diff --git a/src/selfhost/ai.ts b/src/selfhost/ai.ts
index d0e39c5a50..2b5c1efb5c 100644
--- a/src/selfhost/ai.ts
+++ b/src/selfhost/ai.ts
@@ -236,17 +236,24 @@ export function resolveCodexFirstOutputTimeoutMs(env: Record<string, string | un
   return 30_000;
 }
 
-// #4994: the SAME fast-fail deadline as resolveCodexFirstOutputTimeoutMs above, for the claude-code CLI. When this
-// pattern was first built (#codex-first-output-timeout), Claude Code had no prod-observed dead-air hang, so it was
-// deliberately left unwired for that provider (see the historical rationale that used to live on SpawnFn's
-// `firstOutputTimeoutMs` field). That premise is now stale: `selfhost_ai_provider_failed: subscription_cli_timeout`
-// for `provider: claude-code` accumulated 4,030+ events over 12 days in production (GITTENSORY-K/M/8/Z), the exact
-// shape this mechanism exists to catch and distinguish from a genuine full-timeout. Same bounds/defaults as Codex's
-// version for consistency; independent env var so either CLI's deadline can be tuned without affecting the other.
+// #4994/#5053: this mirrored resolveCodexFirstOutputTimeoutMs's shape, but NOT its premise -- codex's own comment
+// explains why ITS deadline is safe: "real JSONL progress from codex --json always lands on stdout" (a genuine
+// hang shows literally zero bytes; a working call shows steady incremental bytes). Claude Code's invocation here
+// uses `--output-format json`, which `claude --help` documents as a "single result" -- fully buffered, not
+// streamed. Confirmed live (#5053): a realistic 274KB/effort:high prompt took 116s to complete successfully with
+// ZERO stdout bytes for the entire run, then the full response arrived at once. A 30s (or even 120s) deadline
+// cannot tell that apart from a genuine hang for THIS CLI mode -- it can only ever be a coin flip between "kill a
+// slow-but-working review" and "wait out a truly dead one," and #4994 mis-set that coin badly (deployed, then
+// caused a total-outage incident: every review killed, tripping the per-provider circuit breaker fleet-wide on a
+// box with no fallback provider configured). Default/ceiling raised to match resolveCliTimeoutFrom's own outer
+// clamp, so `Math.min(this, timeoutMs - 1)` at the call site always resolves to the REAL timeout unless an
+// operator explicitly opts into a shorter, riskier window via CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS -- "stalled no
+// output" then only fires when nothing arrived for the ENTIRE configured budget, a genuine hang, exactly the
+// pre-#4994 behavior. Do NOT copy this default onto Codex's version above; its streaming premise still holds.
 export function resolveClaudeFirstOutputTimeoutMs(env: Record<string, string | undefined>): number {
   const raw = Number(firstConfigured(env.CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS));
-  if (Number.isFinite(raw) && raw > 0) return Math.min(120_000, Math.max(1_000, raw));
-  return 30_000;
+  if (Number.isFinite(raw) && raw > 0) return Math.min(1_800_000, Math.max(1_000, raw));
+  return 1_800_000;
 }
 
 /** Read the per-call repo override matching this provider variant (#3902) -- ollama/openai/openai-compatible
diff --git a/test/unit/selfhost-ai.test.ts b/test/unit/selfhost-ai.test.ts
index 2b5f3102fa..c4beee2605 100644
--- a/test/unit/selfhost-ai.test.ts
+++ b/test/unit/selfhost-ai.test.ts
@@ -78,21 +78,25 @@ describe("provider-specific CLI timeouts (#selfhost — no shared timeout ambigu
     // zero/negative also falls back (raw > 0 false branch)
     expect(resolveCodexFirstOutputTimeoutMs({ CODEX_AI_FIRST_OUTPUT_TIMEOUT_MS: "0" })).toBe(30_000);
   });
-  it("resolveClaudeFirstOutputTimeoutMs defaults to 30s, is independent of effort, and honors + clamps CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS (#4994)", () => {
-    // absent → the 30s default (?? right side)
-    expect(resolveClaudeFirstOutputTimeoutMs({})).toBe(30_000);
+  it("REGRESSION (#5053): resolveClaudeFirstOutputTimeoutMs defaults to a 30-minute ceiling (effectively 'no separate fast-fail window' -- the call site's own Math.min(this, timeoutMs - 1) makes it equal the REAL timeout), unlike Codex's genuinely-streaming 30s default", () => {
+    // absent → the 1_800_000ms default -- `claude --output-format json` is a buffered "single result" (per
+    // `claude --help`), not streamed, so a short fast-fail window cannot distinguish a genuine hang from a
+    // slow-but-working call (confirmed live: a 274KB/effort:high prompt took 116s with zero stdout the whole
+    // time, then succeeded). The call site clamps this down to `timeoutMs - 1` for any realistic configured
+    // timeout, so by default the "first output" deadline IS the real deadline, matching pre-#4994 behavior.
+    expect(resolveClaudeFirstOutputTimeoutMs({})).toBe(1_800_000);
     // effort must NOT scale this deadline — a slow COMPLETION is not a slow first byte.
-    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_EFFORT: "max" })).toBe(30_000);
-    // present + valid → honored verbatim (?? left side, within bounds)
+    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_EFFORT: "max" })).toBe(1_800_000);
+    // present + valid → honored verbatim (an operator can still opt into a SHORTER, riskier window)
     expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "15000" })).toBe(15_000);
     // clamped to the 1s floor
     expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "1" })).toBe(1_000);
-    // clamped to the 120s ceiling (well under the shortest full timeout, 120_000ms)
-    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "999999" })).toBe(120_000);
+    // clamped to the 30-minute ceiling (matches resolveCliTimeoutFrom's own outer clamp)
+    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "99999999" })).toBe(1_800_000);
     // non-finite/garbage falls back to the default (Number.isFinite false branch)
-    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "not-a-number" })).toBe(30_000);
+    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "not-a-number" })).toBe(1_800_000);
     // zero/negative also falls back (raw > 0 false branch)
-    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "0" })).toBe(30_000);
+    expect(resolveClaudeFirstOutputTimeoutMs({ CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "0" })).toBe(1_800_000);
   });
 });
 
@@ -1647,7 +1651,7 @@ describe("subscription CLI helpers + fail-safe", () => {
     );
   });
 
-  it("REGRESSION (GITTENSORY-K/M/8/Z, #4994): a stalled-no-output timeout is thrown as claude_stalled_no_output, distinct from subscription_cli_timeout, and passes firstOutputTimeoutMs through to spawn", async () => {
+  it("REGRESSION (GITTENSORY-K/M/8/Z, #4994; corrected by #5053): a stalled-no-output timeout is thrown as claude_stalled_no_output, distinct from subscription_cli_timeout, and by default the fast-fail deadline EQUALS the full timeout (claude's --output-format json is buffered, not streamed — see #5053)", async () => {
     let capturedOpts: { timeoutMs: number; firstOutputTimeoutMs?: number } | undefined;
     const stalled: StubSpawn = async (_cmd, _args, o) => {
       capturedOpts = o;
@@ -1660,10 +1664,33 @@ describe("subscription CLI helpers + fail-safe", () => {
     await expect(createClaudeCodeAi({ CLAUDE_CODE_OAUTH_TOKEN: "t" }, stalled).run("m", { prompt: "x" })).rejects.not.toThrow(
       /^subscription_cli_timeout/,
     );
-    // The fast-fail deadline defaults to 30s and is strictly less than the (180s-default) full timeout.
-    expect(capturedOpts?.firstOutputTimeoutMs).toBe(30_000);
+    // #5053: by default the fast-fail deadline is clamped to timeoutMs - 1 (not a separate short window) — this
+    // event now only fires for a GENUINE full-budget hang, matching claude's buffered (non-streaming) CLI output.
     expect(capturedOpts?.timeoutMs).toBe(180_000);
-    expect(capturedOpts?.firstOutputTimeoutMs).toBeLessThan(capturedOpts!.timeoutMs);
+    expect(capturedOpts?.firstOutputTimeoutMs).toBe(179_999);
+  });
+
+  it("REGRESSION (#5053): an operator who explicitly configures a shorter CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS still gets it honored (opt-in, not the default)", async () => {
+    let capturedOpts: { timeoutMs: number; firstOutputTimeoutMs?: number } | undefined;
+    const ok: StubSpawn = async (_cmd, _args, o) => {
+      capturedOpts = o;
+      return { stdout: JSON.stringify({ type: "result", result: "hi" }), code: 0 };
+    };
+    await createClaudeCodeAi({ CLAUDE_CODE_OAUTH_TOKEN: "t", CLAUDE_AI_TIMEOUT_MS: "30000", CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "15000" }, ok).run("m", { prompt: "x" });
+    expect(capturedOpts?.timeoutMs).toBe(30_000);
+    expect(capturedOpts?.firstOutputTimeoutMs).toBe(15_000);
+  });
+
+  it("REGRESSION (#5053): clamps firstOutputTimeoutMs below timeoutMs even when CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS is configured >= the full timeout", async () => {
+    let capturedOpts: { timeoutMs: number; firstOutputTimeoutMs?: number } | undefined;
+    const ok: StubSpawn = async (_cmd, _args, o) => {
+      capturedOpts = o;
+      return { stdout: JSON.stringify({ type: "result", result: "hi" }), code: 0 };
+    };
+    await createClaudeCodeAi({ CLAUDE_CODE_OAUTH_TOKEN: "t", CLAUDE_AI_TIMEOUT_MS: "30000", CLAUDE_AI_FIRST_OUTPUT_TIMEOUT_MS: "30000" }, ok).run("m", { prompt: "x" });
+    expect(capturedOpts?.timeoutMs).toBe(30_000);
+    // Would otherwise equal timeoutMs and make the outer safety net unreachable — clamped to timeoutMs - 1.
+    expect(capturedOpts?.firstOutputTimeoutMs).toBe(29_999);
   });
 
   it("a full timeout WITHOUT stalledNoOutput still throws the generic subscription_cli_timeout, not claude_stalled_no_output (some output was produced before the kill)", async () => {