fix: release-train remediation - harness rollback record, release notes series file, MEMORY live verification

[LeXwDeX]

Why

The release-train audit found three deviations and one blocking landmine on the road to the version release:

1. Deviation A/B (process): fix(ci): restore proven specgit-accept install strategy #400 (CI acceptance-workflow rollback) was merged without a specgit delivery issue — retrospective fix: retrospective record for CI acceptance-workflow rollback merged without a delivery issue #402 records it. The release: memory silent-failure repair + dag-auto routing reduction #399 PR description must also disclose the causal chain (parking commit d6ce53a → first main-target PR exposed it → fix(ci): restore proven specgit-accept install strategy #400 rollback).
2. Deviation C (spec gap): workflows/release-train.md step 6 omits the release-notes series-file action.
3. Landmine: release-fork.yml now renders notes fail-closed from .github/releases/vX.Y.Z.md, but no series file exists — the release would fail. Write v1.18.0.md (feat commits in the batch → minor bump from v1.17.11) per RELEASE_NOTES_TEMPLATE.md.
4. MEMORY live verification: the fix: MEMORY topic creation pipeline fails silently with zero observability #395 fix is pinned by mock-server wire tests but never verified against a real provider end-to-end. Run the real stack (checkpoint → background maintenance → topic commit) against the configured proxy; confirm a topic actually lands in the Memory Home, then report.

Scope

• release: memory silent-failure repair + dag-auto routing reduction #399 PR description amended with the causal-chain disclosure
• workflows/release-train.md step 6 gains the series-file action
• .github/releases/v1.18.0.md written (template-conformant, sections filled from this batch's deliveries)
• MEMORY live verification executed and evidence recorded (topic committed to Memory Home via real provider)
• Multi-angle review of the whole remediation + release readiness (the DAG workflow handles this)

Acceptance

• All four scope boxes checked with evidence links
• The delivery PR closes this issue; specgit finish exits 0
• After merge to dev and dev→main promotion, release-fork from main succeeds on the first run

[LeXwDeX]

Delivered via PR #403 → dev → #399 → main (bec6d75). All scope items completed: #399 disclosure, release-train spec series-file step, v1.0.29.md series file (mechanically derived), MEMORY live verification PASS (topic committed in 8.1s against real provider), three-angle review ACCEPT after R1/R2 remediation. specgit finish accepted (exit 0).