diff --git a/packages/agent/src/harness/session/session.ts b/packages/agent/src/harness/session/session.ts
index 6f136208..ce369dff 100644
--- a/packages/agent/src/harness/session/session.ts
+++ b/packages/agent/src/harness/session/session.ts
@@ -234,12 +234,13 @@ export class Session<TMetadata extends SessionMetadata = SessionMetadata> {
 	}
 
 	async appendSessionName(name: string): Promise<string> {
+		const sanitizedName = name.replace(/[\r\n]+/g, " ").trim();
 		return this.appendTypedEntry({
 			type: "session_info",
 			id: await this.storage.createEntryId(),
 			parentId: await this.storage.getLeafId(),
 			timestamp: new Date().toISOString(),
-			name: name.trim(),
+			name: sanitizedName,
 		} satisfies SessionInfoEntry);
 	}
 
diff --git a/packages/agent/test/harness/session.test.ts b/packages/agent/test/harness/session.test.ts
index c9598da8..39e285b5 100644
--- a/packages/agent/test/harness/session.test.ts
+++ b/packages/agent/test/harness/session.test.ts
@@ -86,6 +86,12 @@ async function runSessionSuite(
 			expect(context.messages[1]?.role).toBe("custom");
 		});
 
+		it("normalizes session names", async () => {
+			const session = new Session(await createStorage());
+			await session.appendSessionName(" hello\nworld\r\nagain ");
+			expect(await session.getSessionName()).toBe("hello world again");
+		});
+
 		it("supports labels and session info entries without affecting context", async () => {
 			const session = new Session(await createStorage());
 			const user1 = await session.appendMessage(createUserMessage("one"));
diff --git a/packages/coding-agent/src/core/session-manager.ts b/packages/coding-agent/src/core/session-manager.ts
index b07968b3..e40ed0c4 100644
--- a/packages/coding-agent/src/core/session-manager.ts
+++ b/packages/coding-agent/src/core/session-manager.ts
@@ -1026,12 +1026,13 @@ 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;
diff --git a/packages/coding-agent/src/modes/interactive/interactive-mode.ts b/packages/coding-agent/src/modes/interactive/interactive-mode.ts
index 27e9f88a..fe733f20 100644
--- a/packages/coding-agent/src/modes/interactive/interactive-mode.ts
+++ b/packages/coding-agent/src/modes/interactive/interactive-mode.ts
@@ -5344,8 +5344,12 @@ 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();
 	}
 
diff --git a/packages/coding-agent/test/suite/regressions/5996-session-name-newlines.test.ts b/packages/coding-agent/test/suite/regressions/5996-session-name-newlines.test.ts
new file mode 100644
index 00000000..c33f7760
--- /dev/null
+++ b/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"]);
+	});
+});