Federation foundation + HNSW trial system + Postgres streaming + PRD reframe

Four shipped features and a PRD realignment, all measured end-to-end:

HNSW trial system (Phase 15 horizon item → complete)
- vectord: EmbeddingCache, harness (eval sets + brute-force ground truth),
  TrialJournal, parameterized HnswConfig on build_index_with_config
- /vectors/hnsw/trial, /hnsw/trials/{idx}, /hnsw/trials/{idx}/best,
  /hnsw/evals/{name}/autogen, /hnsw/cache/stats
- Measured on resumes_100k_v2 (100K × 768d): brute-force 44ms -> HNSW 873us
  at 100% recall@10. ec=80 es=30 locked as HnswConfig::default()
- Lower ec values trade recall for build time: 20/30 = 0.96 recall in 8s,
  80/30 = 1.00 recall in 230s

Catalog manifest repair
- catalogd: resync_from_parquet reads parquet footers to restore row_count
  and columns on drifted manifests
- POST /catalog/datasets/{name}/resync + POST /catalog/resync-missing
- All 7 staffing tables recovered to PRD-matching 2,469,278 rows

Federation foundation (ADR-017)
- shared::secrets: SecretsProvider trait + FileSecretsProvider (reads
  /etc/lakehouse/secrets.toml, enforces 0600 perms)
- storaged::registry::BucketRegistry — multi-bucket resolution with
  rescue_bucket read fallback and reachability probing
- storaged::error_journal — bucket op failures visible in one HTTP call
- storaged::append_log — write-once batched append pattern (fixes the RMW
  anti-pattern llms3.com calls out; errors and trial journals both use it)
- /storage/buckets, /storage/errors, /storage/bucket-health,
  /storage/errors/{flush,compact}
- Bucket-aware I/O at /storage/buckets/{bucket}/objects/{*key} with
  X-Lakehouse-Rescue-Used observability headers on fallback

Postgres streaming ingest
- ingestd::pg_stream: DSN parser, batched ORDER BY + LIMIT/OFFSET pagination
  into ArrowWriter, lineage redacts password
- POST /ingest/db — verified against live knowledge_base.team_runs
  (586 rows × 13 cols, 6 batches, 196ms end-to-end)

PRD realignment (2026-04-16)
- Dual use case: staffing analytics + local LLM knowledge substrate
- Removed "multi-tenancy (single-owner system)" from non-goals
- Added invariants 8-11: indexes hot-swappable, per-reader profiles,
  trials-as-data, operational failures findable in one HTTP call
- New phases 16 (hot-swap generations), 17 (model profiles + dataset
  bindings), 18 (Lance vs Parquet+sidecar evaluation)
- Known ceilings table documents the 5M vector wall and escape hatches
- ADR-017 (federation), ADR-018 (append-log pattern) added
- EXECUTION_PLAN.md sequences phases B-E with success gates and
  decision rules

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/DECISIONS.md

@@ -79,3 +79,13 @@
 **Date:** 2026-03-27
 **Decision:** Each contract/search gets a named workspace with saved queries, shortlists, activity logs, and delta layers. Workspaces have daily/weekly/monthly tiers and support instant zero-copy handoff between agents.
 **Rationale:** Staffing workflows are inherently agent-centric — a recruiter works a contract, builds context, then may need to hand it off. The workspace captures that context in a structured, queryable, transferable format. Without it, handoff means "read the email thread and figure it out."
+
+## ADR-017: Federated multi-bucket storage
+**Date:** 2026-04-16
+**Decision:** Every `ObjectRef` belongs to exactly one named bucket. Three bucket classes: `primary` (system default, always present), `profile:{user}` (per-user/per-model workspace bucket), and named tenant buckets (`client_a`, `client_eu`). A single shared `rescue_bucket` handles read fallback on target failure. Writes hard-fail on unreachable target; no silent fallback. Every bucket op failure lands in an error journal at `primary://_errors/bucket_errors/`, queryable via `/storage/errors`. Credentials never live in `lakehouse.toml` — a pluggable `SecretsProvider` trait resolves opaque `secret_ref` handles.
+**Rationale:** The single-backend assumption breaks when we want: tenant data isolation, data residency (EU bucket), per-profile workspaces for local models. DataFusion already supports multiple registered object stores; catalogd is the cross-bucket metadata authority. Rescue bucket + visible error journal makes operational failures diagnosable in one HTTP call. See `docs/ADR-017-federation.md` for full design + success gates.
+
+## ADR-018: Write-once batched append pattern for journals
+**Date:** 2026-04-16
+**Decision:** All append-only journals (error journal, HNSW trial journal, future audit logs) use the `storaged::append_log::AppendLog` helper. Events accumulate in an in-memory buffer; on threshold or explicit `flush()`, the buffer is written as one new timestamped file (`batch_{epoch_us}.jsonl`). Existing files are never rewritten. `compact()` merges all batches into one with a fresh timestamp, preserving chronological sort order.
+**Rationale:** Object stores have no append primitive. Naive "read-modify-write the whole JSONL file on every event" is O(N²) cumulative work and creates the classic small-file / rewrite-amplification anti-pattern that llms3.com flags as the top lakehouse pitfall. Write-once batching is the LSM-tree idea applied to small JSONL events — bounded write amplification, append-only semantics, optional compaction for read efficiency. The in-memory ring buffer preserves O(1) recent-event reads for the `/storage/errors` and `/hnsw/trials` query endpoints.