fix(desktop): give preset harnesses buzz-dev-mcp

desktop/src-tauri/src/managed_agents/discovery.rs

@@ -23,7 +23,7 @@ pub(crate) use login_shell::{
 };
 pub(crate) use presets::{
     canonical_harness_command, command_for_runtime_id, preset_harness_definitions,
-    preset_harness_ids,
+    preset_harness_ids, preset_mcp_command_for,
 };
 use presets::{preset_catalog_entry, PRESET_HARNESSES};
 pub(crate) use runtime_metadata::KnownAcpRuntime;
@@ -286,6 +286,16 @@ pub(crate) fn known_acp_runtime(command: &str) -> Option<&'static KnownAcpRuntim
     })
 }
 
+/// Resolve the MCP sidecar command for an agent harness.
+///
+/// Builtins declare `mcp_command` on `KNOWN_ACP_RUNTIMES`. Presets are not in
+/// that table, so fall through to `preset_mcp_command_for` (#7023).
+pub(crate) fn resolve_mcp_command(command: &str) -> Option<&'static str> {
+    known_acp_runtime(command)
+        .and_then(|runtime| runtime.mcp_command)
+        .or_else(|| preset_mcp_command_for(command))
+}
+
 pub(crate) fn known_acp_runtime_exact(id: &str) -> Option<&'static KnownAcpRuntime> {
     KNOWN_ACP_RUNTIMES.iter().find(|p| p.id == id)
 }

desktop/src-tauri/src/managed_agents/discovery/presets.rs

@@ -63,7 +63,9 @@ pub(super) fn preset_catalog_entry(
             def.command,
             def.args.iter().map(|arg| arg.to_string()).collect(),
         ),
-        mcp_command: None,
+        // Preset ACP harnesses publish replies through buzz-dev-mcp, same as
+        // the built-in runtimes that already carry an MCP command (#7023).
+        mcp_command: Some("buzz-dev-mcp".to_string()),
         model_env_var: None,
         provider_env_var: None,
         thinking_env_var: None,
@@ -217,6 +219,20 @@ pub(super) fn preset_command_for_id(id: &str) -> Option<&'static str> {
         .map(|p| p.command)
 }
 
+/// MCP command for a preset harness matched by command (or path basename).
+///
+/// Presets are absent from `KNOWN_ACP_RUNTIMES`, so spawn must consult this
+/// when resolving `BUZZ_ACP_MCP_COMMAND` (#7023).
+pub(crate) fn preset_mcp_command_for(command: &str) -> Option<&'static str> {
+    let normalized = super::normalize_command_identity(command);
+    PRESET_HARNESSES
+        .iter()
+        .any(|preset| {
+            super::normalize_command_identity(preset.command) == normalized || preset.id == normalized
+        })
+        .then_some("buzz-dev-mcp")
+}
+
 /// Return the primary harness command for a given runtime id, or `None`.
 ///
 /// Checks static builtins, then the static preset list (always available,
@@ -317,6 +333,7 @@ mod tests {
         assert_eq!(entry.binary_path.as_deref(), Some("/usr/local/bin/devin"));
         assert_eq!(entry.auth_status, AuthStatus::NotApplicable);
         assert_eq!(entry.source, HarnessSource::Preset);
+        assert_eq!(entry.mcp_command.as_deref(), Some("buzz-dev-mcp"));
 
         let missing_entry = preset_catalog_entry(preset, |_| None);
         assert_eq!(
@@ -470,4 +487,35 @@ mod tests {
             "uncapped preset (devin) must have max_parallelism: None"
         );
     }
+
+    #[test]
+    fn preset_mcp_command_resolves_for_hermes_and_paths() {
+        assert_eq!(
+            super::preset_mcp_command_for("hermes-acp"),
+            Some("buzz-dev-mcp")
+        );
+        assert_eq!(
+            super::preset_mcp_command_for("/opt/homebrew/bin/hermes-acp"),
+            Some("buzz-dev-mcp")
+        );
+        assert_eq!(
+            super::preset_mcp_command_for("hermes"),
+            Some("buzz-dev-mcp")
+        );
+        assert_eq!(super::preset_mcp_command_for("totally-unknown-agent"), None);
+    }
+
+    #[test]
+    fn resolve_mcp_command_prefers_builtin_then_preset() {
+        assert_eq!(
+            crate::managed_agents::resolve_mcp_command("codex-acp"),
+            Some("buzz-dev-mcp")
+        );
+        assert_eq!(
+            crate::managed_agents::resolve_mcp_command("hermes-acp"),
+            Some("buzz-dev-mcp")
+        );
+        // Goose is a builtin without an MCP sidecar declaration.
+        assert_eq!(crate::managed_agents::resolve_mcp_command("goose"), None);
+    }
 }

desktop/src-tauri/src/managed_agents/runtime.rs

@@ -293,8 +293,7 @@ pub fn build_managed_agent_summary(
             env: Default::default(),
         }
     });
-    let effective_mcp_command = known_acp_runtime(&descriptor.command)
-        .and_then(|r| r.mcp_command)
+    let effective_mcp_command = crate::managed_agents::resolve_mcp_command(&descriptor.command)
         .unwrap_or("")
         .to_string();
 
@@ -477,8 +476,7 @@ pub fn spawn_agent_child(
         .map_err(|error| format!("failed to clone log handle: {error}"))?;
     let resolved_acp_command = resolve_command(&record.acp_command)
         .ok_or_else(|| missing_command_message(&record.acp_command, "ACP harness command"))?;
-    let effective_mcp_command = known_acp_runtime(effective_command)
-        .and_then(|r| r.mcp_command)
+    let effective_mcp_command = crate::managed_agents::resolve_mcp_command(effective_command)
         .unwrap_or("");
     let resolved_mcp_command: Option<std::path::PathBuf> = if effective_mcp_command.is_empty() {
         None

desktop/src-tauri/src/managed_agents/spawn_snapshot.rs

@@ -173,8 +173,7 @@ impl SpawnConfigSnapshot {
             acp_command: record.acp_command.clone(),
             command: descriptor.command.clone(),
             args: descriptor.args.clone(),
-            mcp_command: known_acp_runtime(&descriptor.command)
-                .and_then(|runtime| runtime.mcp_command)
+            mcp_command: crate::managed_agents::resolve_mcp_command(&descriptor.command)
                 .unwrap_or("")
                 .to_string(),
             // Effort has ONE representation in the snapshot: `effort_level`