diff --git a/browse/src/config.ts b/browse/src/config.ts
index d7c8c9ef5..e8770ef45 100644
--- a/browse/src/config.ts
+++ b/browse/src/config.ts
@@ -11,8 +11,10 @@
  */
 
 import * as fs from 'fs';
+import * as os from 'os';
 import * as path from 'path';
 import { mkdirSecure } from './file-permissions';
+import { safeUnlinkQuiet } from './error-handling';
 
 export interface BrowseConfig {
   projectDir: string;
@@ -151,3 +153,57 @@ export function readVersionHash(execPath: string = process.execPath): string | n
     return null;
   }
 }
+
+/**
+ * Resolve the gstack home directory.
+ *
+ * Honors the existing convention used by telemetry.ts and domain-skills.ts:
+ *   1. GSTACK_HOME env (explicit override)
+ *   2. $HOME/.gstack (default)
+ */
+export function resolveGstackHome(): string {
+  return process.env.GSTACK_HOME || path.join(os.homedir(), '.gstack');
+}
+
+/**
+ * Resolve the Chromium profile directory.
+ *
+ * Resolution order:
+ *   1. `explicit` arg (passed via ServerConfig.chromiumProfile by embedders)
+ *   2. CHROMIUM_PROFILE env (used by gbrowser's gbd per-workspace)
+ *   3. <resolveGstackHome()>/chromium-profile (default)
+ */
+export function resolveChromiumProfile(explicit?: string): string {
+  if (explicit && explicit.length > 0) return explicit;
+  const env = process.env.CHROMIUM_PROFILE;
+  if (env && env.length > 0) return env;
+  return path.join(resolveGstackHome(), 'chromium-profile');
+}
+
+/**
+ * Pre-launch / shutdown cleanup of stale Chromium singleton lockfiles
+ * (SingletonLock, SingletonSocket, SingletonCookie). Chromium's
+ * ProcessSingleton refuses to start when these exist from a prior crash
+ * (SIGKILL, hard crash, etc.) since they point at a PID that no longer exists.
+ *
+ * Defensive guard: refuses to operate unless the directory basename is
+ * 'chromium-profile' OR the path matches the explicit CHROMIUM_PROFILE env
+ * value. Prevents accidentally deleting lock files from an unrelated
+ * directory if profile resolution is misconfigured upstream.
+ *
+ * Caller MUST ensure external coordination has already guaranteed no live
+ * peer is using this profile (gbd.lock for gbrowser; single-instance CLI
+ * check for gstack).
+ */
+export function cleanSingletonLocks(userDataDir: string): void {
+  const basename = path.basename(userDataDir);
+  const explicitProfile = process.env.CHROMIUM_PROFILE;
+  const isSafe = basename === 'chromium-profile' || userDataDir === explicitProfile;
+  if (!isSafe) {
+    console.warn(`[browse] cleanSingletonLocks: refusing to clean unrecognized profile dir: ${userDataDir}`);
+    return;
+  }
+  for (const lockFile of ['SingletonLock', 'SingletonSocket', 'SingletonCookie']) {
+    safeUnlinkQuiet(path.join(userDataDir, lockFile));
+  }
+}
diff --git a/browse/test/config.test.ts b/browse/test/config.test.ts
index b36426947..8daa27c3e 100644
--- a/browse/test/config.test.ts
+++ b/browse/test/config.test.ts
@@ -1,5 +1,5 @@
 import { describe, test, expect } from 'bun:test';
-import { resolveConfig, ensureStateDir, readVersionHash, getGitRoot, getRemoteSlug } from '../src/config';
+import { resolveConfig, ensureStateDir, readVersionHash, getGitRoot, getRemoteSlug, resolveGstackHome, resolveChromiumProfile, cleanSingletonLocks } from '../src/config';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
@@ -314,3 +314,132 @@ describe('startup error log', () => {
     fs.rmSync(tmpDir, { recursive: true, force: true });
   });
 });
+
+describe('resolveGstackHome', () => {
+  test('honors GSTACK_HOME env var when set', () => {
+    const orig = process.env.GSTACK_HOME;
+    process.env.GSTACK_HOME = '/tmp/custom-gstack-home';
+    try {
+      expect(resolveGstackHome()).toBe('/tmp/custom-gstack-home');
+    } finally {
+      if (orig === undefined) delete process.env.GSTACK_HOME;
+      else process.env.GSTACK_HOME = orig;
+    }
+  });
+
+  test('falls back to os.homedir() + /.gstack when env unset', () => {
+    const orig = process.env.GSTACK_HOME;
+    delete process.env.GSTACK_HOME;
+    try {
+      expect(resolveGstackHome()).toBe(path.join(os.homedir(), '.gstack'));
+    } finally {
+      if (orig !== undefined) process.env.GSTACK_HOME = orig;
+    }
+  });
+});
+
+describe('resolveChromiumProfile', () => {
+  test('explicit arg wins over env and default', () => {
+    const orig = process.env.CHROMIUM_PROFILE;
+    process.env.CHROMIUM_PROFILE = '/tmp/env-profile';
+    try {
+      expect(resolveChromiumProfile('/tmp/explicit-profile')).toBe('/tmp/explicit-profile');
+    } finally {
+      if (orig === undefined) delete process.env.CHROMIUM_PROFILE;
+      else process.env.CHROMIUM_PROFILE = orig;
+    }
+  });
+
+  test('CHROMIUM_PROFILE env honored when no explicit arg', () => {
+    const orig = process.env.CHROMIUM_PROFILE;
+    process.env.CHROMIUM_PROFILE = '/tmp/env-profile';
+    try {
+      expect(resolveChromiumProfile()).toBe('/tmp/env-profile');
+    } finally {
+      if (orig === undefined) delete process.env.CHROMIUM_PROFILE;
+      else process.env.CHROMIUM_PROFILE = orig;
+    }
+  });
+
+  test('falls back to resolveGstackHome()/chromium-profile when nothing set', () => {
+    const origEnv = process.env.CHROMIUM_PROFILE;
+    const origHome = process.env.GSTACK_HOME;
+    delete process.env.CHROMIUM_PROFILE;
+    process.env.GSTACK_HOME = '/tmp/fallback-gstack';
+    try {
+      expect(resolveChromiumProfile()).toBe('/tmp/fallback-gstack/chromium-profile');
+    } finally {
+      if (origEnv !== undefined) process.env.CHROMIUM_PROFILE = origEnv;
+      if (origHome === undefined) delete process.env.GSTACK_HOME;
+      else process.env.GSTACK_HOME = origHome;
+    }
+  });
+
+  test('ignores empty-string explicit arg, falls through to env/default', () => {
+    const orig = process.env.CHROMIUM_PROFILE;
+    process.env.CHROMIUM_PROFILE = '/tmp/env-profile';
+    try {
+      expect(resolveChromiumProfile('')).toBe('/tmp/env-profile');
+    } finally {
+      if (orig === undefined) delete process.env.CHROMIUM_PROFILE;
+      else process.env.CHROMIUM_PROFILE = orig;
+    }
+  });
+});
+
+describe('cleanSingletonLocks', () => {
+  test('removes SingletonLock/Socket/Cookie when basename is chromium-profile', () => {
+    const tmpDir = path.join(os.tmpdir(), `clean-locks-${Date.now()}`, 'chromium-profile');
+    fs.mkdirSync(tmpDir, { recursive: true });
+    for (const f of ['SingletonLock', 'SingletonSocket', 'SingletonCookie']) {
+      fs.writeFileSync(path.join(tmpDir, f), 'stale');
+    }
+    cleanSingletonLocks(tmpDir);
+    for (const f of ['SingletonLock', 'SingletonSocket', 'SingletonCookie']) {
+      expect(fs.existsSync(path.join(tmpDir, f))).toBe(false);
+    }
+    fs.rmSync(path.dirname(tmpDir), { recursive: true, force: true });
+  });
+
+  test('refuses to clean unrecognized profile dir basename', () => {
+    const tmpDir = path.join(os.tmpdir(), `unrelated-${Date.now()}`);
+    fs.mkdirSync(tmpDir, { recursive: true });
+    const lockFile = path.join(tmpDir, 'SingletonLock');
+    fs.writeFileSync(lockFile, 'should-survive');
+    const origWarn = console.warn;
+    let warned = '';
+    console.warn = (msg: string) => { warned = msg; };
+    try {
+      cleanSingletonLocks(tmpDir);
+      expect(warned).toContain('refusing to clean unrecognized profile dir');
+      expect(fs.existsSync(lockFile)).toBe(true); // not deleted
+    } finally {
+      console.warn = origWarn;
+      fs.rmSync(tmpDir, { recursive: true, force: true });
+    }
+  });
+
+  test('respects explicit CHROMIUM_PROFILE env even with non-standard basename', () => {
+    const tmpDir = path.join(os.tmpdir(), `custom-name-${Date.now()}`);
+    fs.mkdirSync(tmpDir, { recursive: true });
+    fs.writeFileSync(path.join(tmpDir, 'SingletonLock'), 'stale');
+    const orig = process.env.CHROMIUM_PROFILE;
+    process.env.CHROMIUM_PROFILE = tmpDir;
+    try {
+      cleanSingletonLocks(tmpDir);
+      expect(fs.existsSync(path.join(tmpDir, 'SingletonLock'))).toBe(false);
+    } finally {
+      if (orig === undefined) delete process.env.CHROMIUM_PROFILE;
+      else process.env.CHROMIUM_PROFILE = orig;
+      fs.rmSync(tmpDir, { recursive: true, force: true });
+    }
+  });
+
+  test('second call on empty dir does not throw (ENOENT swallowed)', () => {
+    const tmpDir = path.join(os.tmpdir(), `empty-locks-${Date.now()}`, 'chromium-profile');
+    fs.mkdirSync(tmpDir, { recursive: true });
+    expect(() => cleanSingletonLocks(tmpDir)).not.toThrow();
+    expect(() => cleanSingletonLocks(tmpDir)).not.toThrow();
+    fs.rmSync(path.dirname(tmpDir), { recursive: true, force: true });
+  });
+});