fix(acp): default empty omp args to ACP mode to fix initialize timeout

[bradhallett]

Summary

buzz-acp's default_agent_args did not recognize the omp (Oh My Pi) command, so a managed agent configured with command omp and empty/absent agent_args launched omp's interactive mode instead of omp acp. The ACP initialize request then never received a response, and Buzz reported a breaking agent initialize failed: Request timeout.

Fix: map the normalized command identity omp to default args ["acp"] (matching goose), so empty or absent args launch ACP mode. Explicit non-empty args are preserved unchanged. Single-file change in crates/buzz-acp/src/config.rs.

Related issue

None found.

Testing

• cargo test -p buzz-acp — 637 passed; added normalizes_goose_and_omp_args_to_acp covering bare omp and an absolute path with empty args.
• cargo fmt --all -- --check — clean.
• Built the desktop app and verified the bundled buzz-acp spawns omp acp and returns ACP auth methods under an empty-args launch (previously timed out).

Note: local cargo clippy --workspace flags pre-existing clippy::question_mark lints in buzz-acp/src/{queue.rs,lib.rs} and buzz-agent under the newer local toolchain (clippy 1.97.0 vs the pinned 1.88); these are unrelated to this change and out of scope.

[bradhallett]

Closing in favor of #3804, which generalizes the fix to all affected ACP runtimes (omp/grok/opencode/kimi/cursor/openclaw) at the desktop layer — deriving per-runtime launch args from the single-source PRESET_HARNESSES table rather than mirroring them into buzz-acp. See #3804.