Agents show RUNNING/online but never respond — no channel subscriptions resolved, empty harness log (self-hosted, macOS)

**Title:** Agents show RUNNING/online but never respond — no channel subscriptions resolved, empty harness log (self-hosted, macOS)

## Summary

On a self-hosted relay, managed agents start, connect, and report online, but never respond to mentions or DMs. Affects both the Goose and Claude Code harnesses identically. The Harness Log stays empty, so the failure is invisible from the UI.

## Environment

- macOS Tahoe 26.3.1, Apple M1 Max, 64GB
- Self-hosted relay, built from source at `main`, run via `just relay`
- Desktop: packaged Buzz.app (also reproduced with a `just dev` build from the same commit)
- Docker Engine + Postgres/Redis/Typesense/MinIO all healthy
- Buzz Mesh enabled, sharing `unsloth/gemma-4-26B-A4B-it-GGUF:UD-Q4_K_M`

## Steps to reproduce

1. Stand up a relay from source, connect the desktop app to `http://localhost:3000`
2. Enable Share this machine, select a recommended model, wait for download
3. Create an agent — harness Goose, provider OpenAI-compatible, model set to the mesh model ID
4. Add the agent to a channel and @mention it
5. Also try a DM to the agent

## Expected

Agent responds, or surfaces an error.

## Actual

No response via channel mention or DM. Agent card shows a green online dot; runtime status shows RUNNING. Harness Log shows "no activity logged".

## Evidence

**Mesh endpoint is healthy** — `curl http://localhost:9337/v1/models` returns the shared model correctly.

**Goose works standalone** — `goose session` in a terminal responds normally against the same mesh endpoint. `goose info -v` shows provider `openai`, host `http://localhost:9337`, correct model, `configured: true`.

**Relay never sees agent traffic.** After a mention, relay logs show only the human pubkey issuing `/query` and `/events`. In one earlier session an agent pubkey did complete NIP-42 auth, queried once, then never appeared again. Messages (kind 9) are ingested but no agent activity follows.

**Harness processes spawn but freeze.** After several mention attempts:

```
$ ps aux | grep -i -E "goose|buzz-acp" | grep -v grep
... 24 × /Users//.local/bin/goose acp (all spawned in the same second, all at 0:00.04 CPU)
... 2 × /Applications/Buzz.app/Contents/MacOS/buzz-acp
```

24 harness subprocesses spawned from a handful of mentions, all idle at ~0.04s CPU, none ever reaching the relay. A later attempt spawned `buzz-acp` with **no** `goose acp` child at all.

**No logs anywhere.** `~/Library/Logs/Buzz/` does not exist. `log show --predicate 'process == "buzz-acp"' --last 1h --info` returns zero entries. Harness Log in the UI is empty.

**Running the harness manually works up to subscription.** Invoking the bundled binary directly:

```
/Applications/Buzz.app/Contents/MacOS/buzz-acp \
--private-key $BUZZ_PRIVATE_KEY \
--respond-to anyone \
--no-mention-filter \
--agent-command goose \
--model unsloth/gemma-4-26B-A4B-it-GGUF:UD-Q4_K_M
```

produces:

```
INFO buzz_acp: agent initialized ... "name":"goose","version":"1.43.0"
INFO buzz_acp: agent_pool_ready agents=1
INFO buzz_acp: connected to relay at ws://localhost:3000
INFO buzz_acp: subscribed to membership notifications
INFO buzz_acp: no agent owner configured
INFO buzz_acp: discovered 0 channel(s)
WARN buzz_acp: no channel subscriptions resolved — agent will sit idle
INFO buzz_acp: presence set to online
```

Adding `--subscribe all` still yields `discovered 0 channel(s)`.

## Notes / possible issues

1. **Silent failure is the core problem.** An agent that resolves zero channel subscriptions reports RUNNING and online with an empty Harness Log. That warning exists in `buzz-acp` but never surfaces in the UI. Nothing distinguishes "working" from "completely inert."

2. **Subprocess leak.** 24 `goose acp` processes spawned and never reaped. One orphan persisted ~4 hours across app restarts.

3. **DMs also fail**, which suggests the problem is not solely channel-subscription resolution.

4. **Not harness-specific.** Bundled Claude Code personas (Fizz/Honey/Bumble) show the same silence, so this appears to sit above the harness layer.

5. **No UI path to add an agent to a channel by pubkey.** The agent card's ⋮ menu offers only Edit / Duplicate / Share / Delete.

Possibly related: #2292 (agents start without usable provider and exit immediately, missing-provider errors not surfaced).

The named entry points are managed-agent startup, buzz-acp, relay channel-subscription resolution, and the Harness Log; reproduce with the manual buzz-acp command and inspect why it reports discovered 0 channel(s). Trace the same path for channel mentions and DMs, then verify that inert agents surface an actionable status or log and that spawned harness processes are cleaned up.

Written by the indexing model from the issue text.