Add regression coverage for pull_request_read DIFC labeling

[Copilot]

pull_request_read is a canonical PR read surface and must retain the same repo-scoped secrecy and PR-aware integrity handling as get_pull_request.

• Regression coverage
  • Add a focused test asserting pull_request_read produces identical labels and descriptor to get_pull_request.
  • Protects the explicit apply_tool_labels PR match arm from future inventory or refactoring drift.

assert_eq!(actual, expected);
assert_eq!(actual.2, "pr:github/copilot#123");

• Fixes [guard-coverage] Guard coverage gap: 1 operations from github-mcp-server / GitHub CLI not fully covered #10703

[Copilot]

Pull request overview

Adds regression coverage for DIFC labeling parity between pull_request_read and get_pull_request.

Changes:

• Compares both tools’ labels and descriptors.
• Verifies the PR descriptor format.

Show a summary per file

File	Description
guards/github-guard/rust-guard/src/labels/mod.rs	Adds the labeling parity regression test.

Review details

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

[github-actions]

🔒 mcpg Read-Only Stress — default

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

Part	Surface	Op	Result	Expected	Status
A	MCP	reads	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	Error [-32602]: unknown tool	BLOCKED	✅
C	CLI	reads	data returned	ALLOWED	✅
D	CLI	REST writes	gh unauthenticated	BLOCKED	✅
E	CLI	GraphQL mutations	gh unauthenticated	BLOCKED	✅

Overall: PASS

Gateway exposes 22 read-only MCP tools; all 7 write attempts returned Error [-32602]: unknown tool (gateway enforcement). REST/GraphQL blocked by absent GH_TOKEN.

References: §31037394048

🔒 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 (list_issues, list_prs, get_file, list_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, list_prs, list_commits)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	rejected (no GH_TOKEN)	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	rejected (no GH_TOKEN)	BLOCKED	✅

Overall: PASS

Full Report

Part B — MCP Write Errors

Tool	Gateway Error
add_issue_reaction	Error [-32602]: unknown tool "add_issue_reaction"
star_repository	Error [-32602]: unknown tool "star_repository"
create_issue	Error [-32602]: unknown tool "create_issue"
add_issue_comment	Error [-32602]: unknown tool "add_issue_comment"
create_branch	Error [-32602]: unknown tool "create_branch"
create_or_update_file	Error [-32602]: unknown tool "create_or_update_file"
create_pull_request	Error [-32602]: unknown tool "create_pull_request"

Write tools are absent from the gateway tool registry — gateway enforcement, not backend config.

Parts D & E: gh unauthenticated in docker-sbx microVM (no GH_TOKEN), all REST/GraphQL writes rejected.

References: §31037394527

🔒 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 (issues/PRs/file/commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	Error [-32602]: unknown tool — gateway refused all 7	BLOCKED	✅
C	CLI	reads (list issues, get file)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	gh: GH_TOKEN not set — unauthenticated	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	gh: GH_TOKEN not set — unauthenticated	BLOCKED	✅

Overall: PASS

B-surface note: All 7 write tools refused by the gateway with Error [-32602]: unknown tool. The gateway strips write tools from the proxy-exposed tool inventory — enforcement is at the gateway level.

References: §31037393770

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