diff --git a/scripts/test-layout/layout.json b/scripts/test-layout/layout.json
index 4f890cba99..e5425730de 100644
--- a/scripts/test-layout/layout.json
+++ b/scripts/test-layout/layout.json
@@ -641,6 +641,7 @@
     "devin-cli-authmode-migration.test.ts": "providers",
     "devin-cli-login.test.ts": "providers",
     "devin-hardening.test.ts": "providers",
+    "devin-stream-deadline.test.ts": "providers",
     "digitalocean-scaleway-provider.test.ts": "providers",
     "docs-429-failover-claims.test.ts": "ci-workflows",
     "docs-bun-source-requirement.test.ts": "ci-workflows",
diff --git a/src/adapters/devin/cloud-direct/chat.ts b/src/adapters/devin/cloud-direct/chat.ts
index 3e31e97c5c..6e30839aa6 100644
--- a/src/adapters/devin/cloud-direct/chat.ts
+++ b/src/adapters/devin/cloud-direct/chat.ts
@@ -46,8 +46,33 @@ import { resolveDevinApiBaseUrl } from '../../../oauth/devin/api-base.js';
  * we only trigger when the server has genuinely stopped responding.
  */
 const CLOUD_STREAM_IDLE_MS = 120_000;
-/** Time-to-first-byte timeout. */
-const CLOUD_STREAM_TTFB_MS = 60_000;
+/**
+ * Budget for the response HEADERS, which is not the same thing as a connect
+ * timeout. Cognition holds the headers until the model produces its first
+ * token, so on a high-effort reasoning model this bounds generation. A 60s
+ * value killed live swe-2 high turns at exactly 60000ms with no output while
+ * a sibling call on the same account was still alive at 76s, which is the
+ * defect this constant exists to record.
+ *
+ * It has to be at least as generous as the body idle budget above. The cost of
+ * the larger value is bounded and understood: a peer that goes silent at the
+ * TCP level without sending RST/FIN now hangs for this long instead of 60s. A
+ * peer that actually dies still rejects immediately. This timer is the only
+ * bound on that case once `timeout: 0` is set on the fetch, so it must not be
+ * removed. Override with OPENCODEX_DEVIN_TTFB_MS.
+ */
+const CLOUD_STREAM_HEADERS_DEFAULT_MS = 300_000;
+/** Upper bound for the override, so a stray value cannot wedge a turn forever. */
+const CLOUD_STREAM_HEADERS_MAX_MS = 1_800_000;
+function cloudStreamHeadersMs(): number {
+  const raw = process.env.OPENCODEX_DEVIN_TTFB_MS?.trim();
+  if (!raw) return CLOUD_STREAM_HEADERS_DEFAULT_MS;
+  const parsed = Number(raw);
+  if (!Number.isFinite(parsed) || parsed <= 0) return CLOUD_STREAM_HEADERS_DEFAULT_MS;
+  return Math.min(parsed, CLOUD_STREAM_HEADERS_MAX_MS);
+}
+/** Test seam for the headers budget; the resolver itself stays private. */
+export const cloudStreamHeadersMsForTests = cloudStreamHeadersMs;
 /** Maximum acceptable Connect-RPC frame length (16 MB). */
 const MAX_FRAME_LEN = 16 * 1024 * 1024;
 
@@ -1115,12 +1140,24 @@ export async function* streamChatEvents(req: CloudChatRequest): AsyncGenerator<C
   const framed = frameConnectStream(proto, false);
   const body = new Blob([new Uint8Array(framed)], { type: "application/connect+proto" });
 
-  // Compose caller signal with a TTFB timeout. If the cloud takes longer
-  // than CLOUD_STREAM_TTFB_MS to start the response, abort. Once any byte
-  // arrives we cancel the TTFB timer and start the per-chunk idle timer
-  // inside the read loop instead.
+  // Compose the caller signal with a deadline on the response HEADERS. The
+  // timer is cleared in the finally below, which runs when `await fetch`
+  // resolves — and fetch resolves on headers, not on the first body byte. An
+  // earlier comment here claimed "once any byte arrives", which was wrong and
+  // hid the defect: Cognition withholds headers until the first token, so this
+  // budget is a generation deadline. Body silence after headers is a separate
+  // budget, the per-chunk idle timer in the read loop below.
   const ttfbController = new AbortController();
-  const ttfbTimer = setTimeout(() => ttfbController.abort(new Error(`cloud-direct: time-to-first-byte timeout (${CLOUD_STREAM_TTFB_MS}ms)`)), CLOUD_STREAM_TTFB_MS);
+  const headersMs = cloudStreamHeadersMs();
+  // Abort with no reason and remember that we are the one who fired. Bun rejects
+  // the fetch with its own AbortError rather than handing back `signal.reason`,
+  // so attaching a typed error to abort() would be discarded; the catch below is
+  // what actually produces a classifiable failure.
+  let headersDeadlineFired = false;
+  const ttfbTimer = setTimeout(() => {
+    headersDeadlineFired = true;
+    ttfbController.abort();
+  }, headersMs);
   const ttfbSignal = ttfbController.signal;
   // Compose req.signal + ttfbSignal. AbortSignal.any was added in Node
   // 20.3 / Bun 1.0; our `engines` allows Node ≥18, so on Node 18-20.2 the
@@ -1148,7 +1185,28 @@ export async function* streamChatEvents(req: CloudChatRequest): AsyncGenerator<C
       body,
       redirect: 'error',
       signal: initialSignal,
-    });
+      // Bun applies its own fetch idle timeout (~5 minutes) on top of ours.
+      // Two independent deadlines on the same hop means the shorter one wins
+      // silently and this function can no longer explain its own failure, so
+      // the deadline above is made the single authority. Same reason as
+      // src/server/responses/fetch-helpers.ts.
+      timeout: 0,
+    } as RequestInit);
+  } catch (err) {
+    if (headersDeadlineFired) {
+      // Ours, not the upstream failing. Raised as a typed error with an explicit
+      // status because devinErrorClassification reads CloudChatError.status and
+      // would otherwise return {} for a bare Error, leaving src/lib/errors.ts to
+      // guess from the message text. The message deliberately no longer says
+      // "timeout", so the status is the only thing carrying the classification.
+      throw new CloudChatError(
+        `cloud-direct: no response headers within ${headersMs}ms`,
+        undefined,
+        undefined,
+        504,
+      );
+    }
+    throw err;
   } finally {
     clearTimeout(ttfbTimer);
     // The composed signal only guards the headers hop; the body is cancelled
diff --git a/tests/fixtures/test-layout-expected.json b/tests/fixtures/test-layout-expected.json
index 3e8ebbde5c..079a5ac0f3 100644
--- a/tests/fixtures/test-layout-expected.json
+++ b/tests/fixtures/test-layout-expected.json
@@ -472,6 +472,7 @@
   "destination-policy-resolved.test.ts": "routing",
   "devin-adapter.test.ts": "providers",
   "devin-hardening.test.ts": "providers",
+  "devin-stream-deadline.test.ts": "providers",
   "digitalocean-scaleway-provider.test.ts": "providers",
   "docs-429-failover-claims.test.ts": "ci-workflows",
   "docs-bun-source-requirement.test.ts": "ci-workflows",
diff --git a/tests/providers/devin-stream-deadline.test.ts b/tests/providers/devin-stream-deadline.test.ts
new file mode 100644
index 0000000000..bf11cd17f3
--- /dev/null
+++ b/tests/providers/devin-stream-deadline.test.ts
@@ -0,0 +1,100 @@
+import { describe, expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { cloudStreamHeadersMsForTests, CloudChatError } from "../../src/adapters/devin/cloud-direct/chat";
+import { devinErrorClassification } from "../../src/adapters/devin";
+import { repoPath } from "../helpers/repo-root";
+
+const CHAT_SRC = readFileSync(repoPath("src/adapters/devin/cloud-direct/chat.ts"), "utf8");
+
+function withEnv(value: string | undefined, run: () => void): void {
+  const key = "OPENCODEX_DEVIN_TTFB_MS";
+  const before = process.env[key];
+  if (value === undefined) delete process.env[key];
+  else process.env[key] = value;
+  try {
+    run();
+  } finally {
+    if (before === undefined) delete process.env[key];
+    else process.env[key] = before;
+  }
+}
+
+describe("cloud-direct response-headers deadline", () => {
+  // A 60s budget killed live swe-2 high turns at exactly 60000ms with no output
+  // while a sibling call on the same account was still alive at 76s. Cognition
+  // withholds headers until the first token, so this budget bounds generation.
+  test("the default outlives a reasoning model that thinks past a minute", () => {
+    withEnv(undefined, () => {
+      expect(cloudStreamHeadersMsForTests()).toBe(300_000);
+    });
+  });
+
+  test("the headers budget is not shorter than the body idle budget", () => {
+    // Inverting these is what made the pre-header window the tightest part of a
+    // long turn, which is backwards.
+    const idle = Number(/CLOUD_STREAM_IDLE_MS = ([0-9_]+)/.exec(CHAT_SRC)?.[1]?.replace(/_/g, ""));
+    expect(idle).toBeGreaterThan(0);
+    withEnv(undefined, () => {
+      expect(cloudStreamHeadersMsForTests()).toBeGreaterThanOrEqual(idle);
+    });
+  });
+
+  test("an operator override is honoured", () => {
+    withEnv("1000", () => {
+      expect(cloudStreamHeadersMsForTests()).toBe(1000);
+    });
+  });
+
+  test("an override is clamped so a stray value cannot wedge a turn forever", () => {
+    withEnv("999999999", () => {
+      expect(cloudStreamHeadersMsForTests()).toBe(1_800_000);
+    });
+  });
+
+  test.each(["", "   ", "0", "-5", "not-a-number"])("a useless override %p falls back to the default", (raw) => {
+    withEnv(raw, () => {
+      expect(cloudStreamHeadersMsForTests()).toBe(300_000);
+    });
+  });
+});
+
+describe("cloud-direct headers-deadline failure is ours, not the upstream", () => {
+  // The old abort raised a bare Error, so devinErrorClassification returned {}
+  // and the failure was inferred from message text as an upstream 502/504.
+  test("the deadline error classifies as a gateway timeout the caller may retry", () => {
+    const err = new CloudChatError("cloud-direct: no response headers within 300000ms", undefined, undefined, 504);
+    expect(devinErrorClassification(err)).toEqual({ status: 504, retryable: true });
+  });
+
+  test("a bare Error still classifies as nothing, which is why the status is set explicitly", () => {
+    expect(devinErrorClassification(new Error("cloud-direct: no response headers within 300000ms"))).toEqual({});
+  });
+
+  test("the message no longer claims a first-byte measurement it cannot make", () => {
+    // Nothing is on the wire before headers, so "time-to-first-byte" described a
+    // measurement that does not exist. Dropping the word "timeout" from it is why
+    // the explicit 504 above is mandatory rather than cosmetic.
+    expect(CHAT_SRC).not.toContain("time-to-first-byte");
+  });
+});
+
+describe("cloud-direct headers deadline guards", () => {
+  test("the abort callback records that we fired before aborting", () => {
+    // Bun rejects the fetch with its own AbortError instead of handing back
+    // signal.reason, so a typed error passed to abort() would be discarded and
+    // the catch could not tell our deadline from a caller cancel.
+    expect(CHAT_SRC).toMatch(/headersDeadlineFired = true;\s*\n\s*ttfbController\.abort\(\);/);
+    expect(CHAT_SRC).not.toMatch(/ttfbController\.abort\(new /);
+  });
+
+  test("the GetChatMessage fetch disables the competing runtime timeout", () => {
+    // Two independent deadlines on one hop means the shorter wins silently and
+    // this function can no longer explain its own failure.
+    const call = CHAT_SRC.slice(CHAT_SRC.indexOf("ApiServerService/GetChatMessage"));
+    expect(call.slice(0, call.indexOf("} as RequestInit"))).toContain("timeout: 0");
+  });
+
+  test("a caller cancel is re-thrown unchanged", () => {
+    expect(CHAT_SRC).toMatch(/if \(headersDeadlineFired\) \{[\s\S]*?\}\s*\n\s*throw err;/);
+  });
+});