Clean up OpenCode ProviderModelNotFoundError messages

- Detect ProviderModelNotFoundError and show clean message
- Extract provider and model IDs from error
- Suggest: connect provider in opencode, use --provider flag, or edit in UI
- Truncate other stderr to 200 chars to avoid code dumps

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/smarttools/providers.py

@@ -199,7 +199,28 @@ def call_provider(provider_name: str, prompt: str, timeout: int = 300) -> Provid
 
         # Warn if output is empty (provider ran but returned nothing)
         if not result.stdout.strip():
-            stderr_hint = f" (stderr: {result.stderr.strip()})" if result.stderr.strip() else ""
+            stderr = result.stderr.strip()
+
+            # Check for OpenCode's ProviderModelNotFoundError
+            if "ProviderModelNotFoundError" in stderr or "ModelNotFoundError" in stderr:
+                # Extract provider and model info if possible
+                import re
+                provider_match = re.search(r'providerID:\s*"([^"]+)"', stderr)
+                model_match = re.search(r'modelID:\s*"([^"]+)"', stderr)
+                provider_id = provider_match.group(1) if provider_match else "unknown"
+                model_id = model_match.group(1) if model_match else "unknown"
+
+                return ProviderResult(
+                    text="",
+                    success=False,
+                    error=f"Model '{model_id}' from provider '{provider_id}' is not available.\n\n"
+                          f"To fix this, either:\n"
+                          f"  1. Run 'opencode' to connect the {provider_id} provider\n"
+                          f"  2. Use --provider to pick a different model (e.g., --provider opencode-pickle)\n"
+                          f"  3. Run 'smarttools ui' to edit the tool's default provider"
+                )
+
+            stderr_hint = f" (stderr: {stderr[:200]}...)" if len(stderr) > 200 else (f" (stderr: {stderr})" if stderr else "")
             return ProviderResult(
                 text="",
                 success=False,