feat(vertex): add 1M context window beta support for Claude Sonnet 4 (RooCodeInc#10209)

Author: hannesrudolph

src/api/providers/anthropic-vertex.ts

@@ -247,6 +247,14 @@ export class AnthropicVertexHandler extends BaseProvider implements SingleComple
 			betas.push("context-1m-2025-08-07")
 		}
 
+		// Build betas array for request headers
+		const betas: string[] = []
+
+		// Add 1M context beta flag if enabled for supported models
+		if (enable1MContext) {
+			betas.push("context-1m-2025-08-07")
+		}
+
 		// The `:thinking` suffix indicates that the model is a "Hybrid"
 		// reasoning model and that reasoning is required to be enabled.
 		// The actual model ID honored by Anthropic's API does not have this