fix(scanner): attribute a marker to the test it annotates (REQ-326, #892, #787)

[avrabe]

Closes #892. Closes #787.

find_enclosing_function only ever scanned backwards, so a marker written in
the conventional place — on the line above the #[test] it annotates — was
attributed to the function before it. Reported twice, from meld (#892) and
earlier as #787.

#[test]
fn first_unrelated_test() {}

// rivet: verifies REQ-001          → reported: first_unrelated_test
#[test]
fn the_test_that_actually_verifies_it() {}

The damage is narrow and bad

The requirement mapping stays correct — rivet verify still advances, and
coverage percentages are unaffected. What's wrong is the evidence line, which
names a different test than the one that verifies the requirement.

For a reader auditing the right-hand side of the V, that line is the product.
Following it leads to a test that does not test the thing.

Why the fix is bounded

Forward walk, but only across lines that may legitimately separate a marker from
the item it annotates: attributes, comments, blank lines. A marker inside a
body has real code on the next line, so the walk stops and the existing backward
scan returns the enclosing function — which is the shell convention REQ-319
depends on.

Negative-controlled both ways, which is what shows the bound is load-bearing:

remove the forward walk     1 failed   (the reported bug returns)
make the walk unbounded     2 failed   (in-body case AND the shell case)

A mistake in this commit, and what caught it

Inserting these tests spliced a doc comment into the middle of REQ-319's own
doc comment, orphaning its rivet: verifies line onto the wrong function.

cargo test passed. clippy passed. Doc comments concatenate harmlessly, so
nothing in the Rust toolchain could see it. Only rivet coverage --tests caught
it — by reporting REQ-319 against a test with nothing to do with shell scanning.

The tool found a defect the compiler could not. That's worth more than the fix.

Gates

cargo fmt --check · clippy --all-targets -D warnings on 1.97.0 ·
cargo test --workspace (exit 0, 66 ok) · full cli_commands (189 passed) ·
rivet validate · rivet docs check · yamllint — all exit 0.
REQ-326 → verified, 2 test markers, correctly attributed.

[codecov]

Codecov Report

❌ Patch coverage is 97.72727% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rivet-core/src/test_scanner.rs	97.72%	1 Missing ⚠️

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[github-actions]

📐 Rivet artifact delta

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

Graph

graph LR
  REQ_326["REQ-326"]:::added
  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

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Added

• REQ-326

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