fix(camera): fail closed when workspace_only has empty path

[cursor]

Bug and impact

With workspace_only on (default) but workspace_path set to "", camera_capture treated the empty workspace root as “allow all” and wrote caller-supplied JPEG paths anywhere the process can write. write_file already fails closed in the same config.

Concrete trigger (main d367477)

1. Config: [sandbox] workspace_only = true and workspace_path = "" (or equivalent empty after load).
2. Hardware enabled (default); agent calls camera_capture with path=/tmp/pwned.jpg (or any absolute path without .. / shell metacharacters).
3. Capture writes JPEG magic bytes to that host path.

Distinctness

• Not fix(sandbox): keep agent workspace off gateway state files #79 (default ~/.shellclaw colocated with auth_tokens.json).
• Not fix(sandbox): Landlock FS bound plus workspace_only defense-in-depth #89 (sandbox allowlist / Landlock on sandbox_exec only; camera runs in-process).
• Not fix(file): reject dangling-symlink writes outside workspace #90 (dangling workspace symlink ancestor walk).
• Not fix(file): persist workspace writes with atomic replace #78 (truncate-then-write ENOSPC).

Fix

• Distinguish set_workspace(NULL) (workspace_only off) from set_workspace("") (enforced, fail closed).
• tool_hardware_set_config passes "" when workspace_only is on and the path is missing.

Test plan

• test_empty_workspace_enforced_denies_outside
• Existing camera workspace / traversal tests

  

[adriannoes]

Superseded by #94 (já em development).