feat: global LLM coordinator to prevent Ollama overload

- llm_coordinator.py: LLMCoordinator server (runs in Nexus)
  FIFO queue + semaphore, max_concurrent configurable
  local_acquire/release for Nexus, MQTT request/release for sub-agents
- base_agent.py: _llm_slot_acquire/_llm_slot_release around _llm_loop
  MQTT round-trip to agents/llm/request, 90s timeout degraded fallback
  Enabled via use_llm_coordinator: true in config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents_core/base_agent.py

@@ -395,6 +395,8 @@ class BaseAgent(ABC):
     def _llm_loop(self, prompt: str, context: AgentContext,
                   extra_ctx: Optional[str] = None, max_steps: int = 10) -> str:
         """Boucle LLM avec exécution de skills."""
+        slot_id = self._llm_slot_acquire()
+        try:
             response = self.llm.chat(prompt, extra_context=extra_ctx)
 
             for _ in range(max_steps):
@@ -407,9 +409,55 @@ class BaseAgent(ABC):
                 response = self.llm.chat(
                     f"Résultat du skill '{skill_name}':\n{skill_result}\n\nContinue ou donne ta réponse finale."
                 )
+        finally:
+            self._llm_slot_release(slot_id)
 
         return response
 
+    def _llm_slot_acquire(self) -> Optional[str]:
+        """
+        Demande un slot LLM au coordinateur Nexus via MQTT.
+        Retourne un slot_id si accordé (à passer à _llm_slot_release).
+        Retourne None si coordination désactivée ou timeout (appel direct).
+        """
+        if not self.config.get("use_llm_coordinator", False):
+            return None
+
+        import uuid as _uuid
+        slot_id     = _uuid.uuid4().hex[:8]
+        grant_topic = f"agents/{self.agent_id}/llm/grant/{slot_id}"
+        granted_evt = threading.Event()
+
+        def _on_grant(msg, topic):
+            granted_evt.set()
+
+        self.mqtt.subscribe(grant_topic, _on_grant)
+        self.mqtt.publish_raw("agents/llm/request", json.dumps({
+            "agent_id":    self.agent_id,
+            "grant_topic": grant_topic,
+        }))
+        logger.debug(f"[LLM] Slot demandé au coordinateur (id={slot_id})")
+
+        granted = granted_evt.wait(timeout=90)
+        self.mqtt.unsubscribe(grant_topic)
+
+        if not granted:
+            logger.warning("[LLM] Pas de slot accordé en 90s — appel direct (mode dégradé)")
+            return None
+
+        logger.debug(f"[LLM] Slot accordé (id={slot_id})")
+        return slot_id
+
+    def _llm_slot_release(self, slot_id: Optional[str]):
+        """Libère le slot LLM auprès du coordinateur."""
+        if slot_id is None:
+            return
+        self.mqtt.publish_raw("agents/llm/release", json.dumps({
+            "agent_id": self.agent_id,
+            "slot_id":  slot_id,
+        }))
+        logger.debug(f"[LLM] Slot libéré (id={slot_id})")
+
     # ──────────────────────────────────────────────
     # XMPP
     # ──────────────────────────────────────────────

agents_core/llm_coordinator.py

@@ -0,0 +1,147 @@
+"""
+Coordinateur LLM centralisé — évite de surcharger Ollama.
+
+Nexus instancie LLMCoordinator (serveur).
+Les autres agents utilisent le mécanisme MQTT de BaseAgent (client).
+
+Topics MQTT :
+  agents/llm/request  ← agents publient ici pour demander un slot
+                         payload : {"agent_id": "...", "grant_topic": "agents/<id>/llm/grant/<uuid>"}
+  agents/llm/release  ← agents publient ici quand ils libèrent
+                         payload : {"agent_id": "..."}
+  agents/<id>/llm/grant/<uuid>  ← nexus publie ici pour accorder le slot
+"""
+import json
+import logging
+import threading
+from typing import Optional
+
+logger = logging.getLogger(__name__)
+
+
+class LLMCoordinator:
+    """
+    Gestionnaire de slots LLM — s'exécute dans Nexus.
+
+    Garantit qu'au plus `max_concurrent` appels LLM (Nexus compris)
+    sont en cours simultanément sur Ollama.
+    """
+
+    def __init__(self, mqtt_client, max_concurrent: int = 1):
+        self._mqtt        = mqtt_client
+        self._max         = max_concurrent
+        self._active      = 0
+        self._queue       = []          # grant_topics en attente (agents distants)
+        self._local_wait  = []          # threading.Event en attente (Nexus local)
+        self._lock        = threading.Lock()
+
+    def setup(self):
+        """Souscrit aux topics MQTT. À appeler après connexion MQTT."""
+        self._mqtt.subscribe("agents/llm/request", self._on_request)
+        self._mqtt.subscribe("agents/llm/release", self._on_release)
+        logger.info(f"[LLMCoordinator] Démarré — max {self._max} concurrent(s)")
+
+    # ──────────────────────────────────────────────
+    # API locale (Nexus lui-même)
+    # ──────────────────────────────────────────────
+
+    def local_acquire(self, timeout: float = 120) -> bool:
+        """
+        Nexus demande un slot directement (sans MQTT).
+        Retourne True si accordé, False si timeout.
+        """
+        evt = threading.Event()
+        with self._lock:
+            if self._active < self._max:
+                self._active += 1
+                logger.debug(f"[LLMCoordinator] Slot local accordé immédiatement ({self._active}/{self._max})")
+                return True
+            # Slot plein → mise en attente
+            self._local_wait.append(evt)
+            logger.debug(f"[LLMCoordinator] Nexus en attente de slot ({len(self._local_wait)} waiters)")
+
+        granted = evt.wait(timeout=timeout)
+        if not granted:
+            # Timeout : retire de la liste d'attente si encore présent
+            with self._lock:
+                try:
+                    self._local_wait.remove(evt)
+                except ValueError:
+                    pass
+            logger.warning("[LLMCoordinator] Nexus n'a pas obtenu de slot dans le délai imparti")
+        return granted
+
+    def local_release(self):
+        """Nexus libère son slot."""
+        with self._lock:
+            self._active -= 1
+            logger.debug(f"[LLMCoordinator] Slot local libéré ({self._active}/{self._max})")
+            self._try_grant()
+
+    # ──────────────────────────────────────────────
+    # Handlers MQTT (agents distants)
+    # ──────────────────────────────────────────────
+
+    def _on_request(self, msg, topic: str):
+        """Un agent demande un slot."""
+        try:
+            raw = msg if isinstance(msg, str) else (msg.payload if hasattr(msg, 'payload') else str(msg))
+            data = json.loads(raw)
+            grant_topic = data.get("grant_topic")
+            agent_id    = data.get("agent_id", "?")
+            if not grant_topic:
+                return
+        except Exception as e:
+            logger.debug(f"[LLMCoordinator] Requête invalide : {e}")
+            return
+
+        with self._lock:
+            self._queue.append((grant_topic, agent_id))
+            logger.debug(f"[LLMCoordinator] Requête de {agent_id} — file : {len(self._queue)}")
+            self._try_grant()
+
+    def _on_release(self, msg, topic: str):
+        """Un agent libère son slot."""
+        try:
+            raw = msg if isinstance(msg, str) else (msg.payload if hasattr(msg, 'payload') else str(msg))
+            data = json.loads(raw)
+            agent_id = data.get("agent_id", "?")
+        except Exception:
+            agent_id = "?"
+
+        with self._lock:
+            self._active -= 1
+            logger.debug(f"[LLMCoordinator] Slot libéré par {agent_id} ({self._active}/{self._max})")
+            self._try_grant()
+
+    def _try_grant(self):
+        """
+        Accorde des slots aux suivants dans la file.
+        DOIT être appelé avec self._lock tenu.
+        """
+        while self._active < self._max:
+            # Priorité aux waiters locaux (Nexus)
+            if self._local_wait:
+                evt = self._local_wait.pop(0)
+                self._active += 1
+                evt.set()
+                logger.debug(f"[LLMCoordinator] Slot accordé à Nexus (local) ({self._active}/{self._max})")
+            elif self._queue:
+                grant_topic, agent_id = self._queue.pop(0)
+                self._active += 1
+                try:
+                    self._mqtt.publish_raw(grant_topic, '{"granted": true}')
+                    logger.debug(f"[LLMCoordinator] Slot accordé à {agent_id} ({self._active}/{self._max})")
+                except Exception as e:
+                    logger.error(f"[LLMCoordinator] Impossible d'accorder le slot à {agent_id} : {e}")
+                    self._active -= 1
+            else:
+                break
+
+    def status(self) -> str:
+        """Résumé pour /status ou /llm."""
+        with self._lock:
+            return (
+                f"LLM coordinator : {self._active}/{self._max} slot(s) actif(s), "
+                f"{len(self._queue)} en attente"
+            )