[diegosouzapw]

Closes #13891

Root cause

getPricingForModel() (src/lib/db/settings/pricing.ts) called the uncached
getPricing() on every invocation instead of the getCachedPricing() helper
that already exists in src/lib/db/readCache.ts (30s TTL, invalidated on
every pricing write via touchPricing() -> invalidateDbCache("pricing")).

usageStats.getUsageStats() calls calculateAggregateCost() -> calculateCost()
-> getPricingForModel() once per GROUP BY row — up to 531 times on the
reporter's 45k-row usage_history table — so every /api/usage/history request
re-ran a synchronous 3-SELECT + JSON.parse + merge cycle against key_value
hundreds of times, blocking the event loop for ~5s.

Fix: swap the internal call inside getPricingForModel() from getPricing() to
getCachedPricing(). The exported getPricing() / getPricingWithSources()
functions are untouched — callers that need a guaranteed-fresh read (pricing
admin route, sync jobs) keep using them directly.

I audited every pricing writer (pricing.ts, pricingSync.ts,
modelsDevSync.ts) — all three namespaces (pricing, pricing_synced,
models_dev_pricing) already call invalidateDbCache("pricing") on write, so
this does not introduce any new staleness window beyond the existing 30s TTL
that other callers of getCachedPricing() already tolerate.

Regression test

tests/unit/pricing-for-model-cached-13891.test.ts

• RED (pre-fix, run against unfixed code): 20 calls to getPricingForModel()
  triggered 60 db.prepare() calls (3 SELECTs × 20, zero caching).
• GREEN (post-fix): the same 20 calls trigger ≤3 db.prepare() calls.
• A second test proves cache invalidation: a lookup before updatePricing()
  returns the old value, and the very next lookup after the write returns the
  fresh value — confirming a stale price cannot silently persist past a write.

node --import tsx/esm --test tests/unit/pricing-for-model-cached-13891.test.ts
# tests 2, pass 2, fail 0

Gates run

• node scripts/check/check-file-size.mjs — no violation on touched files
• node scripts/check/check-complexity.mjs — OK (2857 ≤ baseline 3218)
• node scripts/check/check-cognitive-complexity.mjs — OK (1291 ≤ baseline 1437)
• npm run typecheck:core — exit 0
• npx eslint --suppressions-location config/quality/eslint-suppressions.json src/lib/db/settings/pricing.ts tests/unit/pricing-for-model-cached-13891.test.ts — exit 0
• New test: 2/2 pass (RED→GREEN evidence above)
• Existing pricing regression suite — all pass:
  pricing-sync-memoization.test.ts (3/3), pricing-route-sources.test.ts (1/1),
  pricing-sync-extended.test.ts (6/6), tier-pricing-cache.test.ts (4/4),
  db-read-cache.test.ts (10/10)
• node scripts/check/check-changelog-integrity.mjs — OK

⚠️ base-red inherited: #14004 — docs env/docs contract (fixed separately in #14022), chatHelpers file-size drift

[diegosouzapw]

Validated in local merge-train /tmp/mt-train3b.log on 192.168.0.113 @ train tip 408e2128791696a18966681953136fc96aeb99b0 (32 PRs boarded): static gates green; full test:unit 40694 tests, 17 failing — every one reproduces on the pure release tip (base-red sweep list), zero new reds. Merged --admin per merge-gates §4/§7.