[BUG] Fast mode silently disabled when Claude starts responding (v2.1.68)

Description

After enabling fast mode via /fast, it gets silently and completely disabled as soon as Claude starts responding. This differs from the documented rate-limit fallback behavior (where ↯ turns gray and auto-reactivates after cooldown).

Steps to Reproduce

1. Start a Claude Code session (v2.1.68)
2. Run /fast to enable fast mode — ↯ icon appears in status bar
3. Send any message to Claude
4. Once Claude starts responding, the ↯ icon disappears
5. Run /fast — it reports fast mode is OFF

Additional reproduction

| Test | Condition | Result |
|------|-----------|--------|
| Test 1 | Plan mode + /fast ON → Claude responds | Fast mode fully OFF |
| Test 2 | Normal mode + /fast ON → subagent spawn | Fast mode fully OFF |

Common pattern: /fast ON → Claude starts responding → ↯ disappears → /fast confirms OFF

Expected Behavior

• Fast mode should remain ON across responses, as documented
• If rate-limited, the ↯ should turn gray and auto-reactivate after cooldown (per docs)
• "fastMode": true in settings.json should persist the setting

Actual Behavior

• Fast mode is completely disabled (not grayed out) when Claude starts responding
• The ↯ icon fully disappears from the status bar
• /fast reports the mode is OFF
• This happens regardless of whether "fastMode": true is set in settings.json

Environment

• Claude Code version: v2.1.68
• OS: macOS (Darwin 25.3.0)
• Plan: Pro (extra usage enabled)
• Settings: "fastMode": true configured in settings.json

Related Issues

• #27713 — Status bar indicator not reflecting actual state (similar but opposite direction)
• #24351 — fastMode setting not applied at startup
• #24345 — Feature request for persistent fast mode
• #24205 — Fast mode not activating in VS Code

None of these describe the exact behavior where fast mode is silently turned off upon response start.