## Summary
Adds observability to the task metadata cache that backs the trigger hot
path. Follow-up to #3930, which made locked-version triggers fall back
to the primary when the read replica returns no row; this makes the
cache's effectiveness (and that fallback) measurable instead of
inferred.
## What it emits
A single bounded counter `task_meta_cache.resolve`, labeled by lookup
path (`locked` / `current`) and the source that satisfied it (`cache` /
`replica` / `writer` / `miss`):
- `cache / total` is the cache hit rate (its inverse is how cold the
cache runs).
- `writer / total` is how often the read replica returned empty for a
row the primary had (the condition #3930 recovers from).
Labels are bounded, with no per-env / worker / slug cardinality.
TRI-10873
Eric Allam