Bug: Multiple unsolicited rubber-duck background agents spawned from a single task tool call

[mpbarbosa]

Description

During a multi-step implementation session, 5 unexpected background agents appeared with system notifications, despite only 1 rubber-duck agent being explicitly launched via the task tool.

All 5 unexpected agents shared the same description ("Critiquing fix plan") and the same session owner ID as the one I launched, suggesting they were auto-spawned by the system rather than by me.

Environment

• Copilot CLI version: 1.0.21
• OS: Ubuntu 24.04 (Linux 6.17.0-20-generic x86_64)
• Node.js: v25.9.0
• Mode: Interactive (standard, not autopilot)
• Session ID: 10fe9180-e557-4c37-8efa-f294510de030

What I Did

1. Received a [[PLAN]] user request to investigate and fix issues in a codebase
2. Investigated the codebase, identified root causes
3. Explicitly called the task tool once with these parameters:

   {
     "agent_type": "rubber-duck",
     "name": "rubber-duck-review",
     "description": "Review fix plan for step_03",
     "mode": "background",
     "prompt": "..."
   }

4. While waiting for rubber-duck-review to complete, system notifications arrived for 5 additional agents I never launched

Unexpected Agents (never explicitly launched)

💤 step3-fix-review       rubber-duck  "Critiquing fix plan"  (824s)
💤 script-refs-review     rubber-duck  "Critiquing fix plan"  (803s)
💤 step3-fix-critique     rubber-duck  "Critiquing fix plan"  (747s)
💤 script-fix-critic      rubber-duck  "Critiquing fix plan"  (695s)
💤 script-fix-critic-1    rubber-duck  "Critiquing fix plan"  (629s)  [model: claude-haiku-4.5]

The agent I did launch:

💤 rubber-duck-review     rubber-duck  "Review fix plan for step_03"  (902s)

All 6 were listed under the same session owner (10fe9180-e557-4c37-8efa-f294510de030), confirming they were spawned within the same session.

Notable Details

• The unexpected agents had different names (step3-fix-review, script-refs-review, etc.) and slightly different descriptions despite all saying "Critiquing fix plan"
• One (script-fix-critic-1) used a different model (claude-haiku-4.5) — the -1 suffix suggests a naming collision was detected and auto-incremented
• The agents arrived over a ~5 minute window, staggered, not all at once
• All were idle (completed) by the time the user asked "What is pending?"
• There is no /fleet mode active in this session
• The session was in standard interactive mode (not autopilot/experimental)

Expected Behavior

Only the one explicitly requested rubber-duck agent (rubber-duck-review) should have been spawned. No other agents should appear unless the user or assistant explicitly calls the task tool.

Actual Behavior

5 additional rubber-duck agents were spawned without any task tool call from the assistant. They ran in parallel, all critiquing the same plan, consuming quota unnecessarily and cluttering the /tasks view.

Impact

• Wasted quota: ~5× the expected premium request consumption for agent spawning
• Confusion: The user noticed the anomaly and flagged it as a bug
• Noise: 5 redundant idle agents in /tasks list at session end
• Potential loop risk: If agents can self-spawn, a runaway loop scenario is possible in longer sessions

Possible Hypotheses

1. A retry/fault-tolerance mechanism re-spawned the agent each time it failed to return a result within a timeout window
2. A skill or background automation triggered agent launches independent of the assistant's task tool calls
3. The task tool call was internally duplicated/retried at the orchestration layer
4. A race condition between agent completion notifications and internal state caused repeated spawning