feat(explorer+daemon): discovery dinamico via broker + query socket

Cierra el "explorer encuentra al daemon de forma totalmente dinamica"
del meta-plan. La UI deja de hardcodear el socket admin: descubre al
daemon nouser via MatchEvent::Available del broker y le consulta sus
Monadas directo.

Pipeline end-to-end:
- Daemon publica engine Card con service_socket = $XDG_RUNTIME_DIR/
  nouser-engine.sock y flow.output = monad-list:json.
- Daemon binda Unix socket en ese path con listener blocking que
  sirve nouser_card::query::QueryRequest::ListMonads, responde
  ListMonadsResponse { engine, monads: Vec<MonadView> }.
- Explorer construye consumer Card con flow.input matched,
  brahman_sidecar::await_provider_blocking le devuelve el socket,
  y nouser_core::engine_socket::client::list_monads lo consulta.
- Cachea el socket; cualquier fallo de query lo invalida y la
  proxima iteracion re-descubre.

Wire types nuevos en nouser_card::query:
- QueryRequest::ListMonads
- ListMonadsResponse { engine: EngineInfo, monads: Vec<MonadView> }
- MonadView: proyeccion slim de MonadManifest SIN centroid ni
  members (KB que no tienen por que viajar cada poll).
- transport::default_socket_path() con env override.

Listener en nouser_core::engine_socket: spawn_listener + client
blocking con QueryError tipado. 3 tests integracion verdes.

Refactor explorer:
- Drop dep brahman-admin, add brahman-sidecar/nouser-card/nouser-core.
- State: socket cache + snapshot + socket_source informativo.
- TickOutcome enum desacopla la I/O del UI.

Trade-offs: polling 2s (no streaming — broker no empuja Data cards
hoy), re-discovery full en error (discovery es barato).

Tests: 10 (nouser-card +3 query) + 27 (nouser-core +3 engine_socket)
+ 4 (sidecar) verdes. Explorer compila clean.

crates/modules/nouser/card/src/query.rs

@@ -0,0 +1,209 @@
+//! Wire types para consultar al daemon `nouser` por sus Mónadas.
+//!
+//! El daemon expone un Unix socket (cuyo path se publica en
+//! `Card.service_socket` y se descubre vía broker MatchEvent). Cada
+//! conexión es single-shot: una request JSON terminada en `\n`,
+//! una response JSON terminada en `\n`, cierre.
+//!
+//! Mismo patrón que `nouser-nous` (mock/real ↔ nouser-core), reusado
+//! ahora para que la UI (`nouser-explorer`) descubra y consulte al
+//! daemon sin hardcodear sockets ni pasar por brahman-admin.
+//!
+//! ## Contrato
+//!
+//! ```text
+//! C → S: {"kind":"list_monads"}\n
+//! S → C: {"engine":{...},"monads":[...]}\n
+//! ```
+//!
+//! En caso de error:
+//!
+//! ```text
+//! S → C: {"error":"unsupported kind"}\n
+//! ```
+
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+use ulid::Ulid;
+
+use crate::{Lens, MonadId, MonadManifest};
+
+// =====================================================================
+// Constants compartidos para el broker brahman
+// =====================================================================
+
+/// Nombre del flow output del daemon (input del consumer/explorer).
+pub const FLOW_MONAD_LIST: &str = "monad-list";
+
+/// Tipo del flow: el wire es JSON, así que el TypeRef es `primitive::json`.
+pub const FLOW_TYPE_NAME: &str = "json";
+
+// =====================================================================
+// Wire request
+// =====================================================================
+
+/// Request al daemon. El wire es JSON line-delimited (un objeto + `\n`
+/// por conexión).
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum QueryRequest {
+    /// Lista todas las Mónadas vivas del daemon, junto con metadata
+    /// del engine. Pensado para que la UI haga snapshot polling.
+    ListMonads,
+}
+
+// =====================================================================
+// Wire response
+// =====================================================================
+
+/// Response a `ListMonads`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ListMonadsResponse {
+    /// Datos del engine (la Card que es "dueña" de las Mónadas).
+    pub engine: EngineInfo,
+    /// Mónadas vivas en este momento. Vista slim sin centroide ni
+    /// member set para que el wire sea liviano: una Mónada con 50k
+    /// archivos no debe transmitir 50k ULIDs cada poll.
+    pub monads: Vec<MonadView>,
+}
+
+/// Identidad del engine (Card kind=Ente que owns las Mónadas).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EngineInfo {
+    pub id: Ulid,
+    pub label: String,
+    /// Path del directorio que el daemon está observando. `None` si
+    /// el daemon corre sin watcher.
+    #[serde(default)]
+    pub watching: Option<String>,
+}
+
+/// Vista slim de una Mónada — los campos que la UI necesita para
+/// renderizar una card sin pull del centroide ni del member set.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct MonadView {
+    pub id: MonadId,
+    pub label: String,
+    #[serde(default)]
+    pub summary: String,
+    #[serde(default)]
+    pub keywords: Vec<String>,
+    pub cardinality: u32,
+    #[serde(default)]
+    pub entropy: f32,
+    #[serde(default)]
+    pub dominant_lens: Lens,
+    #[serde(default)]
+    pub path_hint: Option<String>,
+    #[serde(default)]
+    pub centroid_model: Option<String>,
+}
+
+impl MonadView {
+    /// Proyecta un MonadManifest completo a su vista slim para wire.
+    pub fn from_manifest(m: &MonadManifest) -> Self {
+        Self {
+            id: m.id,
+            label: m.label.clone(),
+            summary: m.summary.clone(),
+            keywords: m.keywords.clone(),
+            cardinality: m.cardinality,
+            entropy: m.entropy,
+            dominant_lens: m.dominant_lens,
+            path_hint: m.path_hint.clone(),
+            centroid_model: m.centroid_model.clone(),
+        }
+    }
+}
+
+/// Error de protocolo retornado en lugar de la response normal.
+#[derive(Debug, Clone, Serialize, Deserialize, Error)]
+#[error("nouser-engine: {error}")]
+pub struct ErrorResponse {
+    pub error: String,
+}
+
+// =====================================================================
+// Transport
+// =====================================================================
+
+pub mod transport {
+    use std::path::PathBuf;
+
+    /// Variable de entorno para sobreescribir la ruta del socket del
+    /// daemon (útil para tests / multi-daemon).
+    pub const SOCKET_ENV: &str = "NOUSER_ENGINE_SOCKET";
+
+    /// Nombre por defecto del socket.
+    pub const SOCKET_NAME: &str = "nouser-engine.sock";
+
+    /// Ruta canónica al socket del daemon. Honra `NOUSER_ENGINE_SOCKET`
+    /// si está set, sino arma sobre `$XDG_RUNTIME_DIR` (con fallback
+    /// `$TMPDIR`).
+    pub fn default_socket_path() -> PathBuf {
+        if let Ok(p) = std::env::var(SOCKET_ENV) {
+            return PathBuf::from(p);
+        }
+        std::env::var_os("XDG_RUNTIME_DIR")
+            .map(PathBuf::from)
+            .unwrap_or_else(std::env::temp_dir)
+            .join(SOCKET_NAME)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn request_roundtrips_json_with_tag() {
+        let req = QueryRequest::ListMonads;
+        let s = serde_json::to_string(&req).unwrap();
+        assert_eq!(s, r#"{"kind":"list_monads"}"#);
+        let back: QueryRequest = serde_json::from_str(&s).unwrap();
+        assert_eq!(back, req);
+    }
+
+    #[test]
+    fn response_roundtrip_preserves_view() {
+        let m = MonadManifest::new("x/src");
+        let view = MonadView::from_manifest(&m);
+        let resp = ListMonadsResponse {
+            engine: EngineInfo {
+                id: Ulid::new(),
+                label: "brahman.nouser_engine".into(),
+                watching: Some("/tmp/x".into()),
+            },
+            monads: vec![view.clone()],
+        };
+        let s = serde_json::to_string(&resp).unwrap();
+        let back: ListMonadsResponse = serde_json::from_str(&s).unwrap();
+        assert_eq!(back.monads.len(), 1);
+        assert_eq!(back.monads[0].label, view.label);
+        assert_eq!(back.engine.label, "brahman.nouser_engine");
+    }
+
+    #[test]
+    fn view_is_slim_no_centroid_no_members() {
+        // Construimos una Mónada con centroid + members "pesados",
+        // proyectamos a view, verificamos que esos campos no viajan.
+        let mut m = MonadManifest::new("test");
+        m.centroid = vec![0.1; 384]; // peso "real-fastembed"
+        m.members.insert(Ulid::new());
+        m.members.insert(Ulid::new());
+        m.cardinality = 2;
+        let view = MonadView::from_manifest(&m);
+        let s = serde_json::to_string(&view).unwrap();
+        // Chequeo con `:` para distinguir el field "centroid" del
+        // field "centroid_model" (que sí es metadata liviana y debe ir).
+        assert!(
+            !s.contains("\"centroid\":"),
+            "MonadView no debe serializar el vector centroid: {s}"
+        );
+        assert!(
+            !s.contains("\"members\":"),
+            "MonadView no debe serializar members: {s}"
+        );
+        assert!(s.contains("\"cardinality\":2"), "cardinality sí va: {s}");
+    }
+}