fix(ralph-loop): add inFlight guard and improve completion detection to prevent infinite loops

Closes #2084

src/hooks/ralph-loop/completion-promise-detector.ts

@@ -79,8 +79,8 @@ export async function detectCompletionInSessionMessages(
 		if (assistantMessages.length === 0) return false
 
 		const pattern = buildPromisePattern(options.promise)
-		const recentAssistants = assistantMessages.slice(-3)
-		for (const assistant of recentAssistants) {
+		for (let index = assistantMessages.length - 1; index >= 0; index -= 1) {
+			const assistant = assistantMessages[index]
 			if (!assistant.parts) continue
 
 			let responseText = ""

src/hooks/ralph-loop/index.test.ts

@@ -494,6 +494,7 @@ describe("ralph-loop", () => {
         config: {
           enabled: true,
           default_max_iterations: 200,
+          default_strategy: "continue",
         },
       })
 
@@ -708,6 +709,57 @@ describe("ralph-loop", () => {
       expect(promptCalls[0].text).toContain("<promise>CALCULATOR_DONE</promise>")
     })
 
+    test("should skip concurrent idle events for same session when handler is in flight", async () => {
+      // given - active loop with delayed prompt injection
+      let releasePromptAsync: (() => void) | undefined
+      const promptAsyncBlocked = new Promise<void>((resolve) => {
+        releasePromptAsync = resolve
+      })
+      let firstPromptStartedResolve: (() => void) | undefined
+      const firstPromptStarted = new Promise<void>((resolve) => {
+        firstPromptStartedResolve = resolve
+      })
+
+      const mockInput = createMockPluginInput() as {
+        client: {
+          session: {
+            promptAsync: (opts: { path: { id: string }; body: { parts: Array<{ type: string; text: string }> } }) => Promise<unknown>
+          }
+        }
+      }
+
+      const originalPromptAsync = mockInput.client.session.promptAsync
+      let promptAsyncCalls = 0
+      mockInput.client.session.promptAsync = async (opts) => {
+        promptAsyncCalls += 1
+        if (promptAsyncCalls === 1) {
+          firstPromptStartedResolve?.()
+        }
+        await promptAsyncBlocked
+        return originalPromptAsync(opts)
+      }
+
+      const hook = createRalphLoopHook(mockInput as Parameters<typeof createRalphLoopHook>[0])
+      hook.startLoop("session-123", "Build feature", { maxIterations: 10 })
+
+      // when - second idle arrives while first idle processing is still in flight
+      const firstIdle = hook.event({
+        event: { type: "session.idle", properties: { sessionID: "session-123" } },
+      })
+      await firstPromptStarted
+      const secondIdle = hook.event({
+        event: { type: "session.idle", properties: { sessionID: "session-123" } },
+      })
+
+      releasePromptAsync?.()
+      await Promise.all([firstIdle, secondIdle])
+
+      // then - only one continuation should be injected
+      expect(promptAsyncCalls).toBe(1)
+      expect(promptCalls.length).toBe(1)
+      expect(hook.getState()?.iteration).toBe(2)
+    })
+
     test("should clear loop state on user abort (MessageAbortedError)", async () => {
       // given - active loop
       const hook = createRalphLoopHook(createMockPluginInput())
@@ -782,8 +834,8 @@ describe("ralph-loop", () => {
       expect(hook.getState()).toBeNull()
     })
 
-    test("should NOT detect completion if promise is older than last 3 assistant messages", async () => {
-      // given - promise appears in an assistant message older than last 3
+    test("should detect completion even when promise is older than previous narrow window", async () => {
+      // given - promise appears in an older assistant message with additional assistant output after it
       mockSessionMessages = [
         { info: { role: "user" }, parts: [{ type: "text", text: "Start task" }] },
         { info: { role: "assistant" }, parts: [{ type: "text", text: "Promise early <promise>DONE</promise>" }] },
@@ -801,9 +853,40 @@ describe("ralph-loop", () => {
         event: { type: "session.idle", properties: { sessionID: "session-123" } },
       })
 
-      // then - loop should continue (promise is older than last 3 assistant messages)
-      expect(promptCalls.length).toBe(1)
-      expect(hook.getState()?.iteration).toBe(2)
+      // then - loop should complete because all assistant messages are scanned
+      expect(promptCalls.length).toBe(0)
+      expect(toastCalls.some((t) => t.title === "Ralph Loop Complete!")).toBe(true)
+      expect(hook.getState()).toBeNull()
+    })
+
+    test("should detect completion when many assistant messages are emitted after promise", async () => {
+      // given - completion promise followed by long assistant output sequence
+      mockSessionMessages = [
+        { info: { role: "user" }, parts: [{ type: "text", text: "Start task" }] },
+        { info: { role: "assistant" }, parts: [{ type: "text", text: "Done now <promise>DONE</promise>" }] },
+      ]
+
+      for (let index = 1; index <= 25; index += 1) {
+        mockSessionMessages.push({
+          info: { role: "assistant" },
+          parts: [{ type: "text", text: `Post-completion assistant output ${index}` }],
+        })
+      }
+
+      const hook = createRalphLoopHook(createMockPluginInput(), {
+        getTranscriptPath: () => join(TEST_DIR, "nonexistent.jsonl"),
+      })
+      hook.startLoop("session-123", "Build something", { completionPromise: "DONE" })
+
+      // when - session goes idle
+      await hook.event({
+        event: { type: "session.idle", properties: { sessionID: "session-123" } },
+      })
+
+      // then - loop should complete despite large trailing output
+      expect(promptCalls.length).toBe(0)
+      expect(toastCalls.some((t) => t.title === "Ralph Loop Complete!")).toBe(true)
+      expect(hook.getState()).toBeNull()
     })
 
     test("should allow starting new loop while previous loop is active (different session)", async () => {

src/hooks/ralph-loop/ralph-loop-event-handler.ts

@@ -25,6 +25,8 @@ export function createRalphLoopEventHandler(
 	ctx: PluginInput,
 	options: RalphLoopEventHandlerOptions,
 ) {
+	const inFlightSessions = new Set<string>()
+
 	return async ({ event }: { event: { type: string; properties?: unknown } }): Promise<void> => {
 		const props = event.properties as Record<string, unknown> | undefined
 
@@ -32,6 +34,15 @@ export function createRalphLoopEventHandler(
 			const sessionID = props?.sessionID as string | undefined
 			if (!sessionID) return
 
+			if (inFlightSessions.has(sessionID)) {
+				log(`[${HOOK_NAME}] Skipped: handler in flight`, { sessionID })
+				return
+			}
+
+			inFlightSessions.add(sessionID)
+
+			try {
+
 				if (options.sessionRecovery.isRecovering(sessionID)) {
 					log(`[${HOOK_NAME}] Skipped: in recovery`, { sessionID })
 					return
@@ -141,6 +152,9 @@ export function createRalphLoopEventHandler(
 					})
 				}
 				return
+			} finally {
+				inFlightSessions.delete(sessionID)
+			}
 		}
 
 		if (event.type === "session.deleted") {

src/hooks/ralph-loop/reset-strategy-race-condition.test.ts

@@ -36,7 +36,7 @@ async function waitUntil(condition: () => boolean): Promise<void> {
 }
 
 describe("ralph-loop reset strategy race condition", () => {
-  test("should continue iteration when old session idle arrives before TUI switch completes", async () => {
+  test("should skip duplicate idle while reset iteration handling is in flight", async () => {
     // given - reset strategy loop with blocked TUI session switch
     const promptCalls: Array<{ sessionID: string; text: string }> = []
     const createSessionCalls: Array<{ parentID?: string }> = []
@@ -85,7 +85,7 @@ describe("ralph-loop reset strategy race condition", () => {
           },
         },
       },
-    } as Parameters<typeof createRalphLoopHook>[0])
+    } as unknown as Parameters<typeof createRalphLoopHook>[0])
 
     hook.startLoop("session-old", "Build feature", { strategy: "reset" })
 
@@ -100,14 +100,12 @@ describe("ralph-loop reset strategy race condition", () => {
       event: { type: "session.idle", properties: { sessionID: "session-old" } },
     })
 
-    await waitUntil(() => selectSessionCalls > 1)
-
     selectSessionDeferred.resolve()
     await Promise.all([firstIdleEvent, secondIdleEvent])
 
-    // then - second idle should not be skipped during reset transition
-    expect(createSessionCalls.length).toBe(2)
-    expect(promptCalls.length).toBe(2)
-    expect(hook.getState()?.iteration).toBe(3)
+    // then - duplicate idle should be skipped to prevent concurrent continuation injection
+    expect(createSessionCalls.length).toBe(1)
+    expect(promptCalls.length).toBe(1)
+    expect(hook.getState()?.iteration).toBe(2)
   })
 })