diff --git a/src/hooks/claude-code-hooks/session-hook-state.ts b/src/hooks/claude-code-hooks/session-hook-state.ts
index a6b4024bd..cef303d30 100644
--- a/src/hooks/claude-code-hooks/session-hook-state.ts
+++ b/src/hooks/claude-code-hooks/session-hook-state.ts
@@ -7,7 +7,12 @@ export const sessionInterruptState = new Map<string, { interrupted: boolean }>()
 export function clearSessionHookState(sessionID: string): void {
 	sessionErrorState.delete(sessionID)
 	sessionInterruptState.delete(sessionID)
-	sessionFirstMessageProcessed.delete(sessionID)
+	// sessionFirstMessageProcessed must NOT be cleared on idle.
+	// It tracks whether the first message of a session has been processed,
+	// so that SessionStart hooks fire only once per session. Clearing it
+	// on idle (which fires after every model response) makes isFirstMessage
+	// always return true, causing SessionStart hooks to fire on every
+	// prompt instead of only the first one.
 }
 
 export function clearAllSessionHookState(): void {