fix(ai): preserve aborted stop reason during lazy setup (#8635)

Fixes #8409

## Summary
- Pass the request abort signal through lazy stream setup wrappers.
- Report setup failures as aborted when the request signal is already
aborted.
- Added a regression test for aborting during a tool execution before
next auth setup.

packages/coding-agent/test/suite/regressions/8409-aborted-tool-auth-setup.test.ts

@@ -0,0 +1,53 @@
+import type { AgentTool } from "@earendil-works/pi-agent-core";
+import { fauxAssistantMessage, fauxToolCall } from "@earendil-works/pi-ai";
+import { Type } from "typebox";
+import { afterEach, describe, expect, it } from "vitest";
+import { createHarness, type Harness } from "../harness.ts";
+
+describe("issue #8409 aborted tool auth setup", () => {
+	let harness: Harness | undefined;
+
+	afterEach(() => {
+		harness?.cleanup();
+		harness = undefined;
+	});
+
+	it("ends the turn as aborted when auth setup sees an already-aborted signal", async () => {
+		let markToolStarted = () => {};
+		const toolStarted = new Promise<void>((resolve) => {
+			markToolStarted = resolve;
+		});
+		const blockingTool: AgentTool = {
+			name: "block",
+			label: "Block",
+			description: "Blocks until aborted",
+			parameters: Type.Object({}),
+			execute: async (_toolCallId, _params, signal) => {
+				markToolStarted();
+				await new Promise<void>((resolve) => {
+					if (signal?.aborted) resolve();
+					else signal?.addEventListener("abort", () => resolve(), { once: true });
+				});
+				return { content: [{ type: "text", text: "tool aborted" }], details: {} };
+			},
+		};
+		harness = await createHarness({ tools: [blockingTool] });
+		const modelRuntime = harness.session.modelRuntime;
+		harness.session.agent.streamFunction = (model, context, options) =>
+			modelRuntime.streamSimple(model, context, options);
+		harness.setResponses([fauxAssistantMessage(fauxToolCall("block", {}), { stopReason: "toolUse" })]);
+
+		const prompt = harness.session.prompt("run the blocking tool");
+		await toolStarted;
+		await harness.session.abort();
+		await prompt;
+
+		const finalAssistant = harness.session.messages
+			.slice()
+			.reverse()
+			.find((message) => message.role === "assistant");
+		expect(finalAssistant?.role).toBe("assistant");
+		if (finalAssistant?.role !== "assistant") throw new Error("Expected final assistant message");
+		expect(finalAssistant.stopReason).toBe("aborted");
+	});
+});