feat: add PreCompact hook support (#267)

Parses [PreCompact Hook] events from the CLI stream and emits a claude:pre-compact Tauri event. Shows a "Compacting context..." toast and thinking state on the frontend, complementing the existing PostCompact handling.

src-tauri/src/types.rs

@@ -330,6 +330,14 @@ pub struct PostCompactEvent {
     pub conversation_id: Option<String>,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PreCompactEvent {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub session_id: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub conversation_id: Option<String>,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct CwdChangedEvent {
     pub cwd: String,
@@ -790,6 +798,30 @@ mod tests {
         assert!(!serialized.contains("conversation_id"));
     }
 
+    #[test]
+    fn test_pre_compact_event_serialization() {
+        let event = PreCompactEvent {
+            session_id: Some("sess-abc".to_string()),
+            conversation_id: Some("conv-123".to_string()),
+        };
+
+        let serialized = serde_json::to_string(&event).unwrap();
+        assert!(serialized.contains("\"session_id\":\"sess-abc\""));
+        assert!(serialized.contains("\"conversation_id\":\"conv-123\""));
+    }
+
+    #[test]
+    fn test_pre_compact_event_omits_none_fields() {
+        let event = PreCompactEvent {
+            session_id: None,
+            conversation_id: None,
+        };
+
+        let serialized = serde_json::to_string(&event).unwrap();
+        assert!(!serialized.contains("session_id"));
+        assert!(!serialized.contains("conversation_id"));
+    }
+
     #[test]
     fn test_cwd_changed_event_serialization() {
         let event = CwdChangedEvent {

src-tauri/src/wsl_bridge.rs

@@ -17,7 +17,7 @@ use crate::types::{
     AgentEndEvent, AgentStartEvent, CharacterState, ClaudeMessage, ConnectionEvent,
     ConnectionStatus, ContentBlock, CwdChangedEvent, ElicitationEvent, ElicitationResultEvent,
     FileChangedEvent, MessageCost, OutputEvent, PermissionDeniedEvent, PermissionPromptEvent,
-    PermissionPromptEventItem, PostCompactEvent, QuestionOption, SessionEvent, StateChangeEvent,
+    PermissionPromptEventItem, PostCompactEvent, PreCompactEvent, QuestionOption, SessionEvent, StateChangeEvent,
     StopFailureEvent, TaskCreatedEvent, TodoItem, TodoUpdateEvent, UserQuestionEvent,
     WorkingDirectoryEvent, WorktreeEvent, WorktreeInfo,
 };
@@ -1173,6 +1173,7 @@ fn handle_stderr(
                 let is_elicitation = line.contains("[Elicitation Hook]");
                 let is_elicitation_result = line.contains("[ElicitationResult Hook]");
                 let is_stop_failure = line.contains("[StopFailure Hook]");
+                let is_pre_compact = line.contains("[PreCompact Hook]");
                 let is_post_compact = line.contains("[PostCompact Hook]");
                 let is_cwd_changed = line.contains("[CwdChanged Hook]");
                 let is_file_changed = line.contains("[FileChanged Hook]");
@@ -1187,7 +1188,7 @@ fn handle_stderr(
                     "elicitation"
                 } else if is_stop_failure {
                     "error"
-                } else if is_post_compact {
+                } else if is_pre_compact || is_post_compact {
                     "compact-prompt"
                 } else if is_cwd_changed {
                     "cwd-changed"
@@ -1313,6 +1314,28 @@ fn handle_stderr(
                             parent_tool_use_id: None,
                         },
                     );
+                } else if is_pre_compact {
+                    let data = parse_pre_compact_hook(&line);
+
+                    let _ = app.emit(
+                        "claude:pre-compact",
+                        PreCompactEvent {
+                            session_id: data.session_id,
+                            conversation_id: conversation_id.clone(),
+                        },
+                    );
+
+                    let _ = app.emit(
+                        "claude:output",
+                        OutputEvent {
+                            line_type: "compact-prompt".to_string(),
+                            content: "Compacting context — conversation history is being summarised to free up space.".to_string(),
+                            tool_name: None,
+                            conversation_id: conversation_id.clone(),
+                            cost: None,
+                            parent_tool_use_id: None,
+                        },
+                    );
                 } else if is_post_compact {
                     let data = parse_post_compact_hook(&line);
 
@@ -1656,6 +1679,16 @@ fn build_stop_failure_message(data: &StopFailureData) -> String {
     }
 }
 
+#[derive(Debug)]
+struct PreCompactData {
+    session_id: Option<String>,
+}
+
+fn parse_pre_compact_hook(line: &str) -> PreCompactData {
+    let session_id = extract_debug_string_value(line, "session_id");
+    PreCompactData { session_id }
+}
+
 #[derive(Debug)]
 struct PostCompactData {
     session_id: Option<String>,
@@ -3920,6 +3953,28 @@ mod tests {
         assert_eq!(data.session_id, None);
     }
 
+    #[test]
+    fn test_parse_pre_compact_hook_with_session_id() {
+        let line =
+            r#"[PreCompact Hook] session_id=Some("sess-abc123"), conversation_id=Some("conv-xyz")"#;
+        let data = parse_pre_compact_hook(line);
+        assert_eq!(data.session_id, Some("sess-abc123".to_string()));
+    }
+
+    #[test]
+    fn test_parse_pre_compact_hook_without_session_id() {
+        let line = "[PreCompact Hook] session_id=None";
+        let data = parse_pre_compact_hook(line);
+        assert_eq!(data.session_id, None);
+    }
+
+    #[test]
+    fn test_parse_pre_compact_hook_empty_line() {
+        let line = "[PreCompact Hook]";
+        let data = parse_pre_compact_hook(line);
+        assert_eq!(data.session_id, None);
+    }
+
     #[test]
     fn test_parse_cwd_changed_hook_with_cwd_key() {
         let line = r#"[CwdChanged Hook] cwd="/home/naomi/code/my-project""#;

src/lib/tauri.ts

@@ -11,6 +11,7 @@ import type {
   ElicitationEvent,
   PermissionPromptEvent,
   PostCompactEvent,
+  PreCompactEvent,
   StopFailureEvent,
   UserQuestionEvent,
 } from "$lib/types/messages";
@@ -661,6 +662,12 @@ export async function initializeTauriListeners() {
   });
   unlisteners.push(stopFailureUnlisten);
 
+  const preCompactUnlisten = await listen<PreCompactEvent>("claude:pre-compact", () => {
+    toastStore.addInfo("Compacting context...", "🗜️");
+    characterState.setTemporaryState("thinking", 3000);
+  });
+  unlisteners.push(preCompactUnlisten);
+
   const postCompactUnlisten = await listen<PostCompactEvent>("claude:post-compact", () => {
     toastStore.addInfo("Context compacted", "🗜️");
     characterState.setTemporaryState("success", 2000);

src/lib/types/messages.ts

@@ -187,6 +187,11 @@ export interface PostCompactEvent {
   conversation_id?: string;
 }
 
+export interface PreCompactEvent {
+  session_id?: string;
+  conversation_id?: string;
+}
+
 export type ConnectionStatus = "disconnected" | "connecting" | "connected" | "error";
 
 export interface Attachment {