chore: add cache hit/miss instrumentation to pagination total cache

[ctron]

Summary

• Add #[instrument] to PaginationCache::cached_total with the cache key and a cache_hit field
• Defaults to cache_hit = true; the init closure sets it to false when actually called (cache miss)
• Helps diagnose whether the pagination total cache is working as expected

Test plan

• Verify cache_hit field appears in traces for paginated list endpoints
• Confirm first request shows cache_hit=false, subsequent identical requests show cache_hit=true

🤖 Generated with Claude Code

Summary by Sourcery

Enhancements:

• Add tracing instrumentation to pagination total cache lookups, including a cache_hit field that distinguishes between cache hits and misses.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds tracing instrumentation to PaginationCache::cached_total to record cache hits vs misses for pagination total caching, wiring the cache key into the span and toggling a cache_hit field based on whether the cache initialization closure runs.

Sequence diagram for cache hit/miss instrumentation in PaginationCache::cached_total

sequenceDiagram
    actor Caller
    participant PaginationCache
    participant Cache
    participant tracing

    Caller->>PaginationCache: cached_total(key, compute)
    PaginationCache->>tracing: span with field cache_hit = true
    PaginationCache->>Cache: try_get_with(key, compute)
    alt cache miss (init closure runs)
        Cache->>tracing: Span::current().record(cache_hit, false)
        Cache->>PaginationCache: compute().await result
    else cache hit (value already cached)
        Cache-->>PaginationCache: cached result (cache_hit remains true)
    end
    PaginationCache-->>Caller: total_count

Loading

File-Level Changes

Change	Details	Files
Instrument pagination total cache lookups with a tracing span that records cache hits versus misses.	Import tracing::instrument for use with function-level instrumentation. Add #[instrument(skip(self, compute), fields(cache_hit = true))] to PaginationCache::cached_total so calls are traced with cache_key and a default cache_hit=true field without logging self or the compute closure. Inside the cache miss initialization closure, increment the misses counter and record cache_hit=false on the current span before invoking compute().	common/src/db/pagination_cache.rs

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[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="common/src/db/pagination_cache.rs" line_range="72" />
<code_context>
         self.cache
             .try_get_with(key, async {
                 misses.add(1, &[]);
+                tracing::Span::current().record("cache_hit", false);
                 compute().await
             })
</code_context>
<issue_to_address>
**suggestion (bug_risk):** Be cautious relying on `Span::current()` inside the `try_get_with` async closure.

Because `try_get_with` controls how the async closure is scheduled, it may run on a different task where the `#[instrument]` span is no longer current, making this `record` call a no-op or updating the wrong span. If you need reliable instrumentation, capture the span at the start of `cached_total` (e.g. `let span = tracing::Span::current();`) and call `span.record("cache_hit", false);` inside the closure instead of using `Span::current()` there.
</issue_to_address>

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[sourcery-ai]

suggestion (bug_risk): Be cautious relying on Span::current() inside the try_get_with async closure.

Because try_get_with controls how the async closure is scheduled, it may run on a different task where the #[instrument] span is no longer current, making this record call a no-op or updating the wrong span. If you need reliable instrumentation, capture the span at the start of cached_total (e.g. let span = tracing::Span::current();) and call span.record("cache_hit", false); inside the closure instead of using Span::current() there.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.41%. Comparing base (551117a) to head (ce4c8bb).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2443      +/-   ##
==========================================
+ Coverage   71.39%   71.41%   +0.01%     
==========================================
  Files         453      453              
  Lines       27254    27251       -3     
  Branches    27254    27251       -3     
==========================================
+ Hits        19459    19460       +1     
+ Misses       6666     6657       -9     
- Partials     1129     1134       +5     

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[ctron]

/backport

[trustify-ci-bot]

Successfully created backport PR for release/0.5.z:

• chore: add cache hit/miss instrumentation to pagination total cache [Backport release/0.5.z] #2447