[Bug] ReferenceError: classifyHandoffIfNeeded undefined in concurrent Task subagent completion

Bug Description
Bug Report: ReferenceError When Multiple Task Subagents Complete Concurrently

Description

Claude Code v2.1.29 throws ReferenceError: classifyHandoffIfNeeded is not defined when multiple Task tool subagents complete concurrently, incorrectly marking successfully executed
tasks as failed.

Environment

• Claude Code Version: 2.1.29
• Platform: macOS (Darwin 23.4.0, arm64)
• Installation Method: Homebrew cask

Symptoms

• Tasks report failed status despite successfully completing all steps and producing valid output
• Error message: classifyHandoffIfNeeded is not defined
• Error only appears in queue-operation notifications, not in agent execution logs
• Sequential task execution works reliably
• Concurrent task execution (≤1 minute apart) triggers the error

Root Cause

The Task tool completion handler calls classifyHandoffIfNeeded() from a lazily-initialized module. When multiple subagents complete concurrently, the function is invoked before the
module finishes loading, causing a ReferenceError.

Evidence

Timing Analysis

Same session, identical parameters, only difference is concurrency:
┌──────────┬────────────┬──────────┬─────────┬────────────────┐
│ Agent ID │ Start Time │ End Time │ Status │ Execution Mode │
├──────────┼────────────┼──────────┼─────────┼────────────────┤
│ a4f3f5e │ 09:21:41 │ 09:26:43 │ FAILED │ Concurrent │
├──────────┼────────────┼──────────┼─────────┼────────────────┤
│ a694bc3 │ 09:22:22 │ 09:25:44 │ FAILED │ Concurrent │
├──────────┼────────────┼──────────┼─────────┼────────────────┤
│ adf02d4 │ 09:25:55 │ 09:28:46 │ SUCCESS │ Sequential │
└──────────┴────────────┴──────────┴─────────┴────────────────┘
Error Message

<task-notification>
<task-id>a694bc3</task-id>
<status>failed</status>
<summary>Agent "Decision-critic SQL vs code fix" failed: classifyHandoffIfNeeded is not defined</summary>
</task-notification>

Reproduction Steps

1. Start a Claude Code session
2. Launch two Task tool subagents in rapid succession (within ~1 minute)
3. Allow both agents to execute and complete around the same time
4. Observe ReferenceError in task-notification for one or both tasks

Impact

• Correctness: Successfully executed tasks incorrectly marked as failed
• Data Loss: Valid task output is discarded
• Workflow: Concurrent task execution is unreliable

Workaround

Execute Task subagents sequentially—wait for one to complete before starting another.

Suggested Labels

bug task-tool race-condition concurrency

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Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.29
• Feedback ID: 89d36a7a-7580-401d-9765-d36417e12cd0

Errors

[{"error":"Error: Failed to initialize LSP server plugin:jdtls-lsp:jdtls: LSP server 'plugin:jdtls-lsp:jdtls': startupTimeout is not yet implemented. Remove this field from the configuration.\n    at _ (/$bunfs/root/claude:2142:32620)\n    at processTicksAndRejections (native:7:39…

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