diff --git a/.gitattributes b/.gitattributes
index 1ce5b29ee45..8f4f884295d 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -8,6 +8,11 @@
 /src/cli/bundled-skill-guides.ts text eol=lf
 # Bundled plugin trees are byte-hashed; CRLF checkout would break the pinned hash.
 /resources/plugins/** text eol=lf
+# Relay assets are copied verbatim into the bundle and hashed byte-for-byte into
+# .version, which names the immutable remote install dir. A CRLF checkout makes a
+# Windows-built client disagree with a mac/Linux-built one on the same release,
+# so one host ends up with two relay trees (#17886 review).
+/config/relay-assets/** text eol=lf
 # Pin the bytes so a patch reads and diffs identically on every host. It is NOT
 # what makes the hash right: pnpm hashes a patch LF-normalized, so a CRLF checkout
 # cannot change it. Believing otherwise put a hand-computed raw digest in the
diff --git a/config/scripts/relay-asset-line-ending-pin.test.mjs b/config/scripts/relay-asset-line-ending-pin.test.mjs
new file mode 100644
index 00000000000..6e0f358f333
--- /dev/null
+++ b/config/scripts/relay-asset-line-ending-pin.test.mjs
@@ -0,0 +1,80 @@
+import { execFileSync } from 'node:child_process'
+import { resolve } from 'node:path'
+import { RELAY_ARTIFACTS } from '../../src/shared/relay-artifacts.ts'
+import { describe, expect, it } from 'vitest'
+
+/**
+ * Guard the `.gitattributes` pin that keeps `config/relay-assets` on LF.
+ *
+ * `core.autocrlf=true` ships in the Git-for-Windows system config, so without a
+ * pin a Windows runner checks these out as CRLF. build-relay.mjs copies them
+ * verbatim into the bundle and hashes them byte-for-byte into `.version`, which
+ * names the immutable remote relay directory -- so a Windows-built client and a
+ * mac/Linux-built one disagree on the same release, and one SSH host ends up with
+ * two relay trees, each paying its own remote native-dep compile.
+ *
+ * Measured on v1.4.197: master-cloexec-patch.cjs shipped at 11229 bytes from the
+ * mac runner and 11547 (= 11229 + 318 lines) from the Windows one.
+ */
+const projectDir = resolve(import.meta.dirname, '../..')
+
+function git(args) {
+  return execFileSync('git', args, { cwd: projectDir, encoding: 'utf8' })
+}
+
+/** `git check-attr -z` emits NUL-separated path/attr/value triples. */
+function eolAttributes(paths) {
+  const fields = git(['check-attr', '-z', 'eol', '--', ...paths]).split('\0')
+  const found = new Map()
+  for (let index = 0; index + 2 < fields.length; index += 3) {
+    found.set(fields[index], fields[index + 2])
+  }
+  return found
+}
+
+/**
+ * Keyed off the manifest, not a directory: build-relay refuses to emit an
+ * artifact absent from RELAY_ARTIFACTS, so relocating an asset cannot slip
+ * past this the way a path glob would. esbuild bundles have no tracked
+ * source and contribute no hits, so they need no classifying.
+ */
+function trackedManifestSources() {
+  const paths = new Set()
+  for (const { filename } of RELAY_ARTIFACTS) {
+    const hits = git(['ls-files', '-z', '--', `*/${filename}`]).split('\0').filter(Boolean)
+    for (const path of hits) {
+      paths.add(path)
+    }
+  }
+  return [...paths]
+}
+
+describe('config/relay-assets line-ending pin', () => {
+  it('pins every tracked relay artifact source to LF', () => {
+    const assets = trackedManifestSources()
+    expect(assets.length).toBeGreaterThan(0)
+
+    const attributes = eolAttributes(assets)
+    const unpinned = assets.filter((path) => attributes.get(path) !== 'lf')
+
+    expect(
+      unpinned,
+      'A relay asset left on the platform default gets CRLF on a Windows runner, ' +
+        'which changes the .version hash and splits one release across two remote ' +
+        'relay directories. Pin it in .gitattributes.'
+    ).toEqual([])
+  })
+
+  // Why: the assertion above only sees files that exist today. These fix the
+  // pattern itself -- broad enough to cover a file added tomorrow, narrow enough
+  // not to claim neighbours.
+  it.each([
+    ['config/relay-assets/example.cjs', 'lf'],
+    ['config/relay-assets/nested/deeper/example.cjs', 'lf'],
+    ['config/relay-assets/example.txt', 'lf'],
+    ['config/relay-assets-extra/example.cjs', 'unspecified'],
+    ['vendor/config/relay-assets/example.cjs', 'unspecified']
+  ])('resolves %s to eol=%s', (path, expected) => {
+    expect(eolAttributes([path]).get(path)).toBe(expected)
+  })
+})