fix(validate,coverage): required-backlink matches inverse-name convention + honours alternate-backlinks

[avrabe]

Closes #349.

The bug

Backlink.link_type stores the forward link-type name (e.g. supports) while several built-in schemas — notably schemas/safety-case.yaml — write required-backlink using the inverse name (e.g. supported-by). The strict equality match at rivet-core/src/validate.rs:906 and rivet-core/src/coverage.rs:200 therefore never matched for any inverse-name rule.

Observable effect on the loom safety case reported in the issue:

ERROR: [SG-1] Every safety goal must be supported by evidence (solution) or decomposed into sub-goals ...

…fired for every safety goal even though every one of them was correctly supported (SOL-1 supports → SG-1, etc.). dev.yaml's required-backlink: satisfies happens to use the forward name and worked; the bug surfaced only on schemas following the inverse-name convention.

The fix

Both call sites now accept either spelling:

bl.link_type == name || bl.inverse_type.as_deref() == Some(name)

Same fix path additionally evaluates rule.alternate_backlinks — validate.rs previously ignored that field outright, so a safety goal satisfied only via an alternate (e.g. decomposed-by from a strategy instead of supported-by) still erroneously fired the rule. coverage.rs had the same gap. The match helper is now closed over the backlinks, called once for the primary and once per alternate; the rule passes when any shape matches.

Acceptance criteria from the issue

The issue lists a primary fix, a secondary bug, and four frictionless-ness suggestions. This PR addresses the two binding items; the frictionless suggestions are intentionally split out as a follow-up (per "one PR per issue, keep PRs focused" — they touch the CLI's rivet get rendering and require a new rivet why command, which is a separate feature).

Issue item	Status	Where
Match against the backlink's inverse name in validate.rs	done	validate.rs:902–941
Match against the backlink's inverse name in coverage.rs	done	coverage.rs:194–225
Evaluate rule.alternate_backlinks in validate.rs (secondary bug)	done	validate.rs:931–935
Evaluate rule.alternate_backlinks in coverage.rs	done	coverage.rs:222–225
rivet get shows inbound backlinks	follow-up	filed as a separate issue would be more appropriate
required-backlink failure message lists found backlinks	follow-up	the diagnostic-message redesign cuts across all rules, not this fix
rivet why <id> <rule> explain mode	follow-up	new CLI surface, separate feature
Per-rule failures generally explainable	follow-up	overlaps with REQ-124 agent-actionable remediation work

Tests

Four regression tests pin the fix — two per engine:

• validate::tests::required_backlink_inverse_name_is_satisfied_by_forward_link — reproduces the loom GSN scenario exactly (rule names supported-by, artifact has forward supports); without the fix the rule fires, with the fix it does not.
• validate::tests::validate_honours_alternate_backlinks — goal satisfied only via the alternate (decomposed-by from a strategy) must not fire the rule.
• coverage::tests::required_backlink_matches_inverse_link_type_name — same scenario from the coverage engine's perspective; without the fix covered = 0, with the fix covered = 1.
• coverage::tests::coverage_honours_alternate_backlinks — alternate-satisfied goal counts as covered, not uncovered.

Full cargo test -p rivet-core --lib → 1086 passed, 0 failed.
rivet validate on the rivet repo itself → PASS unchanged.

End-to-end verification

Reproduced and cleared the loom-style scenario on a minimal safety-case project (SG-1 supported by SOL-1; SG-2 decomposed by STRAT-1; SG-3 with neither):

ERROR: [SG-3] Every safety goal must be supported by evidence ...
Result: FAIL (1 errors, ...)

Only the genuinely-unsupported SG-3 errors — SG-1 (primary backlink path) and SG-2 (alternate-backlink path) both pass, which matches the user's expectation in the bug report.

Files touched

• rivet-core/src/validate.rs — comparison fix + alternate_backlinks evaluation + 2 regression tests
• rivet-core/src/coverage.rs — comparison fix + alternate_backlinks evaluation + 2 regression tests
• CHANGELOG.md — Unreleased entry

Commit trailers: Fixes: REQ-004, Refs: #349.

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Generated by Claude Code

[github-actions]

📐 Rivet artifact delta

No artifact changes in this PR. Code-only changes (renderer, CLI wiring, tests) don't touch the artifact graph.

[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: 015037a	Previous: cb670c8	Ratio
link_graph_build/10000	37966689 ns/iter (± 3420341)	31257613 ns/iter (± 2082341)	1.21

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

[codecov]

Codecov Report

❌ Patch coverage is 99.13793% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rivet-core/src/validate.rs	98.23%	2 Missing ⚠️

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