[BUG] Remote trigger sessions receive no initial prompt — events[].data.message not delivered

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Remote trigger sessions initialize but the prompt from events[0].data.message.content is never delivered to the agent. The session starts, shows an "ideating" animation, and never acts. The agent receives no user message.

However, manually typing into the session works — the agent responds normally. This proves the session itself is functional; the automated prompt injection from the trigger config is what's broken.

Last Working Run

March 31, 2026 (~18:00 UTC). All runs since then produce empty sessions with no prompt delivery.

Timeline

1. March 31 18:00 UTC — last successful run (processed notes, logged results)
2. March 31–April 1 — two runs reported "no MCP access" (prompt arrived but MCP tools not found — possibly related to #35899)
3. April 1 12:00 UTC onward — all runs produce empty sessions. No prompt delivered. Agent shows "ideating" text and never acts.

Isolation Testing

We created three triggers to isolate the issue:

| Test | Config | Result |
|------|--------|--------|
| Full | Git repo + 4 MCP connections + long prompt + Opus | Session starts, no prompt, hangs |
| Minimal | Git repo + 1 MCP (Todoist) + 5-line prompt + Sonnet | Session starts, no prompt, hangs |
| Bare | No git repo, no MCP, no hooks, one-line prompt ("Say hello"), Sonnet | Session starts, no prompt, hangs |

The bare test rules out: prompt size, MCP connections, git repo cloning, SessionStart hooks, and model choice.

In all three cases, manually typing into the created session produces normal responses.

Trigger Configuration

{
  "job_config": {
    "ccr": {
      "environment_id": "env_011F97NGDD4AGHEr55XNKpVn",
      "events": [{
        "data": {
          "message": {
            "content": "Say exactly: \"Hello, prompt received.\" Then stop.",
            "role": "user"
          }
        }
      }],
      "session_context": {
        "model": "claude-sonnet-4-6"
      }
    }
  }
}

Expected Behavior

The prompt in events[0].data.message.content should be delivered as the initial user message when the trigger fires, as it was before March 31.

Actual Behavior

Session initializes, hooks fire (if repo is configured), but no user message is delivered. Agent has nothing to respond to and sits idle until the session times out.

Environment

• Plan: Claude Max
• Platform: Web (claude.ai/code/scheduled)
• Trigger API: POST /v1/code/triggers/{id}/run
• Both manual /run and cron-scheduled executions are affected

Related Issues

• #35899 — MCP connectors not available until user message (different bug, but may share root cause in session initialization)
• #42771 — MCP not visible on first turn of remote trigger
• #42743 — Remote triggers lost gh CLI access around same timeframe