GHSA-2m67-cxxq-c3h8

### Summary Workspace boundary enforcement currently has three related bypass risks. This issue tracks fixing all three in one pull request.

### Details

#### R1 - Dangling Symlink Component Bypass - What happens: Path validation can miss dangling symlink components during traversal checks. - Why it matters: A symlink that is unresolved at validation time can later resolve to an external location. - Impact: Read and write operations may escape workspace boundaries. - Affected area: src/security/path.rs (check_symlink_escape).

#### R2 - TOCTOU Between Validation and Use - What happens: The path is validated first, then used later for filesystem operations. - Why it matters: A concurrent filesystem change can swap path components after validation but before open/write. - Impact: Race-based workspace escape is possible. - Affected area: Filesystem and file-consuming tools that call validate_path_in_workspace before I/O.

#### R3 - Hardlink Alias Bypass - What happens: A file inside workspace can be a hardlink to an inode outside the intended workspace trust boundary. - Why it matters: Prefix and symlink checks can pass while data access still mutates or reads external content. - Impact: Policy bypass for read/write operations. - Affected area: Any tool that reads or writes via validated paths.

#### Risk Matrix

| ID | Risk | Severity | Likelihood | Impact | |---|---|---|---|---| | R1 | Dangling symlink component bypass | High | Medium | Workspace boundary escape for read/write | | R2 | Validate/use TOCTOU race | High | Medium | Race-based boundary escape during file I/O | | R3 | Hardlink alias bypass | Medium | Low-Medium | External inode read/write through in-workspace path |

### PoC

#### R1 - Dangling symlink component bypass 1. Create a symlink inside workspace pointing to a missing target. 2. Validate a path traversing that symlink. 3. Create the target directory outside workspace after validation. 4. Perform file operation and observe potential boundary escape if not fail-closed.

#### R2 - TOCTOU between validation and use 1. Validate a candidate in-workspace path. 2. Before open/write, replace an intermediate component with a link to external location. 3. Continue with the file operation. 4. Observe boundary escape if operation trusts only stale validation result.

#### R3 - Hardlink alias bypass 1. Place a hardlink inside workspace that points to an external inode. 2. Validate the in-workspace hardlink path. 3. Read or write through this path. 4. Observe external inode access through a path that appears in-scope.

### Impacts Unauthorized cross path boundary

## Credit [@zpbrent](https://github.com/zpbrent)

### Patch [f50c17e11ae3e2d40c96730abac41974ef2ee2a8](https://github.com/qhkm/zeptoclaw/commit/f50c17e11ae3e2d40c96730abac41974ef2ee2a8)