enhance(#3304): gate re-verification blockers on deterministic evidence (#4085)

* test(#3304): add failing-first suite for the convergence evidence gate

Content-assertion suite for the Step 7 re-verification evidence gate
(agents/gsd-verifier.md / gsd-core/references/verifier-evidence-gate.md).
Committed before the implementation to prove RED via gsd-test.

* enhance(#3304): gate re-verification blockers on deterministic evidence

Step 7's anti-pattern scan re-runs at full, unbounded scope on every
re-verification pass, independent of the must-haves established in Step 2.
A blocker it finds — other than the self-evidencing debt-marker check —
previously reverted a completed gap-closure round and started another
--gaps cycle on nothing more than the verifier's own new judgment call,
with no bound on how many times that could repeat.

A Step 7 blocker now blocks unconditionally in re-verification mode only
if it is a carried-forward gap (present in the prior VERIFICATION.md's
gaps: list) or the flagged file was git-modified since the prior pass
(a regression; fails closed toward blocking when history is unresolvable).
Otherwise it predates the gap-closure round unflagged and needs
deterministic evidence — a named test run red, or another concrete
reproducible artifact — to stay blocking. Unevidenced, it downgrades to
a new advisory: frontmatter list and report section instead of setting
status: gaps_found, and never reverts a completed must-have.

Maintainer approval was narrowed to this evidence condition only,
explicitly rejecting the broader "advisory whenever untraceable to a
requirement/decision/prior-gap" proposal — implemented and pinned by
tests/verifier-evidence-gate.test.cjs and documented as rejected in
gsd-core/references/verifier-evidence-gate.md so it can't silently
re-expand.

Closes #3304

* fix(#3304): correct window-truncation and indentation bugs in evidence-gate tests

gsd-test's GREEN checkpoint caught 3 real bugs in the test file itself
(not the production prose): a {0,600} match window was shorter than the
724-char paragraph it was scanning (the "exclude from Step 9 Rule 1"
phrase starts at offset 662), and two regexes assumed no indentation
after a markdown list-continuation line break. All three phrases are
confirmed unique across agents/gsd-verifier.md, so the windowed
submatches are replaced with direct whole-string assertions instead of
just widening the window.

Also acknowledges the deliberate byte growth in agents/gsd-verifier.md
that the differential-attribution check (ADR-2719) correctly flagged.

Emitted-Drift-Ack-Growth: gsd-verifier.md — adds the #3304 re-verification evidence gate (Step 7 rule, Advisory bucket, advisory: frontmatter, report section); 1488 bytes, still within the LARGE-tier 48 KiB cap (48751/49152).

* docs(#3304): backfill changeset PR number

---------

Co-authored-by: sim <sim@local>

tests/fixtures/install-tree/kimi-code.json

@@ -170,6 +170,7 @@
   "gsd-core/references/user-story-template.md",
   "gsd-core/references/verification-overrides.md",
   "gsd-core/references/verification-patterns.md",
+  "gsd-core/references/verifier-evidence-gate.md",
   "gsd-core/references/verifier-phase-gates.md",
   "gsd-core/references/verifier-wiring-patterns.md",
   "gsd-core/references/verify-command-path-resolvability.md",