[BUG FIX] Preserve model context across agent handoffs and background tasks

assets/oh-my-opencode.schema.json

@@ -85,6 +85,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -196,6 +199,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -307,6 +313,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -418,6 +427,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -529,6 +541,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -640,6 +655,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -751,6 +769,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -862,6 +883,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -973,6 +997,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {
@@ -1084,6 +1111,9 @@
             "prompt": {
               "type": "string"
             },
+            "prompt_append": {
+              "type": "string"
+            },
             "tools": {
               "type": "object",
               "propertyNames": {

src/agents/librarian.ts

@@ -1,13 +1,16 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
 
-export const librarianAgent: AgentConfig = {
-  description:
-    "Specialized codebase understanding agent for multi-repository analysis, searching remote codebases, retrieving official documentation, and finding implementation examples using GitHub CLI, Context7, and Web Search. MUST BE USED when users ask to look up code in remote repositories, explain library internals, or find usage examples in open source.",
-  mode: "subagent",
-  model: "anthropic/claude-sonnet-4-5",
-  temperature: 0.1,
-  tools: { write: false, edit: false, background_task: false },
-  prompt: `# THE LIBRARIAN
+const DEFAULT_MODEL = "anthropic/claude-sonnet-4-5"
+
+export function createLibrarianAgent(model: string = DEFAULT_MODEL): AgentConfig {
+  return {
+    description:
+      "Specialized codebase understanding agent for multi-repository analysis, searching remote codebases, retrieving official documentation, and finding implementation examples using GitHub CLI, Context7, and Web Search. MUST BE USED when users ask to look up code in remote repositories, explain library internals, or find usage examples in open source.",
+    mode: "subagent",
+    model,
+    temperature: 0.1,
+    tools: { write: false, edit: false, background_task: false },
+    prompt: `# THE LIBRARIAN
 
 You are **THE LIBRARIAN**, a specialized open-source codebase understanding agent.
 
@@ -237,4 +240,7 @@ grep_app_searchGitHub(query: "useQuery")
 5. **BE CONCISE**: Facts > opinions, evidence > speculation
 
 `,
+  }
 }
+
+export const librarianAgent = createLibrarianAgent()

src/agents/utils.ts

@@ -2,7 +2,7 @@ import type { AgentConfig } from "@opencode-ai/sdk"
 import type { BuiltinAgentName, AgentOverrideConfig, AgentOverrides, AgentFactory } from "./types"
 import { createSisyphusAgent } from "./sisyphus"
 import { createOracleAgent } from "./oracle"
-import { librarianAgent } from "./librarian"
+import { createLibrarianAgent } from "./librarian"
 import { exploreAgent } from "./explore"
 import { frontendUiUxEngineerAgent } from "./frontend-ui-ux-engineer"
 import { documentWriterAgent } from "./document-writer"
@@ -14,7 +14,7 @@ type AgentSource = AgentFactory | AgentConfig
 const agentSources: Record<BuiltinAgentName, AgentSource> = {
   Sisyphus: createSisyphusAgent,
   oracle: createOracleAgent,
-  librarian: librarianAgent,
+  librarian: createLibrarianAgent,
   explore: exploreAgent,
   "frontend-ui-ux-engineer": frontendUiUxEngineerAgent,
   "document-writer": documentWriterAgent,

src/features/background-agent/manager.ts

@@ -99,6 +99,7 @@ export class BackgroundManager {
         toolCalls: 0,
         lastUpdate: new Date(),
       },
+      parentModel: input.parentModel,
     }
 
     this.tasks.set(task.id, task)
@@ -322,10 +323,16 @@ export class BackgroundManager {
         const messageDir = getMessageDir(task.parentSessionID)
         const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
 
+        const modelContext = task.parentModel ?? prevMessage?.model
+        const modelField = modelContext?.providerID && modelContext?.modelID
+          ? { providerID: modelContext.providerID, modelID: modelContext.modelID }
+          : undefined
+
         await this.client.session.prompt({
           path: { id: task.parentSessionID },
           body: {
             agent: prevMessage?.agent,
+            model: modelField,
             parts: [{ type: "text", text: message }],
           },
           query: { directory: this.directory },

src/features/background-agent/types.ts

@@ -26,6 +26,7 @@ export interface BackgroundTask {
   result?: string
   error?: string
   progress?: TaskProgress
+  parentModel?: { providerID: string; modelID: string }
 }
 
 export interface LaunchInput {
@@ -34,4 +35,5 @@ export interface LaunchInput {
   agent: string
   parentSessionID: string
   parentMessageID: string
+  parentModel?: { providerID: string; modelID: string }
 }

src/tools/background-task/tools.ts

@@ -1,10 +1,27 @@
 import { tool, type PluginInput } from "@opencode-ai/plugin"
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
 import type { BackgroundManager, BackgroundTask } from "../../features/background-agent"
 import type { BackgroundTaskArgs, BackgroundOutputArgs, BackgroundCancelArgs } from "./types"
 import { BACKGROUND_TASK_DESCRIPTION, BACKGROUND_OUTPUT_DESCRIPTION, BACKGROUND_CANCEL_DESCRIPTION } from "./constants"
+import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
 
 type OpencodeClient = PluginInput["client"]
 
+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
+}
+
 function formatDuration(start: Date, end?: Date): string {
   const duration = (end ?? new Date()).getTime() - start.getTime()
   const seconds = Math.floor(duration / 1000)
@@ -34,12 +51,19 @@ export function createBackgroundTask(manager: BackgroundManager) {
       }
 
       try {
+        const messageDir = getMessageDir(toolContext.sessionID)
+        const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+        const parentModel = prevMessage?.model?.providerID && prevMessage?.model?.modelID
+          ? { providerID: prevMessage.model.providerID, modelID: prevMessage.model.modelID }
+          : undefined
+
         const task = await manager.launch({
           description: args.description,
           prompt: args.prompt,
           agent: args.agent.trim(),
           parentSessionID: toolContext.sessionID,
           parentMessageID: toolContext.messageID,
+          parentModel,
         })
 
         return `Background task launched successfully.