diff --git a/packages/coding-agent/src/eval/__tests__/js-context-manager.test.ts b/packages/coding-agent/src/eval/__tests__/js-context-manager.test.ts
index e572dca6c..08a2d9aa8 100644
--- a/packages/coding-agent/src/eval/__tests__/js-context-manager.test.ts
+++ b/packages/coding-agent/src/eval/__tests__/js-context-manager.test.ts
@@ -1,4 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it } from "bun:test";
+import * as fs from "node:fs";
+import * as path from "node:path";
 import { TempDir } from "@oh-my-pi/pi-utils";
 import { Settings } from "../../config/settings";
 import type { ToolSession } from "../../tools";
@@ -330,6 +332,33 @@ describe.skipIf(process.platform === "win32")("JavaScript eval process isolation
 		expect(reused.output.trim()).toBe("42");
 	});
 
+	it("mirrors the session cwd onto the subprocess's real cwd", async () => {
+		using tempDir = TempDir.createSync("@omp-js-process-cwd-");
+		const session = makeSession(tempDir.path());
+		const evalSessionId = `js-cwd:${crypto.randomUUID()}`;
+		const result = await executeJs("return process.cwd();", {
+			cwd: tempDir.path(),
+			sessionId: evalSessionId,
+			session,
+		});
+		// process.chdir resolves symlinks (macOS tempdirs live under /var ->
+		// /private/var), so compare physical paths.
+		expect(result.output.trim()).toBe(fs.realpathSync(tempDir.path()));
+	});
+
+	it("still runs cells when the session cwd does not exist", async () => {
+		using tempDir = TempDir.createSync("@omp-js-process-cwd-missing-");
+		const missingCwd = path.join(tempDir.path(), "deleted");
+		const session = makeSession(missingCwd);
+		const result = await executeJs("return String(6 * 7);", {
+			cwd: missingCwd,
+			sessionId: `js-cwd-missing:${crypto.randomUUID()}`,
+			session,
+		});
+		expect(result.exitCode).toBe(0);
+		expect(result.output.trim()).toBe("42");
+	});
+
 	it("keeps the isolated process alive after a stackless floated rejection", async () => {
 		using tempDir = TempDir.createSync("@omp-js-process-rejection-");
 		const session = makeSession(tempDir.path());
diff --git a/packages/coding-agent/src/eval/js/process-entry.ts b/packages/coding-agent/src/eval/js/process-entry.ts
index 2308118db..7a30392be 100644
--- a/packages/coding-agent/src/eval/js/process-entry.ts
+++ b/packages/coding-agent/src/eval/js/process-entry.ts
@@ -14,6 +14,14 @@ export function startJsEvalProcess(transport: {
 			// WorkerCore `closed` acknowledgement has crossed IPC.
 			close: () => {},
 		},
-		{ mode: "isolated" },
+		{
+			mode: "isolated",
+			// The subprocess starts with its real cwd at the worker-host entry dir
+			// (a `resolveWorkerSpawnCmd` requirement); mirror the session cwd so
+			// cell code using relative paths or spawning children resolves against
+			// the project instead of the install dir. Worker threads cannot pass
+			// this — `process.chdir` is unavailable there.
+			chdir: cwd => process.chdir(cwd),
+		},
 	);
 }
diff --git a/packages/coding-agent/src/eval/js/worker-core.ts b/packages/coding-agent/src/eval/js/worker-core.ts
index 00bdf5302..354f0c981 100644
--- a/packages/coding-agent/src/eval/js/worker-core.ts
+++ b/packages/coding-agent/src/eval/js/worker-core.ts
@@ -26,7 +26,17 @@ interface ActiveRun {
 type RunResult = Extract<WorkerOutbound, { type: "result" }>;
 
 export type WorkerCoreOptions =
-	| { mode: "isolated" }
+	| {
+			mode: "isolated";
+			/**
+			 * Mirror the session cwd onto the real process cwd so cell code using
+			 * `process.cwd()`, relative paths, or child processes without an explicit
+			 * `cwd` resolves against the project. Only the dedicated subprocess may
+			 * pass this: `process.chdir` is unavailable in Worker threads and would
+			 * mutate the host's own cwd on the inline fallback.
+			 */
+			chdir?: (cwd: string) => void;
+	  }
 	| {
 			mode: "inline";
 			interceptUnhandledRejections(handler: (reason: unknown) => boolean): () => void;
@@ -214,6 +224,7 @@ export class WorkerCore {
 	}
 
 	#ensureRuntime(snapshot: SessionSnapshot): JsRuntime {
+		this.#syncProcessCwd(snapshot.cwd);
 		if (this.#runtime) {
 			this.#runtime.setCwd(snapshot.cwd);
 			return this.#runtime;
@@ -226,6 +237,22 @@ export class WorkerCore {
 		return this.#runtime;
 	}
 
+	#syncProcessCwd(cwd: string): void {
+		if (this.#options.mode !== "isolated" || !this.#options.chdir) return;
+		try {
+			this.#options.chdir(cwd);
+		} catch (error) {
+			// `process.chdir` throws when the session cwd no longer exists; keep
+			// the cell on the runtime's virtual cwd instead of failing the run.
+			this.#transport.send({
+				type: "log",
+				level: "warn",
+				msg: "JS eval subprocess could not enter the session cwd",
+				meta: { cwd, error: errorPayload(error) },
+			});
+		}
+	}
+
 	async #runOne(runId: string, code: string, filename: string, snapshot: SessionSnapshot): Promise<void> {
 		const active: ActiveRun = { runId, filename, pendingTools: new Map(), floatingRejections: [] };
 		this.#runs.set(runId, active);