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# vtcode-exec-events [Root AGENTS.md](../AGENTS.md) | Authoritative `ThreadEvent` contract. All runtime events flow through this crate. ## Key Types `ThreadEvent` enum — the single event type (serde-tagged) | `VersionedThreadEvent` wrapper with schema version | `EventEmitter` trait | `Usage` token accounting | `ThreadItem` + `ThreadItemDetails` item taxonomy | `EVENT_SCHEMA_VERSION` semver string ## ThreadEvent Variants `thread.started` | `thread.completed` | `thread.compact_boundary` | `context.reset` | `turn.started` | `turn.completed` | `turn.failed` | `turn.blocked` | `item.started` | `item.updated` | `item.completed` | `plan.delta` | `plan.approval.requested` | `plan.approval.resolved` | `error` ## Rules - **Do not invent parallel event types.** Extend `ThreadEvent` and `ThreadItemDetails` enums. - `EVENT_SCHEMA_VERSION` must be bumped when the serialized contract changes. - `EventEmitter` trait has a blanket `FnMut(&ThreadEvent)` impl. - Feature-gated emitters: `telemetry-log` (LogEmitter), `telemetry-tracing` (TracingEmitter), `schema-export` (JSON Schema), `serde-json` (JSON helpers). - `atif/` module exports ATIF (Agent Trace Interchange Format). - `trace/` module implements Agent Trace spec for AI code attribution. ## Gotchas - `vtcode-core::exec::events` re-exports these types — consumers should use that path, not depend on this crate directly. - Plan approval state is represented by `PlanApprovalRequestedEvent` and `PlanApprovalResolvedEvent`; keep `PlanApprovalDecision` stable because it is consumed by headless clients and Open Responses adapters. Bounded failure explanations use the existing `ReasoningItem` with stage `"diagnosis"`; do not add a parallel event variant. - `HarnessEventItem` uses `HarnessEventKind` enum — adding variants requires schema version bump. - Schema `0.12.0` adds blocked-handoff resolution metadata; keep legacy payloads readable and ATIF output stable. - Schema `0.14.0` adds `SessionToolLimitIncreased` and `ToolLoopLimitIncreased` harness kinds for same-turn limit grants; schema `0.13.0` added `turn.blocked` plus `TurnBlocked`/`BlockedRecoveryStarted`/`BlockedRecoveryFinished`, emitted alongside `turn.failed` with fuse counters for UI subscribers.