fix(contract): validate headless v3 schema constraints

[BunsDev]

Summary

Enforce the documented headless v3 schema constraints and correct stale contract references. Add a pinned JSON Schema validator to CI so cross-field constraints are tested directly.

Context

• User request: finish useful corrections from dirty worktrees and archive unfinished drafts.
• Scope: runtime contract documentation, fixture schemas, validator script, and CI; one Rust comment is corrected.
• The adapter currently documents v2 and rejects the runtime's review-memory field. This existing cross-repository migration gap is documented explicitly; memory governance and runtime behavior are unchanged.

Changes

• Require a brief contract version and consistent review mode/evidence combinations.
• Enforce null/absent success exit reasons and required failure/needs-input reasons, while retaining optional partial reasons.
• Replace stale artifact links and the inaccurate claim that local fixtures are verbatim adapter copies.
• Validate fixtures and status/evidence combinations with a pinned Draft 2020-12 validator.

Validation

• git diff --check
• rustup run stable cargo fmt --all -- --check
• uv run scripts/test-headless-schemas.py: all four test groups passed; 17 regression cases failed before the schema corrections.
• Independent specification and quality review passed; upstream adapter contract/schema checked live.
• Local workspace check/Clippy/tests: N/A for documentation, JSON Schema, Python validation, and a comment-only Rust change. The PR still runs full Rust and terminal CI.

PR Readiness

• Diff is limited to seven intended files.
• Generated files were not edited by hand.
• User-facing contract documentation is updated.
• No secrets, credentials, local paths, or unrelated logs are included.
• The existing adapter-v2/runtime-v3 migration gap is documented.

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Project	Deployment	Actions	Updated
docs	Ready	Preview	Oct 13, 2026 1:05pm UTC