start of hooks engine (#13276)

(Experimental)

This PR adds a first MVP for hooks, with SessionStart and Stop

The core design is:

- hooks live in a dedicated engine under codex-rs/hooks
- each hook type has its own event-specific file
- hook execution is synchronous and blocks normal turn progression while
running
- matching hooks run in parallel, then their results are aggregated into
a normalized HookRunSummary

On the AppServer side, hooks are exposed as operational metadata rather
than transcript-native items:

- new live notifications: hook/started, hook/completed
- persisted/replayed hook results live on Turn.hookRuns
- we intentionally did not add hook-specific ThreadItem variants

Hooks messages are not persisted, they remain ephemeral. The context
changes they add are (they get appended to the user's prompt)

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -49,6 +49,14 @@ use codex_protocol::protocol::AskForApproval as CoreAskForApproval;
 use codex_protocol::protocol::CodexErrorInfo as CoreCodexErrorInfo;
 use codex_protocol::protocol::CreditsSnapshot as CoreCreditsSnapshot;
 use codex_protocol::protocol::ExecCommandStatus as CoreExecCommandStatus;
+use codex_protocol::protocol::HookEventName as CoreHookEventName;
+use codex_protocol::protocol::HookExecutionMode as CoreHookExecutionMode;
+use codex_protocol::protocol::HookHandlerType as CoreHookHandlerType;
+use codex_protocol::protocol::HookOutputEntry as CoreHookOutputEntry;
+use codex_protocol::protocol::HookOutputEntryKind as CoreHookOutputEntryKind;
+use codex_protocol::protocol::HookRunStatus as CoreHookRunStatus;
+use codex_protocol::protocol::HookRunSummary as CoreHookRunSummary;
+use codex_protocol::protocol::HookScope as CoreHookScope;
 use codex_protocol::protocol::ModelRerouteReason as CoreModelRerouteReason;
 use codex_protocol::protocol::NetworkAccess as CoreNetworkAccess;
 use codex_protocol::protocol::PatchApplyStatus as CorePatchApplyStatus;
@@ -288,6 +296,98 @@ v2_enum_from_core!(
     }
 );
 
+v2_enum_from_core!(
+    pub enum HookEventName from CoreHookEventName {
+        SessionStart, Stop
+    }
+);
+
+v2_enum_from_core!(
+    pub enum HookHandlerType from CoreHookHandlerType {
+        Command, Prompt, Agent
+    }
+);
+
+v2_enum_from_core!(
+    pub enum HookExecutionMode from CoreHookExecutionMode {
+        Sync, Async
+    }
+);
+
+v2_enum_from_core!(
+    pub enum HookScope from CoreHookScope {
+        Thread, Turn
+    }
+);
+
+v2_enum_from_core!(
+    pub enum HookRunStatus from CoreHookRunStatus {
+        Running, Completed, Failed, Blocked, Stopped
+    }
+);
+
+v2_enum_from_core!(
+    pub enum HookOutputEntryKind from CoreHookOutputEntryKind {
+        Warning, Stop, Feedback, Context, Error
+    }
+);
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct HookOutputEntry {
+    pub kind: HookOutputEntryKind,
+    pub text: String,
+}
+
+impl From<CoreHookOutputEntry> for HookOutputEntry {
+    fn from(value: CoreHookOutputEntry) -> Self {
+        Self {
+            kind: value.kind.into(),
+            text: value.text,
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct HookRunSummary {
+    pub id: String,
+    pub event_name: HookEventName,
+    pub handler_type: HookHandlerType,
+    pub execution_mode: HookExecutionMode,
+    pub scope: HookScope,
+    pub source_path: PathBuf,
+    pub display_order: i64,
+    pub status: HookRunStatus,
+    pub status_message: Option<String>,
+    pub started_at: i64,
+    pub completed_at: Option<i64>,
+    pub duration_ms: Option<i64>,
+    pub entries: Vec<HookOutputEntry>,
+}
+
+impl From<CoreHookRunSummary> for HookRunSummary {
+    fn from(value: CoreHookRunSummary) -> Self {
+        Self {
+            id: value.id,
+            event_name: value.event_name.into(),
+            handler_type: value.handler_type.into(),
+            execution_mode: value.execution_mode.into(),
+            scope: value.scope.into(),
+            source_path: value.source_path,
+            display_order: value.display_order,
+            status: value.status.into(),
+            status_message: value.status_message,
+            started_at: value.started_at,
+            completed_at: value.completed_at,
+            duration_ms: value.duration_ms,
+            entries: value.entries.into_iter().map(Into::into).collect(),
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(tag = "type", rename_all = "camelCase")]
 #[ts(tag = "type")]
@@ -4108,6 +4208,15 @@ pub struct TurnStartedNotification {
     pub turn: Turn,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct HookStartedNotification {
+    pub thread_id: String,
+    pub turn_id: Option<String>,
+    pub run: HookRunSummary,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
@@ -4125,6 +4234,15 @@ pub struct TurnCompletedNotification {
     pub turn: Turn,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct HookCompletedNotification {
+    pub thread_id: String,
+    pub turn_id: Option<String>,
+    pub run: HookRunSummary,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]