fix(continuation): mark fallback resumes synthetic

src/plugin/event.model-fallback-pin-agent.test.ts

@@ -18,14 +18,26 @@ function setupConnectedProviderCacheMocks(): void {
 type PromptBody = {
   path: { id: string }
   body: {
-    parts: Array<{ type: "text"; text: string }>
+    parts: Array<{
+      type: "text"
+      text: string
+      synthetic?: boolean
+      metadata?: Record<string, unknown>
+    }>
     agent?: string
     model?: { providerID: string; modelID: string }
     variant?: string
+    noReply?: boolean
   }
   query: { directory: string }
 }
 
+function expectSyntheticContinuation(body: PromptBody["body"]): void {
+  expect(body.noReply).toBeUndefined()
+  expect(body.parts[0]?.synthetic).toBe(true)
+  expect(body.parts[0]?.metadata?.compaction_continue).toBe(true)
+}
+
 describe("createEventHandler - model-fallback auto-continuation pins agent/model/variant", () => {
   const createHandler = (args?: {
     hooks?: any
@@ -127,6 +139,7 @@ describe("createEventHandler - model-fallback auto-continuation pins agent/model
       providerID: "anthropic",
       modelID: "claude-opus-4-7",
     })
+    expectSyntheticContinuation(body)
   })
 
   test("pins agent/model on promptAsync body when continuing after session.error fallback", async () => {
@@ -167,6 +180,7 @@ describe("createEventHandler - model-fallback auto-continuation pins agent/model
       providerID: "anthropic",
       modelID: "claude-opus-4-7",
     })
+    expectSyntheticContinuation(body)
   })
 
   test("pins agent/model on fallback prompt() body when promptAsync is not available (session.status)", async () => {
@@ -223,6 +237,7 @@ describe("createEventHandler - model-fallback auto-continuation pins agent/model
       providerID: "anthropic",
       modelID: "claude-opus-4-7",
     })
+    expectSyntheticContinuation(body)
   })
 
   test("pins variant from agent config when present", async () => {
@@ -268,5 +283,6 @@ describe("createEventHandler - model-fallback auto-continuation pins agent/model
     expect(promptAsyncBodies.length).toBe(1)
     const body = promptAsyncBodies[0]!.body
     expect(body.variant).toBe("thinking")
+    expectSyntheticContinuation(body)
   })
 })

src/plugin/event.test.ts

@@ -1470,6 +1470,15 @@ describe("createEventHandler - session recovery compaction", () => {
 		const sessionID = "ses_recovery_compaction"
 		setMainSession(sessionID)
 		const callOrder: string[] = []
+		const promptBodies: Array<{
+			body?: {
+				noReply?: boolean
+				parts?: Array<{
+					synthetic?: boolean
+					metadata?: Record<string, unknown>
+				}>
+			}
+		}> = []
 
 		const eventHandler = createEventHandler({
 			ctx: asEventHandlerContext({
@@ -1481,8 +1490,9 @@ describe("createEventHandler - session recovery compaction", () => {
 							callOrder.push("summarize")
 							return {}
 						},
-						prompt: async () => {
+						prompt: async (input: { body?: { noReply?: boolean; parts?: Array<{ synthetic?: boolean; metadata?: Record<string, unknown> }> } }) => {
 							callOrder.push("prompt")
+							promptBodies.push(input)
 							return {}
 						},
 					},
@@ -1513,12 +1523,24 @@ describe("createEventHandler - session recovery compaction", () => {
 			},
 		}))
 		expect(callOrder).toEqual(["summarize", "prompt"])
+		expect(promptBodies[0]?.body?.noReply).toBeUndefined()
+		expect(promptBodies[0]?.body?.parts?.[0]?.synthetic).toBe(true)
+		expect(promptBodies[0]?.body?.parts?.[0]?.metadata?.compaction_continue).toBe(true)
 	})
 
 	it("sends continue even if compaction fails", async () => {
 		const sessionID = "ses_recovery_compaction_fail"
 		setMainSession(sessionID)
 		const callOrder: string[] = []
+		const promptBodies: Array<{
+			body?: {
+				noReply?: boolean
+				parts?: Array<{
+					synthetic?: boolean
+					metadata?: Record<string, unknown>
+				}>
+			}
+		}> = []
 
 		const eventHandler = createEventHandler({
 			ctx: asEventHandlerContext({
@@ -1530,8 +1552,9 @@ describe("createEventHandler - session recovery compaction", () => {
 							callOrder.push("summarize")
 							throw new Error("compaction failed")
 						},
-						prompt: async () => {
+						prompt: async (input: { body?: { noReply?: boolean; parts?: Array<{ synthetic?: boolean; metadata?: Record<string, unknown> }> } }) => {
 							callOrder.push("prompt")
+							promptBodies.push(input)
 							return {}
 						},
 					},
@@ -1562,6 +1585,9 @@ describe("createEventHandler - session recovery compaction", () => {
 			},
 		}))
 		expect(callOrder).toEqual(["summarize", "prompt"])
+		expect(promptBodies[0]?.body?.noReply).toBeUndefined()
+		expect(promptBodies[0]?.body?.parts?.[0]?.synthetic).toBe(true)
+		expect(promptBodies[0]?.body?.parts?.[0]?.metadata?.compaction_continue).toBe(true)
 	})
 
 	it("continues dispatching later event hooks when an earlier hook throws", async () => {

src/plugin/event.ts

@@ -25,7 +25,7 @@ import {
   clearBackgroundOutputConsumptionsForTaskSession,
   restoreBackgroundOutputConsumption,
 } from "../shared/background-output-consumption";
-import { resetMessageCursor } from "../shared";
+import { createInternalAgentContinuationTextPart, resetMessageCursor } from "../shared";
 import { getAgentConfigKey } from "../shared/agent-display-names";
 import { readConnectedProvidersCache } from "../shared/connected-providers-cache";
 import { invalidateContextWindowUsageCache } from "../shared/dynamic-truncator";
@@ -162,7 +162,12 @@ export function createEventHandler(args: {
         promptAsync?: (input: {
           path: { id: string };
           body: {
-            parts: Array<{ type: "text"; text: string }>;
+            parts: Array<{
+              type: "text";
+              text: string;
+              synthetic?: boolean;
+              metadata?: Record<string, unknown>;
+            }>;
             agent?: string;
             model?: { providerID: string; modelID: string };
             variant?: string;
@@ -172,7 +177,12 @@ export function createEventHandler(args: {
         prompt: (input: {
           path: { id: string };
           body: {
-            parts: Array<{ type: "text"; text: string }>;
+            parts: Array<{
+              type: "text";
+              text: string;
+              synthetic?: boolean;
+              metadata?: Record<string, unknown>;
+            }>;
             agent?: string;
             model?: { providerID: string; modelID: string };
             variant?: string;
@@ -383,7 +393,7 @@ export function createEventHandler(args: {
         ...(launchAgent ? { agent: launchAgent } : {}),
         ...(launchModel ? { model: launchModel } : {}),
         ...(launchVariant ? { variant: launchVariant } : {}),
-        parts: [{ type: "text" as const, text: "continue" }],
+        parts: [createInternalAgentContinuationTextPart("continue")],
       },
       query: { directory: pluginContext.directory },
     };
@@ -772,7 +782,7 @@ export function createEventHandler(args: {
             await pluginContext.client.session
               .prompt({
                 path: { id: sessionID },
-                body: { parts: [{ type: "text", text: "continue" }] },
+                body: { parts: [createInternalAgentContinuationTextPart("continue")] },
                 query: { directory: pluginContext.directory },
               })
               .catch(() => {});