diff --git a/src/hooks/ralph-loop/index.test.ts b/src/hooks/ralph-loop/index.test.ts
index 5da9f20..885ecc2 100644
--- a/src/hooks/ralph-loop/index.test.ts
+++ b/src/hooks/ralph-loop/index.test.ts
@@ -329,17 +329,19 @@ describe("ralph-loop", () => {
 
     test("should detect completion promise and stop loop", async () => {
       // #given - active loop with transcript containing completion
-      const hook = createRalphLoopHook(createMockPluginInput())
+      const transcriptPath = join(TEST_DIR, "transcript.jsonl")
+      const hook = createRalphLoopHook(createMockPluginInput(), {
+        getTranscriptPath: () => transcriptPath,
+      })
       hook.startLoop("session-123", "Build something", { completionPromise: "COMPLETE" })
 
-      const transcriptPath = join(TEST_DIR, "transcript.jsonl")
       writeFileSync(transcriptPath, JSON.stringify({ content: "Task done <promise>COMPLETE</promise>" }))
 
-      // #when - session goes idle with transcript
+      // #when - session goes idle (transcriptPath now derived from sessionID via getTranscriptPath)
       await hook.event({
         event: {
           type: "session.idle",
-          properties: { sessionID: "session-123", transcriptPath },
+          properties: { sessionID: "session-123" },
         },
       })
 
diff --git a/src/hooks/ralph-loop/index.ts b/src/hooks/ralph-loop/index.ts
index 434a540..80da2d0 100644
--- a/src/hooks/ralph-loop/index.ts
+++ b/src/hooks/ralph-loop/index.ts
@@ -8,6 +8,7 @@ import {
   DEFAULT_COMPLETION_PROMISE,
 } from "./constants"
 import type { RalphLoopState, RalphLoopOptions } from "./types"
+import { getTranscriptPath as getDefaultTranscriptPath } from "../claude-code-hooks/transcript"
 
 export * from "./types"
 export * from "./constants"
@@ -48,6 +49,7 @@ export function createRalphLoopHook(
   const sessions = new Map<string, SessionState>()
   const config = options?.config
   const stateDir = config?.state_dir
+  const getTranscriptPath = options?.getTranscriptPath ?? getDefaultTranscriptPath
 
   function getSessionState(sessionID: string): SessionState {
     let state = sessions.get(sessionID)
@@ -149,7 +151,8 @@ export function createRalphLoopHook(
         return
       }
 
-      const transcriptPath = props?.transcriptPath as string | undefined
+      // Generate transcript path from sessionID - OpenCode doesn't pass it in event properties
+      const transcriptPath = getTranscriptPath(sessionID)
 
       if (detectCompletionPromise(transcriptPath, state.completion_promise)) {
         log(`[${HOOK_NAME}] Completion detected!`, {
diff --git a/src/hooks/ralph-loop/types.ts b/src/hooks/ralph-loop/types.ts
index 5790efb..08a3ccd 100644
--- a/src/hooks/ralph-loop/types.ts
+++ b/src/hooks/ralph-loop/types.ts
@@ -12,4 +12,5 @@ export interface RalphLoopState {
 
 export interface RalphLoopOptions {
   config?: RalphLoopConfig
+  getTranscriptPath?: (sessionId: string) => string
 }