fix(git_discovery): collect all nested modules subtrees, not just the last (#211)

[SAY-5]

Closes #211.

find_git_module_info_dirs::walk tracked the nested modules dir in a single Option<PathBuf>, so a directory listing that yielded more than one entry whose file_name() matched modules would keep only the last one walked. The case is unusual on case-sensitive filesystems but reachable on case-insensitive ones (macOS / NTFS) where modules and Modules can collide as dir entries from different writers, and a future relax of the equality match (icase, alt names) would silently start dropping subtrees.

Fix

Replace the Option<PathBuf> with a Vec<PathBuf> and walk each collected nested-modules dir in turn. The return on the inner fs::read_dir error becomes a continue so a single unreadable nested dir no longer aborts the walk for sibling subtrees in the same parent.

Test plan

• cargo build --manifest-path sdk/Cargo.toml — clean
• cargo test --manifest-path sdk/Cargo.toml --lib policy::git_discovery — 3/3 pass (including test_find_git_module_info_dirs_finds_nested_submodules)

[TrueNine]

Not supported. In our model, each scan is effectively a full check, and the downstream aindex is treated as a complete, whole artifact rather than something incrementally repairable. Continuing after failure would allow partial traversal to leak through as if the result were still valid, which breaks the semantic guarantee of aindex completeness. For that reason, preserving fail-closed behavior here is intentional unless we explicitly redesign the contract around partial results.

[TrueNine]

Not supported. In our model, each scan is effectively a full check, and the downstream aindex is treated as a complete, whole artifact rather than something incrementally repairable. Continuing after read_dir() failure would allow partial traversal to leak through as if the result were still valid, which breaks the semantic guarantee of aindex completeness. For that reason, preserving fail-closed behavior here is intentional unless we explicitly redesign the contract around partial results.

[TrueNine]

Merged into dev via cherry-pick. The PR base was changed from main to dev, which caused conflicts because dev had diverged significantly. All commits have been cherry-picked onto dev and pushed. Thanks for the contributions!

[TrueNine]

Thank you for the contribution! All commits have been cherry-picked and merged into the dev branch. 🙏