docs(project-harness): attribute verdict source and guard green runs

[neoLsH]

Summary

• Add a verdict-source attribution gate to agent-verify-loop.md: red verdicts are classified as local change / infrastructure / upstream asset drift before the diagnose-repair sequence, so only failures the change owns consume repair rounds.
• Add green-verdict integrity guards: an empty run fails, fail fast over silent fallback, and no silent exits — with two matching anti-patterns.

Why

• Issue/Story: [Feature]: CI guidance is missing its interpretation side — propose a verdict attribution doc #119
• User or maintainer outcome: agents stop burning repair rounds editing their own diff for failures owned by CI infrastructure or upstream test-corpus drift, and green runs can no longer hide that the intended cases never executed.

Traceability and Scope

• Spec/ADR, if applicable: none — references guidance only, no runtime behavior.
• Acceptance criteria addressed: per maintainer direction in [Feature]: CI guidance is missing its interpretation side — propose a verdict attribution doc #119 — extend the existing docs rather than adding a new one; the zero-test case is not duplicated but cross-referenced from verification-environment.md; the change is focused and host-agnostic, covering attribution and silent fallback.
• Canonical owners changed: references/project-harness/agent-verify-loop.md (verdict domain and post-verdict sequence already owned here; Ownership Boundary section updated to name the two additions); test/plugins/antigravity-plugin-artifact.test.mjs frozen Markdown-closure counts updated (edges 307 → 308) for the one new cross-reference link.
• Explicit non-goals: no new reference doc; no changes to git-hooks.md, verification-environment.md, or runtime/executable behavior; no companion case study.

Change Type

• Feature
• Bug fix
• Tests only
• Documentation/community
• Refactor with no intended behavior change
• Dependency, packaging, or infrastructure

Test and Review Evidence

Check	Result
npm ci	522 packages installed, clean
npx vitest run test/skills-docs/doc-link-graph.test.mjs	8/8 passed
npx vitest run test/skills-docs/	33/33 passed
npm test	104 files, 1545 passed, 2 pre-existing skips, 0 failures

Manual or visual evidence: full diff reviewed; new sections follow the existing reference style (bold run-in leads, tables, anti-pattern list) and reuse the four-valued verdict domain.

Risk and Recovery

• Compatibility and cross-platform impact: none — guidance prose only, host-agnostic.
• Package, plugin, schema, or generated-file impact: the frozen Markdown-closure edge count in the antigravity plugin artifact test moves 307 → 308 to reflect the added cross-reference link; nodes and files counts unchanged.
• Rollback or recovery path: revert the PR.
• Residual risk or unverified boundary: none identified; no executable behavior touched.

AI Involvement

• Level: Assisted
• Human review and validation: author reviewed the complete diff section by section and verified all test commands and observed results above.

Checklist

• I followed AGENTS.md, CONTRIBUTING.md, and the relevant canonical-owner guidance.
• The change is focused and does not include unrelated local or generated state.
• Tests and documentation match the behavior actually delivered.
• Markdown links were checked when documentation moved or changed.
• Cross-platform behavior was considered for Windows, macOS, and Linux.
• Package/runtime verification was run when shipped files or dependencies changed.
• User-facing or compatibility changes are recorded in CHANGELOG.md.
• I have the right to contribute this work under the repository's MIT License.

Note on the two unchecked items: no shipped files or dependencies changed (docs + one test snapshot constant), and there is no user-facing behavior or compatibility change, so CHANGELOG.md was intentionally left untouched per its "observable behavior and compatibility" scope.