diff --git a/apps/desktop/scripts/before-build.mjs b/apps/desktop/scripts/before-build.mjs
index acb4d5b14c..9dd0ba3856 100644
--- a/apps/desktop/scripts/before-build.mjs
+++ b/apps/desktop/scripts/before-build.mjs
@@ -102,12 +102,53 @@ function writeMsixExtensions() {
     </uap3:Properties>
   </uap3:AppExtension>
 </uap3:Extension>
-${aliases}`
+${aliases}${serviceExtensions()}`
 
   fs.mkdirSync(path.dirname(file), { recursive: true })
   fs.writeFileSync(file, copilot)
 }
 
+/**
+ * The desktop6:Service fragment registering HermesGateway as a Windows
+ * Service (plan: gateway-msix-windows-service; Task 2).
+ *
+ * The service Executable is the payload's own launcher (hermes.exe —
+ * the distlib-minted PE that already serves the AppExecutionAliases):
+ * its `gateway run --service` mode is the SCM frontend
+ * (gateway/windows_service.py). NO separate shim binary.
+ *
+ * Settled decisions baked here (2026-09-03, ethie): user-context
+ * service (StartAccount omitted — desktop6 defaults to the installing
+ * user's context; localSystem explicitly rejected), demand StartupType
+ * (config-only posture: the service arrives STOPPED; `hermes gateway
+ * service on` flips it to automatic-at-logon).
+ *
+ * Content rules (the 0x80080204 playbook): xmlns:desktop6 rides the
+ * fragment root; ONE extension block; Executable must name a real in-
+ * package exe. Requires Win10 1903+ — the minVersion bump in
+ * gen-msix-manifest.mjs matches. Exported pure for tests.
+ */
+export function serviceExtensions({
+  name = 'HermesGateway',
+  executable = ['app', 'resources', 'agent-payload', 'bin', 'hermes.exe'].join(String.fromCharCode(92)),
+  variant = 'bundled',
+} = {}) {
+  // light variant ships no payload → no service; the store variant is
+  // decided by Store policy separately (plan risk item) — both render
+  // service-less for now.
+  if (variant === 'light' || variant === 'store') return ''
+  return `<desktop6:Extension
+    xmlns:desktop6="http://schemas.microsoft.com/appx/manifest/desktop/windows10/6"
+    Category="windows.service"
+    Executable="${executable}"
+    EntryPoint="Windows.FullTrustApplication">
+  <desktop6:Service
+      Name="${name}"
+      StartupType="demand" />
+</desktop6:Extension>
+`
+}
+
 /**
  * One uap5:Extension block per payload CLI launcher, each naming its own
  * Executable (the distlib-minted launcher exes under bin/) and the alias
diff --git a/apps/desktop/scripts/cli-launchers.test.mjs b/apps/desktop/scripts/cli-launchers.test.mjs
index d569cfeda4..446c5344a8 100644
--- a/apps/desktop/scripts/cli-launchers.test.mjs
+++ b/apps/desktop/scripts/cli-launchers.test.mjs
@@ -115,3 +115,46 @@ test('light variant emits no alias fragments', () => {
   assert.ok(appExecutionAliasExtensions(['hermes']).includes('windows.appExecutionAlias'))
   assert.ok(scriptDir.length > 0)
 })
+
+// ── HermesGateway Windows Service fragment (Task 2, plan:
+//    gateway-msix-windows-service) ────────────────────────────────────────
+import { serviceExtensions } from './before-build.mjs'
+
+test('bundled variant registers HermesGateway, demand-start, launcher exe', () => {
+  const frag = serviceExtensions()
+  assert.ok(frag.includes('Category="windows.service"'), 'service category')
+  assert.ok(frag.includes('Name="HermesGateway"'), 'the service name the CLI verbs key off')
+  assert.ok(frag.includes('StartupType="demand"'), 'config-only posture: arrives stopped')
+  // Compose the expected path the same way the source does — no escaping
+  // ambiguity (the appExecutionAliasExtensions precedent).
+  const bs = String.fromCharCode(92)
+  const launcherPath = ['app', 'resources', 'agent-payload', 'bin', 'hermes.exe'].join(bs)
+  assert.ok(
+    frag.includes(`Executable="${launcherPath}"`),
+    'the service Executable is the payload launcher (no shim binary)'
+  )
+  assert.ok(!frag.includes('StartAccount'), 'user-context by default — localSystem rejected')
+})
+
+test('light and store variants render service-less', () => {
+  assert.equal(serviceExtensions({ variant: 'light' }), '')
+  assert.equal(serviceExtensions({ variant: 'store' }), '')
+})
+
+test('one desktop6 extension block with xmlns on the fragment root', () => {
+  const frag = serviceExtensions()
+  assert.equal(
+    (frag.match(/<desktop6:Extension/g) || []).length,
+    1,
+    'the 0x80080204 playbook: ONE extension block'
+  )
+  assert.ok(
+    frag.includes('xmlns:desktop6="http://schemas.microsoft.com/appx/manifest/desktop/windows10/6"'),
+    'namespace rides the fragment root (the copilot-fragment precedent)'
+  )
+})
+
+test('custom name propagates (per-install namespacing)', () => {
+  const frag = serviceExtensions({ name: 'HermesGateway_Tag1' })
+  assert.ok(frag.includes('Name="HermesGateway_Tag1"'))
+})
diff --git a/apps/desktop/scripts/gen-msix-manifest.mjs b/apps/desktop/scripts/gen-msix-manifest.mjs
index da1a5972ce..798dc36d22 100644
--- a/apps/desktop/scripts/gen-msix-manifest.mjs
+++ b/apps/desktop/scripts/gen-msix-manifest.mjs
@@ -105,8 +105,11 @@ const manifest = substituteManifestMacros(template, (m) => {
     case "resourceLanguages": return resourceLanguageTag(options.languages)
     case "capabilities": return `<Capabilities>\n${buildCapabilitiesXml(options.capabilities)}\n</Capabilities>`
     case "extensions": return extensions
-    case "minVersion": return options.minVersion || "10.0.17763.0"
-    case "maxVersionTested": return options.maxVersionTested || options.minVersion || "10.0.17763.0"
+    // Win10 1903 (build 18362) floor: desktop6:Service — the MSIX-shipped
+    // HermesGateway Windows Service — requires 1903+; settled 2026-09-03.
+    // 1809 is a 2018 OS; the bump rides the release notes.
+    case "minVersion": return options.minVersion || "10.0.18362.0"
+    case "maxVersionTested": return options.maxVersionTested || options.minVersion || "10.0.18362.0"
     case "packageIntegrity": return ""
     default: throw new Error(`Macro ${m} is not defined`)
   }