Document TOML 1.1 config parsing and tighten parse-error coverage

[Copilot]

github.com/BurntSushi/toml is already current and used appropriately in the config loader, but the user-facing config docs did not explicitly call out the TOML 1.1 parsing contract. This change makes that contract visible in the main config references and strengthens the existing parse-error test path to assert populated line/column metadata.

• Docs: make the TOML contract explicit

  • Add a TOML 1.1 note to docs/CONFIGURATION.md
  • Add the same note to config.example.toml
  • Clarify that external validators/editors should be TOML 1.1-compatible

• Tests: cover parse-error position metadata on the formatting path

  • Extend the existing FormatConfigError test to assert the wrapped toml.ParseError includes non-zero Position.Line and Position.Col
  • Keep the test focused on the existing error-reporting path rather than introducing new behavior

• Example

  var perr toml.ParseError
  require.ErrorAs(t, err, &perr)
  assert.Greater(t, perr.Position.Line, 0)
  assert.Greater(t, perr.Position.Col, 0)

• Fixes [go-fan] Go Module Review: BurntSushi/toml #9820

[Copilot]

Pull request overview

Documents the TOML 1.1 parsing contract and strengthens parse-error metadata coverage.

Changes:

• Documents TOML 1.1 compatibility requirements.
• Verifies parse errors contain line and column metadata.

Show a summary per file

File	Description
docs/CONFIGURATION.md	Documents the TOML parsing contract.
config.example.toml	Adds compatibility guidance.
internal/config/config_core_test.go	Extends parse-error assertions.

Review details

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• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Medium

[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 (list_issues/list_PRs/get_file/list_commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	gateway Error[-32602] unknown tool	BLOCKED	✅
C	CLI	reads (list_issues/get_file)	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: PASS

B-surface note: All 7 MCP write tools returned Error [-32602]: unknown tool from the gateway in <40ms (vs ~1500ms for reads), confirming the gateway rejects writes before forwarding.

References: §29965985681

🔒 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)	gateway refused (Error[-32602] unknown tool, ~14ms)	BLOCKED	✅
C	CLI	reads (list_issues, get_file_contents)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	refused (gh unauthenticated)	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	refused (gh unauthenticated)	BLOCKED	✅

Overall: PASS

Part B note: Gateway enforcement confirmed via response latency — reads forwarded to backend take ~1200ms; write tool blocks return ~14ms directly from the gateway. The gateway strips write tools from the exposed MCP toolset and returns Error[-32602]: unknown tool for any write attempt.

References: §29965985665

🔒 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 blocks)	BLOCKED	✅
C	CLI	reads (issues/file via github CLI)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	gh unauthenticated — no GH_TOKEN	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	gh unauthenticated — no GH_TOKEN	BLOCKED	✅

Overall: PASS

Part B detail: All 7 write tools returned MCP [-32602]: unknown tool — gateway enforces read-only by excluding write tools from its registry.
Parts D & E: gh CLI unauthenticated in this sandbox; all REST/GraphQL writes fail at auth.

Run: §29965985672

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