fn((callback?: () => void) => {
@@ -223,9 +225,9 @@ function fakeServer() {
       return server;
     }),
     listening: true,
-    on: vi.fn((event: string, handler: () => void) => {
-      if (event === "timeout") {
-        timeoutHandler = handler;
+    on: vi.fn((event: string, handler: ClientErrorHandler) => {
+      if (event === "clientError") {
+        clientErrorHandler = handler;
       }
       return server;
     }),
@@ -237,9 +239,11 @@ function fakeServer() {
     }),
   };
   return {
+    /** The `clientError` handler `bindServer` registered — the real event path Node uses for a
+     * header/request timeout, a parse failure, and a header overflow alike. */
+    clientErrorHandler: () => clientErrorHandler,
     server,
     triggerError: (error: Error) => errorHandler?.(error),
-    triggerTimeout: () => timeoutHandler?.(),
   };
 }
 
@@ -248,12 +252,12 @@ function fakeServer() {
  * resolving synchronously would reference `bindServer`'s own `server` const before it is
  * initialized. */
 function mockSuccessfulServe() {
-  const { server, triggerError, triggerTimeout } = fakeServer();
+  const { clientErrorHandler, server, triggerError } = fakeServer();
   serveMock.mockImplementation((_options: unknown, listeningListener?: () => void) => {
     queueMicrotask(() => listeningListener?.());
     return server;
   });
-  return { server, triggerError, triggerTimeout };
+  return { clientErrorHandler, server, triggerError };
 }
 
 function mockFailingServe(error: Error) {
@@ -586,23 +590,117 @@ describe("Ekklesia API Node server timeouts", () => {
     await running.shutdown();
   });
 
-  it("logs a sanitized operational event, and nothing else, when the underlying server reports a timeout", async () => {
+  // Whether Node actually *emits* anything for a real header/request timeout — and that exactly one
+  // 408 is written, the socket closes, and no handler runs — is proven only at the real transport
+  // boundary, by the raw-socket scenarios in `apps/api/tests/api-http.integration.ts`. Node's
+  // general `'timeout'` event is NOT that path (it belongs to `server.setTimeout()`, which this
+  // server never arms); `'clientError'` is. The tests below therefore deliberately do not claim to
+  // prove the event path at all — they cover only the response-reproduction logic that Node's own
+  // default would otherwise have performed, including the duplicate-response guard, which is
+  // impractical to drive from a real socket.
+  function fakeErrorSocket(overrides: { headersSent?: boolean; writable?: boolean } = {}) {
+    const socket = {
+      _httpMessage:
+        overrides.headersSent === undefined ? undefined : { headersSent: overrides.headersSent },
+      destroy: vi.fn(),
+      destroyed: false,
+      writable: overrides.writable ?? true,
+      write: vi.fn(),
+    };
+    return socket as unknown as import("node:net").Socket & {
+      destroy: ReturnType<typeof vi.fn>;
+      write: ReturnType<typeof vi.fn>;
+    };
+  }
+
+  async function startAndCaptureClientErrorHandler() {
     const poolEnd = vi.fn().mockResolvedValue(undefined);
     poolConstructor.mockImplementation(function fakePool() {
       return { end: poolEnd, on: vi.fn() };
     });
     betterAuthMock.mockReturnValue({ api: { getSession: vi.fn() }, handler: vi.fn() });
-    const { triggerTimeout } = mockSuccessfulServe();
+    const { clientErrorHandler } = mockSuccessfulServe();
+    const running = await startApi(validConfig());
+    const handler = clientErrorHandler();
+    if (!handler) {
+      throw new Error("Expected startApi to register a clientError handler.");
+    }
+    return { handler, running };
+  }
+
+  it("reproduces Node's own client-error responses byte-for-byte, since registering a listener suppresses them", async () => {
+    const { handler, running } = await startAndCaptureClientErrorHandler();
     const errorSpy = vi.spyOn(console, "error").mockImplementation(() => undefined);
 
     try {
-      const running = await startApi(validConfig());
-      triggerTimeout();
+      for (const [code, expected] of [
+        ["ERR_HTTP_REQUEST_TIMEOUT", "HTTP/1.1 408 Request Timeout\r\nConnection: close\r\n\r\n"],
+        [
+          "HPE_HEADER_OVERFLOW",
+          "HTTP/1.1 431 Request Header Fields Too Large\r\nConnection: close\r\n\r\n",
+        ],
+        ["HPE_INVALID_METHOD", "HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n"],
+        [undefined, "HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n"],
+      ] as const) {
+        const socket = fakeErrorSocket();
+        const error = Object.assign(new Error("parser detail that must never be logged"), { code });
+        handler(error, socket);
+
+        expect(socket.write).toHaveBeenCalledTimes(1);
+        expect(socket.write).toHaveBeenCalledWith(expected);
+        expect(socket.destroy).toHaveBeenCalledTimes(1);
+      }
+      await running.shutdown();
+    } finally {
+      errorSpy.mockRestore();
+    }
+  });
+
+  it("never writes a second response when a handler already began responding, but still closes the socket", async () => {
+    const { handler, running } = await startAndCaptureClientErrorHandler();
+    const errorSpy = vi.spyOn(console, "error").mockImplementation(() => undefined);
+
+    try {
+      const socket = fakeErrorSocket({ headersSent: true });
+      handler(Object.assign(new Error("timeout"), { code: "ERR_HTTP_REQUEST_TIMEOUT" }), socket);
+
+      expect(socket.write).not.toHaveBeenCalled();
+      expect(socket.destroy).toHaveBeenCalledTimes(1);
+
+      // An unwritable socket is likewise never written to, only destroyed.
+      const closedSocket = fakeErrorSocket({ writable: false });
+      handler(
+        Object.assign(new Error("timeout"), { code: "ERR_HTTP_REQUEST_TIMEOUT" }),
+        closedSocket,
+      );
+      expect(closedSocket.write).not.toHaveBeenCalled();
+      expect(closedSocket.destroy).toHaveBeenCalledTimes(1);
+
+      await running.shutdown();
+    } finally {
+      errorSpy.mockRestore();
+    }
+  });
+
+  it("logs one fixed sanitized line per client error, never the caught error's own message", async () => {
+    const { handler, running } = await startAndCaptureClientErrorHandler();
+    const errorSpy = vi.spyOn(console, "error").mockImplementation(() => undefined);
+
+    try {
+      handler(
+        Object.assign(new Error("Parse Error: /secret-path?token=abc123"), {
+          code: "HPE_INVALID_METHOD",
+        }),
+        fakeErrorSocket(),
+      );
 
       expect(errorSpy).toHaveBeenCalledTimes(1);
-      const [message] = errorSpy.mock.calls[0] as [string];
-      expect(message).toContain("timeout");
-      expect(message).not.toMatch(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/u);
+      const emitted = errorSpy.mock.calls.flat().map(String).join("\n");
+      expect(emitted).not.toContain("secret-path");
+      expect(emitted).not.toContain("abc123");
+      expect(emitted).not.toContain("Parse Error");
+      expect(emitted).not.toContain("HPE_");
+      expect(emitted).not.toMatch(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/u);
 
       await running.shutdown();
     } finally {
diff --git a/docs/architecture/decisions/0017-public-request-perimeter-hardening.md b/docs/architecture/decisions/0017-public-request-perimeter-hardening.md
index a4c0e26..6ac0043 100644
--- a/docs/architecture/decisions/0017-public-request-perimeter-hardening.md
+++ b/docs/architecture/decisions/0017-public-request-perimeter-hardening.md
@@ -159,7 +159,7 @@ manifest): every existing module fixture, test, and the template (`templates/mod
 index.ts`) are updated in this same pass to declare it explicitly, per module-authoring
 convention documented in [Module development](../../module-development/README.md#http-routes).
 
-### Finite Node header/request timeouts, and a non-obvious operational detail
+### Finite Node header/request timeouts, and two non-obvious operational details
 
 `apps/api/src/server.ts` configures `@hono/node-server`'s `serverOptions` (passed straight through
 to `http.createServer`) with `headersTimeout: 20s`, `requestTimeout: 30s`, and
@@ -177,11 +177,35 @@ configured timeout before Node ever closes it, on top of the configured value. `
 therefore also sets `connectionsCheckingIntervalMs: 5s` explicitly, so a violation is detected
 promptly after it actually elapses rather than after an unrelated, much longer default interval.
 
-A sanitized `server.on("timeout", ...)` listener logs a fixed, generic operational message — never
-the remote address, headers, or request path — purely for observability; it does not participate
-in, and cannot suppress, Node's own `408`/close behavior for `headersTimeout`/`requestTimeout`
-(confirmed directly: only overriding the low-level `'clientError'` event, which this pass does
-not touch, would do that).
+The second detail concerns *observing* those timeouts, and corrects a claim this ADR originally
+made. Node's general server `'timeout'` event belongs to `server.setTimeout()`'s idle-socket timer,
+which this server never arms — it does **not** fire for `headersTimeout`/`requestTimeout`. Driving
+a real slow-header and a real slow-body connection through a real socket against the pinned runtime
+shows the only server-level event either produces is `'clientError'`, carrying
+`err.code === "ERR_HTTP_REQUEST_TIMEOUT"`. A `server.on("timeout", ...)` listener therefore never
+fires in production, and the sanitized operational line it was meant to emit was never actually
+emitted.
+
+`apps/api/src/server.ts` consequently observes `'clientError'` instead. That carries an obligation:
+registering *any* `'clientError'` listener suppresses Node's own default response entirely
+(`_http_server.js` falls back only when `server.emit("clientError", ...)` returns `false`), so a
+listener that merely watched would silently turn every `408`/`400`/`431` into a bare connection
+reset. The handler therefore reproduces Node's default byte-for-byte — `408 Request Timeout` for
+`ERR_HTTP_REQUEST_TIMEOUT`, `431 Request Header Fields Too Large` for `HPE_HEADER_OVERFLOW`, `400
+Bad Request` otherwise — writing it only when the socket is still writable and no response has
+already begun for the in-flight request (mirroring Node's own `_httpMessage`/`headersSent` guard, so
+a handler that already responded before an unread body timed out never receives a second, corrupting
+status line), then destroys the socket exactly as Node would.
+
+Exactly one fixed, sanitized line is logged per event — one message for a timeout, one for any other
+malformed or oversized request. Neither ever contains the request path, query, body, cookies,
+authorization value, client-address header, forwarding chain, raw peer address, stack, or the caught
+error's own message, since a parse failure's message is derived directly from attacker-controlled
+input. This is proven at the real transport boundary rather than by manual event emission: raw-socket
+scenarios in `apps/api/tests/api-http.integration.ts` drive a genuine slow-header connection, a
+genuine slow-body connection, a malformed request line, and an oversized header block, each
+asserting the exact response bytes, exactly one status line, socket closure, non-invocation of any
+handler, and exactly one sanitized log.
 
 Bounded graceful-shutdown deadlines for module `stop()` hooks are a related but distinct concern,
 explicitly deferred to pass 4 and not touched here.
diff --git a/docs/development/api.md b/docs/development/api.md
index 1bdd805..574ce9a 100644
--- a/docs/development/api.md
+++ b/docs/development/api.md
@@ -324,16 +324,37 @@ made explicit). Node's own documented behavior responds `408` and closes the con
 ever invoking a request listener when either timeout is exceeded, so a timed-out connection cannot
 invoke a handler or receive a second response by construction.
 
-One non-obvious detail, found only by reproducing it directly against the pinned Node runtime:
-Node's `http.Server` only *checks* for a timeout violation when its periodic
-`connectionsCheckingInterval` fires, and that option's own default is 30 seconds — leaving it
-unset would silently let a violating connection sit for up to a further 30 seconds past its
-configured timeout. `connectionsCheckingIntervalMs` is therefore also set explicitly (5s). A
-sanitized, fixed operational log line (never the remote address, headers, or request path) is
-emitted on a server-level `'timeout'` event purely for observability; it does not participate in,
-and cannot suppress, Node's own `408`/close behavior. See
+Two non-obvious details, both found only by reproducing them directly against the pinned Node 24
+runtime through a real socket:
+
+1. **Detection latency.** Node's `http.Server` only *checks* for a timeout violation when its
+   periodic `connectionsCheckingInterval` fires, and that option's own default is 30 seconds —
+   leaving it unset would silently let a violating connection sit for up to a further 30 seconds
+   past its configured timeout. `connectionsCheckingIntervalMs` is therefore also set explicitly
+   (5s).
+2. **The observable event is `'clientError'`, not `'timeout'`.** Node's general server `'timeout'`
+   event belongs to `server.setTimeout()`'s idle-socket timer, which this server never arms; it
+   does **not** fire for `headersTimeout`/`requestTimeout`. Those surface as `'clientError'` with
+   `err.code === "ERR_HTTP_REQUEST_TIMEOUT"`. `apps/api/src/server.ts` therefore observes
+   `'clientError'`, and — because registering any `'clientError'` listener *suppresses* Node's own
+   default response entirely (`_http_server.js` only falls back when the emit returns `false`) —
+   that handler reproduces Node's default byte-for-byte rather than merely watching: `408 Request
+   Timeout` for a timeout, `431 Request Header Fields Too Large` for a header overflow, and `400
+   Bad Request` otherwise, each followed by destroying the socket, and each written only when the
+   socket is still writable and no response has already begun (so a handler that already responded
+   before an unread body timed out never receives a second, corrupting status line).
+
+Exactly one fixed, sanitized operational line is logged per transport-level client failure — one
+message for a timeout, one for any other malformed/oversized request. Neither ever contains the
+request path, query, body, cookies, authorization value, client-address header, forwarding chain,
+raw peer address, stack, or the caught error's own message (a parse failure's message is derived
+from attacker-controlled input). This is proven at the real transport boundary by raw-socket
+scenarios in `apps/api/tests/api-http.integration.ts` — a real slow-header connection, a real
+slow-body connection, a malformed request line, and an oversized header block — each asserting the
+exact response bytes, exactly one status line, socket closure, no handler invocation, and exactly
+one sanitized log. See
 [ADR 0017](../architecture/decisions/0017-public-request-perimeter-hardening.md) for the full
-account, including the standalone reproduction that found the `connectionsCheckingInterval` gap.
+account.
 
 ## Module discovery, permission composition, and module runtime startup