feat(desktop): harness-agnostic config bridge

crates/buzz-acp/src/acp.rs

@@ -1215,6 +1215,41 @@ pub fn resolve_model_switch_method(
     None
 }
 
+/// Whether `desired_model` appears in pre-extracted catalog halves.
+///
+/// Mirrors [`resolve_model_switch_method`]'s match, but operates on the
+/// already-extracted `configOptions` (model category) and `models` state that
+/// [`AgentModelCapabilities`](crate::pool::AgentModelCapabilities) caches — the
+/// idle-path pre-cancel guard has those halves, not the full `session/new` JSON.
+pub fn model_in_catalog(
+    config_options: &[serde_json::Value],
+    available_models: Option<&serde_json::Value>,
+    desired_model: &str,
+) -> bool {
+    let in_config_options = config_options.iter().any(|config_opt| {
+        config_opt
+            .get("options")
+            .and_then(|v| v.as_array())
+            .is_some_and(|options| {
+                options
+                    .iter()
+                    .any(|opt| opt.get("value").and_then(|v| v.as_str()) == Some(desired_model))
+            })
+    });
+    if in_config_options {
+        return true;
+    }
+
+    available_models
+        .and_then(|models| models.get("availableModels"))
+        .and_then(|v| v.as_array())
+        .is_some_and(|available| {
+            available
+                .iter()
+                .any(|model| model.get("modelId").and_then(|v| v.as_str()) == Some(desired_model))
+        })
+}
+
 // ─── Drop: kill child process ─────────────────────────────────────────────────
 
 impl Drop for AcpClient {
@@ -1783,6 +1818,58 @@ mod tests {
         );
     }
 
+    // ── model_in_catalog tests ────────────────────────────────────────────
+
+    #[test]
+    fn model_in_catalog_true_when_in_config_options() {
+        let config_options = vec![serde_json::json!({
+            "configId": "model",
+            "category": "model",
+            "options": [
+                { "value": "claude-sonnet-4-20250514" },
+                { "value": "claude-opus-4-20250514" }
+            ]
+        })];
+        assert!(super::model_in_catalog(
+            &config_options,
+            None,
+            "claude-opus-4-20250514"
+        ));
+    }
+
+    #[test]
+    fn model_in_catalog_true_when_in_available_models() {
+        let available = serde_json::json!({
+            "currentModelId": "gpt-5",
+            "availableModels": [
+                { "modelId": "gpt-5" },
+                { "modelId": "o3-pro" }
+            ]
+        });
+        assert!(super::model_in_catalog(&[], Some(&available), "o3-pro"));
+    }
+
+    #[test]
+    fn model_in_catalog_false_when_absent_from_both_halves() {
+        let config_options = vec![serde_json::json!({
+            "configId": "model",
+            "options": [{ "value": "claude-sonnet-4-20250514" }]
+        })];
+        let available = serde_json::json!({
+            "availableModels": [{ "modelId": "gpt-5" }]
+        });
+        assert!(!super::model_in_catalog(
+            &config_options,
+            Some(&available),
+            "nonexistent-model"
+        ));
+    }
+
+    #[test]
+    fn model_in_catalog_false_when_both_halves_empty() {
+        assert!(!super::model_in_catalog(&[], None, "anything"));
+    }
+
     // ── Error variant display ─────────────────────────────────────────────
 
     #[test]

crates/buzz-acp/src/lib.rs

@@ -29,8 +29,8 @@ use filter::SubscriptionRule;
 use futures_util::FutureExt;
 use nostr::{PublicKey, ToBech32};
 use pool::{
-    AgentPool, ControlSignal, OwnedAgent, PromptContext, PromptOutcome, PromptResult, PromptSource,
-    SessionState,
+    AgentPool, ControlSignal, IdleSwitchResult, OwnedAgent, PromptContext, PromptOutcome,
+    PromptResult, PromptSource, SessionState,
 };
 use queue::{EventQueue, QueuedEvent, ThreadTags};
 use relay::{HarnessRelay, RelayEventPublisher};
@@ -718,11 +718,25 @@ fn handle_relay_observer_control_event(
     };
 
     let command_type = payload.get("type").and_then(|value| value.as_str());
-    if command_type != Some("cancel_turn") {
-        tracing::debug!(payload = %payload, "ignoring unknown observer control frame");
-        return;
+    match command_type {
+        Some("cancel_turn") => {
+            handle_cancel_turn_control(&payload, pool, observer);
+        }
+        Some("switch_model") => {
+            handle_switch_model_control(&payload, pool, observer);
+        }
+        _ => {
+            tracing::debug!(payload = %payload, "ignoring unknown observer control frame");
+        }
     }
+}
 
+/// Handle a `cancel_turn` control frame: signal the in-flight task to cancel.
+fn handle_cancel_turn_control(
+    payload: &serde_json::Value,
+    pool: &mut AgentPool,
+    observer: Option<&observer::ObserverHandle>,
+) {
     let Some(channel_id) = payload
         .get("channelId")
         .and_then(|value| value.as_str())
@@ -751,6 +765,83 @@ fn handle_relay_observer_control_event(
     }
 }
 
+/// Handle a `switch_model` control frame (Phase 3a, Option ii).
+///
+/// Busy path: deliver `SwitchModel` over the in-flight task's oneshot — the
+/// task cancels the turn, sets `desired_model`, and requeues the batch so it
+/// re-runs on a fresh session under the new model. A catalog miss surfaces
+/// post-cancel via `create_session_and_apply_model` (the turn restarts on the
+/// unchanged model + an `unsupported_model` result).
+///
+/// Idle path: validate against the cached catalog *before* invalidating
+/// (pre-cancel guard), then set `desired_model` + invalidate. The override
+/// takes visible effect on the agent's next turn.
+fn handle_switch_model_control(
+    payload: &serde_json::Value,
+    pool: &mut AgentPool,
+    observer: Option<&observer::ObserverHandle>,
+) {
+    let Some(channel_id) = payload
+        .get("channelId")
+        .and_then(|value| value.as_str())
+        .and_then(|value| value.parse::<Uuid>().ok())
+    else {
+        tracing::warn!("observer switch_model control frame missing valid channelId");
+        return;
+    };
+    let Some(model_id) = payload.get("modelId").and_then(|value| value.as_str()) else {
+        tracing::warn!("observer switch_model control frame missing modelId");
+        return;
+    };
+
+    // A turn is in flight for this channel iff a task_map entry exists. The
+    // agent is moved out of the pool during a turn, so the control oneshot is
+    // the only reachable lever; an idle channel has no such entry.
+    let turn_in_flight = pool
+        .task_map()
+        .values()
+        .any(|m| m.channel_id == Some(channel_id));
+
+    let status = if turn_in_flight {
+        // Busy path: deliver over the oneshot. `false` means the oneshot was
+        // already consumed this turn (a prior cancel/interrupt) — the turn is
+        // already ending, so the switch cannot land on it.
+        if signal_in_flight_task(
+            pool,
+            channel_id,
+            ControlSignal::SwitchModel(model_id.to_string()),
+        ) {
+            "sent"
+        } else {
+            "turn_ending"
+        }
+    } else {
+        // Idle path: validate against the cached catalog before invalidating.
+        match pool.switch_idle_agent_model(channel_id, model_id) {
+            IdleSwitchResult::Switched => "switched",
+            IdleSwitchResult::UnsupportedModel => "unsupported_model",
+            IdleSwitchResult::NoIdleAgent => "no_active_turn",
+        }
+    };
+
+    if let Some(observer) = observer {
+        observer.emit(
+            "control_result",
+            None,
+            &observer::ObserverContext {
+                channel_id: Some(channel_id.to_string()),
+                session_id: None,
+                turn_id: None,
+            },
+            serde_json::json!({
+                "type": "switch_model",
+                "status": status,
+                "modelId": model_id,
+            }),
+        );
+    }
+}
+
 /// Maximum crashes in a 60-second window before a slot's circuit opens.
 const CIRCUIT_BREAKER_THRESHOLD: usize = 3;
 /// Window for circuit-breaker crash counting.
@@ -1046,6 +1137,7 @@ async fn tokio_main() -> Result<()> {
                             state: SessionState::default(),
                             model_capabilities: None,
                             desired_model: config.model.clone(),
+                            model_overridden: false,
                             protocol_version,
                         }));
                     }
@@ -1482,6 +1574,7 @@ async fn tokio_main() -> Result<()> {
                         state: SessionState::default(),
                         model_capabilities: None,
                         desired_model: config.model.clone(),
+                        model_overridden: false,
                         protocol_version,
                     };
                     pool.return_agent(agent);
@@ -2161,8 +2254,8 @@ fn signal_in_flight_task(
 
     if let Some(meta) = entry {
         if let Some(tx) = meta.control_tx.take() {
-            let _ = tx.send(mode);
             tracing::info!(channel = %channel_id, ?mode, "control signal sent to in-flight task");
+            let _ = tx.send(mode);
             return true;
         }
     }
@@ -3487,6 +3580,7 @@ mod error_outcome_emission_tests {
             state: Default::default(),
             model_capabilities: None,
             desired_model: None,
+            model_overridden: false,
             // Error branches under test never read this; 1 is the legacy
             // non-systemPrompt path, the simplest valid value.
             protocol_version: 1,