diff --git a/packages/coding-agent/src/core/session-manager.ts b/packages/coding-agent/src/core/session-manager.ts
index aab0c0e9..b8b930d8 100644
--- a/packages/coding-agent/src/core/session-manager.ts
+++ b/packages/coding-agent/src/core/session-manager.ts
@@ -1558,8 +1558,7 @@ export class SessionManager {
 	 */
 	static continueRecent(cwd: string, sessionDir?: string): SessionManager {
 		const dir = sessionDir ? normalizePath(sessionDir) : getDefaultSessionDir(cwd);
-		const filterCwd = sessionDir !== undefined && dir !== getDefaultSessionDirPath(cwd);
-		const mostRecent = findMostRecentSession(dir, filterCwd ? cwd : undefined);
+		const mostRecent = findMostRecentSession(dir, cwd);
 		if (mostRecent) {
 			return new SessionManager(cwd, dir, mostRecent, true);
 		}
@@ -1639,10 +1638,9 @@ export class SessionManager {
 	 */
 	static async list(cwd: string, sessionDir?: string, onProgress?: SessionListProgress): Promise<SessionInfo[]> {
 		const dir = sessionDir ? normalizePath(sessionDir) : getDefaultSessionDir(cwd);
-		const filterCwd = sessionDir !== undefined && dir !== getDefaultSessionDirPath(cwd);
 		const resolvedCwd = resolvePath(cwd);
-		const sessions = (await listSessionsFromDir(dir, onProgress)).filter(
-			(session) => !filterCwd || sessionCwdMatches(session.cwd, resolvedCwd),
+		const sessions = (await listSessionsFromDir(dir, onProgress)).filter((session) =>
+			sessionCwdMatches(session.cwd, resolvedCwd),
 		);
 		sessions.sort((a, b) => b.modified.getTime() - a.modified.getTime());
 		return sessions;
diff --git a/packages/coding-agent/test/session-manager/project-isolation.test.ts b/packages/coding-agent/test/session-manager/project-isolation.test.ts
new file mode 100644
index 00000000..ac12118f
--- /dev/null
+++ b/packages/coding-agent/test/session-manager/project-isolation.test.ts
@@ -0,0 +1,65 @@
+import { mkdtempSync, readFileSync, rmSync, utimesSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { SessionManager } from "../../src/core/session-manager.ts";
+import { StepSessionManager } from "../../src/step/session.ts";
+
+describe("colliding default session directories", () => {
+	let root: string;
+	let projectA: string;
+	let projectB: string;
+
+	beforeEach(() => {
+		root = mkdtempSync(join(tmpdir(), "session-project-isolation-"));
+		projectA = join(root, "project-a");
+		projectB = join(root, "project", "a");
+		vi.stubEnv("STEP_CODING_AGENT_DIR", join(root, "agent"));
+		vi.stubEnv("STEP_CODING_AGENT_SESSION_DIR", undefined);
+	});
+
+	afterEach(() => {
+		vi.unstubAllEnvs();
+		rmSync(root, { recursive: true, force: true });
+	});
+
+	function persistHeader(manager: SessionManager, modified: number): string {
+		const file = manager.getSessionFile()!;
+		writeFileSync(file, `${JSON.stringify(manager.getHeader())}\n`);
+		utimesSync(file, modified, modified);
+		return file;
+	}
+
+	for (const [name, manager] of [
+		["native", SessionManager],
+		["Step", StepSessionManager],
+	] as const) {
+		it.each([false, true])(`${name}: scopes list and continue with explicit directory=%s`, async (explicit) => {
+			const a = manager.create(projectA);
+			const b = manager.create(projectB);
+			expect(a.getSessionDir()).toBe(b.getSessionDir());
+			const fileA = persistHeader(a, 1);
+			const fileB = persistHeader(b, 2);
+			const beforeB = readFileSync(fileB, "utf8");
+			const dir = explicit ? a.getSessionDir() : undefined;
+
+			expect.soft((await manager.list(projectA, dir)).map((session) => session.path)).toEqual([fileA]);
+			const continued = manager.continueRecent(projectA, dir);
+			expect.soft(continued.getSessionFile()).toBe(fileA);
+			continued.appendMessage({ role: "user", content: "project A only", timestamp: 1 });
+			expect.soft(readFileSync(fileB, "utf8")).toBe(beforeB);
+			expect((await manager.listAll(a.getSessionDir())).map((session) => session.path).sort()).toEqual(
+				[fileA, fileB].sort(),
+			);
+		});
+
+		it(`${name}: starts fresh when only the other project has a session`, async () => {
+			const b = manager.create(projectB);
+			const fileB = persistHeader(b, 1);
+			expect.soft(await manager.list(projectA)).toEqual([]);
+			const continued = manager.continueRecent(projectA);
+			expect.soft(continued.getSessionFile()).not.toBe(fileB);
+			expect(continued.getSessionId()).not.toBe(b.getSessionId());
+		});
+	}
+});