fix(model-resolver): use connected providers cache when model cache is empty (#1227)

- Remove resolved.model from userModel in tools.ts (was bypassing fallback chain)
- Use connected providers cache in model-resolver when availableModels is empty
- Allows proper provider selection (e.g., github-copilot instead of google)

src/shared/model-resolver.ts

@@ -55,10 +55,27 @@ export function resolveModelWithFallback(
 	// Step 2: Provider fallback chain (with availability check)
 	if (fallbackChain && fallbackChain.length > 0) {
 		if (availableModels.size === 0) {
-			// When model cache is empty, we cannot verify if a provider actually has the model.
-			// Skip fallback chain entirely and fall through to system default.
-			// This prevents selecting provider/model combinations that may not exist.
-			log("No model cache available, skipping fallback chain to use system default")
+			const connectedProviders = readConnectedProvidersCache()
+			const connectedSet = connectedProviders ? new Set(connectedProviders) : null
+
+			if (connectedSet === null) {
+				log("Model fallback chain skipped (no connected providers cache) - falling through to system default")
+			} else {
+				for (const entry of fallbackChain) {
+					for (const provider of entry.providers) {
+						if (connectedSet.has(provider)) {
+							const model = `${provider}/${entry.model}`
+							log("Model resolved via fallback chain (no model cache, using connected provider)", { 
+								provider, 
+								model: entry.model, 
+								variant: entry.variant,
+							})
+							return { model, source: "provider-fallback", variant: entry.variant }
+						}
+					}
+				}
+				log("No connected provider found in fallback chain, falling through to system default")
+			}
 		}
 
 		for (const entry of fallbackChain) {