[ITSGJY]

Add an explicit composition contract to ToolDefinition and a canonical lookup with Denied + Sequential defaults. This provides an initial Phase 0 policy inventory alongside the existing measurement work in yyjeqhc#489.

Only git_review_summary opts in as Allowed + Parallel. Registry tests enforce Parallel => Allowed; the inspection-specific review evidence is tested only for git_review_summary. A real git_status definition verifies that read-only metadata does not imply composition opt-in. All other tools retain the conservative default.

The broader composition proposal remains deferred and exploratory. No composition runtime, execution behavior, authority, Project/Session/Job/Runner/audit semantics, or model-facing projection changes are included.

Validation for 12198f5d6511b5c7b4ea71623b100869d0d762d9:

• Final Fork CI passed: 11 jobs succeeded and 7 were skipped by the existing path classifier.
• Workspace-crates Rust tests, including all six focused composition policy tests, passed.
• Contract checks passed, covering formatting, workspace boundaries, test inventory, and schema/metadata/MCP/OpenAPI checks.
• Server and Runner Rust shards, Linux tooling, MCP conformance, and all required aggregates passed. The seven native platform/Docker child jobs were intentionally skipped.
• Local source review, git diff, and git diff --check passed. No local Cargo/npm compilation or tests were run.

The PR remains limited to five changed files: 293 additions and 31 deletions.

[ITSGJY]

Closing this draft because upstream yyjeqhc#501 implemented and extended the same composition-policy direction as part of Code Mode. Upstream now owns canonical ToolDefinition composition scheduling with Denied / Sequential / Parallel and a runtime consumer, so continuing this branch would duplicate and conflict with the accepted design. Keeping the branch for history; no upstream PR was opened from this draft.