fix: harden session caching and topic transcripts

src/agents/pi-embedded-helpers.ts

@@ -278,14 +278,12 @@ export function pickFallbackThinkingLevel(params: {
  * Gemini requires strict alternating user→assistant→tool→user pattern.
  * This function:
  * 1. Detects consecutive messages from the same role
- * 2. Merges consecutive assistant/tool messages together
+ * 2. Merges consecutive assistant messages together
  * 3. Preserves metadata (usage, stopReason, etc.)
  *
  * This prevents the "function call turn comes immediately after a user turn or after a function response turn" error.
  */
-export function validateGeminiTurns(
-  messages: AgentMessage[],
-): AgentMessage[] {
+export function validateGeminiTurns(messages: AgentMessage[]): AgentMessage[] {
   if (!Array.isArray(messages) || messages.length === 0) {
     return messages;
   }
@@ -299,9 +297,7 @@ export function validateGeminiTurns(
       continue;
     }
 
-    const msgRole = (msg as { role?: unknown }).role as
-      | string
-      | undefined;
+    const msgRole = (msg as { role?: unknown }).role as string | undefined;
     if (!msgRole) {
       result.push(msg);
       continue;

src/agents/pi-embedded-runner.ts

@@ -334,7 +334,6 @@ const EMBEDDED_RUN_WAITERS = new Map<string, Set<EmbeddedRunWaiter>>();
 type SessionManagerCacheEntry = {
   sessionFile: string;
   loadedAt: number;
-  lastAccessAt: number;
 };
 
 const SESSION_MANAGER_CACHE = new Map<string, SessionManagerCacheEntry>();
@@ -362,7 +361,6 @@ function trackSessionManagerAccess(sessionFile: string): void {
   SESSION_MANAGER_CACHE.set(sessionFile, {
     sessionFile,
     loadedAt: now,
-    lastAccessAt: now,
   });
 }
 
@@ -380,9 +378,14 @@ async function prewarmSessionFile(sessionFile: string): Promise<void> {
   if (isSessionManagerCached(sessionFile)) return;
 
   try {
-    // Touch the file to bring it into OS page cache
-    // This is much faster than letting SessionManager.open() do it cold
-    await fs.stat(sessionFile);
+    // Read a small chunk to encourage OS page cache warmup.
+    const handle = await fs.open(sessionFile, "r");
+    try {
+      const buffer = Buffer.alloc(4096);
+      await handle.read(buffer, 0, buffer.length, 0);
+    } finally {
+      await handle.close();
+    }
     trackSessionManagerAccess(sessionFile);
   } catch {
     // File doesn't exist yet, SessionManager will create it