docs(audit): the bats rule carries the trap its own advice creates

[stevensacks]

Closes two of the three follow-ups left open when the machinery-waive widening merged. The third is declined; see below.

What changed

.claude/rules/bats-assertions.md — the !-negation section prescribes writing an absence check as <positive-condition-for-the-bad-case> && return 1 and stops there. As a test's final statement that form inverts its own result: an absent needle leaves grep's non-zero status as the AND-list's status, which becomes the test's return value, so the test fails in exactly the case it exists to pass. Three lines now state the trap and the fix (an explicit trailing true), lifting phrasing already audit-proven in .gaia/tests/lib/doc-machinery-waive-prose.bats's header rather than inventing new.

Placed in the version-independent !-negation section, not the bash-3.2 one: reproduced on bash 3.2.57 and 5.3.15, both fail. cmd && return 1 is an AND-list whose status is cmd's own, and set -e is ignored for a non-final member of an AND-OR list. The section that prescribes the form is where the trap belongs.

.gaia/scripts/check-audit-base-derivation.sh — one clause on _gaia_drop_full_base_matches's awk docstring. It described FULL_BASE as the self-skip base only; the exemption also covers the default member's waive-eligibility derivation, which the assertion-1 charter comment directly above it already states. The two comments now agree. Comment only, no behavior change.

Declined, recorded so it is not re-raised

The macOS BWK awk backslash-stripping gotcha (-v-assigned regex loses \( \)) is not added to any rule. It is awk portability in a per-suite copy-pasted helper rather than assertion hygiene; it produced no false pass, because extract_section_or_fail's vacuous-match guard caught it loudly; and it is already documented at the point it bites, in the header of the suite that hit it. A rule is the wrong altitude for something that fired once.

Verification

• bash .gaia/tests/shell-lint.sh — passes (193 scripts, 181 suites, hook-array guard clean)
• .gaia/scripts/tests/check-audit-base-derivation.bats under the bash 5 guard — 42/42, exit 0
• Quality Gate — skipped, confirmed against wiki/decisions/Quality Gate.md: no staged file matches the source-extension or gate-affecting-config lists, and line 46 names .claude/** and pure-markdown commits explicitly.

No mutation testing: both edits are prose and a comment with no executable behavior.

[github-actions]

code-review-audit skipped: no files in the frontend auditor's scope. GAIA-Audit is already green for this commit's tree, every dispatched member has cleared. No action needed

[stevensacks]

@/var/folders/pn/m58c653j1js2r48m5n358ync0000gn/T/tmp.xt2FdCSRsS