Module session_metrics 

Session hot-path observability.

Thread-safe atomic counters and timing for save/append/serialize/IO operations. Gated behind PI_PERF_TELEMETRY=1 for zero overhead in production: when disabled, all recording methods are instant no-ops.

Design

• TimingCounter: atomic count + total microseconds + max microseconds.
• ByteCounter: atomic count + total bytes.
• SessionMetrics: composes counters for every instrumented phase.
• ScopedTimer: RAII guard that records elapsed time on drop.
• global(): returns &'static SessionMetrics (lazy-initialized once).

Integration points

Currently instrumented (files owned by this bead):

• session_sqlite.rs: save, load, metadata load
• session_index.rs: lock acquisition, upsert, list, reindex

Future instrumentation (requires session.rs access):

• Session::save() JSONL path: queue wait, serialization, IO, persist
• Session::append_*(): in-memory append timing

Structs

ByteCounter

Atomic counter for tracking bytes written/read.

ByteSnapshot

Point-in-time snapshot of a ByteCounter.

MetricsSnapshot

Complete point-in-time snapshot of all session metrics.

ScopedTimer

RAII timer that records elapsed microseconds into a TimingCounter when dropped. If counter is None (metrics disabled), drop is a no-op.

SessionMetrics

Centralized session hot-path metrics collector.

TimingCounter

Atomic counter that tracks invocation count, cumulative time (µs), and peak time (µs) for a single instrumented phase.

TimingSnapshot

Point-in-time snapshot of a TimingCounter.

Functions

global

Return the global SessionMetrics singleton.