fix(hooks): extract model from assistant messages with flat modelID/providerID

OpenCode API returns different structures for user vs assistant messages:
- User: info.model = { providerID, modelID } (nested)
- Assistant: info.modelID, info.providerID (flat top-level)

Previous code only checked nested format, causing model info loss when
continuation hooks fired after assistant messages.

Files modified:
- todo-continuation-enforcer.ts
- ralph-loop/index.ts
- sisyphus-task/tools.ts
- background-agent/manager.ts

Added test for assistant message model extraction.

src/features/background-agent/manager.ts

@@ -826,13 +826,13 @@ Use \`background_output(task_id="${task.id}")\` to retrieve this result when rea
     try {
       const messagesResp = await this.client.session.messages({ path: { id: task.parentSessionID } })
       const messages = (messagesResp.data ?? []) as Array<{
-        info?: { agent?: string; model?: { providerID: string; modelID: string } }
+        info?: { agent?: string; model?: { providerID: string; modelID: string }; modelID?: string; providerID?: string }
       }>
       for (let i = messages.length - 1; i >= 0; i--) {
         const info = messages[i].info
-        if (info?.agent || info?.model) {
+        if (info?.agent || info?.model || (info?.modelID && info?.providerID)) {
           agent = info.agent ?? task.parentAgent
-          model = info.model
+          model = info.model ?? (info.providerID && info.modelID ? { providerID: info.providerID, modelID: info.modelID } : undefined)
           break
         }
       }

src/hooks/ralph-loop/index.ts

@@ -322,13 +322,13 @@ export function createRalphLoopHook(
         try {
           const messagesResp = await ctx.client.session.messages({ path: { id: sessionID } })
           const messages = (messagesResp.data ?? []) as Array<{
-            info?: { agent?: string; model?: { providerID: string; modelID: string } }
+            info?: { agent?: string; model?: { providerID: string; modelID: string }; modelID?: string; providerID?: string }
           }>
           for (let i = messages.length - 1; i >= 0; i--) {
             const info = messages[i].info
-            if (info?.agent || info?.model) {
+            if (info?.agent || info?.model || (info?.modelID && info?.providerID)) {
               agent = info.agent
-              model = info.model
+              model = info.model ?? (info.providerID && info.modelID ? { providerID: info.providerID, modelID: info.modelID } : undefined)
               break
             }
           }

src/hooks/todo-continuation-enforcer.test.ts

@@ -829,4 +829,50 @@ describe("todo-continuation-enforcer", () => {
     expect(promptCalls[0].text).toContain("TODO CONTINUATION")
     expect("model" in promptCalls[0]).toBe(true)
   })
+
+  test("should extract model from assistant message with flat modelID/providerID", async () => {
+    // #given - session with assistant message that has flat modelID/providerID (OpenCode API format)
+    const sessionID = "main-assistant-model"
+    setMainSession(sessionID)
+
+    // OpenCode returns assistant messages with flat modelID/providerID, not nested model object
+    const mockMessagesWithAssistant = [
+      { info: { id: "msg-1", role: "user", agent: "Sisyphus", model: { providerID: "openai", modelID: "gpt-5.2" } } },
+      { info: { id: "msg-2", role: "assistant", agent: "Sisyphus", modelID: "gpt-5.2", providerID: "openai" } },
+    ]
+
+    const mockInput = {
+      client: {
+        session: {
+          todo: async () => ({
+            data: [{ id: "1", content: "Task 1", status: "pending", priority: "high" }],
+          }),
+          messages: async () => ({ data: mockMessagesWithAssistant }),
+          prompt: async (opts: any) => {
+            promptCalls.push({
+              sessionID: opts.path.id,
+              agent: opts.body.agent,
+              model: opts.body.model,
+              text: opts.body.parts[0].text,
+            })
+            return {}
+          },
+        },
+        tui: { showToast: async () => ({}) },
+      },
+      directory: "/tmp/test",
+    } as any
+
+    const hook = createTodoContinuationEnforcer(mockInput, {
+      backgroundManager: createMockBackgroundManager(false),
+    })
+
+    // #when - session goes idle
+    await hook.handler({ event: { type: "session.idle", properties: { sessionID } } })
+    await new Promise(r => setTimeout(r, 2500))
+
+    // #then - model should be extracted from assistant message's flat modelID/providerID
+    expect(promptCalls.length).toBe(1)
+    expect(promptCalls[0].model).toEqual({ providerID: "openai", modelID: "gpt-5.2" })
+  })
 })

src/hooks/todo-continuation-enforcer.ts

@@ -381,15 +381,17 @@ export function createTodoContinuationEnforcer(
           info?: {
             agent?: string
             model?: { providerID: string; modelID: string }
+            modelID?: string
+            providerID?: string
             tools?: Record<string, ToolPermission>
           }
         }>
         for (let i = messages.length - 1; i >= 0; i--) {
           const info = messages[i].info
-          if (info?.agent || info?.model) {
+          if (info?.agent || info?.model || (info?.modelID && info?.providerID)) {
             resolvedInfo = {
               agent: info.agent,
-              model: info.model,
+              model: info.model ?? (info.providerID && info.modelID ? { providerID: info.providerID, modelID: info.modelID } : undefined),
               tools: info.tools,
             }
             break

src/tools/sisyphus-task/tools.ts

@@ -297,13 +297,13 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
           try {
             const messagesResp = await client.session.messages({ path: { id: args.resume } })
             const messages = (messagesResp.data ?? []) as Array<{
-              info?: { agent?: string; model?: { providerID: string; modelID: string } }
+              info?: { agent?: string; model?: { providerID: string; modelID: string }; modelID?: string; providerID?: string }
             }>
             for (let i = messages.length - 1; i >= 0; i--) {
               const info = messages[i].info
-              if (info?.agent || info?.model) {
+              if (info?.agent || info?.model || (info?.modelID && info?.providerID)) {
                 resumeAgent = info.agent
-                resumeModel = info.model
+                resumeModel = info.model ?? (info.providerID && info.modelID ? { providerID: info.providerID, modelID: info.modelID } : undefined)
                 break
               }
             }