refactor(query): delete the dead valuesEqual seam

[zzal]

Part II Wave 1 · #4 — a threaded-but-unused witness

A type-erased Value-equality witness was allocated per query per render and threaded through the whole stack — built in observe(), carried on QueryObservation, stored on QueryEntry — and never called. The comment at commitFetch said it was "reserved" for select change-detection.

Why delete, not wire

Tracing the notify path shows the witness is unusable in its threaded shape, not merely unused. The audit's caveat ("must not suppress the isFetching → false transition") isn't an edge case — it's every commit:

• commitFetch always flips inFlight non-nil → nil
• QueryState exposes that as isFetching
• the client can't know which subscribers render it

→ under the whole-snapshot model there is no settle notify that can be safely value-gated — gating would freeze SWR spinners. Real gating needs select-style subscriptions (components declare the projection they read; notify gates on projection inequality, with isFetching observed separately) — and that witness compares selected projections, not raw Values. Today's witness was mis-shaped for its own intended future.

Change

• Deleted end-to-end: observe()'s closure, QueryObservation.valuesEqual, QueryEntry.valuesEqual + its init (now implicit), and 27 ceremonial test-fixture sites.
• The analysis is recorded at commitFetch's notify — notify-per-settle is documented as deliberate, with the select design inheriting the reasoning.
• Kept Query.Value: Equatable — the zero-cost reserved door for future select (re-adding the constraint later would be source-breaking; the dead runtime plumbing was the waste, not the one-word declaration).
• Bonus: drops a closure allocation per query per render.

Verification

Pure dead-code deletion — no behavior change possible (nothing read it); the existing suites are the pin:

• SwiflowQuery suite (incl. the state-machine fuzz): 126/126
• Full host suite: 1379 tests, 277 suites green
• QueryDemo wasm build clean

🤖 Generated with Claude Code

[github-actions]

📦 Bundle size

Artifact	Baseline	This PR	Δ
App.wasm	5.06 MB	5.15 MB	+1.90%
App.wasm (gzip)	1.80 MB	1.84 MB	+2.19%
JS runtime	54.5 KB	54.5 KB	+0.00%
JS runtime (gzip)	11.3 KB	11.3 KB	+0.00%
Total (gzip)	1.81 MB	1.85 MB	+2.17%

✅ Within budget (≤5% growth allowed).

_{Baseline: Swift 6.3, WASM SDK 6.3-RELEASE, measured 2026-06-18.}