Performance tooling

Two different tools for two jobs:

Tool	Job
serenade-profiler (Web Debug Toolbar)	Per-request browser inspect in dev: routing, timing, logs, SQL, debug notes, views
hotpath (optional app dependency)	Function / async / I/O performance reports (timing, allocations). Not a request toolbar

Serenade does not hard-depend on hotpath in kernel or HTTP crates. Apps opt in.

When to use which

• Debugging “why is this request wrong?” → enable the profiler toolbar.
• Finding “why is this function slow?” → enable hotpath features on the app binary.

App recipe (optional features)

In an application Cargo.toml (example: examples/demo-html):

[features]
default = []
hotpath = ["dep:hotpath"]
hotpath-alloc = ["hotpath", "hotpath/hotpath-alloc"]

[dependencies]
hotpath = { version = "0.28", optional = true, default-features = false }

Instrument with #[cfg_attr(feature = "hotpath", hotpath::measure)] on hot functions, and wrap the binary entry with hotpath’s main/guard when the feature is on. See hotpath docs.

Default make / CI builds without these features (no hotpath compile in the normal gate).

# Normal (CI)
cargo run -p serenade-demo-html

# Local performance report
cargo run -p serenade-demo-html --features hotpath

Non-goals

• Replacing serenade-profiler with hotpath
• Pulling hotpath into serenade-kernel / serenade-http
• Requiring hotpath in org CI