fix(acp): resolve preset launch args by command when no runtime id is set - #8584

Summary

An agent with a known ACP runtime command but no runtime id and no instance args is spawned as the bare command, so ACP-native CLIs start their interactive TUI instead of their ACP/stdio mode. Under headless Buzz there is no controlling TTY, so the JSON-RPC initialize handshake never answers and every pool worker dies with:

ERROR buzz_acp: agent initialize failed: Request timeout — agent did not respond within 60s
Error: all 10 agents failed to start — cannot continue

This is reachable from the shipped app without any manual editing: set preferred_runtime: "omp" in global-agent-config.json, start the Welcome Team agents, and the runtime log shows

agent_cmd=/opt/homebrew/bin/omp        # no "acp" argument

Same class as #3457 (Grok) and #3660 (OpenCode); omp, opencode, kimi, cursor-agent, devin all hit the 60 s initialize timeout, Grok hits ENXIO.

Root cause

resolve_effective_harness_descriptor (managed_agents/readiness.rs) resolves launch args from:

1. explicit non-empty record.agent_args, else
2. the harness definition found via record.runtime → persona runtime →
   lookup_loaded_harness_by_id, else
3. normalize_agent_args(command, record_args).

A command-only pin satisfies neither 1 nor 2, so descriptor.args stays empty even though PRESET_HARNESSES already carries the correct args for that command. The args exist; they are just never consulted on this path.

Fix

Look the preset up by command when no runtime id resolved a definition:

} else if let Some(preset_args) =
    crate::managed_agents::discovery::preset_args_for_command(&effective_command)
{
    normalize_agent_args(&effective_command, preset_args)

preset_args_for_command matches through the existing normalize_command_identity, so a bare name, an absolute path (/opt/homebrew/bin/omp — what the runtime log actually shows) and a Windows .exe all resolve to the same preset. PRESET_HARNESSES stays the single source of truth; nothing is mirrored.

descriptor.args flows to BUZZ_ACP_AGENT_ARGS, the config hash and the agent summary, so this fixes spawn, the dashboard and cache keys in one place.

Tests

presets::tests::preset_args_for_command_matches_bare_and_absolute_commands covers:

• omp and /opt/homebrew/bin/omp → ["acp"]
• C:\tools\omp.exe → ["acp"]
• grok → ["agent", "--always-approve", "stdio"]
• amp-acp (no preset args) → [], unknown command → None

Notes

• Independent of the unrelated changes bundled in fix(acp): launch ACP/stdio mode for managed agents with no runtime preset #3804 (runtime-log mode 0600, resolved-launch marker); this PR is only the args fallback.
• Explicit agent_args still win.
• Verified on Buzz 0.5.28 / macOS arm64: with the equivalent local patch the spawn line becomes agent_cmd=/Users/…/.buzz/bin/omp-acp (wrapper) or omp acp, agent initialized returns in ~120 ms, and the harness connects to the relay.

Refs #3457