feat(trace): rivet trace-results — forward req→test-result trace (REQ-238 pt1, #547)

[avrabe]

What

First slice of #547 ("graphical way to trace req → test results"). Tracing currently runs test→artifact; this adds the reverse — from a requirement, the tests/results that cover it — as a mechanism + CLI surface. The graphical dashboard view is the follow-up slice (that's the part that needs the Playwright E2E gate).

This slice (fully verifiable locally)

• rivet-core result_trace: BFS over backlinks from a requirement (multi-hop through the ASPICE V), each reached artifact annotated with its latest test-result status + a roll-up verdict (passing / failing / no-evidence). Pure, 4 unit tests.
• rivet trace-results <id>: text tree or JSON — the JSON is exactly what the dashboard view will consume. Exits non-zero on a failing covering test (gate-usable). Uses the previously-dead ProjectContext::load_full (loads results).

Test-result trace for REQ-1: ✓ passing
  TEST-1 --verifies--> REQ-1   [pass]

Scope note

REQ-238 stays implemented (not verified) and #547 stays open: the requirement is the graphical view, which this foundation enables but does not render yet. That slice needs the dashboard/serve work + Playwright.

Verification

result_trace 4 + cli_commands 152 green; clippy --all-targets clean. No dashboard code → no Playwright needed for this slice.

🤖 Generated with Claude Code

[github-actions]

📐 Rivet artifact delta

Change	Count
Added	0
Removed	0
Modified	1
Downstream impacted (depth ≤ 5)	0

Graph

graph LR
  REQ_238["REQ-238"]:::modified
  classDef added fill:#d4edda,stroke:#28a745,color:#155724
  classDef removed fill:#f8d7da,stroke:#dc3545,color:#721c24
  classDef modified fill:#fff3cd,stroke:#ffc107,color:#856404
  classDef overflow fill:#e2e3e5,stroke:#6c757d,color:#495057,stroke-dasharray: 3 3

Loading

Modified

ID	Changes
REQ-238

📎 Full HTML dashboard attached as workflow artifact rivet-delta-pr-645 — download from the workflow run.

_{Posted by rivet-delta workflow. The graph shows only changed artifacts; open the HTML dashboard (above) for full context.}

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Rivet Criterion Benchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 6bd945d	Previous: 57eefd5	Ratio
link_graph_build/10000	37365045 ns/iter (± 4643188)	27279600 ns/iter (± 1422247)	1.37

This comment was automatically generated by workflow using github-action-benchmark.

[codecov]

Codecov Report

❌ Patch coverage is 99.36709% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rivet-core/src/result_trace.rs	99.36%	1 Missing ⚠️

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