fix(TST-29): retire oldtasks.md; delete root docs-review artifacts

Migrate the durable session-resilience governance record (Phase 5
orphan-worker reattach deferred-not-planned, EnableOrphanReattach
does not yet exist, settled Phase-4 Viewer-default decision) from
oldtasks.md into a new "Session-Resilience Epic Scope" entry in
docs/DesignDecisions.md, repoint CLAUDE.md and stillpending.md's
oldtasks.md references to the new home / tasks.json, and git rm
oldtasks.md now that it has no unique content left. Flip TST-29 to
Done in the archreview tracking registers.

The five untracked root docs-review artifacts (MxAccessGateway-docs-*,
MxGatewayClient-docs-*) are absent from this worktree; they must be
deleted from the main working tree separately (gitignored, no repo
impact).

archreview/2026-07-12/remediation/60-testing-docs-gaps.md

@@ -14,7 +14,7 @@ Prior-cycle open findings (TST-05..24 where still open) are tracked in the prior
 | TST-26 | Medium | P1 (folded into TST-25) | S | TST-25 | Done | docs/GatewayTesting.md, check-codegen.ps1, and ci.yml comments describe removed CI jobs |
 | TST-27 | Medium | P1 (doc batch) | S | — | Not started | `ShowTagValues` config row still says "Reserved" after SEC-25 made the flag live |
 | TST-28 | Low | P2 | S | relates IPC-02 | Not started | Gateway-side `max_frame_bytes` handshake field untested in the CI-run suite |
-| TST-29 | Low | P2 | S | — | Not started | Retire `oldtasks.md` after folding the Phase-5 governance record into DesignDecisions.md; delete root docs-review artifacts |
+| TST-29 | Low | P2 | S | — | Done | Retire `oldtasks.md` after folding the Phase-5 governance record into DesignDecisions.md; delete root docs-review artifacts |
 | TST-30 | Low | P2 | M | — | Not started | Single shared Gitea runner is a CI throughput/availability bottleneck (cross-repo contention, no run cancel/delete) |
 
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