Phase 28-36 body of work

Accumulated since a6f12e2 (Phase 21 Rust port + Phase 27 versioning):

- Phase 36: embed_semaphore on VectorState (permits=1) serializes
  seed embed calls — prevents sidecar socket collisions under
  concurrent /seed stress load
- Phase 31+: run_stress.ts 6-task diverse stress scaffolding;
  run_e2e_rated.ts + orchestrator.ts tightening
- Catalog dedupe cleanup: 16 duplicate manifests removed; canonical
  candidates.parquet (10.5MB -> 76KB) + placements.parquet (1.2MB ->
  11KB) regenerated post-dedupe; fresh manifests for active datasets
- vectord: harness EvalSet refinements (+181), agent portfolio
  rotation + ingest triggers (+158), autotune + rag adjustments
- catalogd/storaged/ingestd/mcp-server: misc tightening
- docs: Phase 28-36 PRD entries + DECISIONS ADR additions;
  control-plane pivot banner added to top of docs/PRD.md (pointing
  at docs/CONTROL_PLANE_PRD.md which lands in next commit)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/DECISIONS.md

@@ -94,3 +94,8 @@
 **Date:** 2026-04-16
 **Decision:** Keep Parquet + binary-blob vectors + in-RAM HNSW as the primary vector backend. Add Lance as a second backend available per-profile for workloads where Lance wins architecturally. Per-profile `vector_backend: Parquet | Lance` field becomes part of Phase 17 model profiles. Implementation kicks off via the standalone `crates/lance-bench` crate and is promoted into `vectord::lance_store` when the API stabilizes.
 **Rationale:** Head-to-head benchmark on the 100K × 768d `resumes_100k_v2` index (see `docs/ADR-019-vector-storage.md` for the full scorecard). Parquet+HNSW wins current-scale search latency by 2.55× (873us vs 2229us p50). Lance wins index build time by 14× (16s vs 230s), random row access by 112× (311us vs ~35ms full-file scan), and append speed structurally (0.08s vs full Parquet rewrite). Neither strictly dominates — the dual-use PRD framing (staffing + LLM brain) means both workloads exist in the same system. Keeps ADR-008's "Parquet is the format" principle intact for dataset tables; adds Lance as a purpose-built vector-tier option without discarding the tuned HNSW stack.
+
+## ADR-020: `register()` is idempotent by name with a schema-fingerprint gate
+**Date:** 2026-04-19
+**Decision:** `catalogd::Registry::register(name, fingerprint, objects)` is idempotent on `name`. If no manifest for `name` exists, create one. If one exists with the same `schema_fingerprint`, reuse its `DatasetId`, replace `objects`, bump `updated_at`, and write through. If one exists with a different `schema_fingerprint`, reject with `409 Conflict` (HTTP) / `FAILED_PRECONDITION` (gRPC). A one-shot operator endpoint `POST /catalog/dedupe` collapses any pre-existing duplicates (preferring the manifest with a non-null `row_count`, then the most recently updated).
+**Rationale:** Registry was keyed by surrogate `DatasetId` with no uniqueness constraint on `name`, so every caller that re-registered (re-ingest, external cron, gRPC retry) silently created a parallel manifest pointing at the same parquet — accumulating 308× `successful_playbooks` in live state before detection. The fingerprint gate turns re-ingest into an explicit no-op (matching PRD invariant #5 "ingestd is idempotent — re-ingesting the same file is a no-op") while forcing schema drift to be visible instead of silently clobbering. 409 status separates policy rejections from server errors, which matters for the Phase 12 tool-consumer ecosystem. Concurrency: the write lock is held across the storage write to close the check→insert TOCTOU window; serializing registers is acceptable because registers-per-second is low on the ingest path. Audit: idempotent-register events are visible as bumps to the stored manifest's `updated_at` field and in `catalogd` tracing output (tracing is non-durable, operator view only); `DedupeReport` is the return-value audit for cleanup runs. No event-journal entries are emitted — ADR-012 scopes the journal to row-level mutations, not catalog-manifest operations.