Path containment check uses `startswith` without a separator — sibling project directories are readable

[dolceo]

read_file_content resolves the path and then compares string prefixes:

    real_abs = os.path.realpath(abs_path)
    real_repo = os.path.realpath(repo_dir)
    if not real_abs.startswith(real_repo):
        return None

backend/app/services/code_project_service.py:282

get_file_abs_path has the identical check at backend/app/services/code_project_service.py:306.

real_repo for project cproj_aaaa is .../data/code_projects/cproj_aaaa/repo. The string .../data/code_projects/cproj_aaaa/repo_backup/secrets.env also passes startswith. Note that the module already contains a correct implementation a few lines above — _safe_join_repo at backend/app/services/code_project_service.py:147 compares against real_repo + os.sep — it is simply not used on the read paths.

The router-level guard does not help either: it rejects only the literal substring ".." (backend/app/modules/code/code_projects_api.py:270), which a symlink inside the repo defeats without ever containing ...

Trigger: the code generator writes a symlink, or an operator creates any sibling directory sharing the repo-dir prefix; then GET /api/v1/code/projects/cproj_aaaa/file?path=<...>.
Observed: file contents outside the project root are returned as 200.
Expected: _safe_join_repo reused for both readers, plus an os.path.islink rejection.