feat(gateway): surface mid-prewarm models as Loading on /v1/models

The poller now fetches /health alongside /models on each neuron and
stashes the activation snapshot on NodeState. The /v1/models handler
gains a Pass 3 that synthesises Loading locations from each neuron's
activation.in_progress and activation.pending lists, so a catalogued
model that's mid-prewarm surfaces as `status: "loading"` rather than
appearing absent (loaded=false, locations=[]).

Without this, a client polling /v1/models during a beast restart sees
Qwen3.6-27B disappear for the ~5 minutes the q5k load takes, then
reappear. Now it stays visible the whole time with a clear status.

Adds ModelStatus::Loading to cortex-core. The router's per-node priority
loop gets an explicit (no-op) arm: Loading models aren't routable yet,
and falling through to the catalogue cold-load path is the existing
race — no worse than before, but tagged as a known follow-up needing
neuron-side in-flight tracking on /models/load.

New test_poller_captures_activation_from_health exercises the full
round-trip: mock neuron with empty /models but a pre_warming /health
→ poller writes node.activation. Common test helpers gain
spawn_mock_neuron_with_models_and_health and default_health_response.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/cortex-gateway/src/handlers.rs

@@ -385,6 +385,55 @@ async fn list_models(State(fleet): State<Arc<CortexState>>) -> Json<Value> {
         }
     }
 
+    // Pass 3: surface pre-warming models. Each neuron's `/health`
+    // activation snapshot (polled separately from /models) reports
+    // `in_progress` (the model currently materialising) and `pending`
+    // (queued behind it). Neither appears on the neuron's `/models`
+    // yet — that endpoint only knows about fully-loaded handles — so
+    // without this pass a client polling `/v1/models` during pre-warm
+    // sees Qwen3.6-27B with no location and concludes "not there".
+    // Synthesising a Loading location instead tells clients the model
+    // is on its way. Idempotent against Pass 2: if a Loading location
+    // for this node already exists (shouldn't, but be safe) we skip.
+    for node in nodes.values() {
+        let Some(activation) = node.activation.as_ref() else {
+            continue;
+        };
+        let mut loading_ids: Vec<&str> = Vec::new();
+        if let Some(id) = activation.in_progress.as_deref() {
+            loading_ids.push(id);
+        }
+        for id in &activation.pending {
+            loading_ids.push(id.as_str());
+        }
+        for model_id in loading_ids {
+            let location = ModelLocation {
+                node: node.name.clone(),
+                status: cortex_core::node::ModelStatus::Loading,
+                vram_estimate_mb: None,
+            };
+            entries
+                .entry(model_id.to_string())
+                .and_modify(|e| {
+                    let already = e.locations.iter().any(|l| {
+                        l.node == node.name && l.status == cortex_core::node::ModelStatus::Loading
+                    });
+                    if !already {
+                        e.locations.push(location.clone());
+                    }
+                })
+                .or_insert_with(|| CortexModelEntry {
+                    id: model_id.to_string(),
+                    object: "model".into(),
+                    created: now,
+                    owned_by: "helexa".into(),
+                    loaded: false,
+                    feasible_on: Vec::new(),
+                    locations: vec![location],
+                });
+        }
+    }
+
     let data: Vec<Value> = entries.values().map(|e| json!(e)).collect();
     Json(json!({
         "object": "list",

crates/cortex-gateway/src/poller.rs

@@ -3,7 +3,7 @@
 
 use crate::state::CortexState;
 use chrono::Utc;
-use cortex_core::discovery::DiscoveryResponse;
+use cortex_core::discovery::{DiscoveryResponse, HealthResponse};
 use cortex_core::harness::ModelInfo;
 use cortex_core::node::{ModelEntry, ModelStatus};
 use std::sync::Arc;
@@ -142,6 +142,51 @@ async fn poll_neuron(fleet: &CortexState, name: &str, endpoint: &str) {
             node.healthy = false;
         }
     }
+
+    // Release the write lock before the next HTTP call.
+    drop(nodes);
+
+    // Poll /health for the activation snapshot. We don't want this to
+    // flip the node to unhealthy on its own — a neuron that's serving
+    // /models fine is still operational even if /health is briefly
+    // unavailable — so failures are debug-level and leave the existing
+    // activation reading in place.
+    poll_health(fleet, name, endpoint).await;
+}
+
+/// Fetch `/health` and stash the activation snapshot on NodeState.
+/// Decoupled from the /models poll so a /health glitch doesn't mark
+/// the neuron unhealthy or evict the model list.
+async fn poll_health(fleet: &CortexState, name: &str, endpoint: &str) {
+    let url = format!("{endpoint}/health");
+    let resp = match fleet
+        .http_client
+        .get(&url)
+        .timeout(Duration::from_secs(5))
+        .send()
+        .await
+    {
+        Ok(r) if r.status().is_success() => r,
+        Ok(r) => {
+            tracing::debug!(node = name, status = %r.status(), "/health probe non-success");
+            return;
+        }
+        Err(e) => {
+            tracing::debug!(node = name, error = %e, "/health probe failed");
+            return;
+        }
+    };
+    match resp.json::<HealthResponse>().await {
+        Ok(h) => {
+            let mut nodes = fleet.nodes.write().await;
+            if let Some(node) = nodes.get_mut(name) {
+                node.activation = Some(h.activation);
+            }
+        }
+        Err(e) => {
+            tracing::debug!(node = name, error = %e, "failed to parse /health response");
+        }
+    }
 }
 
 fn parse_status(s: &str) -> ModelStatus {
@@ -149,6 +194,7 @@ fn parse_status(s: &str) -> ModelStatus {
         "loaded" => ModelStatus::Loaded,
         "unloaded" => ModelStatus::Unloaded,
         "reloading" => ModelStatus::Reloading,
+        "loading" => ModelStatus::Loading,
         _ => ModelStatus::Loaded,
     }
 }

crates/cortex-gateway/src/router.rs

@@ -79,6 +79,15 @@ pub async fn resolve(
                             unloaded_route = Some((node.name.clone(), node.endpoint.clone(), true));
                         }
                     }
+                    // Loading is gateway-synthesised from neuron's
+                    // activation snapshot; it never appears on the
+                    // wire from neuron's `/models`. Skip — the model
+                    // isn't actually servable yet. The pre-existing
+                    // race (catalogue cold_load fires a parallel
+                    // /models/load against the in-flight load) is no
+                    // worse than before; fixing it needs neuron-side
+                    // in-flight tracking on /models/load itself.
+                    ModelStatus::Loading => {}
                 }
             }
         }

crates/cortex-gateway/src/state.rs

@@ -27,6 +27,7 @@ impl CortexState {
                     lifecycle_cycles: 0,
                     last_poll: None,
                     discovery: None,
+                    activation: None,
                 },
             );
         }

crates/cortex-gateway/tests/common/mod.rs

@@ -164,6 +164,33 @@ pub async fn spawn_streaming_mock_neuron(chunk_count: usize, chunk_delay: Durati
 
 /// Spawns a mock neuron with a custom models list.
 pub async fn spawn_mock_neuron_with_models(models_response: Value) -> String {
+    spawn_mock_neuron_with_models_and_health(models_response, default_health_response()).await
+}
+
+/// Default `/health` response used by mocks that don't care about the
+/// activation field — empty devices, no in-flight pre-warm, state=ready.
+pub fn default_health_response() -> Value {
+    json!({
+        "uptime_secs": 0,
+        "devices": [],
+        "activation": {
+            "state": "ready",
+            "pending": [],
+            "in_progress": null,
+            "completed": [],
+            "failed": []
+        }
+    })
+}
+
+/// Variant of `spawn_mock_neuron_with_models` that also serves a
+/// `/health` body. Used by tests that drive the gateway's activation
+/// surface (poller reading /health, /v1/models synthesising Loading
+/// locations from in_progress / pending).
+pub async fn spawn_mock_neuron_with_models_and_health(
+    models_response: Value,
+    health_response: Value,
+) -> String {
     let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
     let addr = listener.local_addr().unwrap();
     let base_url = format!("http://{addr}");
@@ -177,6 +204,13 @@ pub async fn spawn_mock_neuron_with_models(models_response: Value) -> String {
                 async move { Json(resp) }
             }),
         )
+        .route(
+            "/health",
+            get(move || {
+                let resp = health_response.clone();
+                async move { Json(resp) }
+            }),
+        )
         .route(
             "/models/{model_id}/endpoint",
             get(move |Path(_model_id): Path<String>| {

crates/cortex-gateway/tests/poller.rs

@@ -237,3 +237,58 @@ async fn test_poller_removes_stale_models() {
     assert!(node.models.contains_key("keep-me"));
     assert!(!node.models.contains_key("drop-me"));
 }
+
+#[tokio::test]
+async fn test_poller_captures_activation_from_health() {
+    // Mock neuron is mid-prewarm: /models reports nothing (the loading
+    // model hasn't been inserted into the harness map yet), but
+    // /health's activation says model-x is in_progress and model-y is
+    // queued behind it.
+    let mock_url = common::spawn_mock_neuron_with_models_and_health(
+        json!([]),
+        json!({
+            "uptime_secs": 30,
+            "devices": [],
+            "activation": {
+                "state": "pre_warming",
+                "pending": ["Qwen/model-y"],
+                "in_progress": "Qwen/model-x",
+                "completed": [],
+                "failed": []
+            }
+        }),
+    )
+    .await;
+
+    let config = GatewayConfig {
+        gateway: GatewaySettings {
+            listen: "127.0.0.1:0".into(),
+            metrics_listen: "127.0.0.1:0".into(),
+        },
+        eviction: EvictionSettings {
+            strategy: EvictionStrategy::Lru,
+            defrag_after_cycles: 0,
+        },
+        neurons: vec![NeuronEndpoint {
+            name: "prewarm-node".into(),
+            endpoint: mock_url,
+        }],
+        models_config: "/dev/null".into(),
+    };
+
+    let fleet = Arc::new(CortexState::from_config(&config));
+    cortex_gateway::poller::poll_once(&fleet).await;
+
+    let nodes = fleet.nodes.read().await;
+    let node = nodes.get("prewarm-node").unwrap();
+    assert!(node.healthy);
+    // /models was empty — no entries in the per-node model map.
+    assert!(node.models.is_empty());
+    // But /health's activation should be captured.
+    let activation = node
+        .activation
+        .as_ref()
+        .expect("activation should be populated after /health poll");
+    assert_eq!(activation.in_progress.as_deref(), Some("Qwen/model-x"));
+    assert_eq!(activation.pending, vec!["Qwen/model-y".to_string()]);
+}