fix: improve background task completion detection and message extraction (#638)

* fix: background task completion detection and silent notifications

- Fix TS2742 by adding explicit ToolDefinition type annotations
- Add stability detection (3 consecutive stable polls after 10s minimum)
- Remove early continue when sessionStatus is undefined
- Add silent notification system via tool.execute.after hook injection
- Change task retention from 200ms to 5 minutes for background_output retrieval
- Fix formatTaskResult to sort messages by time descending

Fixes hanging background tasks that never complete due to missing sessionStatus.

* fix: improve background task completion detection and message extraction

- Add stability-based completion detection (10s min + 3 stable polls)
- Fix message extraction to recognize 'reasoning' parts from thinking models
- Switch from promptAsync() to prompt() for proper agent initialization
- Remove model parameter from prompt body (use agent's configured model)
- Add fire-and-forget prompt pattern for sisyphus_task sync mode
- Add silent notification via tool.execute.after hook injection
- Fix indentation issues in manager.ts and index.ts

Incorporates fixes from:
- PR #592: Stability detection mechanism
- PR #610: Model parameter passing (partially)
- PR #628: Completion detection improvements

Known limitation: Thinking models (e.g. claude-*-thinking-*) cause
JSON Parse errors in child sessions. Use non-thinking models for
background agents until OpenCode core resolves this.

* fix: add tool_result handling and pendingByParent tracking for resume/external tasks

Addresses code review feedback from PR #638:

P1: Add tool_result type to validateSessionHasOutput() to prevent
    false negatives for tool-only background tasks that would otherwise
    timeout after 30 minutes despite having valid results.

P2: Add pendingByParent tracking to resume() and registerExternalTask()
    to prevent premature 'ALL COMPLETE' notifications when mixing
    launched and resumed tasks.

* fix: address code review feedback - log messages, model passthrough, sorting, race condition

- Fix misleading log messages: 'promptAsync' -> 'prompt (fire-and-forget)'
- Restore model passthrough in launch() for Sisyphus category configs
- Fix call-omo-agent sorting: use time.created number instead of String(time)
- Fix race condition: check promptError inside polling loop, not just after 100ms

src/hooks/background-compaction/index.ts

@@ -0,0 +1,85 @@
+import type { BackgroundManager } from "../../features/background-agent"
+
+interface CompactingInput {
+  sessionID: string
+}
+
+interface CompactingOutput {
+  context: string[]
+  prompt?: string
+}
+
+/**
+ * Background agent compaction hook - preserves task state during context compaction.
+ * 
+ * When OpenCode compacts session context to save tokens, this hook injects
+ * information about running and recently completed background tasks so the
+ * agent doesn't lose awareness of delegated work.
+ */
+export function createBackgroundCompactionHook(manager: BackgroundManager) {
+  return {
+    "experimental.session.compacting": async (
+      input: CompactingInput,
+      output: CompactingOutput
+    ): Promise<void> => {
+      const { sessionID } = input
+
+      // Get running tasks for this session
+      const running = manager.getRunningTasks()
+        .filter(t => t.parentSessionID === sessionID)
+        .map(t => ({
+          id: t.id,
+          agent: t.agent,
+          description: t.description,
+          startedAt: t.startedAt,
+        }))
+
+      // Get recently completed tasks (still in memory within 5-min retention)
+      const completed = manager.getCompletedTasks()
+        .filter(t => t.parentSessionID === sessionID)
+        .slice(-10) // Last 10 completed
+        .map(t => ({
+          id: t.id,
+          agent: t.agent,
+          description: t.description,
+          status: t.status,
+        }))
+
+      // Early exit if nothing to preserve
+      if (running.length === 0 && completed.length === 0) return
+
+      const sections: string[] = ["<background-tasks>"]
+
+      // Running tasks section
+      if (running.length > 0) {
+        sections.push("## Running Background Tasks")
+        sections.push("")
+        for (const t of running) {
+          const elapsed = Math.floor((Date.now() - t.startedAt.getTime()) / 1000)
+          sections.push(`- **\`${t.id}\`** (${t.agent}): ${t.description} [${elapsed}s elapsed]`)
+        }
+        sections.push("")
+        sections.push("> **Note:** You WILL be notified when tasks complete.")
+        sections.push("> Do NOT poll - continue productive work.")
+        sections.push("")
+      }
+
+      // Completed tasks section
+      if (completed.length > 0) {
+        sections.push("## Recently Completed Tasks")
+        sections.push("")
+        for (const t of completed) {
+          const statusEmoji = t.status === "completed" ? "✅" : t.status === "error" ? "❌" : "⏱️"
+          sections.push(`- ${statusEmoji} **\`${t.id}\`**: ${t.description}`)
+        }
+        sections.push("")
+      }
+
+      sections.push("## Retrieval")
+      sections.push('Use `background_output(task_id="<id>")` to retrieve task results.')
+      sections.push("</background-tasks>")
+
+      output.context.push(sections.join("\n"))
+    }
+  }
+}

src/hooks/background-notification/index.ts

@@ -9,6 +9,12 @@ interface EventInput {
   event: Event
 }
 
+/**
+ * Background notification hook - handles event routing to BackgroundManager.
+ * 
+ * Notifications are now delivered directly via session.prompt({ noReply }) 
+ * from the manager, so this hook only needs to handle event routing.
+ */
 export function createBackgroundNotificationHook(manager: BackgroundManager) {
   const eventHandler = async ({ event }: EventInput) => {
     manager.handleEvent(event)

src/hooks/index.ts

@@ -14,6 +14,7 @@ export { createThinkModeHook } from "./think-mode";
 export { createClaudeCodeHooksHook } from "./claude-code-hooks";
 export { createRulesInjectorHook } from "./rules-injector";
 export { createBackgroundNotificationHook } from "./background-notification"
+export { createBackgroundCompactionHook } from "./background-compaction"
 export { createAutoUpdateCheckerHook } from "./auto-update-checker";
 
 export { createAgentUsageReminderHook } from "./agent-usage-reminder";