Add agents.interrupt_message for interruption markers (#19351)

## Why

Agent interruptions currently always persist a model-visible
interrupted-turn marker before emitting `TurnAborted`. That marker is
useful by default because it gives the next model turn context about a
deliberately interrupted task, but some deployments need to suppress
that history injection entirely while still keeping the client-visible
interruption event.

## What changed

- Add `[agents] interrupt_message = false` to disable the model-visible
interrupted-turn marker.
- Resolve the setting into `Config::agent_interrupt_message_enabled`,
defaulting to `true` so existing behavior is unchanged.
- Apply the setting to both live interrupted turns and interrupted fork
snapshots.
- Keep emitting `TurnAborted` even when the history marker is disabled.
- Regenerate `core/config.schema.json` for the new
`agents.interrupt_message` field.

## Testing

- `cargo test -p codex-core load_config_resolves_agent_interrupt_message
-- --nocapture`
- `cargo test -p codex-core
disabled_interrupted_fork_snapshot_appends_only_interrupt_event --
--nocapture`
- `cargo test -p codex-core
multi_agent_v2_interrupted_marker_uses_developer_input_message --
--nocapture`
- `cargo test -p codex-core
multi_agent_v2_followup_task_can_disable_interrupted_marker --
--nocapture`
- `cargo test -p codex-core
multi_agent_v2_followup_task_interrupts_busy_child_without_losing_message
-- --nocapture`
- `cargo check -p codex-core`

codex-rs/config/src/config_toml.rs

@@ -566,6 +566,9 @@ pub struct AgentsToml {
     /// Default maximum runtime in seconds for agent job workers.
     #[schemars(range(min = 1))]
     pub job_max_runtime_seconds: Option<u64>,
+    /// Whether to record a model-visible message when an agent turn is interrupted.
+    /// Defaults to true.
+    pub interrupt_message: Option<bool>,
 
     /// User-defined role declarations keyed by role name.
     ///