refactor(tmux-subagent): state-first architecture with decision engine (#1125)

* refactor(tmux-subagent): add state-first architecture with decision engine

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* feat(tmux): add pane spawn callbacks for background and sync sessions

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

---------

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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

@@ -776,7 +776,7 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
       parentModel: { providerID: "old", modelID: "old-model" },
     }
     const currentMessage: CurrentMessage = {
-      agent: "Sisyphus",
+      agent: "sisyphus",
       model: { providerID: "anthropic", modelID: "claude-opus-4-5" },
     }
 
@@ -784,7 +784,7 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
     const promptBody = buildNotificationPromptBody(task, currentMessage)
 
     // #then - uses currentMessage values, not task.parentModel/parentAgent
-    expect(promptBody.agent).toBe("Sisyphus")
+    expect(promptBody.agent).toBe("sisyphus")
     expect(promptBody.model).toEqual({ providerID: "anthropic", modelID: "claude-opus-4-5" })
   })
 
@@ -827,11 +827,11 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
       status: "completed",
       startedAt: new Date(),
       completedAt: new Date(),
-      parentAgent: "Sisyphus",
+      parentAgent: "sisyphus",
       parentModel: { providerID: "anthropic", modelID: "claude-opus" },
     }
     const currentMessage: CurrentMessage = {
-      agent: "Sisyphus",
+      agent: "sisyphus",
       model: { providerID: "anthropic" },
     }
 
@@ -839,7 +839,7 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
     const promptBody = buildNotificationPromptBody(task, currentMessage)
 
     // #then - model not passed due to incomplete data
-    expect(promptBody.agent).toBe("Sisyphus")
+    expect(promptBody.agent).toBe("sisyphus")
     expect("model" in promptBody).toBe(false)
   })
 
@@ -856,7 +856,7 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
       status: "completed",
       startedAt: new Date(),
       completedAt: new Date(),
-      parentAgent: "Sisyphus",
+      parentAgent: "sisyphus",
       parentModel: { providerID: "anthropic", modelID: "claude-opus" },
     }
 
@@ -864,7 +864,7 @@ describe("BackgroundManager.notifyParentSession - dynamic message lookup", () =>
     const promptBody = buildNotificationPromptBody(task, null)
 
     // #then - falls back to task.parentAgent, no model
-    expect(promptBody.agent).toBe("Sisyphus")
+    expect(promptBody.agent).toBe("sisyphus")
     expect("model" in promptBody).toBe(false)
   })
 })

src/features/background-agent/manager.ts

@@ -55,6 +55,14 @@ interface QueueItem {
   input: LaunchInput
 }
 
+export interface SubagentSessionCreatedEvent {
+  sessionID: string
+  parentID: string
+  title: string
+}
+
+export type OnSubagentSessionCreated = (event: SubagentSessionCreatedEvent) => Promise<void>
+
 export class BackgroundManager {
   private static cleanupManagers = new Set<BackgroundManager>()
   private static cleanupRegistered = false
@@ -70,6 +78,7 @@ export class BackgroundManager {
   private shutdownTriggered = false
   private config?: BackgroundTaskConfig
   private tmuxEnabled: boolean
+  private onSubagentSessionCreated?: OnSubagentSessionCreated
 
   private queuesByKey: Map<string, QueueItem[]> = new Map()
   private processingKeys: Set<string> = new Set()
@@ -77,7 +86,10 @@ export class BackgroundManager {
   constructor(
     ctx: PluginInput,
     config?: BackgroundTaskConfig,
-    tmuxConfig?: TmuxConfig
+    options?: {
+      tmuxConfig?: TmuxConfig
+      onSubagentSessionCreated?: OnSubagentSessionCreated
+    }
   ) {
     this.tasks = new Map()
     this.notifications = new Map()
@@ -86,7 +98,8 @@ export class BackgroundManager {
     this.directory = ctx.directory
     this.concurrencyManager = new ConcurrencyManager(config)
     this.config = config
-    this.tmuxEnabled = tmuxConfig?.enabled ?? false
+    this.tmuxEnabled = options?.tmuxConfig?.enabled ?? false
+    this.onSubagentSessionCreated = options?.onSubagentSessionCreated
     this.registerProcessCleanup()
   }
 
@@ -228,9 +241,27 @@ export class BackgroundManager {
     const sessionID = createResult.data.id
     subagentSessions.add(sessionID)
 
-    // Wait for TmuxSessionManager to spawn pane via event hook
-    if (this.tmuxEnabled && isInsideTmux()) {
-      await new Promise(r => setTimeout(r, 500))
+    log("[background-agent] tmux callback check", {
+      hasCallback: !!this.onSubagentSessionCreated,
+      tmuxEnabled: this.tmuxEnabled,
+      isInsideTmux: isInsideTmux(),
+      sessionID,
+      parentID: input.parentSessionID,
+    })
+
+    if (this.onSubagentSessionCreated && this.tmuxEnabled && isInsideTmux()) {
+      log("[background-agent] Invoking tmux callback NOW", { sessionID })
+      await this.onSubagentSessionCreated({
+        sessionID,
+        parentID: input.parentSessionID,
+        title: input.description,
+      }).catch((err) => {
+        log("[background-agent] Failed to spawn tmux pane:", err)
+      })
+      log("[background-agent] tmux callback completed, waiting 200ms")
+      await new Promise(r => setTimeout(r, 200))
+    } else {
+      log("[background-agent] SKIP tmux callback - conditions not met")
     }
 
     // Update task to running state