diff --git a/src/shared/prompt-async-gate-path-compat.test.ts b/src/shared/prompt-async-gate-path-compat.test.ts
new file mode 100644
index 000000000..8c147356c
--- /dev/null
+++ b/src/shared/prompt-async-gate-path-compat.test.ts
@@ -0,0 +1,92 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, mock, test } from "bun:test"
+
+import {
+  dispatchInternalPrompt,
+  releaseAllPromptAsyncReservationsForTesting,
+} from "./prompt-async-gate"
+
+type CompatPromptInput = {
+  readonly path: { readonly id: string } | string
+  readonly body: {
+    readonly parts: readonly []
+  }
+}
+
+function createPathSensitivePrompt() {
+  const calls: CompatPromptInput[] = []
+  const prompt = mock(async (input: CompatPromptInput) => {
+    calls.push(input)
+    if (typeof input.path !== "string") {
+      throw new TypeError('The "path" property must be of type string, got object')
+    }
+    return { ok: true }
+  })
+
+  return { calls, prompt }
+}
+
+describe("dispatchInternalPrompt path compatibility", () => {
+  afterEach(() => {
+    releaseAllPromptAsyncReservationsForTesting()
+  })
+
+  test("#given sync prompt rejects object-form session path #when dispatching #then it retries with string-form path", async () => {
+    // given
+    const { calls, prompt } = createPathSensitivePrompt()
+    const client = { session: { prompt } }
+
+    // when
+    const result = await dispatchInternalPrompt<CompatPromptInput>({
+      mode: "sync",
+      client,
+      sessionID: "ses_sync_path_compat",
+      source: "test:path-compat:sync",
+      settleMs: 0,
+      checkStatus: false,
+      checkToolState: false,
+      queueBehavior: "defer",
+      input: {
+        path: { id: "ses_sync_path_compat" },
+        body: { parts: [] },
+      },
+    })
+
+    // then
+    expect(result.status).toBe("dispatched")
+    expect(calls.map((call) => call.path)).toEqual([
+      { id: "ses_sync_path_compat" },
+      "ses_sync_path_compat",
+    ])
+  })
+
+  test("#given async prompt rejects object-form session path #when dispatching #then it retries with string-form path", async () => {
+    // given
+    const { calls, prompt } = createPathSensitivePrompt()
+    const client = { session: { promptAsync: prompt } }
+
+    // when
+    const result = await dispatchInternalPrompt<CompatPromptInput>({
+      mode: "async",
+      client,
+      sessionID: "ses_async_path_compat",
+      source: "test:path-compat:async",
+      settleMs: 0,
+      checkStatus: false,
+      checkToolState: false,
+      queueBehavior: "defer",
+      input: {
+        path: { id: "ses_async_path_compat" },
+        body: { parts: [] },
+      },
+    })
+
+    // then
+    expect(result.status).toBe("dispatched")
+    expect(calls.map((call) => call.path)).toEqual([
+      { id: "ses_async_path_compat" },
+      "ses_async_path_compat",
+    ])
+  })
+})
diff --git a/src/shared/prompt-async-gate.ts b/src/shared/prompt-async-gate.ts
index 234f1e65d..1236e7ade 100644
--- a/src/shared/prompt-async-gate.ts
+++ b/src/shared/prompt-async-gate.ts
@@ -68,6 +68,47 @@ function createDefaultDedupeKey(source: string, input: unknown): string {
   return `${source}:${fingerprint.length}:${fingerprint.slice(0, 8192)}`
 }
 
+type ObjectPathPromptInput = {
+  readonly path?: { readonly id?: string } | string
+  readonly [key: string]: unknown
+}
+
+function hasObjectSessionPath(input: unknown): input is ObjectPathPromptInput & { readonly path: { readonly id: string } } {
+  return typeof input === "object"
+    && input !== null
+    && "path" in input
+    && typeof input.path === "object"
+    && input.path !== null
+    && "id" in input.path
+    && typeof input.path.id === "string"
+}
+
+function isObjectPathTypeError(error: unknown): boolean {
+  const message = error instanceof Error
+    ? error.message
+    : typeof error === "string" ? error : ""
+  return message.includes('The "path" property must be of type string') && message.includes("got object")
+}
+
+async function dispatchWithPathCompatibility<TInput>(
+  dispatch: (dispatchInput: TInput) => Promise<unknown>,
+  input: TInput,
+): Promise<unknown> {
+  try {
+    return await dispatch(input)
+  } catch (error) {
+    if (!isObjectPathTypeError(error) || !hasObjectSessionPath(input)) {
+      throw error
+    }
+
+    const retryInput = {
+      ...input,
+      path: input.path.id,
+    } as TInput
+    return dispatch(retryInput)
+  }
+}
+
 export async function dispatchInternalPrompt<TInput = PromptAsyncInput>(
   args: InternalPromptDispatchArgs<TInput>,
 ): Promise<InternalPromptDispatchResult> {
@@ -131,7 +172,7 @@ export async function dispatchInternalPrompt<TInput = PromptAsyncInput>(
       dispatchTimeoutMs,
       checkStatus: args.checkStatus !== false,
       checkToolState: args.checkToolState !== false,
-      dispatch,
+      dispatch: (dispatchInput) => dispatchWithPathCompatibility(dispatch, dispatchInput),
     })
   }
 
@@ -150,7 +191,7 @@ export async function dispatchInternalPrompt<TInput = PromptAsyncInput>(
       queueRetryMs,
       checkStatus: args.checkStatus !== false,
       checkToolState: args.checkToolState !== false,
-      dispatch: async (_dispatchInput: unknown) => dispatch(input),
+      dispatch: async (_dispatchInput: unknown) => dispatchWithPathCompatibility(dispatch, input),
     })
   }
 
@@ -166,7 +207,7 @@ export async function dispatchInternalPrompt<TInput = PromptAsyncInput>(
     dispatchTimeoutMs,
     checkStatus: args.checkStatus !== false,
     checkToolState: args.checkToolState !== false,
-    dispatch,
+    dispatch: (dispatchInput) => dispatchWithPathCompatibility(dispatch, dispatchInput),
   })
 }
 
diff --git a/src/shared/prompt-async-gate/types.ts b/src/shared/prompt-async-gate/types.ts
index 082693692..521e90a97 100644
--- a/src/shared/prompt-async-gate/types.ts
+++ b/src/shared/prompt-async-gate/types.ts
@@ -1,5 +1,7 @@
+export type PromptSessionPath = { readonly id?: string } | string
+
 export type PromptAsyncInput = {
-  readonly path?: { readonly id?: string }
+  readonly path?: PromptSessionPath
   readonly body?: unknown
   readonly query?: unknown
   readonly signal?: unknown