fix(router-provider): single-flight ensureModelFetched and earlier call site

Make ensureModelFetched single-flight so concurrent callers share a
single in-flight fetch instead of firing duplicates. Move the call site
before the cachedStreamingModel snapshot so the model info is accurate
from the start of the streaming session, not just for context management.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: JamesRobert20

src/api/providers/__tests__/zoo-gateway.spec.ts

@@ -659,6 +659,16 @@ describe("ZooGatewayHandler", () => {
 			expect(getModels).not.toHaveBeenCalled()
 		})
 
+		it("deduplicates concurrent calls into a single fetch", async () => {
+			const handler = new ZooGatewayHandler(mockOptions)
+			const { getModels } = await import("../fetchers/modelCache")
+			vitest.mocked(getModels).mockClear()
+
+			await Promise.all([handler.ensureModelFetched(), handler.ensureModelFetched()])
+
+			expect(getModels).toHaveBeenCalledTimes(1)
+		})
+
 		it("makes getModel return the fetched context window instead of the default", async () => {
 			const { getModels } = await import("../fetchers/modelCache")
 			vitest.mocked(getModels).mockResolvedValueOnce({

src/api/providers/router-provider.ts

@@ -61,9 +61,18 @@ export abstract class RouterProvider extends BaseProvider {
 		return this.getModel()
 	}
 
+	private modelFetchPromise?: Promise<void>
+
 	async ensureModelFetched(): Promise<void> {
 		if (Object.keys(this.models).length === 0) {
-			await this.fetchModel()
+			const fetchPromise = (this.modelFetchPromise ??= this.fetchModel().then(() => undefined))
+			try {
+				await fetchPromise
+			} finally {
+				if (this.modelFetchPromise === fetchPromise) {
+					this.modelFetchPromise = undefined
+				}
+			}
 		}
 	}
 

src/core/task/Task.ts

@@ -2762,6 +2762,8 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 
 				await this.diffViewProvider.reset()
 
+				await this.api.ensureModelFetched?.()
+
 				// Cache model info once per API request to avoid repeated calls during streaming
 				// This is especially important for tools and background usage collection
 				this.cachedStreamingModel = this.api.getModel()