[test] Add tests for guard.ConfigureGlobalCompilationCache

[github-actions]

Test Coverage Improvement: ConfigureGlobalCompilationCache

Function Analyzed

• Package: internal/guard
• Function: ConfigureGlobalCompilationCache
• Previous Coverage: 95.2%
• New Coverage: 100.0%
• Complexity: High (manages shared process-level state under a mutex, multiple error-handling branches, resource cleanup with error joining)

Why This Function?

ConfigureGlobalCompilationCache replaces the process-level wazero WASM compilation cache and is security/reliability critical: it must correctly release the previous cache and roll back cleanly on failure. While the function was already well tested (95.2%), one branch was completely uncovered: the case where both the previous cache's Close() and the newly-created replacement cache's Close() fail. This path uses errors.Join to combine both errors and must leave the global cache state pointing at the (still-open) previous cache. This is exactly the kind of tricky double-failure error-handling logic that's easy to get wrong and valuable to lock in with a test.

Implementation Note

newCompilationCache is called internally and there was no existing way to inject a cache whose Close() fails for the replacement cache (only the previous cache could be swapped directly via the existing globalCompilationCache package variable in tests). I added a minimal, behavior-preserving test seam: a package-level function variable newCompilationCacheFn that defaults to newCompilationCache and is only reassigned in tests. Production code path is unchanged.

Tests Added

• ✅ New sub-test joins errors when both previous and replacement cache close fail in TestWasmGuardCompilationCache (table-driven t.Run style consistent with existing tests in the file)
• ✅ Verifies errors.Join output contains both underlying error messages
• ✅ Verifies both the previous and replacement mock caches had Close() invoked
• ✅ Verifies the global cache is left pointing at the original (previous) cache, not swapped, since the operation failed

Coverage Report

Before: internal/guard/wasm_lifecycle.go:123: ConfigureGlobalCompilationCache  95.2%
After:  internal/guard/wasm_lifecycle.go:123: ConfigureGlobalCompilationCache  100.0%

Package internal/guard overall: 95.2% -> 96.5%

Test Execution

All tests pass:

=== RUN   TestWasmGuardCompilationCache
--- PASS: TestWasmGuardCompilationCache (0.01s)
    --- PASS: TestWasmGuardCompilationCache/joins_errors_when_both_previous_and_replacement_cache_close_fail (0.00s)
    ... (all other existing subtests pass unchanged)
PASS
ok  	github.com/github/gh-aw-mcpg/internal/guard	0.022s

go vet ./internal/guard/... and gofmt -l internal/guard/ both clean.

---

Generated by Test Coverage Improver
Next run will target the next most complex under-tested function

Generated by Test Coverage Improver · auto · 219.5 AIC · ⊞ 10.6K · ◷

[Copilot]

Pull request overview

Adds targeted coverage for dual cache-close failures in WASM cache replacement.

Changes:

• Adds an injectable cache factory for testing.
• Tests cleanup, retained global state, and combined errors.

Show a summary per file

File	Description
internal/guard/wasm_lifecycle.go	Adds the test seam.
internal/guard/wasm_test.go	Covers dual close failures.

Review details

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[github-actions]

🔒 mcpg Read-Only Stress — default AWF

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: default AWF (normal container isolation)

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (issues/PRs/file/commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	tools absent	BLOCKED	⚠️
C	CLI	reads (issues/PRs/file/commits)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	unauthenticated	BLOCKED	⚠️
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	unauthenticated	BLOCKED	⚠️

Overall: INCONCLUSIVE

Notes:

• ⚠️ Part B (all 7 targets): Write tools absent from the MCP tool catalog — GITHUB_READ_ONLY=1 is unconditionally set by the gh-aw framework, so the GitHub MCP backend never registers write tools. This is defense-in-depth but does not independently confirm gateway-level DIFC enforcement. Gateway DIFC enforcement is covered by internal/guard and internal/difc unit tests.
• ⚠️ Part D/E: gh CLI is not authenticated in this sandbox (no GH_TOKEN). All REST/GraphQL write attempts returned auth errors — this proves token-scope enforcement is untestable in this run, not that writes are blocked by the gateway. No writes leaked.
• No writes succeeded in any part; no artifacts created.

Run: §32587684434

🔒 mcpg read-only stress (default AWF runtime) by Read-Only Stress: default runtime

[github-actions]

🔒 mcpg Read-Only Stress — docker-sbx

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: docker-sbx (KVM-isolated microVM)

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (issues/PRs/file/commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	tool not found	BLOCKED	⚠️
C	CLI	reads (issues/file)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	401 Bad credentials	BLOCKED	⚠️
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	401 Bad credentials	BLOCKED	⚠️

Overall: INCONCLUSIVE

⚠️ Part B: All 7 write tools were absent from the MCP tool catalog (catalog has 23 read-only tools). The backend runs with GITHUB_READ_ONLY=1, so write tools are never registered. This confirms the backend defense-in-depth layer works, but does not confirm mcpg's own DIFC/guard enforcement layer independently. No writes leaked (no FAIL).

⚠️ Parts D/E: gh token is invalid (Bad credentials on all calls). Cannot confirm the token-scope boundary for REST/GraphQL writes this run. All write attempts returned 401 — no writes leaked.

No writes leaked. Run is INCONCLUSIVE (not FAIL).

References:

• §32587684567

🔒 mcpg read-only stress (docker-sbx runtime) by Read-Only Stress: docker-sbx runtime

[github-actions]

🔒 mcpg Read-Only Stress — gVisor

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: gVisor (runsc) kernel-level isolation

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (list_issues / list_pull_requests / get_file_contents / list_commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	all 7 "unknown tool" (-32602)	BLOCKED	⚠️
C	CLI	reads (github list_issues / get_file_contents)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	gh unauthenticated	BLOCKED	⚠️
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	gh unauthenticated	BLOCKED	⚠️

Overall: INCONCLUSIVE

⚠️ Part B — All 7 write tools (add_issue_comment, star_repository, issue_write, create_branch, create_or_update_file, create_pull_request) were absent from the 23-tool read-only catalog (Error -32602: "unknown tool"). Blocking proved by backend toolset exclusion (gh-aw tools.github: forces GITHUB_READ_ONLY=1), not independently by gateway/DIFC enforcement. Per test methodology this is INCONCLUSIVE — no write leaked.

⚠️ Parts D/E — gh CLI is not authenticated in this environment (GH_TOKEN not set). All REST and GraphQL write attempts returned "To use GitHub CLI in a GitHub Actions workflow, set the GH_TOKEN environment variable." Token-scope boundary could not be validated this run; no write leaked.

No writes leaked in any part. Zero sentinel issues/branches/comments created.

References: §32587684415

🔒 mcpg read-only stress (gVisor runtime) by Read-Only Stress: gVisor runtime