diff --git a/src/circuit-breaker.test.ts b/src/circuit-breaker.test.ts
new file mode 100644
index 0000000..d8c996c
--- /dev/null
+++ b/src/circuit-breaker.test.ts
@@ -0,0 +1,197 @@
+/**
+ * Unit tests for the startup circuit breaker.
+ *
+ * Covers state transitions, the documented backoff schedule, and the
+ * fresh-install case where DATA_DIR doesn't exist yet (the breaker runs
+ * before initDb, so it has to create the dir itself).
+ */
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+
+// vi.mock factories are hoisted above imports, so they can't close over local
+// consts. vi.hoisted is hoisted alongside the mock and runs before any
+// `import` — so it can only use globals (no path/os modules). Use require()
+// inside the callback to compute the test dir.
+const { TEST_DIR } = vi.hoisted(() => {
+  const nodePath = require('path') as typeof import('path');
+  const nodeOs = require('os') as typeof import('os');
+  return { TEST_DIR: nodePath.join(nodeOs.tmpdir(), 'nanoclaw-cb-test') };
+});
+const CB_PATH = path.join(TEST_DIR, 'circuit-breaker.json');
+
+vi.mock('./config.js', async () => {
+  const actual = await vi.importActual<typeof import('./config.js')>('./config.js');
+  return { ...actual, DATA_DIR: TEST_DIR };
+});
+
+vi.mock('./log.js', () => ({
+  log: {
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    fatal: vi.fn(),
+  },
+}));
+
+import { enforceStartupBackoff, resetCircuitBreaker } from './circuit-breaker.js';
+
+function readState(): { attempt: number; timestamp: string } {
+  return JSON.parse(fs.readFileSync(CB_PATH, 'utf-8'));
+}
+
+function seedState(attempt: number, timestamp = new Date().toISOString()): void {
+  fs.writeFileSync(CB_PATH, JSON.stringify({ attempt, timestamp }));
+}
+
+beforeEach(() => {
+  if (fs.existsSync(TEST_DIR)) fs.rmSync(TEST_DIR, { recursive: true });
+  fs.mkdirSync(TEST_DIR, { recursive: true });
+});
+
+afterEach(() => {
+  vi.useRealTimers();
+  if (fs.existsSync(TEST_DIR)) fs.rmSync(TEST_DIR, { recursive: true });
+});
+
+describe('resetCircuitBreaker', () => {
+  it('deletes the state file', () => {
+    seedState(3);
+    expect(fs.existsSync(CB_PATH)).toBe(true);
+    resetCircuitBreaker();
+    expect(fs.existsSync(CB_PATH)).toBe(false);
+  });
+
+  it('is a no-op when the file does not exist', () => {
+    expect(fs.existsSync(CB_PATH)).toBe(false);
+    expect(() => resetCircuitBreaker()).not.toThrow();
+  });
+});
+
+describe('enforceStartupBackoff — state transitions', () => {
+  it('first run writes attempt=1 and does not delay', async () => {
+    vi.useFakeTimers();
+    const start = Date.now();
+    await enforceStartupBackoff();
+    // No timers should have been queued — clean first start is 0s.
+    expect(Date.now() - start).toBe(0);
+    expect(readState().attempt).toBe(1);
+  });
+
+  it('within reset window, attempt is incremented', async () => {
+    seedState(1);
+    vi.useFakeTimers();
+    const promise = enforceStartupBackoff();
+    await vi.runAllTimersAsync();
+    await promise;
+    expect(readState().attempt).toBe(2);
+  });
+
+  it('outside reset window (>1h), attempt resets to 1', async () => {
+    const longAgo = new Date(Date.now() - 2 * 60 * 60 * 1000).toISOString();
+    seedState(5, longAgo);
+    await enforceStartupBackoff();
+    expect(readState().attempt).toBe(1);
+  });
+
+  it('exactly at the reset window boundary still counts as "within"', async () => {
+    // RESET_WINDOW_MS = 60min. Use 59min59s to stay inside even if the test
+    // takes a few ms to execute.
+    const justInside = new Date(Date.now() - (60 * 60 * 1000 - 1000)).toISOString();
+    seedState(2, justInside);
+    vi.useFakeTimers();
+    const promise = enforceStartupBackoff();
+    await vi.runAllTimersAsync();
+    await promise;
+    expect(readState().attempt).toBe(3);
+  });
+
+  it('treats a malformed state file as no prior state', async () => {
+    fs.writeFileSync(CB_PATH, '{ this is not json');
+    await enforceStartupBackoff();
+    expect(readState().attempt).toBe(1);
+  });
+
+  it('resetCircuitBreaker after a startup actually clears the counter for the next startup', async () => {
+    // Simulate: crash, restart (attempt=2), graceful shutdown, restart again.
+    seedState(1);
+    vi.useFakeTimers();
+    const p1 = enforceStartupBackoff();
+    await vi.runAllTimersAsync();
+    await p1;
+    expect(readState().attempt).toBe(2);
+
+    resetCircuitBreaker();
+    expect(fs.existsSync(CB_PATH)).toBe(false);
+
+    await enforceStartupBackoff();
+    expect(readState().attempt).toBe(1);
+  });
+});
+
+describe('enforceStartupBackoff — backoff schedule', () => {
+  /**
+   * Documented schedule:
+   *
+   *   clean start → 1 crash → 2 crash → 3 crash → 4 crash → 5 crash → 6+ crash
+   *      0s    →    0s    →   10s   →   30s   →   2min  →   5min  →   15min cap
+   *
+   * Each row is [priorAttempt seeded in the file, expected delay this run
+   * produces in seconds]. priorAttempt=null = no file = very first start.
+   *
+   * To assert the *requested* delay (not just observed elapsed real time),
+   * we spy on global.setTimeout and look at the longest call. runAllTimersAsync
+   * lets the function complete so we can move on.
+   */
+  const cases: Array<{ label: string; priorAttempt: number | null; expectedDelaySec: number }> = [
+    { label: 'clean first start (no file)', priorAttempt: null, expectedDelaySec: 0 },
+    { label: 'first crash (attempt=2)', priorAttempt: 1, expectedDelaySec: 0 },
+    { label: 'second crash (attempt=3)', priorAttempt: 2, expectedDelaySec: 10 },
+    { label: 'third crash (attempt=4)', priorAttempt: 3, expectedDelaySec: 30 },
+    { label: 'fourth crash (attempt=5)', priorAttempt: 4, expectedDelaySec: 120 },
+    { label: 'fifth crash (attempt=6)', priorAttempt: 5, expectedDelaySec: 300 },
+    { label: 'sixth crash (attempt=7) — cap', priorAttempt: 6, expectedDelaySec: 900 },
+    { label: 'far past cap (attempt=20)', priorAttempt: 19, expectedDelaySec: 900 },
+  ];
+
+  for (const { label, priorAttempt, expectedDelaySec } of cases) {
+    it(`${label}: delays ${expectedDelaySec}s`, async () => {
+      if (priorAttempt !== null) seedState(priorAttempt);
+
+      vi.useFakeTimers();
+      const setTimeoutSpy = vi.spyOn(global, 'setTimeout');
+
+      const promise = enforceStartupBackoff();
+      await vi.runAllTimersAsync();
+      await promise;
+
+      // enforceStartupBackoff only calls setTimeout when delaySec > 0. Pick
+      // the longest delay it requested (vitest may queue small internal
+      // timers we don't care about).
+      const requestedDelays = setTimeoutSpy.mock.calls.map((c) => c[1] ?? 0);
+      const maxDelayMs = requestedDelays.length ? Math.max(...requestedDelays) : 0;
+
+      expect(maxDelayMs).toBe(expectedDelaySec * 1000);
+    });
+  }
+});
+
+describe('enforceStartupBackoff — fresh install (DATA_DIR missing)', () => {
+  /**
+   * The breaker runs before initDb (which is what creates DATA_DIR). On a
+   * fresh checkout the dir doesn't exist yet, so write() must create it
+   * before writing the state file — otherwise the host crashes on its very
+   * first start.
+   */
+  it('creates DATA_DIR on demand and does not throw', async () => {
+    fs.rmSync(TEST_DIR, { recursive: true });
+    expect(fs.existsSync(TEST_DIR)).toBe(false);
+
+    await expect(enforceStartupBackoff()).resolves.toBeUndefined();
+    expect(fs.existsSync(TEST_DIR)).toBe(true);
+    expect(fs.existsSync(CB_PATH)).toBe(true);
+    expect(readState().attempt).toBe(1);
+  });
+});
diff --git a/src/circuit-breaker.ts b/src/circuit-breaker.ts
index 4288eb4..20211f0 100644
--- a/src/circuit-breaker.ts
+++ b/src/circuit-breaker.ts
@@ -6,7 +6,9 @@ import { log } from './log.js';
 
 const CB_PATH = path.join(DATA_DIR, 'circuit-breaker.json');
 const RESET_WINDOW_MS = 60 * 60 * 1000; // 1 hour
-const BACKOFF_SCHEDULE_S = [0, 0, 10, 30, 120, 300, 900]; // index = attempt number, 6+ capped at 15min
+// Index = number of consecutive crashes (0 = clean start, attempt 1).
+// 6+ crashes capped at 15min.
+const BACKOFF_SCHEDULE_S = [0, 0, 10, 30, 120, 300, 900];
 
 interface CircuitBreakerState {
   attempt: number;
@@ -23,11 +25,14 @@ function read(): CircuitBreakerState | null {
 }
 
 function write(state: CircuitBreakerState): void {
+  // The breaker runs before initDb (which is what creates DATA_DIR), so on a
+  // fresh checkout the dir may not exist yet.
+  fs.mkdirSync(DATA_DIR, { recursive: true });
   fs.writeFileSync(CB_PATH, JSON.stringify(state, null, 2) + '\n');
 }
 
 function getDelay(attempt: number): number {
-  const idx = Math.min(attempt, BACKOFF_SCHEDULE_S.length - 1);
+  const idx = Math.min(attempt - 1, BACKOFF_SCHEDULE_S.length - 1);
   return BACKOFF_SCHEDULE_S[idx];
 }
 
diff --git a/src/index.ts b/src/index.ts
index 6235525..9ded3d6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -178,9 +178,15 @@ async function shutdown(signal: string): Promise<void> {
   }
   stopDeliveryPolls();
   stopHostSweep();
-  await teardownChannelAdapters();
-  resetCircuitBreaker();
-  process.exit(0);
+  try {
+    await teardownChannelAdapters();
+  } finally {
+    // Always reset on graceful shutdown — even if teardown threw, we got here
+    // via SIGTERM/SIGINT, not a crash, so the next start shouldn't be counted
+    // as one.
+    resetCircuitBreaker();
+    process.exit(0);
+  }
 }
 
 process.on('SIGTERM', () => shutdown('SIGTERM'));