refactor(background-agent): split manager.ts into focused modules

Extract 30+ single-responsibility modules from manager.ts (1556 LOC):
- task lifecycle: task-starter, task-completer, task-canceller, task-resumer
- task queries: task-queries, task-poller, task-queue-processor
- notifications: notification-builder, notification-tracker, parent-session-notifier
- session handling: session-validator, session-output-validator, session-todo-checker
- spawner: spawner/ directory with focused spawn modules
- utilities: duration-formatter, error-classifier, message-storage-locator
- result handling: result-handler-context, background-task-completer
- shutdown: background-manager-shutdown, process-signal

src/features/background-agent/parent-session-context-resolver.ts

@@ -0,0 +1,75 @@
+import type { OpencodeClient } from "./constants"
+import type { BackgroundTask } from "./types"
+import { findNearestMessageWithFields } from "../hook-message-injector"
+import { getMessageDir } from "./message-storage-locator"
+
+type AgentModel = { providerID: string; modelID: string }
+
+function isObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function extractAgentAndModelFromMessage(message: unknown): {
+  agent?: string
+  model?: AgentModel
+} {
+  if (!isObject(message)) return {}
+  const info = message["info"]
+  if (!isObject(info)) return {}
+
+  const agent = typeof info["agent"] === "string" ? info["agent"] : undefined
+  const modelObj = info["model"]
+  if (isObject(modelObj)) {
+    const providerID = modelObj["providerID"]
+    const modelID = modelObj["modelID"]
+    if (typeof providerID === "string" && typeof modelID === "string") {
+      return { agent, model: { providerID, modelID } }
+    }
+  }
+
+  const providerID = info["providerID"]
+  const modelID = info["modelID"]
+  if (typeof providerID === "string" && typeof modelID === "string") {
+    return { agent, model: { providerID, modelID } }
+  }
+
+  return { agent }
+}
+
+export async function resolveParentSessionAgentAndModel(input: {
+  client: OpencodeClient
+  task: BackgroundTask
+}): Promise<{ agent?: string; model?: AgentModel }> {
+  const { client, task } = input
+
+  let agent: string | undefined = task.parentAgent
+  let model: AgentModel | undefined
+
+  try {
+    const messagesResp = await client.session.messages({
+      path: { id: task.parentSessionID },
+    })
+
+    const messagesRaw = "data" in messagesResp ? messagesResp.data : []
+    const messages = Array.isArray(messagesRaw) ? messagesRaw : []
+
+    for (let i = messages.length - 1; i >= 0; i--) {
+      const extracted = extractAgentAndModelFromMessage(messages[i])
+      if (extracted.agent || extracted.model) {
+        agent = extracted.agent ?? task.parentAgent
+        model = extracted.model
+        break
+      }
+    }
+  } catch {
+    const messageDir = getMessageDir(task.parentSessionID)
+    const currentMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+    agent = currentMessage?.agent ?? task.parentAgent
+    model =
+      currentMessage?.model?.providerID && currentMessage?.model?.modelID
+        ? { providerID: currentMessage.model.providerID, modelID: currentMessage.model.modelID }
+        : undefined
+  }
+
+  return { agent, model }
+}