fix(fs): open files through workspace symlinks

packages/web/server/lib/fs/DOCUMENTATION.md

@@ -35,5 +35,6 @@ Own filesystem API behavior for the web server runtime, including workspace-boun
 ## Notes for contributors
 - Keep filesystem policy (workspace root checks, error mapping, exec timeout behavior) inside this module, not in the composition root.
 - Filesystem `EPERM`/`EACCES` failures use the stable `reason: "os-permission"` response marker. Policy denials such as workspace-boundary or missing-grant failures must not use that marker because a native folder picker cannot remediate them.
+- Read-only routes authorize the requested path against the workspace before resolving symlinks. A symlink reached through the workspace may therefore target a file outside it, while a directly requested outside path still requires an exact-path grant. Write routes keep canonical-target boundary checks.
 - If adding new `/api/fs/*` endpoints, add them in `routes.js` and extend this document.
 - `GET /api/fs/list` may resolve symlinks with `realpath` to read directory contents, but the response `path` and each entry `path` must stay in the caller's requested path space (`path.join(requestedPath, name)`). Returning real paths breaks file-tree expansion for directories reached through workspace symlinks.

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

@@ -758,14 +758,7 @@ export const registerFsRoutes = (app, dependencies) => {
         return res.status(400).json({ error: resolved.error });
       }
 
-      const [canonicalPath, canonicalBase] = await Promise.all([
-        fsPromises.realpath(resolved.resolved),
-        fsPromises.realpath(resolved.base).catch(() => path.resolve(resolved.base)),
-      ]);
-
-      if (!isPathWithinRoot(canonicalPath, canonicalBase, path, os)) {
-        return res.status(403).json({ error: 'Access to file denied' });
-      }
+      const canonicalPath = await fsPromises.realpath(resolved.resolved);
 
       const stats = await fsPromises.stat(canonicalPath);
       if (!stats.isFile()) {
@@ -815,14 +808,7 @@ export const registerFsRoutes = (app, dependencies) => {
         return res.status(400).json({ error: resolved.error });
       }
 
-      const [canonicalPath, canonicalBase] = await Promise.all([
-        fsPromises.realpath(resolved.resolved),
-        fsPromises.realpath(resolved.base).catch(() => path.resolve(resolved.base)),
-      ]);
-
-      if (!isPathWithinRoot(canonicalPath, canonicalBase, path, os)) {
-        return res.status(403).json({ error: 'Access to file denied' });
-      }
+      const canonicalPath = await fsPromises.realpath(resolved.resolved);
 
       const stats = await fsPromises.stat(canonicalPath);
       if (!stats.isFile()) {
@@ -886,14 +872,7 @@ export const registerFsRoutes = (app, dependencies) => {
         return res.status(400).json({ error: resolved.error });
       }
 
-      const [canonicalPath, canonicalBase] = await Promise.all([
-        fsPromises.realpath(resolved.resolved),
-        fsPromises.realpath(resolved.base).catch(() => path.resolve(resolved.base)),
-      ]);
-
-      if (!isPathWithinRoot(canonicalPath, canonicalBase, path, os)) {
-        return res.status(403).json({ error: 'Access to file denied' });
-      }
+      const canonicalPath = await fsPromises.realpath(resolved.resolved);
 
       const stats = await fsPromises.stat(canonicalPath);
       if (!stats.isFile()) {
@@ -971,14 +950,7 @@ export const registerFsRoutes = (app, dependencies) => {
         return res.status(400).json({ error: resolved.error });
       }
 
-      const [canonicalPath, canonicalBase] = await Promise.all([
-        fsPromises.realpath(resolved.resolved),
-        fsPromises.realpath(resolved.base).catch(() => path.resolve(resolved.base)),
-      ]);
-
-      if (!isPathWithinRoot(canonicalPath, canonicalBase, path, os)) {
-        return res.status(403).json({ error: 'Access to file denied' });
-      }
+      const canonicalPath = await fsPromises.realpath(resolved.resolved);
 
       const stats = await fsPromises.stat(canonicalPath);
       if (!stats.isFile()) {

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

@@ -341,6 +341,24 @@ describe('fs write', () => {
 });
 
 describe('fs read', () => {
+  it('reads workspace files through symlinks that resolve outside the workspace', async () => {
+    const fsPromises = {
+      realpath: vi.fn(async (targetPath) => {
+        if (targetPath === '/repo/link.txt') return '/shared/target.txt';
+        return targetPath;
+      }),
+      stat: vi.fn(async () => ({ isFile: () => true, size: 6 })),
+      readFile: vi.fn(async () => 'shared'),
+    };
+    const handler = registerRead(fsPromises);
+
+    const res = await callRead(handler, { path: '/repo/link.txt' });
+
+    expect(res.statusCode).toBe(200);
+    expect(res.body).toBe('shared');
+    expect(fsPromises.readFile).toHaveBeenCalledWith('/shared/target.txt', 'utf8');
+  });
+
   it('rejects outside workspace reads without a grant', async () => {
     const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
     const fsPromises = {