fix(ai): own Anthropic SSE parsing to avoid SDK JSON.parse hard-failures

Bypass the Anthropic SDK streaming parser entirely. Use
client.messages.create().asResponse() and decode the SSE stream
ourselves with defensive JSON parsing that repairs invalid escape
sequences and control characters inside string literals.

- Switch from SDK .stream() to .asResponse() + pi-owned SSE decoder
- Add repairJson() / parseJsonWithRepair() to json-parse.ts
- Add anthropic-sse-parsing.test.ts regression for malformed tool deltas
- Update github-copilot-anthropic.test.ts mock to match new call path
- Update deprecated claude-3-5-haiku-20241022 refs to claude-haiku-4-5
- Remove stale non-reasoning model test

fixes #3175

packages/ai/test/github-copilot-anthropic.test.ts

@@ -4,37 +4,42 @@ import type { Context } from "../src/types.js";
 
 const mockState = vi.hoisted(() => ({
 	constructorOpts: undefined as Record<string, unknown> | undefined,
-	streamParams: undefined as Record<string, unknown> | undefined,
+	createParams: undefined as Record<string, unknown> | undefined,
 }));
 
 vi.mock("@anthropic-ai/sdk", () => {
-	const fakeStream = {
-		async *[Symbol.asyncIterator]() {
-			yield {
+	function createSseResponse(): Response {
+		const body = [
+			`event: message_start\ndata: ${JSON.stringify({
 				type: "message_start",
 				message: {
+					id: "msg_test",
 					usage: { input_tokens: 10, output_tokens: 0 },
 				},
-			};
-			yield {
+			})}\n`,
+			`event: message_delta\ndata: ${JSON.stringify({
 				type: "message_delta",
 				delta: { stop_reason: "end_turn" },
 				usage: { output_tokens: 5 },
-			};
-		},
-		finalMessage: async () => ({
-			usage: { input_tokens: 10, output_tokens: 5, cache_creation_input_tokens: 0, cache_read_input_tokens: 0 },
-		}),
-	};
+			})}\n`,
+		].join("\n");
+
+		return new Response(body, {
+			status: 200,
+			headers: { "content-type": "text/event-stream" },
+		});
+	}
 
 	class FakeAnthropic {
 		constructor(opts: Record<string, unknown>) {
 			mockState.constructorOpts = opts;
 		}
 		messages = {
-			stream: (params: Record<string, unknown>) => {
-				mockState.streamParams = params;
-				return fakeStream;
+			create: (params: Record<string, unknown>) => {
+				mockState.createParams = params;
+				return {
+					asResponse: async () => createSseResponse(),
+				};
 			},
 		};
 	}
@@ -79,7 +84,7 @@ describe("Copilot Claude via Anthropic Messages", () => {
 		expect(beta).not.toContain("fine-grained-tool-streaming");
 
 		// Payload is valid Anthropic Messages format
-		const params = mockState.streamParams!;
+		const params = mockState.createParams!;
 		expect(params.model).toBe("claude-sonnet-4");
 		expect(params.stream).toBe(true);
 		expect(params.max_tokens).toBeGreaterThan(0);