[BUG] Prompt suggestions stopped generating after v2.1.29 — subagent never spawns

Description

Contextual prompt suggestions (the grayed-out follow-up predictions after Claude responds) stopped working somewhere between v2.1.29 and v2.1.50. The startup hint ("try how do I log an error?") still appears, but no contextual suggestions are generated after responses.

Evidence from local subagent logs

The agent-aprompt_suggestion subagent files in ~/.claude/projects/ confirm the feature worked on v2.1.29 (Feb 3-4) — generating contextual suggestions like "what's next for mvp1" after responses.

Zero suggestion subagent files exist after Feb 4. The subagent simply isn't being spawned anymore.

# Last working suggestion files (v2.1.29, Feb 4):
~/.claude/projects/-Users-mao/<session>/subagents/agent-aprompt_suggestion-ceb078.jsonl

# Current sessions on v2.1.50: no suggestion files at all

Steps to reproduce

1. cd into a git repo with recent commit history
2. Launch: CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=true claude
3. Startup hint appears (e.g. "try how do I log an error?")
4. Send any message and wait for a response
5. After response completes, wait 15+ seconds — no follow-up suggestion appears
6. Confirm no agent-aprompt_suggestion-* files were created in the session's subagents/ directory

Tested configurations

| Method | Startup hint | Follow-up suggestions |
|--------|-------------|----------------------|
| Env var in settings.json env block | Yes | No |
| Shell CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=true (no settings.json env) | Yes | No |
| /config toggle off → on | Yes | No |

Expected behavior

After each Claude response, a grayed-out contextual suggestion should appear in the input field (as it did on v2.1.29).

Environment

• Claude Code v2.1.50 (latest as of Feb 22, 2026)
• macOS 26.2 (Apple Silicon M2)
• Subscription plan (Claude Max)