chore(retrieval,history,recall): review fixes and test coverage [skip-tag]

[lIang70]

Summary

Apply review fixes across sdk/retrieval, sdk/history, and sdk/recall, plus the supporting tests. This is a maintenance batch with no release-relevant API changes — [skip-tag] is set in the title so auto-tag.yml's patch bumper does not roll a tag for this merge.

retrieval — high priority correctness

• HybridShortCircuit forwards Debug. Previously SearchRequest.Debug was dropped on the native-hybrid path; backends that honour Capabilities.Debug now receive it and the pipeline merges their SearchExecution into the response so callers observe one consistent explanation regardless of which path ran.
• Stable lane order. Pipeline.Run emits SearchExecution.Lanes by well-known LaneKey first, then lexical, so dashboards / golden tests don't flake from Go map iteration order.
• pickFinalish no longer aliases Reranked / Fused. Lifting now shallow-copies, so in-place rescoring stages (BM25Boost, TimeDecay, EntityBoost, ...) cannot retroactively corrupt earlier snapshots.
• BM25Boost uses ±Inf seeds for clearer min/max semantics.
• MemoryIndex.Search drops MinScore on the hybrid (RRF) branch. RRF scores live on a different scale than raw BM25/cosine; SearchRequest.MinScore now documents the single-modality contract. Hybrid filtering should use pipeline.ScoreThreshold.
• Removed dead liftRecall short-circuit guard; LTM factory expresses the "BM25 is a boost, not a recall expander" rule via a clearer addBM25Boost local.

retrieval — small but visible

• normalizeJSONish coerces every numeric kind to float64 — Filter.Eq{"score": 5} now matches metadata decoded as float64(5).
• PartialError reports only failing rows; empty form is now stable.
• journal.Wrap projects the inner backend's optional sub-interfaces (DocGetter / Filterable / DeletableByFilter / Droppable / Iterable / Snapshottable / Hybridable / Vectorizable) and fans bulk DeleteByFilter / Drop into per-doc OpDelete events so the audit log stays complete.
• EmbedQuery cache gains MaxEntries (default 1024) with TTL-aware eviction; -1 disables caching.
• Entity recall lane scores by overlap count (was constant 1.0), giving WeightedFusion / RRF a real signal.
• stages_rerank.go switches to math.Sqrt; the hand-rolled Newton iteration is gone.
• types.go documents every Filter field and the reserved _content key.
• sdkx/retrieval/{postgres,sqlite}: List doc notes the in-memory scan cost and points bulk export at Iterate; the new offset >= len(all) guard short-circuits stale page tokens.

history / recall

• history.{compactor,store,tools,archive,doc} — same review pass: refines compactor coordination, adds dedicated coordinator / token / tools tests, folds deprecated knobs into a focused deprecated.go surface.
• recall.{recall,save,sweeper,merger,memory,telemetry} — introduces namespace_registry as the single authority for ns → backend lookup, hardens save / sweep semantics, surfaces telemetry counters.
• Adds regression tests for explain output, save context, sweep, and merger so the contract surface is locked in.

Tests added

• retrieval: errors_test.go, filter_match_test.go, explain_test.go, plus pipeline/{stages_boost,stages_query,pipeline}_test.go additions for lane-order stability, hybrid Debug forwarding, and pickFinalish isolation; journal/wrap_test.go covers sub-interface delegation and bulk-delete journaling.
• history: coordinator_test.go, store_test.go, summary_store_test.go, token_test.go, tools_test.go.
• recall: merger_test.go, namespace_registry_test.go, recall_explain_test.go, save_context_test.go, sweeper_test.go, test_helpers_regression_test.go.

Test plan

• go vet ./sdk/... ./sdkx/...
• go test ./sdk/... ./sdkx/...
• CI green

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