## Why
`ext/goal` already had the tool specs and contributor wiring for
`/goal`, but the installed tools still depended on a placeholder backend
that always errored. That meant the extension could not actually own
goal persistence even though the dedicated `thread_goals` store already
exists.
This change wires the extension tools directly to the dedicated goal
store so the extension can create, read, and complete goals against real
state instead of falling back to host-side placeholders.
## What changed
- make `install_with_backend(...)` require
`Arc<codex_state::StateRuntime>` so goal storage is always available
when the extension is installed
- remove the unused no-backend/public backend abstraction from
`ext/goal` and have the tool executors talk directly to `StateRuntime`
- map `thread_goals` rows into the existing protocol response shape for
`get_goal`, `create_goal`, and `update_goal`
- preserve current thread-list behavior by filling an empty thread
preview from the goal objective when a goal is created through the
extension path
- add integration coverage for the installed tool surface, including
successful goal creation and duplicate-create rejection
## Testing
- `cargo test -p codex-goal-extension`
## Why
Goal creation and completion are moving through the goal extension, but
the rest of Codex still observes goal state through `ThreadGoalUpdated`
events. Without an event from the extension-owned tool path, a
model-initiated `create_goal` or `update_goal` can mutate the backend
and return a tool result while app-server and TUI listeners miss the
goal state transition.
## What changed
- Added `GoalEventEmitter` as a small wrapper around the host
`ExtensionEventSink` to build `EventMsg::ThreadGoalUpdated` events for
goal updates.
- Threaded the registry event sink into `GoalExtension` and the
`GoalToolExecutor`s created by the extension. The public
`GoalExtension::new` constructor keeps a `NoopExtensionEventSink`
fallback for standalone use.
- Emitted a goal update after successful `create_goal` and `update_goal`
tool calls. Until `ToolCall` exposes the current turn submission id,
these events use the tool call id as the event id and leave `turn_id`
unset.
Relevant code:
-
[`GoalEventEmitter::thread_goal_updated`](https://github.com/openai/codex/blob/1fe2d73890df9a50996f67f705d4da4cc3d4b866/codex-rs/ext/goal/src/events.rs#L19-L32)
- [`GoalToolExecutor` emission
points](https://github.com/openai/codex/blob/1fe2d73890df9a50996f67f705d4da4cc3d4b866/codex-rs/ext/goal/src/tool.rs#L161-L190)
## Testing
- `cargo test -p codex-goal-extension`
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