/btw command blocks instead of answering in background (v2.1.73)

Description

When using /btw while Claude is actively working on a task, the yellow overlay message appears correctly, but the response does not come back in the background. Instead, it waits until the main task completes before answering the /btw question.

Expected behavior

Per the docs: "The side question runs independently and does not interrupt the main turn." The /btw response should appear asynchronously in the overlay while Claude continues working on the main task.

Actual behavior

1. Start a long-running task (e.g., running a test suite)
2. Type /btw some quick question
3. Yellow overlay appears with the question
4. No response until the main task finishes
5. After main task completes, /btw gets answered

Environment

• Claude Code version: 2.1.73
• OS: macOS Darwin 25.3.0 (Apple Silicon)
• Shell: zsh
• Node.js: v22.14.0

Additional context

• CLAUDE_CODE_DISABLE_BACKGROUND_TASKS is not set
• Also, typing /btw when Claude is idle routes it to the skill system which returns "Unknown skill: btw" instead of being handled as a built-in command