feat(compaction): wire TaskHistory into BackgroundManager and compaction pipeline

Records task history at 6 status transitions (pending, running×2, error,
cancelled, completed). Exports TaskHistory from background-agent barrel.
Passes backgroundManager and sessionID through compaction hook chain.

src/features/background-agent/index.ts

@@ -1,4 +1,5 @@
 export * from "./types"
 export { BackgroundManager, type SubagentSessionCreatedEvent, type OnSubagentSessionCreated } from "./manager"
+export { TaskHistory, type TaskHistoryEntry } from "./task-history"
 export { ConcurrencyManager } from "./concurrency"
 export { TaskStateManager } from "./state"

src/features/background-agent/manager.ts

@@ -5,6 +5,7 @@ import type {
   LaunchInput,
   ResumeInput,
 } from "./types"
+import { TaskHistory } from "./task-history"
 import { log, getAgentToolRestrictions, promptWithModelSuggestionRetry } from "../../shared"
 import { ConcurrencyManager } from "./concurrency"
 import type { BackgroundTaskConfig, TmuxConfig } from "../../config/schema"
@@ -90,6 +91,7 @@ export class BackgroundManager {
   private completionTimers: Map<string, ReturnType<typeof setTimeout>> = new Map()
   private idleDeferralTimers: Map<string, ReturnType<typeof setTimeout>> = new Map()
   private notificationQueueByParent: Map<string, Promise<void>> = new Map()
+  readonly taskHistory = new TaskHistory()
 
   constructor(
     ctx: PluginInput,
@@ -144,6 +146,7 @@ export class BackgroundManager {
     }
 
     this.tasks.set(task.id, task)
+    this.taskHistory.record(input.parentSessionID, { id: task.id, agent: input.agent, description: input.description, status: "pending", category: input.category })
 
     // Track for batched notifications immediately (pending state)
     if (input.parentSessionID) {
@@ -291,6 +294,7 @@ export class BackgroundManager {
     task.concurrencyKey = concurrencyKey
     task.concurrencyGroup = concurrencyKey
 
+    this.taskHistory.record(input.parentSessionID, { id: task.id, sessionID, agent: input.agent, description: input.description, status: "running", category: input.category, startedAt: task.startedAt })
     this.startPolling()
 
     log("[background-agent] Launching task:", { taskId: task.id, sessionID, agent: input.agent })
@@ -486,6 +490,7 @@ export class BackgroundManager {
     this.tasks.set(task.id, task)
     subagentSessions.add(input.sessionID)
     this.startPolling()
+    this.taskHistory.record(input.parentSessionID, { id: task.id, sessionID: input.sessionID, agent: input.agent || "task", description: input.description, status: "running", startedAt: task.startedAt })
 
     if (input.parentSessionID) {
       const pending = this.pendingByParent.get(input.parentSessionID) ?? new Set()
@@ -741,6 +746,7 @@ export class BackgroundManager {
       task.status = "error"
       task.error = errorMessage ?? "Session error"
       task.completedAt = new Date()
+      this.taskHistory.record(task.parentSessionID, { id: task.id, sessionID: task.sessionID, agent: task.agent, description: task.description, status: "error", category: task.category, startedAt: task.startedAt, completedAt: task.completedAt })
 
       if (task.concurrencyKey) {
         this.concurrencyManager.release(task.concurrencyKey)
@@ -951,6 +957,7 @@ export class BackgroundManager {
     if (reason) {
       task.error = reason
     }
+    this.taskHistory.record(task.parentSessionID, { id: task.id, sessionID: task.sessionID, agent: task.agent, description: task.description, status: "cancelled", category: task.category, startedAt: task.startedAt, completedAt: task.completedAt })
 
     if (task.concurrencyKey) {
       this.concurrencyManager.release(task.concurrencyKey)
@@ -1095,6 +1102,7 @@ export class BackgroundManager {
     // Atomically mark as completed to prevent race conditions
     task.status = "completed"
     task.completedAt = new Date()
+    this.taskHistory.record(task.parentSessionID, { id: task.id, sessionID: task.sessionID, agent: task.agent, description: task.description, status: "completed", category: task.category, startedAt: task.startedAt, completedAt: task.completedAt })
 
     // Release concurrency BEFORE any async operations to prevent slot leaks
     if (task.concurrencyKey) {

src/index.ts

@@ -82,7 +82,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
       if (!hooks.compactionContextInjector) {
         return
       }
-      output.context.push(hooks.compactionContextInjector())
+      output.context.push(hooks.compactionContextInjector(_input.sessionID))
     },
   }
 }

src/plugin/hooks/create-continuation-hooks.ts

@@ -53,7 +53,7 @@ export function createContinuationHooks(args: {
     : null
 
   const compactionContextInjector = isHookEnabled("compaction-context-injector")
-    ? safeHook("compaction-context-injector", () => createCompactionContextInjector())
+    ? safeHook("compaction-context-injector", () => createCompactionContextInjector(backgroundManager))
     : null
 
   const compactionTodoPreserver = isHookEnabled("compaction-todo-preserver")