Subagent SessionEnd crash: classifyHandoffIfNeeded is not defined

Bug

When a Task subagent completes, the session end process crashes with:

classifyHandoffIfNeeded is not defined

Reproduction

1. Spawn a subagent via the Task tool (subagent_type: "general-purpose")
2. Let it complete its work normally
3. Agent reports status: failed with the above error

Observed behavior

• The subagent completes all its work (file edits land in the working tree)
• The crash happens during session teardown, not during execution
• The function classifyHandoffIfNeeded does not exist in any user-controllable hook code — it appears to be internal to Claude Code
• Custom SessionEnd hooks (.claude/settings.json → session_end.py) are not the cause — the crash occurs before/outside user hooks

Expected behavior

Subagent should report status: completed when its work finishes successfully.

Impact

• Misleading: agents report "failed" when they actually succeeded
• The parent session has to check the working tree to determine if work was actually done
• Reproducible — happened on 3 consecutive subagent runs

Environment

• Claude Code CLI (latest as of 2026-02-09)
• macOS Darwin 25.2.0
• Model: claude-sonnet-4-5-20250929 (subagent), claude-opus-4-6 (parent)