Harden Rust guard visibility logging tests

[Copilot]

Visibility log formatting was duplicated, and poisoned cache-test mutexes could cascade unrelated test failures.

• Visibility logging

  • Add visibility_str(bool) for consistent private/public log values.
  • Use it for cache-hit and rate-limit fallback logs.

• Test lock resilience

  • Recover the shared cache test mutex with PoisonError::into_inner().
  • Route direct test lock acquisitions through the recovery helper.

CACHE_TEST_LOCK
    .lock()
    .unwrap_or_else(|poisoned| poisoned.into_inner())

• Fixes [rust-guard] Rust Guard: dedupe visibility ternary and fix poisonable test lock in backend.rs #10711

[Copilot]

Pull request overview

Hardens Rust guard visibility logging and cache-test synchronization, resolving #10711.

Changes:

• Centralizes visibility formatting with visibility_str.
• Recovers poisoned cache-test mutexes and routes direct locking through the helper.
• Adds visibility formatting tests.

Show a summary per file

File	Description
guards/github-guard/rust-guard/src/labels/backend.rs	Deduplicates visibility logs and improves test-lock resilience.

Review details

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• Files reviewed: 1/1 changed files
• Comments generated: 0
• 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)	unknown tool [-32602]	BLOCKED	✅
C	MCP CLI	reads (list_issues/get_file via github bridge)	data returned	ALLOWED	✅
D	CLI REST	writes (reaction/star/issue/comment/file)	gh: GH_TOKEN not set	BLOCKED	✅
E	CLI GraphQL	mutations (addReaction/addStar/createIssue)	gh: GH_TOKEN not set	BLOCKED	✅

Overall: PASS

Full Report

Part B detail

Gateway enforces read-only by removing write tools from the MCP registry. All 7 write attempts returned Error [-32602]: unknown tool — tool absent at protocol level, not merely backend config.

Part D/E detail

gh CLI is unauthenticated (no GH_TOKEN). All REST/GraphQL write attempts rejected at auth layer.

References: §31037453881

🔒 mcpg read-only stress (default AWF runtime) by Read-Only Stress: default 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 (issues/PRs/file/commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	Error [-32602]: unknown tool (gateway-level)	BLOCKED	✅
C	CLI	reads (list_issues/get_file_contents)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	rejected (gh unauthenticated)	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	rejected (gh unauthenticated)	BLOCKED	✅

Note on Part B: Gateway returns MCP status=200 with JSON-RPC error -32602 for all write tools — gateway-level tool filtering confirmed.

Note on Parts D/E: gh CLI carries no token in this workflow; all REST/GraphQL writes rejected before reaching GitHub.

Overall: PASS

References: §31037453628

🔒 mcpg read-only stress (gVisor runtime) by Read-Only Stress: gVisor 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)	Error [-32602]: unknown tool	BLOCKED	✅
C	CLI	reads (list_issues/get_file_contents)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	gh unauthenticated — rejected	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	gh unauthenticated — rejected	BLOCKED	✅

Overall: PASS

Notes:

• Part B: All 7 write tools absent from gateway-filtered tool list (Error [-32602]: unknown tool). Gateway enforces read-only by removing write tools entirely.
• Part D/E: gh CLI has no token in this environment; all REST/GraphQL write attempts fail at auth. This is the expected security boundary (mcpg read-only + token scopes).

References: §31037452170

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