feat: Toolsのシンボリックリンク対応

docs/file-ref-symlinks.md

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+# File references and symlinks
+
+FileRef resolution and file tools follow symlinks only after the resolved target passes the Pod scope check. A symlink placed inside the workspace does not grant access to the target by itself.
+
+Recommended external-reference workflow:
+
+- Prefer adding the real external project path, such as a local `external checkout` clone, to the Pod read scope when the Pod is started or spawned.
+- If a workspace symlink is used, the symlink target still must be inside readable scope. For writes, the resolved target must be inside writable scope.
+- If a relative symlink is broken, recreate it with the correct relative target from the symlink's parent directory, or use an absolute symlink.
+- Directory traversal tools such as Glob and Grep do not follow symlink directories. Use the resolved target directory directly when it is in read scope.
+
+This preserves symlink escape safety: access decisions are made on the canonicalized target whenever the target exists, and broken or out-of-scope symlinks are rejected with diagnostics that include the original path and target where possible.