fix(cases): tell an unreachable path from an absent one, scope the stall cap

The bounded path probe answered "absent" both when a path did not exist and
when it simply did not answer, so a stalled linked case 404'd and the Run
button scaffolded a stray local case over it, and two stalled paths anywhere
made every unrelated path read as absent (hooks skipped, statusLine
overridden, the clone warning lost).

- probePath()/probePathKind() are tri-state: present (or directory/file),
  absent (ENOENT/ENOTDIR only) and unknown (timeout, other errors, refusal).
  boundedPathExists() stays as the display-only boolean.
- A stalled path takes only its own mount out of probing (deepest mount
  point from /proc/self/mounts, never /; just the path itself when there is
  no mount table). Unrelated paths keep probing. The process-wide cap is a
  backstop that answers unknown, and a single-path user request can probe
  past it ({ pastCap: true }), still bounded and still recorded as stalled.
  One console.warn when a path first stalls and one when the cap engages.
- GET /api/cases/:name keeps NOT_FOUND for definite absence only. An
  unreachable linked case answers with its registered path and
  unreachable: true; a local one answers OPERATION_FAILED. runClaude and
  runShell create a case only on errorCode NOT_FOUND. The case list keeps an
  unreachable linked case, marked unreachable, instead of dropping it, and
  fix-plan reports an unreadable plan as an error, not "no plan".
- applyWorkspaceHooks and the statusLine helpers skip only a workspace that
  is absent or on the stalled mount; a capacity refusal no longer stops
  hooks being installed elsewhere, and an unreadable settings file never
  lets the exporter override a user's own statusLine.
- The clone flow's repo-settings warning is back on its synchronous check,
  and stripCaseEnvKeys uses pathExistsForWrite.
- POST /api/sessions (workingDir) and POST /api/quick-start (case folder)
  probe with the bounded probe instead of statSync/existsSync. Missing and
  non-directory keep INVALID_INPUT; unknown is OPERATION_FAILED, and
  quick-start never scaffolds over a folder that did not answer.
- PATH_PROBE_TIMEOUT_MS and MAX_STALLED_PATH_PROBES move to
  src/config/path-probe.ts, overridable via CODEMAN_PATH_PROBE_TIMEOUT_MS
  (default 1500) and CODEMAN_PATH_PROBE_MAX_STALLED (default 3), and are
  documented in the Settings Reference.
- The probe is exported from the utils barrel and imported from there.

test/routes/case-routes.test.ts

@@ -13,13 +13,24 @@
  * behavior matches production exactly).
  */
 
-import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { describe, it, expect, beforeEach, afterEach, afterAll, vi } from 'vitest';
 import Fastify, { type FastifyInstance } from 'fastify';
 import fastifyCookie from '@fastify/cookie';
 import { createMockRouteContext, type MockRouteContext } from '../mocks/index.js';
 import { installRouteErrorHandler } from '../../src/web/route-error-handler.js';
 import { ApiErrorCode, httpStatusForErrorCode } from '../../src/types.js';
 import { registerCaseRoutes } from '../../src/web/routes/case-routes.js';
+import { probePath } from '../../src/utils/index.js';
+import { MAX_STALLED_PATH_PROBES } from '../../src/config/path-probe.js';
+
+// A short path-probe timeout keeps the unreachable-mount tests quick. Read when the
+// probe's config module is first imported, so it is set before any import runs.
+vi.hoisted(() => {
+  process.env.CODEMAN_PATH_PROBE_TIMEOUT_MS = '300';
+});
+afterAll(() => {
+  delete process.env.CODEMAN_PATH_PROBE_TIMEOUT_MS;
+});
 
 // Mock filesystem modules
 vi.mock('node:fs', async (importOriginal) => {
@@ -251,8 +262,19 @@ describe('case-routes', () => {
 
       expect(res.statusCode).toBe(200);
       expect(elapsed).toBeLessThan(BLOCK_MS - 1_000);
-      // The unreachable case is left out rather than holding the list hostage.
-      expect(JSON.parse(res.body).data).toEqual([]);
+      // The unreachable case is listed as such rather than holding the list
+      // hostage, or vanishing as though it had been deleted.
+      expect(JSON.parse(res.body).data).toEqual([
+        {
+          name: 'linked-nfs',
+          path: stalledPath,
+          hasClaudeMd: false,
+          linked: true,
+          location: 'linked-local',
+          unreachable: true,
+        },
+      ]);
+      await new Promise((r) => setTimeout(r, 0)); // let the released stat clear its stall
     });
   });
 
@@ -714,6 +736,64 @@ describe('case-routes', () => {
       expect(body.data.name).toBe('regular-case');
     });
 
+    it('answers a linked case on an unreachable mount with its registered path, not NOT_FOUND', async () => {
+      // The timeout path: the mount does not answer at all.
+      const stalledPath = '/mnt/unreachable/linked-get';
+      mockedReadFile.mockResolvedValue(JSON.stringify({ 'linked-get': stalledPath }) as never);
+      let release: (() => void) | undefined;
+      mockedStat.mockImplementation((p) => {
+        if (String(p) !== stalledPath) {
+          return Promise.reject(Object.assign(new Error('ENOENT'), { code: 'ENOENT' }));
+        }
+        return new Promise((resolve) => {
+          release = () => resolve({ isDirectory: () => true } as never);
+        });
+      });
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/cases/linked-get' });
+      release?.();
+      await new Promise((r) => setTimeout(r, 0)); // let the released stat clear its stall
+
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.success).toBe(true);
+      expect(body.data).toMatchObject({ name: 'linked-get', path: stalledPath, linked: true, unreachable: true });
+    });
+
+    it('still answers a healthy case while unrelated mounts are stalled past the cap', async () => {
+      const dead = Array.from({ length: MAX_STALLED_PATH_PROBES }, (_, i) => `/mnt/dead-${i}/linked`);
+      const releases: Array<() => void> = [];
+      mockedReadFile.mockRejectedValue(Object.assign(new Error('ENOENT'), { code: 'ENOENT' }));
+      mockedStat.mockImplementation((p) => {
+        if (dead.includes(String(p))) {
+          return new Promise((resolve) => releases.push(() => resolve({ isDirectory: () => true } as never)));
+        }
+        return Promise.resolve({ isDirectory: () => true } as never);
+      });
+      expect(await Promise.all(dead.map((p) => probePath(p)))).toEqual(dead.map(() => 'unknown'));
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/cases/healthy-local' });
+      releases.forEach((release) => release());
+      await new Promise((r) => setTimeout(r, 0));
+
+      expect(res.statusCode).toBe(200);
+      expect(JSON.parse(res.body).data).toMatchObject({ name: 'healthy-local' });
+      expect(JSON.parse(res.body).data.unreachable).toBeUndefined();
+    });
+
+    it('answers a local case it cannot read with a non-NOT_FOUND error', async () => {
+      // A soft mount that gave up (EIO) is not proof the case is gone, and the Run
+      // button creates a case on NOT_FOUND.
+      mockedReadFile.mockRejectedValue(Object.assign(new Error('ENOENT'), { code: 'ENOENT' }));
+      mockedStat.mockRejectedValue(Object.assign(new Error('EIO'), { code: 'EIO' }));
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/cases/eio-case' });
+      const body = JSON.parse(res.body);
+      expect(body.success).toBe(false);
+      expect(body.errorCode).toBe('OPERATION_FAILED');
+      expect(res.statusCode).not.toBe(404);
+    });
+
     it('returns error when case not found anywhere', async () => {
       mockedReadFile.mockRejectedValue(Object.assign(new Error('ENOENT'), { code: 'ENOENT' }));
       mockedExistsSync.mockReturnValue(false);
@@ -748,6 +828,16 @@ describe('case-routes', () => {
       expect(body.data.todos).toEqual([]);
     });
 
+    it('reports an unreadable fix plan as an error, not as "no plan"', async () => {
+      mockedReadFile.mockRejectedValue(Object.assign(new Error('ENOENT'), { code: 'ENOENT' }));
+      mockedStat.mockRejectedValue(Object.assign(new Error('EIO'), { code: 'EIO' }));
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/cases/my-case/fix-plan' });
+      const body = JSON.parse(res.body);
+      expect(body.success).toBe(false);
+      expect(body.errorCode).toBe('OPERATION_FAILED');
+    });
+
     it('parses fix plan with todos and stats', async () => {
       const fixPlanContent = [
         '# Fix Plan',