Session Event Persistence

VT Code stores the authoritative vtcode_exec_events::ThreadEvent stream for interactive and exec sessions at:

<workspace>/.vtcode/sessions/<session_id>/events.jsonl

The session directory also contains the manifest, turn index, and derived artifacts. The canonical event sink uses bounded, non-blocking handoffs to a dedicated blocking drain. Filesystem I/O does not run on the async executor. If a bounded queue fills, persistence fails closed and the run cannot be reported as successful; accepted events are drained before the failure is returned. A run may be reported as successful only after its terminal thread.completed event and the canonical drain have completed successfully.

agent.harness.event_log_path and exec --events are explicit compatibility exports. They are optional, independently bounded, and may report drops or write failures without changing the canonical event contract. No global ~/.vtcode/sessions harness file is created by default. ATIF and Open Responses exports configured by the interactive harness are derived under <session>/derived/.

Retention defaults to 50 sessions or 30 days. It operates after session closure/startup on a blocking task, preserves active/current sessions, skips symlinks, and removes only validated direct children of the sessions root.

Verification:

cargo nextest run -p vtcode-memory
cargo nextest run -p vtcode-core -E 'test(/session_store_sink|event/)'
cargo nextest run -p vtcode -E 'test(/harness/)'