Slack-specific prompt logic leaks into the adapter host runtime

[akrentsel]

Summary

compose_inbound_wakeup_prompt in the host branches on adapter_type == "slack" and appends Slack-specific prompt text, reading two metadata keys (dmTarget, isActiveThread) that the Slack worker invents. This puts protocol-specific behavior in the host, coupled to the worker by untyped string keys across a language boundary.

The forthcoming architecture doc in #171 states the rule this breaks:

The host owns supervision, routing, durable message records, retries, and conversation wakeups. Protocol-specific behavior stays in each worker.

Where

Host side — crates/executor/src/adapter/runtime.rs:910-925:

if config.adapter_type == "slack" {
    if let Some(dm_target) = metadata.get("dmTarget").and_then(|value| value.as_str()) {
        prompt.push_str(&format!(
            "\n\nSlack sender DM target: `{dm_target}`. Use this only for appropriate private follow-up; do not use DM to bypass safety policy.",
        ));
    }
    if metadata.get("isActiveThread").and_then(|value| value.as_bool()) == Some(true) {
        prompt.push_str(
            "\n\nThis Slack message is from an active thread, but it may be ambient conversation. Only call send_adapter_message if the message appears directed at Exo, ...",
        );
    }
}

Worker side — examples/exo/adapters/slack/worker.ts:771,775 emits isActiveThread and dmTarget into the event metadata.

Related instances of the same pattern (not the subject of this issue, but relevant if a general fix is preferred):

• crates/executor/src/adapter/tools.rs:904 — Slack dm: target validation

Suggested fix

metadata is already free-form JSON fully controlled by the worker, so the guidance can travel with it. Have workers emit their own prompt notes and let the host append them generically:

{
  "type": "message",
  "target": "C123:1700000000.000000",
  "text": "...",
  "metadata": {
    "promptNotes": [
      "This Slack message is from an active thread, but it may be ambient conversation. Only call send_adapter_message if ..."
    ]
  }
}

Host side, replacing the adapter_type == "slack" block:

if let Some(notes) = metadata.get("promptNotes").and_then(|v| v.as_array()) {
    for note in notes.iter().filter_map(|n| n.as_str()) {
        prompt.push_str("\n\n");
        prompt.push_str(note);
    }
}