The post-merge review on #584 surfaced two real bugs in the new
summary-call telemetry:
1. The cache-hit percentage used `cache_hit + cache_miss` as the
denominator. Providers that populate `prompt_cache_hit_tokens` but
leave `prompt_cache_miss_tokens` as `None` (the rest of the codebase
already infers misses from `input_tokens` for cost reporting and
`/cache`) were silently reported as a flat 100% hit rate, masking the
actual ratio. Switch the denominator to `usage.input_tokens` so the
ratio matches how the rest of the project reasons about cache spread.
Extract the calc into a small `summary_cache_hit_percent` helper so
the invariant is unit-testable.
2. The doc comment on the emit site advertised that
`RUST_LOG=deepseek_tui::compaction=debug` would also work as a
filter. It does not — `EnvFilter` matches the explicit target string
when one is set, so only `RUST_LOG=compaction=debug` activates the
event. Drop the misleading parenthetical and call out the filter
semantics explicitly.
The new unit test pins the partial-telemetry guard so a future regress
to `(hit + miss)` denominator would be caught immediately.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Hunter Bown
dcadb5d388