diff --git a/TODOS.md b/TODOS.md
index 3675715ac..54afab27f 100644
--- a/TODOS.md
+++ b/TODOS.md
@@ -514,6 +514,18 @@ coverage fill. Remaining, in rough priority order:
   post-migration flake data exists (the Codex outside-voice's "green means
   green is not delivered while paid stays advisory" point — correct, and
   deliberately a branch-protection decision, not repo YAML). Effort S.
+- **P2 — browse daemon lifecycle vs in-suite browsers (top remaining free-suite
+  flake).** The post-#994 daemon deliberately outlives its parent and lingers
+  across test FILES in a shard process; a later file's browser use can then
+  fight it ('[browse] FATAL: Chromium process crashed' + 5s element-wait
+  timeouts). Receipts: commands+snapshot in one bun process fails identically
+  WITH and WITHOUT per-file CHROMIUM_PROFILE isolation (pre-existing; PR
+  #2721 triage), and CI shard 1 on d9b78b5a died at model-overlay-sonnet-5
+  after a daemon-spawning file. Per-shard + per-file profile isolation
+  (landed) removed the cross-shard kills; the intra-shard daemon handoff
+  needs a real design: tests that spawn the daemon should stop it in
+  afterAll, or the daemon should detect a foreign CHROMIUM_PROFILE env and
+  refuse reuse. Effort M.
 - **P2 — browse daemon /tmp-namespace hardening.** Every file-path transport
   to the daemon (eval <file>, load-html --from-file, pdf output, upload,
   cookie-import) assumes client and daemon share one /tmp view; a sandboxed
diff --git a/browse/test/batch.test.ts b/browse/test/batch.test.ts
index 452f60e08..f8d924f5b 100644
--- a/browse/test/batch.test.ts
+++ b/browse/test/batch.test.ts
@@ -5,7 +5,10 @@
  * newtab/closetab handling, and batch validation.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 
@@ -62,6 +65,24 @@ import { handleMetaCommand } from '../src/meta-commands';
 import { handleSnapshot } from '../src/snapshot';
 import { READ_COMMANDS, WRITE_COMMANDS } from '../src/commands';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 const handleReadCommand = (cmd: string, args: string[], b: BrowserManager) =>
   _handleReadCommand(cmd, args, b.getActiveSession());
 const handleWriteCommand = (cmd: string, args: string[], b: BrowserManager) =>
diff --git a/browse/test/commands.test.ts b/browse/test/commands.test.ts
index 83ae4707c..762dda674 100644
--- a/browse/test/commands.test.ts
+++ b/browse/test/commands.test.ts
@@ -5,7 +5,8 @@
  * A real browse server is started and commands are sent via the CLI HTTP interface.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 import { resolveServerScript } from '../src/cli';
@@ -18,6 +19,24 @@ import * as fs from 'fs';
 import { spawn } from 'child_process';
 import * as path from 'path';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 // Thin wrappers that bridge old test calls (bm as 3rd arg) to new signatures (session + bm)
 const handleReadCommand = (cmd: string, args: string[], b: BrowserManager) =>
   _handleReadCommand(cmd, args, b.getActiveSession(), b);
diff --git a/browse/test/compare-board.test.ts b/browse/test/compare-board.test.ts
index 10130d94b..664e3e380 100644
--- a/browse/test/compare-board.test.ts
+++ b/browse/test/compare-board.test.ts
@@ -10,7 +10,8 @@
  * No LLM involved — this is a deterministic functional test.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { BrowserManager } from '../src/browser-manager';
 import { handleReadCommand as _handleReadCommand } from '../src/read-commands';
 import { handleWriteCommand as _handleWriteCommand } from '../src/write-commands';
@@ -23,6 +24,24 @@ import { generateCompareHtml } from '../../design/src/compare';
 import * as fs from 'fs';
 import * as path from 'path';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 // QUARANTINED (opt-in via GSTACK_COMPARE_BOARD_TESTS=1): all 16 tests fail
 // identically on origin/main v1.64.1.0, solo, on dev machines — verified per
 // the blame protocol during the 2026-08 test-infra pass. Main's own CI lane
diff --git a/browse/test/content-security.test.ts b/browse/test/content-security.test.ts
index 69de52497..823a90294 100644
--- a/browse/test/content-security.test.ts
+++ b/browse/test/content-security.test.ts
@@ -11,7 +11,8 @@
  *   7. Chain security (domain + tab enforcement)
  */
 
-import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
+import * as os from 'os';
+import { afterAll, beforeAll, beforeEach, describe, expect, test } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 import { startTestServer } from './test-server';
@@ -25,6 +26,24 @@ import {
 } from '../src/content-security';
 import { generateInstructionBlock } from '../src/cli';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 // Source-level tests
 const SERVER_SRC = fs.readFileSync(path.join(import.meta.dir, '../src/server.ts'), 'utf-8');
 const CLI_SRC = fs.readFileSync(path.join(import.meta.dir, '../src/cli.ts'), 'utf-8');
diff --git a/browse/test/fill-change-event.test.ts b/browse/test/fill-change-event.test.ts
index c11c88e10..6209b67d5 100644
--- a/browse/test/fill-change-event.test.ts
+++ b/browse/test/fill-change-event.test.ts
@@ -8,11 +8,32 @@
  * the framework's own validator still reports a mismatch.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 import { handleWriteCommand as _handleWriteCommand } from '../src/write-commands';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 const handleWriteCommand = (cmd: string, args: string[], b: BrowserManager) =>
   _handleWriteCommand(cmd, args, b.getActiveSession(), b);
 
diff --git a/browse/test/handoff.test.ts b/browse/test/handoff.test.ts
index 22d87b3af..bbdee9e51 100644
--- a/browse/test/handoff.test.ts
+++ b/browse/test/handoff.test.ts
@@ -5,12 +5,33 @@
  * Integration tests cover the full handoff flow with real Playwright browsers.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager, type BrowserState } from '../src/browser-manager';
 import { handleWriteCommand as _handleWriteCommand } from '../src/write-commands';
 import { handleMetaCommand } from '../src/meta-commands';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 const handleWriteCommand = (cmd: string, args: string[], b: BrowserManager) =>
   _handleWriteCommand(cmd, args, b.getActiveSession(), b);
 
diff --git a/browse/test/security-live-playwright.test.ts b/browse/test/security-live-playwright.test.ts
index 415073977..131f58441 100644
--- a/browse/test/security-live-playwright.test.ts
+++ b/browse/test/security-live-playwright.test.ts
@@ -20,12 +20,30 @@
  * CI). To prime: `bun run browse/src/sidebar-agent.ts` for ~30s and kill it.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
+
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
 import {
   markHiddenElements,
   getCleanTextWithStripping,
diff --git a/browse/test/session-persist.test.ts b/browse/test/session-persist.test.ts
index 88f98a26b..bf7bfa8bd 100644
--- a/browse/test/session-persist.test.ts
+++ b/browse/test/session-persist.test.ts
@@ -15,7 +15,7 @@
  *      shutdown, and the gate is BROWSE_PERSIST_STATE (default off).
  */
 
-import { describe, test, expect, afterAll } from 'bun:test';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { canRevokeWrites } from '../../test/helpers/fs-caps';
 import * as fs from 'fs';
 import * as os from 'os';
@@ -26,6 +26,24 @@ import {
 } from '../src/session-persist';
 import type { BrowserState } from '../src/browser-manager';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 const tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'browse-persist-'));
 afterAll(() => { fs.rmSync(tmpRoot, { recursive: true, force: true }); });
 
diff --git a/browse/test/snapshot.test.ts b/browse/test/snapshot.test.ts
index 85150308a..61a28290e 100644
--- a/browse/test/snapshot.test.ts
+++ b/browse/test/snapshot.test.ts
@@ -5,7 +5,9 @@
  * ref invalidation on navigation, and ref resolution in commands.
  */
 
-import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as path from 'path';
+import * as os from 'os';
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 import { handleReadCommand as _handleReadCommand } from '../src/read-commands';
@@ -13,6 +15,24 @@ import { handleWriteCommand as _handleWriteCommand } from '../src/write-commands
 import { handleMetaCommand } from '../src/meta-commands';
 import * as fs from 'fs';
 
+// Per-FILE Chromium profile: this file launches an in-process persistent
+// context (BrowserManager.launch()), and sharing a profile dir with the
+// long-lived browse daemon a sibling file may have spawned kills one side's
+// Chromium (ProcessSingleton on user-data-dir). Scoped via hooks, never
+// module scope (see test/gstack-home-module-scope.test.ts's rationale).
+const ORIGINAL_CHROMIUM_PROFILE = process.env.CHROMIUM_PROFILE;
+let CHROMIUM_PROFILE_DIR: string | undefined;
+beforeAll(() => {
+  CHROMIUM_PROFILE_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-test-profile-'));
+  process.env.CHROMIUM_PROFILE = CHROMIUM_PROFILE_DIR;
+});
+afterAll(() => {
+  if (ORIGINAL_CHROMIUM_PROFILE === undefined) delete process.env.CHROMIUM_PROFILE;
+  else process.env.CHROMIUM_PROFILE = ORIGINAL_CHROMIUM_PROFILE;
+  if (CHROMIUM_PROFILE_DIR) { try { fs.rmSync(CHROMIUM_PROFILE_DIR, { recursive: true, force: true }); } catch {} }
+});
+
+
 const handleReadCommand = (cmd: string, args: string[], b: BrowserManager) =>
   _handleReadCommand(cmd, args, b.getActiveSession(), b);
 const handleWriteCommand = (cmd: string, args: string[], b: BrowserManager) =>