refactor(#1762): clarify verification-missing/unknown routing text (#3439)

* test(#1762): assert reassuring verification-routing wording (RED)

Regression test for #1762 — asserts readVerificationStatus's missing/
unknown next_action text reassures the user that execute-phase resumes
at the verification gates without redoing work, instead of reading as
a blind re-run instruction. Fails against current wording; the fix
lands in the next commit.

* fix(#1762): reassure verification-missing/unknown routing text is safe to run

readVerificationStatus's 'missing' and 'unknown' next_action text read as
"redo the implementation", when execute-phase's own discover_and_group_plans
step (#2868) already resumes at the verification gates and skips
execute_waves/checkpoint_handling entirely when every plan already has a
SUMMARY.md. Reword both to say so explicitly, and soften the 'unknown'
message to acknowledge a non-standard status may be an intentional marker
rather than presuming re-verification is always the fix.

Also updates progress.md's Route V.missing / V.unknown to consume the
dynamic $VERIFICATION_NEXT_ACTION (matching V.gaps/V.human) instead of a
hand-duplicated string, so the reassurance lands there too without a second
copy to keep in sync.

No change to next_command routing, status values, or the isPhaseComplete
completeness predicate (still gated on status === 'passed' per the #2957
DISK-STRICT decision) — advisory text only.

* fix(#1762): drop duplicated reassurance clause in progress.md routing text

Review finding: the SUMMARY.md reassurance was stated once via the
interpolated $VERIFICATION_NEXT_ACTION and again as a parenthetical on
the command line, in both Route V.missing and Route V.unknown. Trimmed
the parenthetical so $VERIFICATION_NEXT_ACTION stays the single source
of truth.

* docs(#1762): add changeset fragment

Type Changed with a docs-exempt marker — advisory routing text only,
no docs page documents this specific message today.

* test(#1762): acknowledge progress.md emitted-content growth

Route V.missing/V.unknown now render a small block referencing
${VERIFICATION_NEXT_ACTION} instead of a bare command line, growing
progress.md by 376 bytes. Deliberate per the differential attribution
check (ADR-2719).

* chore: drop spent progress.md ack from #3218's emitted-drift fragment

The #3218 growth it described is already on next (inert, per the
lint's own note that spent acks 'can no longer clear anything').
Its presence collided with the new #1762 fragment naming the same
bare filename, which lint-emitted-drift-ack rejects outright ('two
ack sources may never name the same path'). #3218's other two
acks (plan-phase.md, plan-review-convergence.md) are untouched.

* docs(#1762): backfill changeset PR number

---------

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

gsd-core/workflows/progress.md

@@ -458,7 +458,17 @@ UAT.md exists with `status: partial` — testing session ended before all items
 All plans have summaries, but canonical verification has not passed. The phase is implementation-complete, not phase-complete.
 
 ```
-`/gsd:execute-phase {phase} ${GSD_WS}` — re-run execution verification
+---
+
+## Verification Report Missing
+
+**Phase {phase}** has all plans summarized, but no canonical `*-VERIFICATION.md` exists yet. ${VERIFICATION_NEXT_ACTION}
+
+`/clear` then:
+
+`/gsd:execute-phase {phase} ${GSD_WS}` — resumes at the verification gates
+
+---
 ```
 
 ---
@@ -468,7 +478,17 @@ All plans have summaries, but canonical verification has not passed. The phase i
 VERIFICATION.md has an unexpected status. The phase is implementation-complete, not phase-complete.
 
 ```
+---
+
+## Verification Status Unexpected
+
+**Phase {phase}** has all plans summarized, but its `*-VERIFICATION.md` reports an unexpected status. ${VERIFICATION_NEXT_ACTION}
+
+`/clear` then:
+
 `/gsd:execute-phase {phase} ${GSD_WS}` — regenerate verification
+
+---
 ```
 
 ---