spec/v0.9.0

## [0.9.0] — 2026-08-28

Spec version: `0.9.0`

### Added

- Automation catalogue and automation-run channels, including self-contained host-defined event triggers and automation-origin messages, for shared trigger-based agent session workflows.
- Turn errors are durable response parts, and resumable errors can reopen the same turn through `chat/turnResume`.
- `InitializeResult._meta` for hosts to advertise implementation-specific extension capabilities in initialize responses.

### Changed

- Annotations now carry an `origin` with a required session URI and optional chat URI and turn ID.
- Renamed the failed session lifecycle value from `creationFailed` to `failed`.
- `TerminalSessionClaim` now requires the chat URI that owns the terminal.
- Terminal state now uses an explicit `running`/`exited` lifecycle that preserves exits without an exit code.
- Generated clients now preserve unknown values for nonexhaustive protocol enums and their discriminated unions.
- `SessionToolClientExecutionRequest.toolCall` is narrowed to a running tool-call state.
- Automation catalogue snapshots now use `AutomationState.entries`, whose items are named `AutomationEntry`.

### Removed

- Removed `error` from `changeset/contentChanged`; changeset failures are represented by `changeset/statusChanged`.
- Removed session-level forking from `createSession`; use chat forking instead.
- `ContentNotFound` is no longer an exported AHP error code; `-32006` remains reserved and unassigned.

### Fixed

- Chat reducers now derive `modifiedAt` from turn action data instead of local wall clocks.