docs(adr,architecture): finalize ADRs 0005–0009 + extend reviewer checklist (Step 1.1f)

[officialCodeWork]

Summary

Closes the Phase-1 refactor window (Steps 1.1a–1.1f) by:

• Promoting ADRs 0005–0009 from "Accepted (draft)" to "Accepted with implementation-path backlinks" — each ADR now has an explicit table pointing to the concrete files / SPI surfaces that realise it, plus the PRs in which the implementation landed.
• Extending the reviewer checklist in docs/architecture/performance.md so every one of the five ADRs is covered by an explicit item reviewers can apply at PR time.
• Adding module-level ADR backlinks to the two SPI files that were missing them: rag_core.spi.reranker (ADR-0006) and rag_core.spi.storage (ADR-0007). All other relevant modules (rag_core.types, rag_core.spi.vector_store, the three cache SPIs, rag_policy.*, the vector backends) already carried ADR references from earlier steps.

After this PR, Step 1.2 (Connectors framework) is the next actionable step.

Per-ADR finalization

ADR	Decision	Implementation already landed in
ADR-0005 — PolicyEngine PDP	Single SPI for ACL / PII / quotas / redaction; coverage linter on every call site.	Step 1.1c, #46
ADR-0006 — Two-stage rerank	fast_rerank (ChunkRef) + precise_rerank (Chunk) + should_early_exit from day 1.	Decision now; SPI lands in Step 2.7
ADR-0007 — Tiered storage with BlobRef	Chunk.text: str | BlobRef; resolution via existing Storage SPI.	Step 1.1a, #44
ADR-0008 — Cost-aware planner	QueryPlan / PlanNode / Cost / Budget / StageEvent; planner mutates plan before dispatch.	Step 1.1a, #44
ADR-0009 — Vector index strategy + quantization	IndexHint selects index by scale tier; Embedding.dtype enables int8 / binary quantization.	Steps 1.1a / 1.1b, #44 / #45

Reviewer checklist extensions

docs/architecture/performance.md already had 11 items covering ctx-threading, ACL, logging, queue-bounding, Pydantic discipline, PolicyEngine call sites, hydration discipline, Batcher, p99 budgets, cache-key correctness, and BlobRef-safety. This PR:

• Tags BlobRef-safe with (ADR-0007).
• Adds Plan + budget aware — new code consumes QueryPlan + RequestContext.budget; nodes carry estimated_cost; emits StageEvent for the online cost estimator. (ADR-0008)
• Adds Index-hint + dtype honored — new VectorIndexBackend code accepts IndexHint at initialize() and respects Embedding.dtype on read and write. (ADR-0009)
• Adds Two-stage rerank shape — new Reranker implementations (Step 2.7+) ship the three-method cascade, not a single rerank(). (ADR-0006)
• Cross-links all 5 ADRs (not just 0006 / 0008 / 0009) from the "Related" section.

TRACKER sync

• Step 1.1e: 🚧 → ✅, PR #51 recorded.
• Step 1.1f: ⏳ → 🚧 on this branch.
• Phase 1 progress: 5 / 16 → 7 / 16; total 18 / 84 → 20 / 84.
• "Next action" line advanced to Step 1.2 (Connectors framework).
• PR history table updated with #51.

Documentation

File	Change
docs/adr/ADR-0005-policy-engine.md	Implementation table (engine, types, filter, noop, writer, coverage linter); status note; performance.md backlink.
docs/adr/ADR-0006-two-stage-rerank.md	Implementation-status note; performance.md backlink.
docs/adr/ADR-0007-tiered-storage.md	Implementation table (BlobRef, Chunk, Storage); reviewer-rule backlink.
docs/adr/ADR-0008-cost-aware-planner.md	Implementation table (Cost, PlanNode, QueryPlan, Budget, StageEvent); request-context backlink.
docs/adr/ADR-0009-vector-index-strategy.md	Implementation table (IndexHint, WriteVolume, Embedding.dtype, vector SPI split, pgvector + Qdrant backends).
docs/architecture/performance.md	4 reviewer-checklist items added; ADR-0005 / 0007 added to "Related".
packages/core/src/rag_core/spi/reranker.py	Module docstring backlinks ADR-0006.
packages/core/src/rag_core/spi/storage.py	Module docstring backlinks ADR-0007.
TRACKER.md	1.1e ✅, 1.1f 🚧, milestone counts, "Next action", PR history.

Test plan

• uv run ruff check passes on touched Python files.
• uv run mypy --strict passes on touched Python files.
• Doc-only PR otherwise — no runtime / SPI shape changes; existing 1.1a–1.1e conformance suites continue to apply unchanged.
• CI: lint + mypy --strict + pytest + RAG001 logging check + log-schema gates green on Ubuntu / macOS / Windows.

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