refactor(skills): SDD e2e verification becomes pre-finish offer with disclosure doc

The predicate-keyed at-skill-start trigger is replaced by an unconditional
offer to the human after the final whole-branch review, before
finishing-a-development-branch. The procedure (spec discovery,
author/checker/runner flow, fix-wave rules) moves to spec-derived-e2e.md;
SKILL.md keeps the offer, a flowchart node, and the Integration reference.
Micro-tested 6/6: four controllers at the post-review point all offer
before finishing (including under wrap-up-efficiently pressure with the
human away); two accepted-offer controllers follow the disclosure doc with
the checker run by the controller, one fix subagent, and a fix-diff review
gate. Deviation recorded in the design spec.

skills/subagent-driven-development/spec-derived-e2e.md

@@ -0,0 +1,39 @@
+# Spec-Derived E2E Verification
+
+Live end-to-end evidence for the branch: scenario cards derived from the
+governing spec, run against the built code. Results land before
+superpowers:finishing-a-development-branch, so "ready to merge" includes
+live-scenario evidence, not just review verdicts.
+
+## Finding the governing spec
+
+Open the spec the plan names. If the plan names none, check the repo's spec
+directory (e.g. `docs/superpowers/specs/`) for specs governing the code the
+plan touches.
+
+- Spec with an "E2E scenario cards" section: cards derive from the table's
+  falsification lines verbatim.
+- Spec without the section: the bootstrap path in
+  superpowers:agentic-end-to-end-testing's authoring-cards-from-a-spec.md
+  backports a table from the spec's requirements (flagged for human review).
+- No governing spec at all: there is nothing to derive cards from. Tell your
+  human partner and proceed to finishing — or they can write a spec first
+  and re-run the offer.
+
+## Procedure
+
+Use superpowers:agentic-end-to-end-testing:
+
+1. Dispatch a card-author subagent per its authoring-cards-from-a-spec.md.
+2. Run its scripts/check-cards-against-spec yourself on the author's output
+   — self-attestation is not the gate.
+3. Dispatch a runner subagent per its runner-prompt.md against the built
+   branch.
+
+## Failure handling
+
+Card FAILs are findings: dispatch ONE fix subagent with the complete list,
+then re-run the failed cards. The card author never fixes. Fix-wave commits
+land after the final whole-branch review, so give the fix diff its own
+task-review gate before finishing — a green re-run alone does not ship
+unreviewed changes.