fix(scanner): attribute a marker to the test it annotates (REQ-326, #892, #787) - #897

, #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. Three lines reproduce it:
 #[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, so `rivet
verify` still advances and coverage percentages are unaffected. What is wrong is
the EVIDENCE LINE, which names a different test than the one that verifies the
requirement — and for a reader auditing the right-hand side of the V, that line
is the entire product. Following it leads to a test that does not test the thing.
Fixed by walking FORWARD first, but only across lines that may legitimately
separate a marker from the item it annotates: attributes, comments, blank lines.
The bound is what makes it correct rather than merely different. A marker inside
a function body has real code on the next line, so the walk stops there and the
existing backward scan returns the enclosing function — which is the shell
convention REQ-319 depends on.
Negative-controlled both ways at --lib scope, which is what shows the bound is
load-bearing rather than decorative:
 remove the forward walk 1 failed (the reported bug returns)
 make the walk unbounded 2 failed (in-body case AND the shell case)
Worth recording how a mistake in this commit was caught. 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` and `clippy`
both passed — doc comments concatenate harmlessly — and only
`rivet coverage --tests` caught it, by reporting REQ-319 against a test that has
nothing to do with shell scanning. The tool found a defect the compiler could
not see, which is the case for the tool existing.
Confirmed with cargo fmt --check, clippy --all-targets -D warnings on 1.97.0,
cargo test --workspace (exit 0, 66 ok, 0 failed), the full cli_commands suite
(189 passed), rivet validate, rivet docs check, yamllint — all exit 0.
Implements: REQ-326
Verifies: REQ-326

...(REQ-326)
The PR-diff mutation gate found five survivors, every one a `||`-to-`&&` in the
`is_separator` chain. The fixtures used `#[test]` and nothing else, so no test
could distinguish any other disjunct.
The fix is not more fixtures for eight disjuncts — it is that eight was wrong:
 #[attr] #!inner # comment all start with '#', so one check covers three
 pub async sit on the `fn` line the pattern already
 matches, so as separate lines they never occur
Four remain — blank, `#`, `//`, `@` — each genuinely distinct and each now
exercised by its own case, plus a case proving a NON-separator stops the walk so
the backward scan wins. Without that last one the other four would also pass
under an unbounded walk, which is the mistake the earlier round already made
once.
Negative-controlled at --lib, the scope the gate uses: turning any one of the
four into `&&` reddens two tests. Baseline 16 pass.
Worth stating plainly: the gate did not just find missing tests here, it found
dead predicate. Three of the eight disjuncts could never change an outcome and
two could never be reached, so no test could have killed those mutants — the
honest fix was to delete them rather than to write tests asserting behaviour
that does not exist.
Confirmed with cargo fmt --check, clippy --all-targets -D warnings on 1.97.0,
cargo test --workspace (exit 0, 66 ok), the full cli_commands suite (189
passed), rivet validate — all exit 0. REQ-326 now shows 3 test markers, each
correctly attributed.
Verifies: REQ-326