diff --git a/src/tests/bridge-package-root.test.ts b/src/tests/bridge-package-root.test.ts
new file mode 100644
index 000000000..8e46101ff
--- /dev/null
+++ b/src/tests/bridge-package-root.test.ts
@@ -0,0 +1,71 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { readFileSync } from 'node:fs'
+import { join } from 'node:path'
+
+/**
+ * Regression test for #1881: Windows web mode — hardcoded Linux CI path in
+ * standalone build.
+ *
+ * The Next.js standalone build bakes import.meta.url into compiled chunks as
+ * the CI runner's absolute Linux path (file:///home/runner/work/gsd-2/gsd-2/…).
+ * On Windows, fileURLToPath() rejects this with "File URL path must be
+ * absolute". The fix wraps the derivation in safePackageRootFromImportUrl()
+ * so the module-level constant never throws, and resolveBridgeRuntimeConfig
+ * falls through to the GSD_WEB_PACKAGE_ROOT env var.
+ */
+
+import { safePackageRootFromImportUrl } from '../web/safe-import-meta-resolve.ts'
+
+test('safePackageRootFromImportUrl returns a path for a valid native file URL', () => {
+  const result = safePackageRootFromImportUrl(import.meta.url)
+  assert.ok(result !== null, 'should return a path for a valid native file URL')
+  assert.ok(typeof result === 'string')
+  assert.ok(result.length > 0)
+})
+
+test('safePackageRootFromImportUrl returns null for a non-file URL', () => {
+  const result = safePackageRootFromImportUrl('https://example.com/foo/bar.ts')
+  assert.equal(result, null)
+})
+
+test('safePackageRootFromImportUrl returns null for empty input', () => {
+  const result = safePackageRootFromImportUrl('')
+  assert.equal(result, null)
+})
+
+test('safePackageRootFromImportUrl returns null for malformed URL', () => {
+  const result = safePackageRootFromImportUrl('not-a-url')
+  assert.equal(result, null)
+})
+
+test('safePackageRootFromImportUrl respects ancestorLevels', () => {
+  // With 0 levels, should return the directory of the module itself
+  const level0 = safePackageRootFromImportUrl(import.meta.url, 0)
+  const level2 = safePackageRootFromImportUrl(import.meta.url, 2)
+  assert.ok(level0 !== null)
+  assert.ok(level2 !== null)
+  // level0 is deeper than level2
+  assert.ok(level0.length > level2.length)
+})
+
+test('bridge-service.ts uses safePackageRootFromImportUrl for DEFAULT_PACKAGE_ROOT', () => {
+  const source = readFileSync(join(process.cwd(), 'src', 'web', 'bridge-service.ts'), 'utf-8')
+  assert.ok(
+    source.includes('safePackageRootFromImportUrl(import.meta.url)'),
+    'bridge-service.ts must derive DEFAULT_PACKAGE_ROOT via the safe helper',
+  )
+  const rawPattern = 'const DEFAULT_PACKAGE_ROOT = resolve(dirname(fileURLToPath(import.meta.url'
+  assert.ok(
+    !source.includes(rawPattern),
+    'bridge-service.ts must not use raw fileURLToPath for DEFAULT_PACKAGE_ROOT',
+  )
+})
+
+test('bridge-service resolveBridgeRuntimeConfig falls back to lazy default', () => {
+  const source = readFileSync(join(process.cwd(), 'src', 'web', 'bridge-service.ts'), 'utf-8')
+  assert.ok(
+    source.includes('env.GSD_WEB_PACKAGE_ROOT || getDefaultPackageRoot()'),
+    'resolveBridgeRuntimeConfig must fall back to lazy default package root',
+  )
+})
diff --git a/src/web/bridge-service.ts b/src/web/bridge-service.ts
index 2f8a4f212..b5f87cdce 100644
--- a/src/web/bridge-service.ts
+++ b/src/web/bridge-service.ts
@@ -2,9 +2,10 @@ import { execFile, spawn, type ChildProcess, type SpawnOptions } from "node:chil
 import { existsSync, readdirSync, readFileSync, statSync } from "node:fs";
 import { StringDecoder } from "node:string_decoder";
 import type { Readable } from "node:stream";
-import { join, resolve, dirname } from "node:path";
-import { fileURLToPath, pathToFileURL } from "node:url";
+import { join, resolve } from "node:path";
+import { pathToFileURL } from "node:url";
 import { resolveTypeStrippingFlag, resolveSubprocessModule, buildSubprocessPrefixArgs } from "./ts-subprocess-flags.ts";
+import { safePackageRootFromImportUrl } from "./safe-import-meta-resolve.ts";
 
 import type { AgentSessionEvent, SessionStateChangeReason } from "../../packages/pi-coding-agent/src/core/agent-session.ts";
 import type {
@@ -39,23 +40,14 @@ import {
 } from "./auto-dashboard-service.ts";
 import { resolveGsdCliEntry } from "./cli-entry.ts";
 
-// Lazily computed fallback — import.meta.url is baked in at build time by
-// webpack, so when the standalone bundle built on Linux CI runs on Windows the
-// literal file:// URL contains a Unix path that fileURLToPath() rejects.
-// Deferring the computation means it only fires when GSD_WEB_PACKAGE_ROOT is
-// absent, and if it does fire we handle the cross-platform failure gracefully.
+// The standalone Next.js bundle bakes import.meta.url at build time with the
+// CI runner's absolute path.  On Windows, fileURLToPath() rejects a Linux
+// file:// URL at module load time.  Use a lazy getter so the derivation is
+// deferred to first use (not module load) and falls back to cwd on failure.
 let _defaultPackageRoot: string | undefined;
 function getDefaultPackageRoot(): string {
   if (_defaultPackageRoot !== undefined) return _defaultPackageRoot;
-  try {
-    _defaultPackageRoot = resolve(dirname(fileURLToPath(import.meta.url)), "../..");
-  } catch {
-    // Standalone bundle running on a different OS than the builder — the
-    // baked-in import.meta.url is not a valid local file URL.  Fall back to
-    // cwd which is the best available approximation; callers that need the
-    // real package root should set GSD_WEB_PACKAGE_ROOT.
-    _defaultPackageRoot = process.cwd();
-  }
+  _defaultPackageRoot = safePackageRootFromImportUrl(import.meta.url) ?? process.cwd();
   return _defaultPackageRoot;
 }
 
@@ -63,6 +55,7 @@ function getDefaultPackageRoot(): string {
 export function resetDefaultPackageRootForTests(): void {
   _defaultPackageRoot = undefined;
 }
+
 const RESPONSE_TIMEOUT_MS = 30_000;
 const START_TIMEOUT_MS = 150_000;
 const MAX_STDERR_BUFFER = 8_000;
diff --git a/src/web/safe-import-meta-resolve.ts b/src/web/safe-import-meta-resolve.ts
new file mode 100644
index 000000000..95c388c5a
--- /dev/null
+++ b/src/web/safe-import-meta-resolve.ts
@@ -0,0 +1,33 @@
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+/**
+ * Derive a package root from an import.meta.url, returning null on failure.
+ *
+ * The Next.js standalone build bakes import.meta.url as the CI runner's
+ * absolute path (e.g. file:///home/runner/work/gsd-2/gsd-2/src/web/bridge-service.ts).
+ * On Windows, fileURLToPath() rejects this Linux path with
+ * "File URL path must be absolute".
+ *
+ * This helper catches that error so the module-level constant never throws,
+ * letting resolveBridgeRuntimeConfig() fall through to the GSD_WEB_PACKAGE_ROOT
+ * env var that web-mode.ts always sets at launch time.
+ *
+ * @param importUrl - The value of import.meta.url at the call site.
+ * @param ancestorLevels - How many directory levels to ascend from the module's
+ *   directory to reach the package root (default 2: src/web/ -> root).
+ * @returns Resolved absolute package root path, or null if the URL cannot be
+ *   converted to a native path on this platform.
+ */
+export function safePackageRootFromImportUrl(
+  importUrl: string,
+  ancestorLevels = 2,
+): string | null {
+  try {
+    const moduleDir = dirname(fileURLToPath(importUrl));
+    const segments = Array.from({ length: ancestorLevels }, () => "..");
+    return resolve(moduleDir, ...segments);
+  } catch {
+    return null;
+  }
+}