perf(resolution): worker connection recycling — WAL-depth writes-under-readers fix, superphase −11.4% at 8c (#1362)

The §7a.6 anomaly probed to its mechanism with five discriminating runs
(§7a.7 table): main-thread B-tree writes triple under attached readers
because READERS PIN WAL checkpoint progress — the deep WAL taxes every
writer page operation (deletes 42.6s pool-off vs 118.8s pool-4 on
identical hardware; an aggressive 64MB valve recovers the writes but
overpays +129s in full-park folds; the v2 cache resurrection was
falsified — long-tail name traffic is uncacheable at any capacity).

Fix: workers close and reopen their read-only connections every 8
batches at the double-buffer's worker-idle boundary
(ResolverPool.recycleWorkers + QueryBuilder.rebind + a cadence call).
Reopens are sub-millisecond, resolver caches survive (only prepared
statements re-prepare), and the existing checkpoints advance instead of
parking. Failed recycle downgrades to sequential, same as a failed
fan-out.

Measured (8c pool-4, linux v7.2-rc2, cadence 25 → 8 iterated):
resolution superphase 715.0 → 633.6s (−11.4%), envelope best 14.8min,
recreate 59.7 → 45.3s. Byte-neutral everywhere: git dumps byte-identical
old-vs-new, linux dump sha 6dd1185b reproduced (10,446,478 lines),
counts 2,049,153/6,413,518, suite 2517 green. 2c unchanged by
construction (no pool → no recycling).

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -21,6 +21,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - `codegraph install` and `codegraph upgrade` now offer CodeGraph Pro beta access after finishing — answer yes, type your email, and you join the same waitlist as the getcodegraph.com homepage form. Strictly opt-in and asked at most once per machine total: nothing is sent unless you say yes and enter an email, either answer is remembered so no later install or upgrade ever re-asks, and non-interactive runs (`--yes`, scripts, CI) never see the question.
 - Every release is now cryptographically verifiable: npm packages publish with npm provenance (the "Provenance" badge on npmjs.com, proving each version was built by this repository's release workflow from a specific commit), and the GitHub Release bundles carry signed build attestations you can check with `gh attestation verify <file> -R colbymchenry/codegraph`.
 - Indexing inside CPU- or memory-limited containers (Docker, CI runners) now sizes its worker pools from the container's actual allowance instead of the host machine's, and giant codebases no longer balloon temporary database files during indexing (previously tens of GB of transient disk on Linux-kernel-scale projects). Together these prevent out-of-memory and out-of-disk failures on constrained machines; set `CODEGRAPH_RESOLVE_WORKERS` to override the resolution worker count explicitly.
+- Indexing very large projects on multi-core machines got faster again: the parallel-resolution workers now periodically refresh their read-only database connections, which lets database housekeeping advance instead of silently building up a backlog behind long-lived readers — a backlog that was taxing the indexer's own writes. Graphs remain byte-for-byte identical; the win is largest at Linux-kernel scale on many-core machines.
 
 ### Fixes