feat(aisidebar): implement Ollama availability handling and graceful startup

- Add comprehensive Ollama connection error handling strategy
- Implement OllamaClient with non-blocking initialization and connection checks
- Create OllamaAvailabilityMonitor for periodic Ollama connection tracking
- Update design and requirements to support graceful Ollama unavailability
- Add new project structure for AI sidebar module with initial implementation
- Enhance error handling to prevent application crashes when Ollama is not running
- Prepare for future improvements in AI sidebar interaction and resilience

ollama_client.py

@@ -25,17 +25,39 @@ class OllamaClient:
         self._host = host
         self._client = None
         self._cached_models: list[str] | None = None
+        self._is_available = False
 
         if ollama is None:
             return
 
-        if host and hasattr(ollama, "Client"):
-            self._client = ollama.Client(host=host)  # type: ignore[call-arg]
+        # Try to initialize client and check connection
+        try:
+            if host and hasattr(ollama, "Client"):
+                self._client = ollama.Client(host=host)  # type: ignore[call-arg]
+            
+            # Test connection by attempting to list models
+            self._check_connection()
+        except Exception:
+            # Silently fail - availability flag remains False
+            pass
 
     # ------------------------------------------------------------------ helpers
+    def _check_connection(self) -> None:
+        """Check if Ollama is available and update internal flag."""
+        if ollama is None:
+            self._is_available = False
+            return
+        
+        try:
+            # Attempt a simple list call to verify connection
+            self._call_sdk("list")  # type: ignore[arg-type]
+            self._is_available = True
+        except Exception:
+            self._is_available = False
+    
     @property
     def is_available(self) -> bool:
-        return ollama is not None
+        return self._is_available
 
     @property
     def default_model(self) -> str | None:
@@ -52,7 +74,13 @@ class OllamaClient:
 
         try:
             response = self._call_sdk("list")  # type: ignore[arg-type]
+            # Update availability flag on successful call
+            self._is_available = True
         except OllamaClientError:
+            self._is_available = False
+            return []
+        except Exception:
+            self._is_available = False
             return []
 
         models: list[str] = []
@@ -84,10 +112,16 @@ class OllamaClient:
     ) -> dict[str, str] | None:
         """Execute a blocking chat call against Ollama."""
         if not self.is_available:
-            return {
-                "role": "assistant",
-                "content": "Ollama SDK is not installed; install `ollama` to enable responses.",
-            }
+            if ollama is None:
+                return {
+                    "role": "assistant",
+                    "content": "Ollama SDK is not installed; install `ollama` to enable responses.",
+                }
+            else:
+                return {
+                    "role": "assistant",
+                    "content": "Ollama is not running. Start Ollama with: ollama serve",
+                }
 
         try:
             result = self._call_sdk(
@@ -96,10 +130,19 @@ class OllamaClient:
                 messages=list(messages),
                 stream=False,
             )
+            # Update availability flag on successful call
+            self._is_available = True
         except OllamaClientError as exc:
+            self._is_available = False
             return {
                 "role": "assistant",
-                "content": f"Unable to reach Ollama: {exc}",
+                "content": f"Unable to reach Ollama: {exc}\n\nStart Ollama with: ollama serve",
+            }
+        except Exception as exc:
+            self._is_available = False
+            return {
+                "role": "assistant",
+                "content": f"Unable to reach Ollama: {exc}\n\nStart Ollama with: ollama serve",
             }
 
         # Handle both dict responses (old SDK) and Pydantic objects (new SDK)