fix(ui): scope file-reference stat probes to the session directory (#3022)

* test: add regression test for stat directory scoping (#3019)

* fix: scope file-reference stat probes to the session directory (#3019)

The /api/fs/stat probe sent by the markdown renderer carried no
directory hint, so the server resolved the workspace from
settings.lastDirectory. When the browsed directory differs from the
session directory the stat returns 400 and the renderer treats it as
file-does-not-exist, silently disabling file-reference links.

Send effectiveDirectory as x-opencode-directory on the probe and
qualify the stat cache key by directory so a rejection under one
directory cannot leak into another. The probe logic moves from
MarkdownRendererImpl into fileReferenceStat with unit coverage.

packages/web/server/lib/fs/routes.test.js

@@ -3,6 +3,7 @@ import path from 'path';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { mintOutsideFileGrant, registerFsRoutes } from './routes.js';
+import { createProjectDirectoryRuntime } from '../opencode/project-directory-runtime.js';
 
 const createRouteRegistry = () => {
   const routes = new Map();
@@ -1048,3 +1049,78 @@ describe('fs list symlink path space (issue 2627)', () => {
     });
   }
 });
+
+describe('fs stat directory scope (issue 3019)', () => {
+  // Wires the real project-directory runtime so the stat route resolves the
+  // workspace exactly as the server does: explicit x-opencode-directory header
+  // first, then the settings.lastDirectory fallback. The renderer's file
+  // reference probes must send the header because lastDirectory reflects the
+  // directory the UI last browsed, not the session's directory.
+  const registerStatWithProjectDirectoryRuntime = () => {
+    const projectDirectoryRuntime = createProjectDirectoryRuntime({
+      fsPromises: {
+        stat: async (targetPath) => {
+          if (targetPath === '/repo-a' || targetPath === '/repo-b') {
+            return { isDirectory: () => true };
+          }
+          return { isDirectory: () => false, isFile: () => true, size: 12 };
+        },
+        realpath: async (targetPath) => targetPath,
+      },
+      path: { resolve: (p) => path.posix.resolve(p) },
+      normalizeDirectoryPath: (p) => p,
+      readSettingsFromDiskMigrated: async () => ({ lastDirectory: '/repo-a', projects: [] }),
+      getReadSettingsFromDiskMigrated: undefined,
+      sanitizeProjects: (input) => input,
+    });
+
+    const { app, getRoute } = createRouteRegistry();
+    registerFsRoutes(app, {
+      os: { homedir: () => '/home/user' },
+      path: path.posix,
+      fsPromises: {
+        realpath: async (targetPath) => targetPath,
+        stat: async () => ({ isFile: () => true, size: 12 }),
+      },
+      spawn: vi.fn(),
+      crypto: { randomUUID: () => 'job-0' },
+      normalizeDirectoryPath: (p) => p,
+      resolveProjectDirectory: projectDirectoryRuntime.resolveProjectDirectory,
+      buildAugmentedPath: () => '/usr/bin',
+      resolveGitBinaryForSpawn: () => 'git',
+      openchamberUserConfigRoot: '/home/user/.config',
+    });
+    return getRoute('GET', '/api/fs/stat');
+  };
+
+  const callStat = async (handler, { headers = {}, query }) => {
+    const res = createMockResponse();
+    const req = {
+      query,
+      get: (name) => headers[name.toLowerCase()] ?? undefined,
+    };
+    await handler(req, res);
+    return res;
+  };
+
+  it('rejects a stat for a file under the session directory when only lastDirectory resolves the workspace', async () => {
+    const handler = registerStatWithProjectDirectoryRuntime();
+
+    const res = await callStat(handler, { query: { path: '/repo-b/src/index.ts', optional: 'true' } });
+
+    expect(res.statusCode).toBe(400);
+    expect(res.body).toEqual({ error: 'Path is outside of active workspace' });
+  });
+
+  it('accepts the same stat when the session directory rides the x-opencode-directory header', async () => {
+    const handler = registerStatWithProjectDirectoryRuntime();
+
+    const res = await callStat(handler, {
+      headers: { 'x-opencode-directory': '/repo-b' },
+      query: { path: '/repo-b/src/index.ts', optional: 'true' },
+    });
+
+    expect(res.statusCode).toBe(200);
+    expect(res.body.isFile).toBe(true);
+  });
+});