diff --git a/extension/src/content/detector.ts b/extension/src/content/detector.ts
index f369f0e..bfc19d8 100644
--- a/extension/src/content/detector.ts
+++ b/extension/src/content/detector.ts
@@ -93,9 +93,21 @@ setupFillListener();
 scan();
 
 // Watch for DOM changes (SPA navigation, dynamically loaded forms).
-const observer = new MutationObserver(() => {
-  scan();
-});
+// Plan C Phase 5: SPA churn fires the MutationObserver many times per
+// second. Trailing-edge debounce coalesces bursts so we run the full
+// scan() at most once per quiet 200ms window.
+const SCAN_DEBOUNCE_MS = 200;
+let scanTimer: ReturnType<typeof setTimeout> | undefined;
+
+function scheduleScan(): void {
+  if (scanTimer !== undefined) clearTimeout(scanTimer);
+  scanTimer = setTimeout(() => {
+    scanTimer = undefined;
+    scan();
+  }, SCAN_DEBOUNCE_MS);
+}
+
+const observer = new MutationObserver(scheduleScan);
 
 observer.observe(document.body, {
   childList: true,
diff --git a/extension/src/popup/components/__tests__/devices.test.ts b/extension/src/popup/components/__tests__/devices.test.ts
index 60c31b7..2b0233c 100644
--- a/extension/src/popup/components/__tests__/devices.test.ts
+++ b/extension/src/popup/components/__tests__/devices.test.ts
@@ -95,6 +95,32 @@ describe('devices view', () => {
     expect(app.querySelector<HTMLButtonElement>('#register-confirm-btn')).not.toBeNull();
   });
 
+  // Plan C Phase 5 — defensive Promise.allSettled:
+  // a rejected secondary feed (list_revoked) should not kill the whole render.
+  it('renders devices when revoked list fails (load-error slot shown)', async () => {
+    (sendMessage as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ok: true, data: { devices: [{ name: 'CLI', public_key: 'k', added_at: 1 }] } })
+      .mockRejectedValueOnce(new Error('boom'));
+
+    await renderDevices(app);
+
+    // Primary list still rendered.
+    expect(app.innerHTML).toContain('CLI');
+    // Inline fallback slot present.
+    expect(app.innerHTML).toContain("Couldn't load revoked devices");
+  });
+
+  it('renders devices when revoked list returns {ok:false}', async () => {
+    (sendMessage as ReturnType<typeof vi.fn>)
+      .mockResolvedValueOnce({ ok: true, data: { devices: [{ name: 'CLI', public_key: 'k', added_at: 1 }] } })
+      .mockResolvedValueOnce({ ok: false, error: 'list_revoked_failed' });
+
+    await renderDevices(app);
+
+    expect(app.innerHTML).toContain('CLI');
+    expect(app.innerHTML).toContain("Couldn't load revoked devices");
+  });
+
   it('confirming register sends register_this_device with the entered name', async () => {
     (chrome.storage.local.get as ReturnType<typeof vi.fn>).mockResolvedValueOnce({ device_name: 'Unknown' });
     // Initial render: list_devices + list_revoked.
diff --git a/extension/src/popup/components/devices.ts b/extension/src/popup/components/devices.ts
index 1c83394..8b85373 100644
--- a/extension/src/popup/components/devices.ts
+++ b/extension/src/popup/components/devices.ts
@@ -31,35 +31,64 @@ export function teardown(): void {
   // No cleanup needed
 }
 
+/**
+ * DEV-C P2: defensive per-slot rendering. The active list is the primary
+ * feed — if it fails entirely, we still surface an error page. The
+ * revoked list is secondary — its failure renders an inline "couldn't
+ * load" slot but doesn't kill the page.
+ */
+function revokedLoadErrorHtml(): string {
+  return `
+    <details class="revoked-section">
+      <summary class="muted">▸ revoked devices</summary>
+      <div class="revoked-section__body">
+        <p class="muted">Couldn't load revoked devices.</p>
+      </div>
+    </details>
+  `;
+}
+
 export async function renderDevices(app: HTMLElement): Promise<void> {
   // Get current device name from local storage
   const stored = await chrome.storage.local.get(['device_name']);
   const currentDeviceName: string | undefined = stored.device_name as string | undefined;
 
-  // Fetch active device list and revoked list in parallel
-  const [devicesResp, revokedResp] = await Promise.all([
+  // Fetch active device list and revoked list in parallel. allSettled so a
+  // rejected secondary feed doesn't kill the whole render.
+  const [devicesSettled, revokedSettled] = await Promise.allSettled([
     sendMessage({ type: 'list_devices' }),
     sendMessage({ type: 'list_revoked' }),
   ]);
 
-  if (!devicesResp.ok) {
+  if (devicesSettled.status === 'rejected' || !devicesSettled.value.ok) {
     app.innerHTML = `<div class="pad"><p class="error">Failed to load devices</p></div>`;
     return;
   }
 
-  const devices = (devicesResp.data as { devices: Device[] }).devices;
-  const revokedDevices: RevokedEntry[] = revokedResp.ok
-    ? (revokedResp.data as { revoked: RevokedEntry[] }).revoked
+  // devicesSettled.value.ok is true here (guarded above), so .data is present.
+  const devicesData = (devicesSettled.value as { ok: true; data: unknown }).data;
+  const devices = (devicesData as { devices: Device[] }).devices;
+  const revokedOk = revokedSettled.status === 'fulfilled' && revokedSettled.value.ok;
+  const revokedDevices: RevokedEntry[] = revokedOk
+    ? ((revokedSettled.value as { ok: true; data: unknown }).data as { revoked: RevokedEntry[] }).revoked
     : [];
 
   const isRegistered = currentDeviceName && devices.some((d) => d.name === currentDeviceName);
 
-  // Precompute fingerprints for all active devices
+  // Precompute fingerprints for all active devices. allSettled so one bad
+  // public key doesn't kill the whole list — fall back to '(unknown)'.
   const fingerprints = new Map<string, string>();
-  await Promise.all(devices.map(async (d) => {
-    const fp = await sshFingerprint(d.public_key);
-    fingerprints.set(d.name, fp ?? '(unknown)');
-  }));
+  const fpResults = await Promise.allSettled(
+    devices.map((d) => sshFingerprint(d.public_key).then((fp) => [d.name, fp] as const)),
+  );
+  for (let i = 0; i < devices.length; i += 1) {
+    const r = fpResults[i];
+    if (r.status === 'fulfilled' && r.value[1]) {
+      fingerprints.set(r.value[0], r.value[1]);
+    } else {
+      fingerprints.set(devices[i].name, '(unknown)');
+    }
+  }
 
   const activeDevicesHtml = devices.length === 0
     ? `<p class="muted" style="text-align:center;margin-top:32px;">No devices registered</p>`
@@ -82,7 +111,9 @@ export async function renderDevices(app: HTMLElement): Promise<void> {
         `;
       }).join('');
 
-  const revokedSectionHtml = revokedDevices.length === 0 ? '' : `
+  const revokedSectionHtml = !revokedOk
+    ? revokedLoadErrorHtml()
+    : revokedDevices.length === 0 ? '' : `
     <details class="revoked-section">
       <summary class="muted">▸ show ${revokedDevices.length} revoked device${revokedDevices.length !== 1 ? 's' : ''}</summary>
       <div class="revoked-section__body">
@@ -117,7 +148,7 @@ export async function renderDevices(app: HTMLElement): Promise<void> {
       ` : ''}
       ${devices.length > 0 ? `<div class="section-header">ACTIVE · ${devices.length}</div>` : ''}
       ${activeDevicesHtml}
-      ${revokedDevices.length > 0 ? `<div class="section-header">REVOKED · ${revokedDevices.length}</div>` : ''}
+      ${!revokedOk ? `<div class="section-header">REVOKED · ?</div>` : (revokedDevices.length > 0 ? `<div class="section-header">REVOKED · ${revokedDevices.length}</div>` : '')}
       ${revokedSectionHtml}
     </div>
   `;
diff --git a/extension/src/popup/components/settings-vault.ts b/extension/src/popup/components/settings-vault.ts
index cc5038e..36add5b 100644
--- a/extension/src/popup/components/settings-vault.ts
+++ b/extension/src/popup/components/settings-vault.ts
@@ -9,6 +9,7 @@ import type {
 import type { SessionTimeoutConfig } from '../../shared/messages';
 import { relativeTime } from '../../shared/relative-time';
 import { openGeneratorPanel, closeGeneratorPanel, isGeneratorPanelOpen } from './generator-panel';
+import { teardownSettingsCommon } from './settings';
 import { GLYPH_NEXT } from '../../shared/glyphs';
 
 let pendingSettings: VaultSettings | null = null;
@@ -17,11 +18,7 @@ let pendingSession: SessionTimeoutConfig | null = null;
 let baseSession: SessionTimeoutConfig | null = null;
 
 export function teardown(): void {
-  closeGeneratorPanel();
-  if (activeKeyHandler) {
-    document.removeEventListener('keydown', activeKeyHandler);
-    activeKeyHandler = null;
-  }
+  activeKeyHandler = teardownSettingsCommon(activeKeyHandler);
   pendingSettings = null;
   pendingSession = null;
   baseSession = null;
diff --git a/extension/src/popup/components/settings.ts b/extension/src/popup/components/settings.ts
index a4021ba..cacd7e6 100644
--- a/extension/src/popup/components/settings.ts
+++ b/extension/src/popup/components/settings.ts
@@ -53,13 +53,29 @@ export async function renderSettings(container: HTMLElement): Promise<void> {
   await renderSection(activeSection);
 }
 
-export function teardownSettings(): void {
+/**
+ * Common cleanup invoked by both the device-settings teardown
+ * (settings.ts) and the vault-settings teardown (settings-vault.ts).
+ * Centralized to avoid the "regression class with known prior leaks"
+ * DEV-C P2 flagged.
+ *
+ * Closes the generator popover and detaches the supplied keydown
+ * handler from the document if present. Returns the new handler value
+ * (always null), so the caller can do `handler = teardownSettingsCommon(handler)`.
+ */
+export function teardownSettingsCommon(
+  keyHandler: ((e: KeyboardEvent) => void) | null,
+): null {
   closeGeneratorPanel();
-  teardownSecuritySection();
-  if (activeKeyHandler) {
-    document.removeEventListener('keydown', activeKeyHandler);
-    activeKeyHandler = null;
+  if (keyHandler) {
+    document.removeEventListener('keydown', keyHandler);
   }
+  return null;
+}
+
+export function teardownSettings(): void {
+  activeKeyHandler = teardownSettingsCommon(activeKeyHandler);
+  teardownSecuritySection();
   pendingVaultSettings = null;
   sessionHandle = null;
 }
diff --git a/extension/src/service-worker/__tests__/session-timer.test.ts b/extension/src/service-worker/__tests__/session-timer.test.ts
index 39a56fc..93a04aa 100644
--- a/extension/src/service-worker/__tests__/session-timer.test.ts
+++ b/extension/src/service-worker/__tests__/session-timer.test.ts
@@ -1,5 +1,6 @@
 import { describe, expect, it, vi, beforeEach, afterEach } from 'vitest';
 import * as timer from '../session-timer';
+import { READ_ONLY_CONTENT_CALLABLE } from '../session-timer';
 
 describe('session-timer', () => {
   beforeEach(() => {
@@ -97,3 +98,29 @@ describe('session-timer', () => {
     expect(cb).not.toHaveBeenCalled();
   });
 });
+
+describe('READ_ONLY_CONTENT_CALLABLE — inversion exclusion set', () => {
+  // The SW handler invokes resetTimer() on every message whose type is NOT
+  // in this set. These cases encode the documented inversion contract from
+  // Plan C Phase 5: popup-only messages reset, content-callable writes
+  // reset, only passive content reads (currently just get_autofill_candidates)
+  // do NOT reset.
+
+  it('popup-only message would reset the timer (not in exclusion set)', () => {
+    // e.g. list_items — popup interaction is unambiguously active use
+    expect(READ_ONLY_CONTENT_CALLABLE.has('list_items')).toBe(false);
+  });
+
+  it('content-callable get_autofill_candidates does NOT reset (in exclusion set)', () => {
+    expect(READ_ONLY_CONTENT_CALLABLE.has('get_autofill_candidates')).toBe(true);
+  });
+
+  it('content-callable capture_save_login DOES reset (write op = active use)', () => {
+    expect(READ_ONLY_CONTENT_CALLABLE.has('capture_save_login')).toBe(false);
+  });
+
+  it('content-callable check_credential DOES reset', () => {
+    // Asking "is this credential already saved" is user-initiated.
+    expect(READ_ONLY_CONTENT_CALLABLE.has('check_credential')).toBe(false);
+  });
+});
diff --git a/extension/src/service-worker/index.ts b/extension/src/service-worker/index.ts
index e3dec89..2c68a3e 100644
--- a/extension/src/service-worker/index.ts
+++ b/extension/src/service-worker/index.ts
@@ -2,12 +2,12 @@
 /// forwards every message into router/index.route().
 
 import type { Request, Response, SessionTimeoutConfig } from '../shared/messages';
-import { CONTENT_CALLABLE_TYPES } from '../shared/messages';
 import type { RouterState } from './router/index';
 import { route } from './router/index';
 import * as vault from './vault';
 import { clearCurrent } from './session';
 import * as sessionTimer from './session-timer';
+import { READ_ONLY_CONTENT_CALLABLE } from './session-timer';
 
 // @ts-ignore TS2307 — resolved by webpack alias / copy
 import initDefault, { initSync } from '../../wasm/relicario_wasm.js';
@@ -53,6 +53,9 @@ sessionTimer.onExpired(() => {
   console.log('[relicario sw] session expired — locking vault');
   clearCurrent();
   state.manifest = null;
+  // Plan C Phase 5: don't leak the cached git-host client across a lock.
+  // The initializer rebuilds gitHost on demand, so clearing here is safe.
+  state.gitHost = null;
   // Best-effort broadcast — receiver may not exist yet.
   chrome.runtime.sendMessage({ type: 'session_expired' }).catch(() => {});
 });
@@ -73,7 +76,10 @@ chrome.commands.onCommand.addListener((command) => {
 chrome.runtime.onMessage.addListener(
   (request: Request, sender: chrome.runtime.MessageSender, sendResponse: (r: Response) => void) => {
     (async () => {
-      if (!CONTENT_CALLABLE_TYPES.has(request.type as never)) {
+      // Plan C Phase 5: invert the reset rule. Reset on every message
+      // except a documented passive-read exclusion set, so an active
+      // autofiller / content-driven flow keeps the vault alive.
+      if (!READ_ONLY_CONTENT_CALLABLE.has(request.type)) {
         sessionTimer.resetTimer();
       }
       if (!state.wasm) {
diff --git a/extension/src/service-worker/session-timer.ts b/extension/src/service-worker/session-timer.ts
index 9948586..2a7800a 100644
--- a/extension/src/service-worker/session-timer.ts
+++ b/extension/src/service-worker/session-timer.ts
@@ -48,3 +48,17 @@ export function stopTimer(): void {
     timerId = null;
   }
 }
+
+/**
+ * Content-callable message types that should NOT reset the inactivity timer.
+ *
+ * Rationale: a content script reading available autofill candidates is a
+ * passive query — it shouldn't keep the vault alive indefinitely while the
+ * user isn't actually interacting with it.
+ *
+ * Today this is the only known passive read; if a future content message
+ * is also passive, add it here with a one-line justification.
+ */
+export const READ_ONLY_CONTENT_CALLABLE: ReadonlySet<string> = new Set([
+  'get_autofill_candidates',
+]);