fix(coding-agent): normalize session names

packages/coding-agent/src/core/session-manager.ts

@@ -1025,12 +1025,13 @@ export class SessionManager {
 
 	/** Append a session info entry (e.g., display name). Returns entry id. */
 	appendSessionInfo(name: string): string {
+		const sanitizedName = name.replace(/[\r\n]+/g, " ").trim();
 		const entry: SessionInfoEntry = {
 			type: "session_info",
 			id: generateId(this.byId),
 			parentId: this.leafId,
 			timestamp: new Date().toISOString(),
-			name: name.trim(),
+			name: sanitizedName,
 		};
 		this._appendEntry(entry);
 		return entry.id;

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -5340,8 +5340,12 @@ export class InteractiveMode {
 		}
 
 		this.session.setSessionName(name);
+		const sessionName = this.sessionManager.getSessionName();
+		if (sessionName !== name) {
+			this.showWarning(`Session name was normalized from ${JSON.stringify(name)} to ${JSON.stringify(sessionName)}`);
+		}
 		this.chatContainer.addChild(new Spacer(1));
-		this.chatContainer.addChild(new Text(theme.fg("dim", `Session name set: ${name}`), 1, 0));
+		this.chatContainer.addChild(new Text(theme.fg("dim", `Session name set: ${sessionName ?? name}`), 1, 0));
 		this.ui.requestRender();
 	}
 

packages/coding-agent/test/suite/regressions/5996-session-name-newlines.test.ts

@@ -0,0 +1,40 @@
+import { afterEach, describe, expect, it } from "vitest";
+import type { ExtensionAPI } from "../../../src/index.ts";
+import { createHarness, type Harness } from "../harness.ts";
+
+describe("regression #5996: session names do not contain newlines", () => {
+	const harnesses: Harness[] = [];
+
+	afterEach(() => {
+		while (harnesses.length > 0) {
+			harnesses.pop()?.cleanup();
+		}
+	});
+
+	it("filters newlines when AgentSession.setSessionName is called", async () => {
+		const harness = await createHarness();
+		harnesses.push(harness);
+
+		harness.session.setSessionName("hello\nworld\r\nagain");
+
+		expect(harness.sessionManager.getSessionName()).toBe("hello world again");
+		expect(harness.eventsOfType("session_info_changed").map((event) => event.name)).toEqual(["hello world again"]);
+	});
+
+	it("filters newlines when an extension calls pi.setSessionName", async () => {
+		let api: ExtensionAPI | undefined;
+		const harness = await createHarness({
+			extensionFactories: [
+				(pi) => {
+					api = pi;
+				},
+			],
+		});
+		harnesses.push(harness);
+
+		api?.setSessionName("from\nextension");
+
+		expect(harness.sessionManager.getSessionName()).toBe("from extension");
+		expect(harness.eventsOfType("session_info_changed").map((event) => event.name)).toEqual(["from extension"]);
+	});
+});