fix(cases): bound linked-workspace path probes so an unreachable mount cannot freeze the server

A linked case can live on a network mount. When that mount goes away, a
hard mount makes stat() wait indefinitely, and the existsSync() probes in
the case routes and the workspace hook/statusline helpers ran on the event
loop, so a single GET /api/cases (or a session create in that workspace)
froze the whole web server until the mount came back.

Add boundedPathExists() (src/utils/bounded-path-probe.ts): an async stat
that answers "absent" after 1.5 s, shares one in-flight probe per path,
remembers a timed-out path until its stat finally settles, and refuses to
start new probes while two stalled ones still hold libuv threadpool
workers. Route the read-side probes in case-routes.ts and hooks-config.ts
through it. The settings writers in hooks-config.ts use an async lstat
that treats only ENOENT as missing, so an unreachable workspace is never
mistaken for an empty one and has its settings recreated.

src/hooks-config.ts

@@ -30,7 +30,6 @@
  */
 
 import { randomBytes } from 'node:crypto';
-import { existsSync } from 'node:fs';
 import { readFile, writeFile, mkdir, lstat, readdir, realpath, rename, unlink, rmdir, chmod } from 'node:fs/promises';
 import { homedir } from 'node:os';
 import { join, dirname } from 'node:path';
@@ -40,6 +39,25 @@ import type { HookEventType } from './types.js';
 import { HOOK_TIMEOUT_SECONDS } from './config/auth-config.js';
 import { dataPath } from './config/instance.js';
 import { readJsonConfig, SETTINGS_PATH } from './web/route-helpers.js';
+import { boundedPathExists } from './utils/bounded-path-probe.js';
+
+/**
+ * Existence check for a WRITER. Unlike `boundedPathExists`, which answers
+ * "absent" for a path it could not reach in time, this tells "missing" apart
+ * from "unreachable": only ENOENT reads as absent, anything else throws, so a
+ * stalled or unreadable workspace can never be mistaken for an empty one and
+ * have its settings recreated over the top. It is async, so a dead mount ties
+ * up a threadpool worker rather than the event loop.
+ */
+async function pathExistsForWrite(path: string): Promise<boolean> {
+  try {
+    await lstat(path);
+    return true;
+  } catch (err) {
+    if ((err as NodeJS.ErrnoException).code === 'ENOENT') return false;
+    throw err;
+  }
+}
 
 /**
  * Serializes read-modify-write access to a `settings.local.json` path. Every
@@ -558,7 +576,7 @@ export async function stripCaseEnvKeys(casePath: string, keysToRemove: readonly
   if (keysToRemove.length === 0) return;
 
   await withSafeSettingsWrite(casePath, 'env-key removal', async (_claudeDir, settingsPath) => {
-    if (!existsSync(settingsPath)) return;
+    if (!(await boundedPathExists(settingsPath))) return;
 
     let existing: Record<string, unknown>;
     try {
@@ -590,7 +608,7 @@ export async function stripCaseEnvKeys(casePath: string, keysToRemove: readonly
  */
 export async function updateCaseEnvVars(casePath: string, envVars: Record<string, string>): Promise<void> {
   await withSafeSettingsWrite(casePath, 'env vars', async (claudeDir, settingsPath) => {
-    if (!existsSync(claudeDir)) {
+    if (!(await pathExistsForWrite(claudeDir))) {
       await mkdir(claudeDir, { recursive: true });
     }
 
@@ -621,7 +639,7 @@ export async function updateCaseEnvVars(casePath: string, envVars: Record<string
  */
 export async function updateCaseModel(casePath: string, model: string | null): Promise<void> {
   await withSafeSettingsWrite(casePath, 'model', async (claudeDir, settingsPath) => {
-    if (!existsSync(claudeDir)) {
+    if (!(await pathExistsForWrite(claudeDir))) {
       await mkdir(claudeDir, { recursive: true });
     }
 
@@ -650,7 +668,7 @@ export async function updateCaseModel(casePath: string, model: string | null): P
  */
 export async function writeHooksConfig(casePath: string): Promise<void> {
   await withSafeSettingsWrite(casePath, 'hooks', async (claudeDir, settingsPath) => {
-    if (!existsSync(claudeDir)) {
+    if (!(await pathExistsForWrite(claudeDir))) {
       await mkdir(claudeDir, { recursive: true });
     }
 
@@ -698,7 +716,7 @@ export async function writeHooksConfig(casePath: string): Promise<void> {
  */
 export async function ensureCodemanHooks(casePath: string): Promise<void> {
   await withSafeSettingsWrite(casePath, 'hooks (ensure)', async (claudeDir, settingsPath) => {
-    if (!existsSync(claudeDir)) {
+    if (!(await pathExistsForWrite(claudeDir))) {
       await mkdir(claudeDir, { recursive: true });
     }
 
@@ -738,7 +756,7 @@ export async function ensureCodemanHooks(casePath: string): Promise<void> {
  * when the hooks aren't ours, so it is cheap enough to call on every Claude spawn.
  */
 export async function refreshStaleCodemanHooks(casePath: string): Promise<void> {
-  if (!existsSync(join(casePath, '.claude', 'settings.local.json'))) return;
+  if (!(await boundedPathExists(join(casePath, '.claude', 'settings.local.json')))) return;
   await withSafeSettingsWrite(casePath, 'hooks (refresh)', async (_claudeDir, settingsPath) => {
     let existing: Record<string, unknown>;
     try {
@@ -820,7 +838,7 @@ export async function refreshStaleCodemanHooks(casePath: string): Promise<void>
  */
 export async function applyWorkspaceHooks(workspace: string, install?: boolean): Promise<void> {
   try {
-    if (!existsSync(workspace)) return;
+    if (!(await boundedPathExists(workspace))) return;
     const shouldInstall = install ?? (await readWorkspaceHooksEnabled());
     await (shouldInstall ? ensureCodemanHooks(workspace) : refreshStaleCodemanHooks(workspace));
   } catch {
@@ -883,7 +901,7 @@ export function generateStatusLineCommand(): string {
 export async function applyStatusLineConfig(casePath: string, enabled: boolean): Promise<void> {
   await withSafeSettingsWrite(casePath, 'statusLine', async (claudeDir, settingsPath) => {
     let existing: Record<string, unknown> = {};
-    if (existsSync(settingsPath)) {
+    if (await pathExistsForWrite(settingsPath)) {
       try {
         existing = JSON.parse(await readFile(settingsPath, 'utf-8'));
       } catch {
@@ -898,7 +916,7 @@ export async function applyStatusLineConfig(casePath: string, enabled: boolean):
       const desired = generateStatusLineCommand();
       if (isOurs && current?.command === desired) return; // already current — skip rewrite
       if (current && !isOurs) return; // user has their OWN statusLine — never clobber it
-      if (!existsSync(claudeDir)) await mkdir(claudeDir, { recursive: true });
+      if (!(await pathExistsForWrite(claudeDir))) await mkdir(claudeDir, { recursive: true });
       existing.statusLine = { type: 'command', command: desired }; // add, or update an out-of-date ours
     } else {
       if (!isOurs) return; // nothing of ours to remove (leave a user's own statusLine alone)
@@ -957,7 +975,7 @@ function statusLineExporterScriptContent(): string {
 }
 
 async function readStatusLineCommandFromFile(settingsPath: string): Promise<string | undefined> {
-  if (!existsSync(settingsPath)) return undefined;
+  if (!(await boundedPathExists(settingsPath))) return undefined;
   try {
     const parsed = JSON.parse(await readFile(settingsPath, 'utf-8'));
     const current = parsed.statusLine as { command?: unknown } | undefined;
@@ -1103,7 +1121,7 @@ export async function resolveStatusLineCliCommand(
 ): Promise<string | undefined> {
   const settingsPath = join(casePath, '.claude', 'settings.local.json');
   let userHasOwnStatusLine = false;
-  if (existsSync(settingsPath)) {
+  if (await boundedPathExists(settingsPath)) {
     try {
       const existing = JSON.parse(await readFile(settingsPath, 'utf-8'));
       const current = existing.statusLine as { command?: unknown } | undefined;