Kpa-clawbot 59bff5462c fix: rate-limit cache invalidation to prevent 0% hit rate (#533) (#546) ...

## Summary

Fixes #533 — server cache hit rate always 0%.

## Root Cause

`invalidateCachesFor()` is called at the end of every
`IngestNewFromDB()` and `IngestNewObservations()` cycle (~2-5s). Since
new data arrives continuously, caches are cleared faster than any
analytics request can hit them, resulting in a permanent 0% cache hit
rate. The cache TTL (15s/60s) is irrelevant because entries are evicted
by invalidation long before they expire.

## Fix

Rate-limit cache invalidation with a 10-second cooldown:

- First call after cooldown goes through immediately
- Subsequent calls during cooldown accumulate dirty flags in
`pendingInv`
- Next call after cooldown merges pending + current flags and applies
them
- Eviction bypasses cooldown (data removal requires immediate clearing)

Analytics data may be at most ~10s stale, which is acceptable for a
dashboard.

## Changes

- **`store.go`**: Added `lastInvalidated`, `pendingInv`, `invCooldown`
fields. Refactored `invalidateCachesFor()` to rate-limit non-eviction
invalidation. Extracted `applyCacheInvalidation()` helper.
- **`cache_invalidation_test.go`**: Added 4 new tests:
- `TestInvalidationRateLimited` — verifies caches survive during
cooldown
  - `TestInvalidationCooldownAccumulatesFlags` — verifies flag merging
- `TestEvictionBypassesCooldown` — verifies eviction always clears
immediately
- `BenchmarkCacheHitDuringIngestion` — confirms 100% hit rate during
rapid ingestion (was 0%)

## Perf Proof

```
BenchmarkCacheHitDuringIngestion-16    3467889    1018 ns/op    100.0 hit%
```

Before: 0% hit rate under continuous ingestion. After: 100% hit rate
during cooldown periods.

Co-authored-by: you <you@example.com>

2026-04-03 13:53:58 -07:00

..

ingestor

test: push ingestor coverage from 70% to 84% (#344) (#492)

2026-04-02 17:31:47 -07:00

server

fix: rate-limit cache invalidation to prevent 0% hit rate (#533) (#546)

2026-04-03 13:53:58 -07:00