🤖 refactor: remove plan subagent auto-handoff by ammar-agent · Pull Request #3033 · coder/mux

ammar-agent · 2026-03-19T14:56:35Z

Summary

Remove plan-mode subagent auto-handoff after propose_plan, along with the executor-routing settings and backend router that supported it.

Background

Plan auto-handoff originally let plan-mode subagents compact into a plan and continue under exec or orchestrator. In practice it now collides with grouped task workflows: planning-only best-of batches can silently turn into implementation work. Removing the feature restores a clearer boundary: planning stays top-level, and task subagents stay implementation-oriented.

Implementation

removed the taskService stream-end handoff path that compacted history, switched agents, and posted synthetic Implement the plan / orchestrator kickoff messages
removed the plan-to-executor routing config surface from task settings, the settings UI, and the dedicated router/status modules
made the built-in plan agent non-runnable as a subagent again and added a task creation guard that rejects any plan-like subagent, including custom agents that inherit from plan
deleted the obsolete plan auto-routing story and updated orchestrator/docs copy to direct complex planning back to top-level plan workspaces instead of subagent auto-handoff

Validation

bun test src/common/types/tasks.test.ts
bun test src/node/services/taskService.test.ts
make static-check

Risks

Low-to-moderate. This intentionally removes an existing subagent workflow, so users relying on plan subagents that automatically continue into implementation will need to do planning in a top-level workspace instead. The change reduces surprising execution fan-out, and the new creation-time rejection keeps custom plan-like subagents from falling into an unsupported half-working state.

Generated with mux • Model: openai:gpt-5.4 • Thinking: high • Cost: $2.78

ammar-agent · 2026-03-19T14:56:45Z

@codex review

ammar-agent · 2026-03-19T15:02:41Z

@codex review

ammar-agent · 2026-03-19T15:06:25Z

@codex review

ammar-agent · 2026-03-19T15:10:55Z

@codex review

ammar-agent · 2026-03-19T15:13:34Z

@codex review

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src/node/builtinAgents/orchestrator.md

ammar-agent · 2026-03-19T15:25:43Z

@codex review

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mux/src/node/services/taskService.ts

Lines 3076 to 3080 in bb69d48

    
           if (status !== "awaiting_report") { 
        
             await this.setTaskStatus(workspaceId, "awaiting_report"); 
        
           } 
        
           await this.promptTaskForRequiredCompletionTool(workspaceId, { reason: "stream_end" });

Treat successful propose_plan as terminal task completion

This path now always pushes plan-like tasks into awaiting_report recovery without first checking whether event.parts already contains a successful propose_plan result, so legacy/in-flight plan-like subagent tasks (e.g. after upgrading with existing tasks) can get stuck in a loop where they are repeatedly told to call propose_plan and never finalize or clean up. Before this change, a successful propose_plan stream-end had a dedicated terminal path; removing it without a replacement leaves affected tasks non-terminating.

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ammar-agent · 2026-03-19T15:40:39Z

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src/node/services/taskService.ts

ammar-agent · 2026-03-19T15:54:44Z

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src/node/services/taskService.ts

ammar-agent · 2026-03-19T16:02:54Z

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src/node/services/taskService.ts

ammar-agent · 2026-03-19T16:13:27Z

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chatgpt-codex-connector · 2026-03-19T16:19:21Z

Codex Review: Didn't find any major issues. Chef's kiss.

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Remove plan-mode subagent auto-handoff after propose_plan, drop the executor-routing settings and backend router, reject plan-like task creation, and update related docs/stories/tests. --- _Generated with `mux` • Model: `openai:gpt-5.4` • Thinking: `high` • Cost: `$2.78`_

ammar-agent · 2026-03-19T16:21:57Z

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Codex Review: Didn't find any major issues. Breezy!

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JiwaniZakir

The diff is truncated mid-sentence at the docs/agents/index.mdx change — "If the implementation approach is still unc" — so it's unclear whether the replacement guidance is complete as written or if the rendered document will have a dangling incomplete instruction. That should be verified before merging.

Beyond that, the new framing in index.mdx replaces the plan sub-agent path with "do a small amount of parent-side framing first so the exec brief includes the goal, constraints, sequencing, and key files," but offers no threshold for what constitutes "a small amount" versus when a dedicated planning phase is genuinely warranted. The old guidance was prescriptive (plan for multi-file refactors, cross-module changes, unfamiliar subsystems), while the new guidance leaves that judgment entirely to the orchestrator without comparable concrete heuristics — the "Good fit" list is preserved but the routing decision it used to drive is now undefined.

In docs/AGENTS.md, the phrase "use a top-level plan workspace when you need a separate planning phase before delegation" introduces a new concept ("top-level plan workspace") that isn't defined or linked anywhere else in the visible diff; an agent reading only this file would have no way to know what that workspace is or how to enter it.

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	if (status !== "awaiting_report") {
	await this.setTaskStatus(workspaceId, "awaiting_report");
	}

	await this.promptTaskForRequiredCompletionTool(workspaceId, { reason: "stream_end" });

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ammar-agent commented Mar 19, 2026

Summary

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Implementation

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