feat: dynamic Opus/Sonnet model switching based on rolling quota

Implement intelligent model selection to manage 7-day Opus quota burn rate:

- Add _select_model_based_on_quota() method to AgentLoop
  - Reads rate limit data from memory/rate_limits.json
  - Calculates expected vs actual quota usage (100%/168h = 0.595% per hour)
  - If actual > expected × 1.17 (17% overage), downgrades to Sonnet
  - If actual ≤ expected, uses Opus
  - Caches decision for 5 minutes to minimize file I/O

- Add /quota slash command to display real-time quota status
  - Shows current usage vs expected usage
  - Shows hours until weekly reset
  - Shows selected model and burn rate multiplier

- Main agent now calls _select_model_based_on_quota() before each conversation
  - Heartbeat subagent unaffected (explicitly uses claude-sonnet-4-20250514)

This replaces the wrong approach from PR #5 which throttled heartbeat
frequency instead of switching the main agent's model.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

nanobot/agent/loop.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import json
+import time
 from pathlib import Path
 from typing import Any
 
@@ -74,8 +75,10 @@ class AgentLoop:
             exec_config=self.exec_config,
             restrict_to_workspace=restrict_to_workspace,
         )
-        
+
         self._running = False
+        self._quota_cache: dict[str, Any] = {}  # {model: str, cached_at: float}
+        self._quota_cache_ttl: float = 300.0  # 5 minutes
         self._register_default_tools()
     
     def _register_default_tools(self) -> None:
@@ -143,7 +146,95 @@ class AgentLoop:
         """Stop the agent loop."""
         self._running = False
         logger.info("Agent loop stopping")
-    
+
+    def _select_model_based_on_quota(self) -> str:
+        """Select Opus or Sonnet based on rolling weekly quota burn rate."""
+        # Check cache
+        now = time.time()
+        if self._quota_cache and (now - self._quota_cache.get("cached_at", 0)) < self._quota_cache_ttl:
+            return self._quota_cache["model"]
+
+        # Default models
+        OPUS = "claude-opus-4-6"
+        SONNET = "claude-sonnet-4-5"
+        TOLERANCE = 1.17  # 17% overage triggers downgrade
+
+        # Read rate limits
+        rate_limits_path = self.workspace / "memory" / "rate_limits.json"
+        if not rate_limits_path.exists():
+            logger.warning("rate_limits.json not found, defaulting to Sonnet")
+            return SONNET
+
+        try:
+            with open(rate_limits_path) as f:
+                limits = json.load(f)
+
+            actual_usage = limits.get("weekly_all_models")
+            weekly_reset = limits.get("weekly_reset")
+
+            if actual_usage is None or weekly_reset is None:
+                logger.warning("Rate limit data incomplete, defaulting to Sonnet")
+                return SONNET
+
+            # Calculate expected usage
+            actual_pct = actual_usage * 100
+            week_start = weekly_reset - (168 * 3600)
+            hours_elapsed = max(0, min((now - week_start) / 3600, 168))
+            expected_pct = (hours_elapsed / 168) * 100
+            threshold = expected_pct * TOLERANCE
+
+            # Decision logic
+            if actual_pct > threshold:
+                model = SONNET
+                logger.info(
+                    f"Quota: {actual_pct:.1f}% used, expected {expected_pct:.1f}%, "
+                    f"threshold {threshold:.1f}% → Sonnet"
+                )
+            else:
+                model = OPUS
+                logger.info(
+                    f"Quota: {actual_pct:.1f}% used, expected {expected_pct:.1f}%, "
+                    f"threshold {threshold:.1f}% → Opus"
+                )
+
+            # Cache decision
+            self._quota_cache = {"model": model, "cached_at": now}
+            return model
+
+        except Exception as e:
+            logger.error(f"Error checking quota: {e}, defaulting to Sonnet")
+            return SONNET
+
+    def _get_quota_status(self) -> str:
+        """Return human-readable quota status."""
+        rate_limits_path = self.workspace / "memory" / "rate_limits.json"
+        if not rate_limits_path.exists():
+            return "⚠️ No quota data available yet."
+
+        try:
+            with open(rate_limits_path) as f:
+                limits = json.load(f)
+
+            actual_pct = limits.get("weekly_all_models", 0) * 100
+            reset_ts = limits.get("weekly_reset", 0)
+            now = time.time()
+
+            hours_until_reset = (reset_ts - now) / 3600
+            week_start = reset_ts - (168 * 3600)
+            hours_elapsed = max(0, (now - week_start) / 3600)
+            expected_pct = (hours_elapsed / 168) * 100
+
+            model = self._select_model_based_on_quota()
+
+            return f"""📊 Quota Status:
+• Used: {actual_pct:.1f}% (expected {expected_pct:.1f}%)
+• Resets in: {hours_until_reset:.1f}h
+• Current model: {model}
+• Burn rate: {actual_pct / max(expected_pct, 0.01):.2f}x target"""
+
+        except Exception as e:
+            return f"⚠️ Error reading quota: {e}"
+
     async def _process_message(self, msg: InboundMessage, session_key: str | None = None) -> OutboundMessage | None:
         """
         Process a single inbound message.
@@ -177,8 +268,11 @@ class AgentLoop:
                                   content="🐈 New session started. Memory consolidated.")
         if cmd == "/help":
             return OutboundMessage(channel=msg.channel, chat_id=msg.chat_id,
-                                  content="🐈 nanobot commands:\n/new — Start a new conversation\n/help — Show available commands")
-        
+                                  content="🐈 nanobot commands:\n/new — Start a new conversation\n/help — Show available commands\n/quota — Show quota status")
+        if cmd == "/quota":
+            status = self._get_quota_status()
+            return OutboundMessage(channel=msg.channel, chat_id=msg.chat_id, content=status)
+
         # Consolidate memory before processing if session is too large
         if len(session.messages) > self.memory_window:
             await self._consolidate_memory(session)
@@ -204,20 +298,23 @@ class AgentLoop:
             channel=msg.channel,
             chat_id=msg.chat_id,
         )
-        
+
+        # Select model based on quota
+        selected_model = self._select_model_based_on_quota()
+
         # Agent loop
         iteration = 0
         final_content = None
         tools_used: list[str] = []
-        
+
         while iteration < self.max_iterations:
             iteration += 1
-            
+
             # Call LLM
             response = await self.provider.chat(
                 messages=messages,
                 tools=self.tools.get_definitions(),
-                model=self.model
+                model=selected_model
             )
             
             # Handle tool calls

nanobot/channels/telegram.py

@@ -92,6 +92,7 @@ class TelegramChannel(BaseChannel):
         BotCommand("start", "Start the bot"),
         BotCommand("new", "Start a new conversation"),
         BotCommand("help", "Show available commands"),
+        BotCommand("quota", "Show current quota status"),
     ]
     
     def __init__(
@@ -127,6 +128,7 @@ class TelegramChannel(BaseChannel):
         self._app.add_handler(CommandHandler("start", self._on_start))
         self._app.add_handler(CommandHandler("new", self._forward_command))
         self._app.add_handler(CommandHandler("help", self._forward_command))
+        self._app.add_handler(CommandHandler("quota", self._forward_command))
         
         # Add message handler for text, photos, voice, documents
         self._app.add_handler(