Detect compaction from message data instead of event

- Scan messages for assistant messages with info.summary === true
- Run compaction detection on every checkSession call, not just init
- Remove session.compacted event handler (no longer needed)
- Remove lastCompacted from persistence (derived from messages now)
- Remove unused checkForCompaction function

This ensures compaction is detected even when:
- Plugin was disabled during compaction
- Session was loaded before plugin was installed
- Any other case where the event wasn't captured

Author: Tarquinen

lib/hooks.ts

@@ -48,11 +48,6 @@ export function createEventHandler(
             return
         }
 
-        if (event.type === "session.compacted") {
-            logger.info("Session compaction detected - updating state")
-            state.lastCompaction = Date.now()
-        }
-
         if (event.type === "session.status" && event.properties.status.type === "idle") {
             if (!config.strategies.onIdle.enabled) {
                 return

lib/shared-utils.ts

@@ -1,4 +1,3 @@
-import { Logger } from "./logger"
 import { SessionState, WithParts } from "./state"
 
 export const isMessageCompacted = (
@@ -20,12 +19,4 @@ export const getLastUserMessage = (
     return null
 }
 
-export const checkForCompaction = (
-    state: SessionState,
-    messages: WithParts[],
-    logger: Logger
-): void => {
-    for (const msg of messages) {
 
-    }
-}

lib/state/persistence.ts

@@ -16,7 +16,6 @@ export interface PersistedSessionState {
     prune: Prune
     stats: SessionStats;
     lastUpdated: string;
-    lastCompacted: number
 }
 
 const STORAGE_DIR = join(
@@ -55,8 +54,7 @@ export async function saveSessionState(
             sessionName: sessionName,
             prune: sessionState.prune,
             stats: sessionState.stats,
-            lastUpdated: new Date().toISOString(),
-            lastCompacted: sessionState.lastCompaction
+            lastUpdated: new Date().toISOString()
         };
 
         const filePath = getSessionFilePath(sessionState.sessionId);

lib/state/state.ts

@@ -21,11 +21,18 @@ export const checkSession = async (
     if (state.sessionId === null || state.sessionId !== lastSessionId) {
         logger.info(`Session changed: ${state.sessionId} -> ${lastSessionId}`)
         try {
-            await ensureSessionInitialized(client, state, lastSessionId, logger)
+            await ensureSessionInitialized(client, state, lastSessionId, logger, messages)
         } catch (err: any) {
             logger.error("Failed to initialize session state", { error: err.message })
         }
     }
+
+    // Always check for compaction on every message check
+    const lastCompactionTimestamp = findLastCompactionTimestamp(messages)
+    if (lastCompactionTimestamp > state.lastCompaction) {
+        state.lastCompaction = lastCompactionTimestamp
+        logger.info("Detected compaction from messages", { timestamp: lastCompactionTimestamp })
+    }
 }
 
 export function createSessionState(): SessionState {
@@ -66,7 +73,8 @@ export async function ensureSessionInitialized(
     client: any,
     state: SessionState,
     sessionId: string,
-    logger: Logger
+    logger: Logger,
+    messages: WithParts[]
 ): Promise<void> {
     if (state.sessionId === sessionId) {
         return;
@@ -97,5 +105,17 @@ export async function ensureSessionInitialized(
         pruneTokenCounter: persisted.stats?.pruneTokenCounter || 0,
         totalPruneTokens: persisted.stats?.totalPruneTokens || 0,
     }
-    state.lastCompaction = persisted.lastCompacted || 0
+}
+
+function findLastCompactionTimestamp(messages: WithParts[]): number {
+    let lastTimestamp = 0
+    for (const msg of messages) {
+        if (msg.info.role === "assistant" && msg.info.summary === true) {
+            const created = msg.info.time.created
+            if (created > lastTimestamp) {
+                lastTimestamp = created
+            }
+        }
+    }
+    return lastTimestamp
 }

lib/strategies/prune-tool.ts

@@ -66,14 +66,14 @@ export function createPruneTool(
                 return "No numeric IDs provided. Format: [reason, id1, id2, ...] where reason is 'completion', 'noise', or 'consolidation'."
             }
 
-            await ensureSessionInitialized(ctx.client, state, sessionId, logger)
-
             // Fetch messages to calculate tokens and find current agent
             const messagesResponse = await client.session.messages({
                 path: { id: sessionId }
             })
             const messages: WithParts[] = messagesResponse.data || messagesResponse
 
+            await ensureSessionInitialized(ctx.client, state, sessionId, logger, messages)
+
             const currentParams = getCurrentParams(messages, logger)
             const toolIdList: string[] = buildToolIdList(state, messages, logger)