Benchmark long-lived PET sessions, real concurrent resolves, and inventory scaling

Start with crates/pet/tests/e2e_performance.rs and .github/workflows/perf-tests.yml, including the linked cold/warm summary and concurrent-resolve test; review dependencies #531, #529, and #530 before designing the workload. Done means CI runs reproducible long-lived and actually concurrent scenarios, catches identity replacements, reports calibrated latency/resource measurements, and documents fast versus stress invocations.

Tracking plan: #528
Priority: P2, required before structural performance optimization. Evidence: source inspection and existing benchmark inventory.

Problem

The gated summary starts a fresh PET process for both members of every cold/warm pair. It measures persisted-cache warmth, not repeated operations in a long-lived VS Code session. The function named test_concurrent_resolve_performance actually resolves sequentially, and the workflow selects only the summary test. Inventory checks compare counts, not identities.

The exact-audit-revision release workload contains only 5 environments on Linux, 8 on Windows, and 10 on macOS. This cannot establish bounds on thread growth, cache retention, or large workspace behavior. Existing real-manager benchmarks remain valuable and should not be replaced.

Sources: cold/warm summary, sequential concurrent-resolve test, performance workflow.

Scope

Add a deterministic fixture workload alongside the installed-manager benchmark. Separate process-cold/disk-warm/same-process-warm scenarios, and exercise actual overlapping refresh/resolve/configure activity. Sweep representative inventory/workspace sizes (for example 1, 10, 100, and 1000), with expensive stress/soak variants isolated from the fast PR gate if necessary.

Measure client latency, first-result latency, peak workers/threads, subprocess counts, cache/resource growth, and retained memory where reliable platform APIs exist. Compare normalized environment/manager identities, not just counts. Keep diagnostic output privacy-safe and ensure measurement does not backpressure the timed transport.

Acceptance criteria

• CI runs a repeated-refresh workload against one server process and an actually concurrent resolve workload; test naming and selection match behavior.
• Create/delete/edit/alias-churn scenarios verify fresh, correctly identified environments in a long-lived process.
• Inventory assertions detect one environment disappearing and another replacing it even when counts match.
• Size/concurrency sweeps produce usable latency and resource measurements with explicit sample counts and reproducible fixtures.
• Resource expectations/budgets are calibrated from measurements rather than arbitrary performance claims or unstable host-wide counters.
• Fast deterministic checks remain PR-friendly; longer stress runs have a documented invocation and CI schedule/entry point.

Dependencies

Depends on #531 for accurate timing definitions and #529 for reliable process teardown. Reuse the subprocess fixtures/cleanup contract from #530. Outputs establish the baseline for bounded scheduling, output-lock isolation, and Poetry indexing under #528.