HydraCache 0.26.0

HydraCache 0.26.0

Status: published.

0.26.0 is a hot-path and allocation hardening release. After the 0.25.0
owner-side loading work, the next step is to make sure optional listeners and
diagnostics do not add unnecessary allocation cost to ordinary local cache
operations.

Highlights

• Added internal event-publication preflight before owned CacheEvent
  construction.
• Made key, tag, cache, and single-flight event construction lazy on
  unobserved paths.
• Kept listener APIs source-compatible.
• Added focused tests for subscriber and no-subscriber behavior.
• Added allocation/performance smoke coverage for event publication modes.
• Added POST /demo/events/preflight/run to explain event preflight behavior
  in the sandbox and Swagger/OpenAPI lab.
• Added README, rustdoc, and testing-doc examples for the listener cost model.

Intended Shape

Applications should keep using the same listener API:

use hydracache::{CacheEventKind, CacheOptions, HydraCache};

# async fn example() -> hydracache::CacheResult<()> {
let cache = HydraCache::local().build();
let mut events = cache.subscribe_mutations();

cache
    .put("user:42", "Ada".to_owned(), CacheOptions::new().tag("users"))
    .await?;

let event = events.recv().await.expect("event");
assert_eq!(event.kind(), CacheEventKind::Stored);
# Ok(())
# }

The release changes the internal cost model, not the public behavior: when no
subscriber exists, HydraCache skips building the owned event payload. Access
events still need both subscribe_access() and enable_access_events(true).

The sandbox route reports four scenarios:

• no subscriber: attempted cache operations publish zero events;
• mutation subscriber: mutation events are observed and counted;
• access subscriber with access events disabled: hit/miss streams stay silent;
• access subscriber with access events enabled: access events are observed.

Validation

Focused checks:

cargo test -p hydracache --lib --locked events::tests::preflight
cargo test -p hydracache --lib --locked cache::tests::lazy
cargo test -p hydracache --test performance_smoke --locked event_preflight
cargo test -p hydracache-sandbox --locked swagger_api_exercises_library_features_and_reports
cargo test --doc -p hydracache --locked

Expected full release gate:

cargo fmt --all -- --check
cargo check --workspace --all-targets --locked
cargo test --workspace --locked
cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
cargo test --doc --workspace --locked
$env:RUSTDOCFLAGS='-D warnings'; cargo doc --workspace --no-deps --locked

See
the 0.26.0 plan
for the implementation checklist.