diff --git a/extension/src/classes/JobManager.ts b/extension/src/classes/JobManager.ts
index b4517c0..bc0a162 100644
--- a/extension/src/classes/JobManager.ts
+++ b/extension/src/classes/JobManager.ts
@@ -15,6 +15,11 @@ import type { Job, Serializable, ErrorLike, DispatchArgs } from '../types';
 // jobs only need to survive long enough for the CLI to poll their result.
 export const MAX_FINISHED_JOBS = 20;
 
+// Cap simultaneously running background jobs. A hung job has a watchdog, but a
+// command flood could still pin many timers/results for up to JOB_TIMEOUT_MS.
+// Rejecting above this bound keeps service-worker memory predictable.
+export const MAX_RUNNING_JOBS = 32;
+
 // Watchdog: if a runner never resolves/rejects (e.g. executeScript against a
 // dead tab), finalize the job as an error so its persist interval stops instead
 // of writing to api.storage.local every second forever.
@@ -77,6 +82,11 @@ export class JobManager {
   }
 
   async start(command: string, args: DispatchArgs, runner: JobRunner) {
+    const runningCount = [...this.jobs.values()].filter(job => job.status === "running").length;
+    if (runningCount >= MAX_RUNNING_JOBS) {
+      throw new Error(`too many background jobs running (${runningCount}); wait for jobs to finish or cancel one`);
+    }
+
     const jobId = `${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 10)}`;
     const job: Job = {
       id: jobId,
diff --git a/extension/src/commands/perf.ts b/extension/src/commands/perf.ts
index ea86e84..ca4fe45 100644
--- a/extension/src/commands/perf.ts
+++ b/extension/src/commands/perf.ts
@@ -1,7 +1,7 @@
 import { getLargeOperationThrottle, getPerformanceProfile, hasAudibleTabs, setPerformanceProfile } from '../core';
 import { CommandGroup } from '../classes/CommandGroup';
 import type { CommandEntry } from '../classes/CommandGroup';
-import type { PerfSetProfileArgs, JobIdArgs } from '../types';
+import type { Job, PerfSetProfileArgs, JobIdArgs } from '../types';
 
 // PerfCommands also owns the jobs.* status/cancel queries: they read the same
 // JobManager (ctx.jobs) that perf.status reports, and there is no dedicated
@@ -15,6 +15,19 @@ export class PerfCommands extends CommandGroup {
     "jobs.cancel":      (a: JobIdArgs) => this.ctx.jobs.cancel(a),
   };
 
+  private jobSummary(job: Job) {
+    return {
+      id: job.id,
+      command: job.command,
+      status: job.status,
+      phase: job.phase,
+      current: job.current,
+      total: job.total,
+      percent: job.percent,
+      cancelRequested: job.cancelRequested,
+    };
+  }
+
   private async perfStatus() {
     const profile = await getPerformanceProfile();
     const audible = await hasAudibleTabs();
@@ -23,16 +36,7 @@ export class PerfCommands extends CommandGroup {
       performanceProfile: profile,
       audible,
       throttle,
-      jobs: this.ctx.jobs.list().map(job => ({
-        id: job.id,
-        command: job.command,
-        status: job.status,
-        phase: job.phase,
-        current: job.current,
-        total: job.total,
-        percent: job.percent,
-        cancelRequested: job.cancelRequested,
-      })),
+      jobs: this.ctx.jobs.list().map(job => this.jobSummary(job)),
     };
   }
 }
diff --git a/extension/src/commands/windows.ts b/extension/src/commands/windows.ts
index 761b66d..3c414e3 100644
--- a/extension/src/commands/windows.ts
+++ b/extension/src/commands/windows.ts
@@ -14,9 +14,31 @@ export class WindowsCommands extends CommandGroup {
     "windows.open":   (a: WindowsOpenArgs) => this.windowsOpen(a),
   };
 
+  private async activeWindowIds(): Promise<Set<number>> {
+    const windows = await api.windows.getAll({});
+    return new Set(windows.map(w => w.id).filter(id => typeof id === "number"));
+  }
+
+  private async pruneAliases(activeIds?: Set<number>): Promise<Record<string, string>> {
+    const aliases = await getAliases();
+    const liveIds = activeIds || await this.activeWindowIds();
+    const pruned: Record<string, string> = {};
+    let changed = false;
+    for (const [id, alias] of Object.entries(aliases)) {
+      if (liveIds.has(Number(id))) {
+        pruned[id] = alias;
+      } else {
+        changed = true;
+      }
+    }
+    if (changed) await api.storage.local.set({ windowAliases: pruned });
+    return pruned;
+  }
+
   private async windowsList() {
     const windows = await api.windows.getAll({ populate: true });
-    const aliases = await getAliases();
+    const activeIds = new Set(windows.map(w => w.id).filter(id => typeof id === "number"));
+    const aliases = await this.pruneAliases(activeIds);
     return windows.map(w => ({
       id: w.id,
       alias: aliases[w.id] || null,
@@ -27,7 +49,7 @@ export class WindowsCommands extends CommandGroup {
   }
 
   private async windowsRename({ windowId, name }: WindowsRenameArgs) {
-    const aliases = await getAliases();
+    const aliases = await this.pruneAliases();
     aliases[windowId] = name;
     await api.storage.local.set({ windowAliases: aliases });
     return { windowId, name };
@@ -35,6 +57,11 @@ export class WindowsCommands extends CommandGroup {
 
   private async windowsClose({ windowId }: WindowsCloseArgs) {
     await api.windows.remove(windowId);
+    const aliases = await this.pruneAliases();
+    if (windowId in aliases) {
+      delete aliases[windowId];
+      await api.storage.local.set({ windowAliases: aliases });
+    }
     return { windowId };
   }
 
diff --git a/extension/test/jobs.test.ts b/extension/test/jobs.test.ts
index f5b8dac..3bc0fa9 100644
--- a/extension/test/jobs.test.ts
+++ b/extension/test/jobs.test.ts
@@ -1,7 +1,7 @@
 // @ts-nocheck
 import { test, mock } from 'node:test';
 import assert from 'node:assert/strict';
-import { JobManager, JOB_TIMEOUT_MS, MAX_FINISHED_JOBS, pruneFinishedJobs } from '../src/classes/JobManager';
+import { JobManager, JOB_TIMEOUT_MS, MAX_FINISHED_JOBS, MAX_RUNNING_JOBS, pruneFinishedJobs } from '../src/classes/JobManager';
 import { makeChromeMock } from './chrome-mock';
 
 // Drain pending microtasks (finalize() chains several awaits). setImmediate is
@@ -129,6 +129,21 @@ test('JobManager: a runner that settles after the watchdog cannot resurrect the
   mock.timers.reset();
 });
 
+test('JobManager: rejects new background jobs above the running-job cap', async () => {
+  mock.timers.enable({ apis: ['setInterval', 'setTimeout'] });
+  globalThis.chrome = makeChromeMock();
+  const mgr = new JobManager();
+  for (let i = 0; i < MAX_RUNNING_JOBS; i++) {
+    await mgr.start(`running${i}`, {}, () => new Promise(() => {}));
+  }
+  await assert.rejects(
+    () => mgr.start('overflow', {}, async () => 'nope'),
+    /too many background jobs running/,
+  );
+  assert.equal(mgr.list().filter(job => job.status === 'running').length, MAX_RUNNING_JOBS);
+  mock.timers.reset();
+});
+
 test('JobManager: persisted set keeps running jobs even past the finished cap', async () => {
   mock.timers.enable({ apis: ['setInterval', 'setTimeout'] });
   globalThis.chrome = makeChromeMock();
diff --git a/extension/test/windows.test.ts b/extension/test/windows.test.ts
new file mode 100644
index 0000000..1ef41e6
--- /dev/null
+++ b/extension/test/windows.test.ts
@@ -0,0 +1,69 @@
+// @ts-nocheck
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { WindowsCommands } from '../src/commands/windows';
+import { makeChromeMock } from './chrome-mock';
+
+function makeWindowsChromeMock(windows) {
+  const chrome = makeChromeMock();
+  chrome.windows = {
+    getAll: async () => windows,
+    remove: async () => {},
+    create: async () => ({ id: 99 }),
+  };
+  return chrome;
+}
+
+test('windows.list prunes aliases for closed windows', async () => {
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [{ id: 10 }] },
+    { id: 2, focused: false, state: 'minimized', tabs: [] },
+  ]);
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    2: 'side',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  const result = await commands.commands['windows.list']({});
+
+  assert.deepEqual(result.map(w => [w.id, w.alias]), [[1, 'main'], [2, 'side']]);
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main', 2: 'side' });
+});
+
+test('windows.rename prunes stale aliases before saving the new name', async () => {
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [] },
+    { id: 2, focused: false, state: 'normal', tabs: [] },
+  ]);
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  await commands.commands['windows.rename']({ windowId: 2, name: 'work' });
+
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main', 2: 'work' });
+});
+
+test('windows.close removes the closed window alias immediately', async () => {
+  let removed = null;
+  globalThis.chrome = makeWindowsChromeMock([
+    { id: 1, focused: true, state: 'normal', tabs: [] },
+    { id: 2, focused: false, state: 'normal', tabs: [] },
+  ]);
+  globalThis.chrome.windows.remove = async id => { removed = id; };
+  globalThis.chrome.storage.local._store.windowAliases = {
+    1: 'main',
+    2: 'side',
+    999: 'closed',
+  };
+
+  const commands = new WindowsCommands({ jobs: {} });
+  await commands.commands['windows.close']({ windowId: 2 });
+
+  assert.equal(removed, 2);
+  assert.deepEqual(globalThis.chrome.storage.local._store.windowAliases, { 1: 'main' });
+});