perf(#2351): batch path-existence checks via Git Trees API

[fullsend-ai-coder]

Add forge.Client.ListRepositoryFiles to retrieve all file paths in a repository's default branch with a single Git Trees API call (refs → commit → tree?recursive=1). This replaces the O(N) GetFileContent pattern used by ComparePathPresence, reducing 100+ sequential API calls to 3 fixed calls regardless of path count.

Changes:

• forge.Client: add ListRepositoryFiles(ctx, owner, repo)
• github.LiveClient: implement using Git Trees API (reuses the
  same refs/commits/trees pattern as CommitFiles)
• forge.FakeClient: implement using FileContents map keys
• scaffold.ComparePathPresence: new batch implementation that
  calls ListRepositoryFiles once and checks membership locally
• Tests: 6 ComparePathPresence tests including a guard that
  GetFileContent is never called; error injection and thread
  safety coverage for the new forge method

PR #1954 introduces a naive ComparePathPresence in vendormanifest.go that loops GetFileContent per path. When that PR merges, its version should be replaced with this batch implementation.

---

Closes #2351

Post-script verification

• Branch is not main/master (agent/2351-batch-path-presence)
• Secret scan passed (gitleaks — 32f73a4f93301493d2c31be3970aa4c51a26acc7..HEAD)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

[github-actions]

E2E tests are running

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[github-actions]

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Commit: ee77525b5f06145397eb9d6cb3d26da48886f652

[fullsend-ai-review]

🤖 Finished Review · ✅ Success · Started 7:30 PM UTC · Completed 7:41 PM UTC
Commit: dd9fc10 · View workflow run →

[codecov]

Codecov Report

❌ Patch coverage is 89.61039% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/forge/github/github.go	84.00%	4 Missing and 4 partials ⚠️

📢 Thoughts on this report? Let us know!

[fullsend-ai-review]

Review

Findings

Medium

• [error-handling] internal/forge/github/github.go:1024 — When the Git Trees API response is truncated (repository too large), the function returns a hard error with no sentinel type, making it impossible for callers to detect and fall back to per-path checks. The interface comment in forge.go does not document this failure mode. If any repository legitimately exceeds the GitHub tree size limit (~100k entries or 7MB response), every call to ComparePathPresence will fail permanently with no recourse.
  Remediation: Add a sentinel error (e.g., ErrTreeTruncated) so callers can detect this specific failure and fall back to per-path checks. Document the truncation risk in the ListRepositoryFiles interface comment. See also: [api-documentation-completeness] finding at internal/forge/forge.go:195.

Low

• [api-documentation-completeness] internal/forge/forge.go:195 — The interface documentation for ListRepositoryFiles states "Returns ErrNotFound if the repository does not exist" but does not document the truncation behavior when the repository tree is too large. See also: [error-handling] finding at internal/forge/github/github.go:1024.
• [error-wrapping-inconsistency] internal/forge/github/github.go:968 — Error wrapping uses get repo: %w which is slightly abbreviated compared to some other methods that use more descriptive prefixes like get repo for default branch: %w.
• [error-handling-inconsistency] internal/forge/github/github.go:970 — The retryOnTransient call uses label get branch ref and the inner function also wraps errors with get branch ref:, creating double-wrapping on exhaustion. This matches the existing pattern in commitFilesTo but is still a pre-existing code smell.
• [non-deterministic-output] internal/forge/fake.go:411 — FakeClient.ListRepositoryFiles iterates over a map (f.FileContents), producing non-deterministic ordering of the returned paths. Current callers build a map from the result so order does not matter.
• [retry-consistency] internal/forge/github/github.go:958 — Only step 2 (get branch ref) is wrapped in retryOnTransient. Steps 1, 3, and 4 are not retried. This is consistent with the existing pattern in commitFilesTo.

Info

• [documentation-style] internal/scaffold/pathpresence.go:10 — The function comment mentions "Git Trees API call" which leaks GitHub-specific implementation details into a forge-agnostic layer.
• [scope-alignment] PR scope aligns with issue Vendor analyze: batch path existence checks instead of O(N) GetFileContent calls #2351. No scope creep detected.
• [architectural-coherence] The new forge.Client interface method correctly follows the forge abstraction pattern (ADR-0005). The method name ListRepositoryFiles is appropriately forge-neutral.
• [internal-interface-evolution] Additive change to internal interface. No cross-repo contract risk.

[ifireball]

/fs-fix resolve merge conflicts, address review findings, and make codecov happy please

[fullsend-ai-coder]

🤖 Finished Fix · ✅ Success · Started 10:43 AM UTC · Completed 11:05 AM UTC
Commit: e8381e3 · View workflow run →

[ifireball]

/fs-fix resolve merge conflicts, and make codecov happy please

[fullsend-ai-coder]

🤖 Finished Fix · ✅ Success · Started 11:07 AM UTC · Completed 11:33 AM UTC
Commit: e8381e3 · View workflow run →

[fullsend-ai-retro]

🤖 Finished Retro · ✅ Success · Started 12:28 PM UTC · Completed 12:38 PM UTC
Commit: ee77525 · View workflow run →

[fullsend-ai-retro]

PR #2360 batched path-existence checks via the Git Trees API, replacing O(N) sequential GetFileContent calls with a single ListRepositoryFiles call. The code agent created the initial implementation on June 16, the review agent found valid findings (1 medium, 5 low, 4 info) within 15 minutes, and the PR then sat idle for 21 days until a human engaged on July 7. The human triggered two /fs-fix iterations: the first addressed review findings and added tests but did not resolve merge conflicts; the second properly merged main and added more coverage tests. The human approved and merged the same day with no additional comments beyond the review agent's findings.

Review quality was strong — the medium finding (missing ErrTreeTruncated sentinel for truncated Git Trees API responses) was a real correctness issue that the code agent should have caught by replicating the existing truncation handling already present in the same file's commitFilesTo method. The 21-day idle period adds evidence to #966 (surface agent-approved PRs awaiting human review). The fix agent's two-iteration pattern adds evidence to #2728 (fix agent should verify explicit success criteria). Skipping a dedicated proposal for each since those issues already capture the pattern well.

Proposals filed

• Code agent should replicate error handling from sibling methods using the same API endpoint (in fullsend-ai/fullsend)
• Fix agent should resolve merge conflicts as a prerequisite before code changes (in fullsend-ai/fullsend)