fix: reduce session.messages() calls with event-based caching to prevent memory leaks

- Replace session.messages() fetch in context-window-monitor with message.updated event cache
- Replace session.messages() fetch in preemptive-compaction with message.updated event cache
- Add per-session transcript cache (5min TTL) to avoid full rebuild per tool call
- Remove session.messages() from background-agent polling (use event-based progress)
- Add TTL pruning to todo-continuation-enforcer session state Map
- Add setInterval.unref() to tool-input-cache cleanup timer

Fixes #1222

src/hooks/context-window-monitor.ts

@@ -15,23 +15,21 @@ You are using Anthropic Claude with 1M context window.
 You have plenty of context remaining - do NOT rush or skip tasks.
 Complete your work thoroughly and methodically.`
 
-interface AssistantMessageInfo {
-  role: "assistant"
-  providerID: string
-  tokens: {
-    input: number
-    output: number
-    reasoning: number
-    cache: { read: number; write: number }
-  }
+interface TokenInfo {
+  input: number
+  output: number
+  reasoning: number
+  cache: { read: number; write: number }
 }
 
-interface MessageWrapper {
-  info: { role: string } & Partial<AssistantMessageInfo>
+interface CachedTokenState {
+  providerID: string
+  tokens: TokenInfo
 }
 
 export function createContextWindowMonitorHook(ctx: PluginInput) {
   const remindedSessions = new Set<string>()
+  const tokenCache = new Map<string, CachedTokenState>()
 
   const toolExecuteAfter = async (
     input: { tool: string; sessionID: string; callID: string },
@@ -41,44 +39,28 @@ export function createContextWindowMonitorHook(ctx: PluginInput) {
 
     if (remindedSessions.has(sessionID)) return
 
-    try {
-      const response = await ctx.client.session.messages({
-        path: { id: sessionID },
-      })
+    const cached = tokenCache.get(sessionID)
+    if (!cached) return
 
-      const messages = (response.data ?? response) as MessageWrapper[]
+    if (cached.providerID !== "anthropic") return
 
-      const assistantMessages = messages
-        .filter((m) => m.info.role === "assistant")
-        .map((m) => m.info as AssistantMessageInfo)
+    const lastTokens = cached.tokens
+    const totalInputTokens = (lastTokens?.input ?? 0) + (lastTokens?.cache?.read ?? 0)
 
-      if (assistantMessages.length === 0) return
+    const actualUsagePercentage = totalInputTokens / ANTHROPIC_ACTUAL_LIMIT
 
-      const lastAssistant = assistantMessages[assistantMessages.length - 1]
-      if (lastAssistant.providerID !== "anthropic") return
+    if (actualUsagePercentage < CONTEXT_WARNING_THRESHOLD) return
 
-      // Use only the last assistant message's input tokens
-      // This reflects the ACTUAL current context window usage (post-compaction)
-      const lastTokens = lastAssistant.tokens
-      const totalInputTokens = (lastTokens?.input ?? 0) + (lastTokens?.cache?.read ?? 0)
+    remindedSessions.add(sessionID)
 
-      const actualUsagePercentage = totalInputTokens / ANTHROPIC_ACTUAL_LIMIT
+    const displayUsagePercentage = totalInputTokens / ANTHROPIC_DISPLAY_LIMIT
+    const usedPct = (displayUsagePercentage * 100).toFixed(1)
+    const remainingPct = ((1 - displayUsagePercentage) * 100).toFixed(1)
+    const usedTokens = totalInputTokens.toLocaleString()
+    const limitTokens = ANTHROPIC_DISPLAY_LIMIT.toLocaleString()
 
-      if (actualUsagePercentage < CONTEXT_WARNING_THRESHOLD) return
-
-      remindedSessions.add(sessionID)
-
-      const displayUsagePercentage = totalInputTokens / ANTHROPIC_DISPLAY_LIMIT
-      const usedPct = (displayUsagePercentage * 100).toFixed(1)
-      const remainingPct = ((1 - displayUsagePercentage) * 100).toFixed(1)
-      const usedTokens = totalInputTokens.toLocaleString()
-      const limitTokens = ANTHROPIC_DISPLAY_LIMIT.toLocaleString()
-
-      output.output += `\n\n${CONTEXT_REMINDER}
+    output.output += `\n\n${CONTEXT_REMINDER}
 [Context Status: ${usedPct}% used (${usedTokens}/${limitTokens} tokens), ${remainingPct}% remaining]`
-    } catch {
-      // Graceful degradation - do not disrupt tool execution
-    }
   }
 
   const eventHandler = async ({ event }: { event: { type: string; properties?: unknown } }) => {
@@ -88,8 +70,27 @@ export function createContextWindowMonitorHook(ctx: PluginInput) {
       const sessionInfo = props?.info as { id?: string } | undefined
       if (sessionInfo?.id) {
         remindedSessions.delete(sessionInfo.id)
+        tokenCache.delete(sessionInfo.id)
       }
     }
+
+    if (event.type === "message.updated") {
+      const info = props?.info as {
+        role?: string
+        sessionID?: string
+        providerID?: string
+        finish?: boolean
+        tokens?: TokenInfo
+      } | undefined
+
+      if (!info || info.role !== "assistant" || !info.finish) return
+      if (!info.sessionID || !info.providerID || !info.tokens) return
+
+      tokenCache.set(info.sessionID, {
+        providerID: info.providerID,
+        tokens: info.tokens,
+      })
+    }
   }
 
   return {