fix: use dynamic message lookup for model/agent context in prompts

Instead of using stale parentModel/parentAgent from task state, now
dynamically looks up the current message to get fresh model/agent values.
Applied across all prompt injection points:
- background-agent notifyParentSession
- ralph-loop continuation
- sisyphus-orchestrator boulder continuation
- sisyphus-task resume

🤖 Generated with [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode) assistance

src/features/background-agent/manager.test.ts

@@ -675,119 +675,141 @@ describe("LaunchInput.skillContent", () => {
   })
 })
 
-describe("BackgroundManager.notifyParentSession - agent context preservation", () => {
-  test("should never pass model field - let OpenCode use session's lastModel", async () => {
-    // #given - task with parentModel defined
+interface CurrentMessage {
+  agent?: string
+  model?: { providerID?: string; modelID?: string }
+}
+
+describe("BackgroundManager.notifyParentSession - dynamic message lookup", () => {
+  test("should use currentMessage model/agent when available", async () => {
+    // #given - currentMessage has model and agent
     const task: BackgroundTask = {
-      id: "task-with-model",
+      id: "task-1",
       sessionID: "session-child",
       parentSessionID: "session-parent",
       parentMessageID: "msg-parent",
-      description: "task with model context",
+      description: "task with dynamic lookup",
       prompt: "test",
       agent: "explore",
       status: "completed",
       startedAt: new Date(),
       completedAt: new Date(),
-      parentAgent: "Sisyphus",
-      parentModel: { providerID: "anthropic", modelID: "claude-opus-4-5" },
+      parentAgent: "OldAgent",
+      parentModel: { providerID: "old", modelID: "old-model" },
+    }
+    const currentMessage: CurrentMessage = {
+      agent: "Sisyphus",
+      model: { providerID: "anthropic", modelID: "claude-opus-4-5" },
     }
 
     // #when
-    const promptBody = buildNotificationPromptBody(task)
+    const promptBody = buildNotificationPromptBody(task, currentMessage)
 
-    // #then - model MUST NOT be passed (OpenCode uses session's lastModel)
-    expect("model" in promptBody).toBe(false)
+    // #then - uses currentMessage values, not task.parentModel/parentAgent
     expect(promptBody.agent).toBe("Sisyphus")
+    expect(promptBody.model).toEqual({ providerID: "anthropic", modelID: "claude-opus-4-5" })
   })
 
-  test("should not pass agent field when parentAgent is undefined", async () => {
+  test("should fallback to parentAgent when currentMessage.agent is undefined", async () => {
     // #given
     const task: BackgroundTask = {
-      id: "task-no-agent",
+      id: "task-2",
       sessionID: "session-child",
       parentSessionID: "session-parent",
       parentMessageID: "msg-parent",
-      description: "task without agent context",
+      description: "task fallback agent",
       prompt: "test",
       agent: "explore",
       status: "completed",
       startedAt: new Date(),
       completedAt: new Date(),
-      parentAgent: undefined,
-      parentModel: { providerID: "anthropic", modelID: "claude-opus" },
-    }
-
-    // #when
-    const promptBody = buildNotificationPromptBody(task)
-
-    // #then - no agent, no model (let OpenCode handle)
-    expect("agent" in promptBody).toBe(false)
-    expect("model" in promptBody).toBe(false)
-  })
-
-  test("should include agent field when parentAgent is defined", async () => {
-    // #given
-    const task: BackgroundTask = {
-      id: "task-with-agent",
-      sessionID: "session-child",
-      parentSessionID: "session-parent",
-      parentMessageID: "msg-parent",
-      description: "task with agent context",
-      prompt: "test",
-      agent: "explore",
-      status: "completed",
-      startedAt: new Date(),
-      completedAt: new Date(),
-      parentAgent: "Sisyphus",
-      parentModel: { providerID: "anthropic", modelID: "claude-opus" },
-    }
-
-    // #when
-    const promptBody = buildNotificationPromptBody(task)
-
-    // #then
-    expect(promptBody.agent).toBe("Sisyphus")
-    expect("model" in promptBody).toBe(false)
-  })
-
-  test("should not pass model field even when parentModel is undefined", async () => {
-    // #given
-    const task: BackgroundTask = {
-      id: "task-no-model",
-      sessionID: "session-child",
-      parentSessionID: "session-parent",
-      parentMessageID: "msg-parent",
-      description: "task without model context",
-      prompt: "test",
-      agent: "explore",
-      status: "completed",
-      startedAt: new Date(),
-      completedAt: new Date(),
-      parentAgent: "Sisyphus",
+      parentAgent: "FallbackAgent",
       parentModel: undefined,
     }
+    const currentMessage: CurrentMessage = { agent: undefined, model: undefined }
 
     // #when
-    const promptBody = buildNotificationPromptBody(task)
+    const promptBody = buildNotificationPromptBody(task, currentMessage)
 
-    // #then - model never passed regardless of parentModel
+    // #then - falls back to task.parentAgent
+    expect(promptBody.agent).toBe("FallbackAgent")
     expect("model" in promptBody).toBe(false)
+  })
+
+  test("should not pass model when currentMessage.model is incomplete", async () => {
+    // #given - model missing modelID
+    const task: BackgroundTask = {
+      id: "task-3",
+      sessionID: "session-child",
+      parentSessionID: "session-parent",
+      parentMessageID: "msg-parent",
+      description: "task incomplete model",
+      prompt: "test",
+      agent: "explore",
+      status: "completed",
+      startedAt: new Date(),
+      completedAt: new Date(),
+      parentAgent: "Sisyphus",
+      parentModel: { providerID: "anthropic", modelID: "claude-opus" },
+    }
+    const currentMessage: CurrentMessage = {
+      agent: "Sisyphus",
+      model: { providerID: "anthropic" },
+    }
+
+    // #when
+    const promptBody = buildNotificationPromptBody(task, currentMessage)
+
+    // #then - model not passed due to incomplete data
     expect(promptBody.agent).toBe("Sisyphus")
+    expect("model" in promptBody).toBe(false)
+  })
+
+  test("should handle null currentMessage gracefully", async () => {
+    // #given - no message found (messageDir lookup failed)
+    const task: BackgroundTask = {
+      id: "task-4",
+      sessionID: "session-child",
+      parentSessionID: "session-parent",
+      parentMessageID: "msg-parent",
+      description: "task no message",
+      prompt: "test",
+      agent: "explore",
+      status: "completed",
+      startedAt: new Date(),
+      completedAt: new Date(),
+      parentAgent: "Sisyphus",
+      parentModel: { providerID: "anthropic", modelID: "claude-opus" },
+    }
+
+    // #when
+    const promptBody = buildNotificationPromptBody(task, null)
+
+    // #then - falls back to task.parentAgent, no model
+    expect(promptBody.agent).toBe("Sisyphus")
+    expect("model" in promptBody).toBe(false)
   })
 })
 
-function buildNotificationPromptBody(task: BackgroundTask): Record<string, unknown> {
+function buildNotificationPromptBody(
+  task: BackgroundTask,
+  currentMessage: CurrentMessage | null
+): Record<string, unknown> {
   const body: Record<string, unknown> = {
     parts: [{ type: "text", text: `[BACKGROUND TASK COMPLETED] Task "${task.description}" finished.` }],
   }
 
-  if (task.parentAgent !== undefined) {
-    body.agent = task.parentAgent
-  }
+  const agent = currentMessage?.agent ?? task.parentAgent
+  const model = currentMessage?.model?.providerID && currentMessage?.model?.modelID
+    ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+    : undefined
 
-  // Don't pass model - let OpenCode use session's existing lastModel
-  // This prevents model switching when parentModel is undefined or different
+  if (agent !== undefined) {
+    body.agent = agent
+  }
+  if (model !== undefined) {
+    body.model = model
+  }
 
   return body
 }

src/features/background-agent/manager.ts

@@ -11,6 +11,9 @@ import type { BackgroundTaskConfig } from "../../config/schema"
 
 import { subagentSessions } from "../claude-code-session-state"
 import { getTaskToastManager } from "../task-toast-manager"
+import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../hook-message-injector"
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
 
 const TASK_TTL_MS = 30 * 60 * 1000
 const MIN_STABILITY_TIME_MS = 10 * 1000  // Must run at least 10s before stability detection kicks in
@@ -638,15 +641,32 @@ Use \`background_output(task_id="${task.id}")\` to retrieve this result when rea
 </system-reminder>`
     }
 
-    // Inject notification via session.prompt with noReply
-    // Don't pass model - let OpenCode use session's existing lastModel (like todo-continuation)
-    // This prevents model switching when parentModel is undefined
+    // Dynamically lookup the parent session's current message context
+    // This ensures we use the CURRENT model/agent, not the stale one from task creation time
+    const messageDir = getMessageDir(task.parentSessionID)
+    const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+
+    const agent = currentMessage?.agent ?? task.parentAgent
+    const model = currentMessage?.model?.providerID && currentMessage?.model?.modelID
+      ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+      : undefined
+
+    log("[background-agent] notifyParentSession context:", {
+      taskId: task.id,
+      messageDir: !!messageDir,
+      currentAgent: currentMessage?.agent,
+      currentModel: currentMessage?.model,
+      resolvedAgent: agent,
+      resolvedModel: model,
+    })
+
     try {
       await this.client.session.prompt({
         path: { id: task.parentSessionID },
         body: {
           noReply: !allComplete,
-          ...(task.parentAgent !== undefined ? { agent: task.parentAgent } : {}),
+          ...(agent !== undefined ? { agent } : {}),
+          ...(model !== undefined ? { model } : {}),
           parts: [{ type: "text", text: notification }],
         },
       })
@@ -841,3 +861,16 @@ if (lastMessage) {
     }
   }
 }
+
+function getMessageDir(sessionID: string): string | null {
+  if (!existsSync(MESSAGE_STORAGE)) return null
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) return directPath
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) return sessionPath
+  }
+  return null
+}

src/hooks/ralph-loop/index.ts

@@ -1,5 +1,6 @@
-import { existsSync, readFileSync } from "node:fs"
 import type { PluginInput } from "@opencode-ai/plugin"
+import { existsSync, readFileSync, readdirSync } from "node:fs"
+import { join } from "node:path"
 import { log } from "../../shared/logger"
 import { readState, writeState, clearState, incrementIteration } from "./storage"
 import {
@@ -9,6 +10,18 @@ import {
 } from "./constants"
 import type { RalphLoopState, RalphLoopOptions } from "./types"
 import { getTranscriptPath as getDefaultTranscriptPath } from "../claude-code-hooks/transcript"
+import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+
+function getMessageDir(sessionID: string): string | null {
+  if (!existsSync(MESSAGE_STORAGE)) return null
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) return directPath
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) return sessionPath
+  }
+  return null
+}
 
 export * from "./types"
 export * from "./constants"
@@ -302,9 +315,18 @@ export function createRalphLoopHook(
         .catch(() => {})
 
       try {
+        const messageDir = getMessageDir(sessionID)
+        const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+        const agent = currentMessage?.agent
+        const model = currentMessage?.model?.providerID && currentMessage?.model?.modelID
+          ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+          : undefined
+
         await ctx.client.session.prompt({
           path: { id: sessionID },
           body: {
+            ...(agent !== undefined ? { agent } : {}),
+            ...(model !== undefined ? { model } : {}),
             parts: [{ type: "text", text: continuationPrompt }],
           },
           query: { directory: ctx.directory },

src/hooks/sisyphus-orchestrator/index.ts

@@ -407,10 +407,17 @@ export function createSisyphusOrchestratorHook(
     try {
       log(`[${HOOK_NAME}] Injecting boulder continuation`, { sessionID, planName, remaining })
 
+      const messageDir = getMessageDir(sessionID)
+      const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+      const model = currentMessage?.model?.providerID && currentMessage?.model?.modelID
+        ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+        : undefined
+
       await ctx.client.session.prompt({
         path: { id: sessionID },
         body: {
           agent: "orchestrator-sisyphus",
+          ...(model !== undefined ? { model } : {}),
           parts: [{ type: "text", text: prompt }],
         },
         query: { directory: ctx.directory },

src/tools/sisyphus-task/tools.ts

@@ -218,9 +218,18 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
         })
 
         try {
+          const resumeMessageDir = getMessageDir(args.resume)
+          const resumeMessage = resumeMessageDir ? findNearestMessageWithFields(resumeMessageDir) : null
+          const resumeAgent = resumeMessage?.agent
+          const resumeModel = resumeMessage?.model?.providerID && resumeMessage?.model?.modelID
+            ? { providerID: resumeMessage.model.providerID, modelID: resumeMessage.model.modelID }
+            : undefined
+
           await client.session.prompt({
             path: { id: args.resume },
             body: {
+              ...(resumeAgent !== undefined ? { agent: resumeAgent } : {}),
+              ...(resumeModel !== undefined ? { model: resumeModel } : {}),
               tools: {
                 task: false,
                 sisyphus_task: false,