fix(compaction): recover checkpointed agent config after compaction

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/compaction-context-injector/index.test.ts

@@ -17,6 +17,27 @@ mock.module("../../shared/system-directive", () => ({
 import { createCompactionContextInjector } from "./index"
 import { TaskHistory } from "../../features/background-agent/task-history"
 
+function createMockContext(
+  messageResponses: Array<Array<{ info?: Record<string, unknown> }>>,
+  promptAsyncMock = mock(async () => ({})),
+) {
+  let callIndex = 0
+
+  return {
+    client: {
+      session: {
+        messages: mock(async () => {
+          const response = messageResponses[Math.min(callIndex, messageResponses.length - 1)] ?? []
+          callIndex += 1
+          return { data: response }
+        }),
+        promptAsync: promptAsyncMock,
+      },
+    },
+    directory: "/tmp/test",
+  }
+}
+
 describe("createCompactionContextInjector", () => {
   describe("Agent Verification State preservation", () => {
     it("includes Agent Verification State section in compaction prompt", async () => {
@@ -24,7 +45,7 @@ describe("createCompactionContextInjector", () => {
       const injector = createCompactionContextInjector()
 
       //#when
-      const prompt = injector()
+      const prompt = injector.inject()
 
       //#then
       expect(prompt).toContain("Agent Verification State")
@@ -37,7 +58,7 @@ describe("createCompactionContextInjector", () => {
       const injector = createCompactionContextInjector()
 
       //#when
-      const prompt = injector()
+      const prompt = injector.inject()
 
       //#then
       expect(prompt).toContain("Previous Rejections")
@@ -50,7 +71,7 @@ describe("createCompactionContextInjector", () => {
       const injector = createCompactionContextInjector()
 
       //#when
-      const prompt = injector()
+      const prompt = injector.inject()
 
       //#then
       expect(prompt).toContain("Pending Verifications")
@@ -63,7 +84,7 @@ describe("createCompactionContextInjector", () => {
     const injector = createCompactionContextInjector()
 
     //#when
-    const prompt = injector()
+    const prompt = injector.inject()
 
     //#then
     expect(prompt).toContain("Explicit Constraints (Verbatim Only)")
@@ -77,7 +98,7 @@ describe("createCompactionContextInjector", () => {
       const injector = createCompactionContextInjector()
 
       //#when
-      const prompt = injector()
+      const prompt = injector.inject()
 
       //#then
       expect(prompt).toContain("Delegated Agent Sessions")
@@ -89,10 +110,10 @@ describe("createCompactionContextInjector", () => {
       //#given
       const mockManager = { taskHistory: new TaskHistory() } as any
       mockManager.taskHistory.record("ses_parent", { id: "t1", sessionID: "ses_child", agent: "explore", description: "Find patterns", status: "completed", category: "quick" })
-      const injector = createCompactionContextInjector(mockManager)
+      const injector = createCompactionContextInjector({ backgroundManager: mockManager })
 
       //#when
-      const prompt = injector("ses_parent")
+      const prompt = injector.inject("ses_parent")
 
       //#then
       expect(prompt).toContain("Active/Recent Delegated Sessions")
@@ -104,13 +125,152 @@ describe("createCompactionContextInjector", () => {
     it("does not inject task history section when no entries exist", async () => {
       //#given
       const mockManager = { taskHistory: new TaskHistory() } as any
-      const injector = createCompactionContextInjector(mockManager)
+      const injector = createCompactionContextInjector({ backgroundManager: mockManager })
 
       //#when
-      const prompt = injector("ses_empty")
+      const prompt = injector.inject("ses_empty")
 
       //#then
       expect(prompt).not.toContain("Active/Recent Delegated Sessions")
     })
   })
+
+  describe("agent checkpoint recovery", () => {
+    it("re-injects checkpointed agent config after compaction when latest agent is lost", async () => {
+      //#given
+      const promptAsyncMock = mock(async () => ({}))
+      const ctx = createMockContext(
+        [
+          [
+            {
+              info: {
+                role: "user",
+                agent: "atlas",
+                model: { providerID: "openai", modelID: "gpt-5" },
+                tools: { bash: "allow" },
+              },
+            },
+          ],
+          [
+            {
+              info: {
+                role: "user",
+                agent: "compaction",
+                model: { providerID: "anthropic", modelID: "claude-opus-4-1" },
+              },
+            },
+          ],
+          [
+            {
+              info: {
+                role: "user",
+                agent: "atlas",
+                model: { providerID: "openai", modelID: "gpt-5" },
+              },
+            },
+          ],
+        ],
+        promptAsyncMock,
+      )
+      const injector = createCompactionContextInjector({ ctx })
+
+      //#when
+      await injector.capture("ses_checkpoint")
+      await injector.event({
+        event: { type: "session.compacted", properties: { sessionID: "ses_checkpoint" } },
+      })
+
+      //#then
+      expect(promptAsyncMock).toHaveBeenCalledWith({
+        path: { id: "ses_checkpoint" },
+        body: {
+          noReply: true,
+          agent: "atlas",
+          model: { providerID: "openai", modelID: "gpt-5" },
+          tools: { bash: true },
+          parts: [
+            {
+              type: "text",
+              text: expect.stringContaining("restore checkpointed session agent configuration"),
+            },
+          ],
+        },
+        query: { directory: "/tmp/test" },
+      })
+    })
+
+    it("recovers after five consecutive assistant messages with no text", async () => {
+      //#given
+      const promptAsyncMock = mock(async () => ({}))
+      const ctx = createMockContext(
+        [
+          [
+            {
+              info: {
+                role: "user",
+                agent: "atlas",
+                model: { providerID: "openai", modelID: "gpt-5" },
+              },
+            },
+          ],
+          [
+            {
+              info: {
+                role: "user",
+                agent: "atlas",
+                model: { providerID: "openai", modelID: "gpt-5" },
+              },
+            },
+          ],
+          [
+            {
+              info: {
+                role: "user",
+                agent: "atlas",
+                model: { providerID: "openai", modelID: "gpt-5" },
+              },
+            },
+          ],
+        ],
+        promptAsyncMock,
+      )
+      const injector = createCompactionContextInjector({ ctx })
+
+      await injector.capture("ses_no_text_tail")
+      await injector.event({
+        event: { type: "session.compacted", properties: { sessionID: "ses_no_text_tail" } },
+      })
+
+      //#when
+      for (let index = 1; index <= 5; index++) {
+        await injector.event({
+          event: {
+            type: "message.updated",
+            properties: {
+              info: {
+                id: `msg_${index}`,
+                role: "assistant",
+                sessionID: "ses_no_text_tail",
+              },
+            },
+          },
+        })
+      }
+      await injector.event({
+        event: { type: "session.idle", properties: { sessionID: "ses_no_text_tail" } },
+      })
+
+      //#then
+      expect(promptAsyncMock).toHaveBeenCalledTimes(1)
+      expect(promptAsyncMock).toHaveBeenCalledWith(
+        expect.objectContaining({
+          path: { id: "ses_no_text_tail" },
+          body: expect.objectContaining({
+            noReply: true,
+            agent: "atlas",
+          }),
+        }),
+      )
+    })
+  })
 })