feat: make Windows generally available

3 files changed, 206 insertions, 44 deletions

diff --git a/scripts/changelog.py b/scripts/changelog.py
index 4d023ccc..9a96ea4e 100644
--- a/scripts/changelog.py
+++ b/scripts/changelog.py
@@ -19,13 +19,17 @@ DEFAULT_RELEASE_REPO = "herdrdev/herdr"
 DEFAULT_LATEST_JSON_PATH = Path("website/latest.json")
 DEFAULT_PRODUCT_ANNOUNCEMENT_PATH = Path("docs/next/product-announcement.json")
 PROTOCOL_SOURCE_PATH = Path("src/protocol/wire.rs")
-ASSET_TARGETS = (
+CORE_ASSET_TARGETS = (
     "linux-x86_64",
     "linux-aarch64",
     "macos-x86_64",
     "macos-aarch64",
 )
-EXPECTED_ASSET_NAMES = {target: f"herdr-{target}" for target in ASSET_TARGETS}
+ASSET_TARGETS = (*CORE_ASSET_TARGETS, "windows-x86_64")
+EXPECTED_ASSET_NAMES = {
+    **{target: f"herdr-{target}" for target in CORE_ASSET_TARGETS},
+    "windows-x86_64": "herdr-windows-x86_64.zip",
+}
 
 
 @dataclass(frozen=True)
@@ -169,16 +173,22 @@ def infer_protocol_from_notes(notes: str) -> int | None:
     return int(match.group(1))
 
 
-def normalize_assets(value: Any, label: str) -> dict[str, str]:
+def normalize_assets(
+    value: Any,
+    label: str,
+    required_targets: tuple[str, ...] = ASSET_TARGETS,
+) -> dict[str, str]:
     if not isinstance(value, dict):
         raise ChangelogError(f"{label} must be an object")
 
-    missing_targets = [target for target in ASSET_TARGETS if target not in value]
+    missing_targets = [target for target in required_targets if target not in value]
     if missing_targets:
         raise ChangelogError(f"{label} is missing asset URL for {', '.join(missing_targets)}")
 
     normalized_assets: dict[str, str] = {}
     for target in ASSET_TARGETS:
+        if target not in value:
+            continue
         url = value.get(target)
         if not isinstance(url, str) or not url.strip():
             raise ChangelogError(f"{label} is missing asset URL for {target}")
@@ -186,12 +196,22 @@ def normalize_assets(value: Any, label: str) -> dict[str, str]:
     return normalized_assets
 
 
-def normalize_sha256(value: Any, label: str) -> dict[str, str]:
+def normalize_sha256(
+    value: Any,
+    label: str,
+    required_targets: tuple[str, ...] = ASSET_TARGETS,
+) -> dict[str, str]:
     if not isinstance(value, dict):
         raise ChangelogError(f"{label} must be an object")
 
+    missing_targets = [target for target in required_targets if target not in value]
+    if missing_targets:
+        raise ChangelogError(f"{label} has invalid SHA-256 for {missing_targets[0]}")
+
     checksums: dict[str, str] = {}
     for target in ASSET_TARGETS:
+        if target not in value:
+            continue
         checksum = value.get(target)
         if not isinstance(checksum, str) or re.fullmatch(
             r"[0-9a-fA-F]{64}", checksum.strip()
@@ -225,11 +245,19 @@ def normalize_release_metadata(value: Any, label: str, version: str) -> dict[str
         if inferred_protocol is not None:
             metadata["protocol"] = inferred_protocol
     if "assets" in value:
-        metadata["assets"] = normalize_assets(value.get("assets"), f"{label}.assets")
+        metadata["assets"] = normalize_assets(
+            value.get("assets"),
+            f"{label}.assets",
+            required_targets=CORE_ASSET_TARGETS,
+        )
     else:
         metadata["assets"] = default_release_assets(version)
     if "sha256" in value:
-        metadata["sha256"] = normalize_sha256(value.get("sha256"), f"{label}.sha256")
+        metadata["sha256"] = normalize_sha256(
+            value.get("sha256"),
+            f"{label}.sha256",
+            required_targets=CORE_ASSET_TARGETS,
+        )
     announcement = normalize_announcement(value.get("announcement"), label)
     if announcement is not None:
         metadata["announcement"] = announcement
@@ -306,11 +334,12 @@ def build_latest_json(
 
 
 def default_release_assets(version: str, repo: str = DEFAULT_RELEASE_REPO) -> dict[str, str]:
+    """Return legacy release URLs for versions published before Windows stable assets."""
     normalized_version = normalize_version(version)
     tag = f"v{normalized_version}"
     return {
         target: f"https://github.com/{repo}/releases/download/{tag}/{EXPECTED_ASSET_NAMES[target]}"
-        for target in ASSET_TARGETS
+        for target in CORE_ASSET_TARGETS
     }
 
 
@@ -468,12 +497,20 @@ def archived_releases_from_current_manifest(manifest: dict[str, Any]) -> dict[st
             metadata["protocol"] = protocol
         assets = manifest.get("assets")
         if isinstance(assets, dict):
-            metadata["assets"] = normalize_assets(assets, "current root assets")
+            metadata["assets"] = normalize_assets(
+                assets,
+                "current root assets",
+                required_targets=CORE_ASSET_TARGETS,
+            )
         else:
             metadata["assets"] = default_release_assets(normalized_version)
         sha256 = manifest.get("sha256")
         if isinstance(sha256, dict):
-            metadata["sha256"] = normalize_sha256(sha256, "current root sha256")
+            metadata["sha256"] = normalize_sha256(
+                sha256,
+                "current root sha256",
+                required_targets=CORE_ASSET_TARGETS,
+            )
         announcement = normalize_announcement(manifest.get("announcement"), "current root")
         if announcement is not None:
             metadata["announcement"] = announcement
diff --git a/scripts/test_changelog.py b/scripts/test_changelog.py
index ad384734..6a9d12dd 100644
--- a/scripts/test_changelog.py
+++ b/scripts/test_changelog.py
@@ -24,20 +24,33 @@ from scripts.changelog import (
 )
 
 
+def release_assets(version: str) -> dict[str, str]:
+    normalized = version.removeprefix("v")
+    return {
+        **default_release_assets(normalized),
+        "windows-x86_64": f"https://github.com/herdrdev/herdr/releases/download/v{normalized}/herdr-windows-x86_64.zip",
+    }
+
+
 def release_sha256() -> dict[str, str]:
     return {
         "linux-x86_64": "a" * 64,
         "linux-aarch64": "b" * 64,
         "macos-x86_64": "c" * 64,
         "macos-aarch64": "d" * 64,
+        "windows-x86_64": "e" * 64,
     }
 
 
 def release_assets_with_digests() -> list[dict[str, str]]:
     return [
         {
-            "name": f"herdr-{target}",
-            "url": f"https://example.com/{target}",
+            "name": (
+                "herdr-windows-x86_64.zip"
+                if target == "windows-x86_64"
+                else f"herdr-{target}"
+            ),
+            "url": f"https://example.com/{target}{'.zip' if target == 'windows-x86_64' else ''}",
             "digest": f"sha256:{digest * 64}",
         }
         for target, digest in (
@@ -45,6 +58,7 @@ def release_assets_with_digests() -> list[dict[str, str]]:
             ("linux-aarch64", "b"),
             ("macos-x86_64", "c"),
             ("macos-aarch64", "d"),
+            ("windows-x86_64", "e"),
         )
     ]
 
@@ -79,7 +93,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.1",
                 "\n### Fixed\n- One\n\n",
-                default_release_assets("0.1.1"),
+                release_assets("0.1.1"),
                 release_sha256(),
             )
         )
@@ -92,7 +106,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "v0.1.1",
                 "### Fixed\n- Smoothed Claude flapping.\n",
-                default_release_assets("0.1.1"),
+                release_assets("0.1.1"),
                 release_sha256(),
             )
         )
@@ -107,6 +121,7 @@ class ChangelogScriptTests(unittest.TestCase):
                 "linux-aarch64": "https://github.com/herdrdev/herdr/releases/download/v0.1.1/herdr-linux-aarch64",
                 "macos-x86_64": "https://github.com/herdrdev/herdr/releases/download/v0.1.1/herdr-macos-x86_64",
                 "macos-aarch64": "https://github.com/herdrdev/herdr/releases/download/v0.1.1/herdr-macos-aarch64",
+                "windows-x86_64": "https://github.com/herdrdev/herdr/releases/download/v0.1.1/herdr-windows-x86_64.zip",
             },
         )
         self.assertEqual(manifest["releases"]["0.1.1"]["assets"], manifest["assets"])
@@ -118,7 +133,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.1",
                 "### Fixed\n- One",
-                default_release_assets("0.1.1"),
+                release_assets("0.1.1"),
                 release_sha256(),
                 announcement={"id": "keybinding-v2", "title": "Keybind Refactor", "body": "body"},
             )
@@ -138,7 +153,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.2",
                 "### Fixed\n- Two",
-                default_release_assets("0.1.2"),
+                release_assets("0.1.2"),
                 release_sha256(),
                 releases={"0.1.1": {"notes": "### Fixed\n- One"}},
             )
@@ -147,7 +162,7 @@ class ChangelogScriptTests(unittest.TestCase):
         self.assertEqual(list(manifest["releases"]), ["0.1.2", "0.1.1"])
         self.assertEqual(manifest["releases"]["0.1.2"]["notes"], "### Fixed\n- Two")
         self.assertEqual(manifest["releases"]["0.1.2"]["protocol"], read_protocol_version())
-        self.assertEqual(manifest["releases"]["0.1.2"]["assets"], default_release_assets("0.1.2"))
+        self.assertEqual(manifest["releases"]["0.1.2"]["assets"], release_assets("0.1.2"))
         self.assertEqual(manifest["releases"]["0.1.1"]["notes"], "### Fixed\n- One")
         self.assertEqual(manifest["releases"]["0.1.1"]["assets"], default_release_assets("0.1.1"))
 
@@ -157,7 +172,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.2",
                 "### Fixed\n- Two",
-                default_release_assets("0.1.2"),
+                release_assets("0.1.2"),
                 release_sha256(),
                 releases={"0.1.1": {"notes": "### Fixed\n- One", "assets": assets}},
             )
@@ -170,7 +185,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.2",
                 "### Fixed\n- Two",
-                default_release_assets("0.1.2"),
+                release_assets("0.1.2"),
                 release_sha256(),
                 releases={"0.1.1": {"notes": "### Fixed\n- One", "protocol": 7}},
             )
@@ -183,7 +198,7 @@ class ChangelogScriptTests(unittest.TestCase):
             build_latest_json(
                 "0.1.2",
                 "### Fixed\n- Two",
-                default_release_assets("0.1.2"),
+                release_assets("0.1.2"),
                 release_sha256(),
                 releases={
                     "0.1.1": {
@@ -337,6 +352,7 @@ class ChangelogScriptTests(unittest.TestCase):
                     "linux-aarch64": "https://example.com/linux-aarch64",
                     "macos-x86_64": "https://example.com/macos-x86_64",
                     "macos-aarch64": "https://example.com/macos-aarch64",
+                    "windows-x86_64": "https://example.com/windows-x86_64.zip",
                 },
                 "sha256": release_sha256(),
             },
@@ -426,6 +442,7 @@ class ChangelogScriptTests(unittest.TestCase):
                 "linux-aarch64": "https://example.com/linux-aarch64",
                 "macos-x86_64": "https://example.com/macos-x86_64",
                 "macos-aarch64": "https://example.com/macos-aarch64",
+                "windows-x86_64": "https://example.com/windows-x86_64.zip",
             },
             "sha256": release_sha256(),
         }
@@ -438,6 +455,7 @@ class ChangelogScriptTests(unittest.TestCase):
                 "linux-aarch64": "https://example.com/linux-aarch64",
                 "macos-x86_64": "https://example.com/macos-x86_64",
                 "macos-aarch64": "https://example.com/macos-aarch64",
+                "windows-x86_64": "https://example.com/windows-x86_64.zip",
             },
             "sha256": release_sha256(),
         }
@@ -446,7 +464,7 @@ class ChangelogScriptTests(unittest.TestCase):
         self.assertEqual(canonical, expected)
 
     def test_current_release_assets_must_be_mirrored(self) -> None:
-        assets = default_release_assets("0.1.1")
+        assets = release_assets("0.1.1")
         ensure_current_release_assets_are_mirrored(
             {
                 "version": "0.1.1",
@@ -472,12 +490,12 @@ class ChangelogScriptTests(unittest.TestCase):
                     "version": "0.1.1",
                     "protocol": read_protocol_version(),
                     "notes": "### Fixed\n- One",
-                    "assets": default_release_assets("0.1.1"),
+                    "assets": release_assets("0.1.1"),
                     "sha256": release_sha256(),
                     "releases": {
                         "0.1.1": {
                             "notes": "### Fixed\n- One",
-                            "assets": default_release_assets("0.1.0"),
+                            "assets": release_assets("0.1.0"),
                             "sha256": release_sha256(),
                         }
                     },
@@ -497,6 +515,7 @@ class ChangelogScriptTests(unittest.TestCase):
                         "linux-aarch64": "https://example.com/linux-aarch64",
                         "macos-x86_64": "https://example.com/macos-x86_64",
                         "macos-aarch64": "https://example.com/macos-aarch64",
+                        "windows-x86_64": "https://example.com/windows-x86_64.zip",
                     },
                     "sha256": release_sha256(),
                 },
@@ -509,6 +528,7 @@ class ChangelogScriptTests(unittest.TestCase):
                         "linux-aarch64": "https://example.com/linux-aarch64",
                         "macos-x86_64": "https://example.com/macos-x86_64",
                         "macos-aarch64": "https://example.com/macos-aarch64",
+                        "windows-x86_64": "https://example.com/windows-x86_64.zip",
                     },
                     "sha256": release_sha256(),
                 },
@@ -531,14 +551,14 @@ class ChangelogScriptTests(unittest.TestCase):
             "version": "0.1.1",
             "protocol": read_protocol_version() + 1,
             "notes": "### Fixed\n- One",
-            "assets": default_release_assets("0.1.1"),
+            "assets": release_assets("0.1.1"),
             "sha256": release_sha256(),
         }
         expected = {
             "version": "0.1.1",
             "protocol": read_protocol_version(),
             "notes": "### Fixed\n- One",
-            "assets": default_release_assets("0.1.1"),
+            "assets": release_assets("0.1.1"),
             "sha256": release_sha256(),
         }
 
diff --git a/scripts/windows_install_conpty_package_test.ps1 b/scripts/windows_install_conpty_package_test.ps1
index 95b31c4a..f4c4fc60 100644
--- a/scripts/windows_install_conpty_package_test.ps1
+++ b/scripts/windows_install_conpty_package_test.ps1
@@ -82,7 +82,7 @@ $listener = [System.Net.Sockets.TcpListener]::new([System.Net.IPAddress]::Loopba
 $listener.Start()
 $port = ([System.Net.IPEndPoint]$listener.LocalEndpoint).Port
 $listener.Stop()
-$manifest = @{
+$previewManifest = @{
     channel = "preview"
     base_version = "0.0.0"
     build_id = "installer-test"
@@ -94,18 +94,35 @@ $manifest = @{
         }
     }
 } | ConvertTo-Json -Depth 5
-$manifestPath = Join-Path $webRoot "preview.json"
-$manifest | Out-File -LiteralPath $manifestPath -Encoding utf8
+$legacyStableManifest = @{
+    version = "0.0.0"
+    assets = @{}
+} | ConvertTo-Json -Depth 5
+$stableManifest = @{
+    version = "0.0.1"
+    assets = @{
+        "windows-x86_64" = "http://127.0.0.1:$port/herdr-windows-x86_64.zip"
+    }
+    sha256 = @{
+        "windows-x86_64" = $hash
+    }
+} | ConvertTo-Json -Depth 5
+$previewManifestPath = Join-Path $webRoot "preview.json"
+$stableManifestPath = Join-Path $webRoot "latest.json"
+$previewManifest | Out-File -LiteralPath $previewManifestPath -Encoding utf8
+$legacyStableManifest | Out-File -LiteralPath $stableManifestPath -Encoding utf8
 
 $server = $null
 $oldHerdrHome = $env:HERDR_HOME
+$oldProcessPath = $env:Path
 try {
     $server = Start-Process python -ArgumentList @("-m", "http.server", "$port", "--bind", "127.0.0.1", "--directory", $webRoot) -PassThru -WindowStyle Hidden
     $env:HERDR_HOME = Join-Path $root "unused\..\home"
-    $manifestUrl = "http://127.0.0.1:$port/preview.json"
+    $previewManifestUrl = "http://127.0.0.1:$port/preview.json"
+    $stableManifestUrl = "http://127.0.0.1:$port/latest.json"
     for ($attempt = 0; $attempt -lt 20; $attempt++) {
         try {
-            Invoke-WebRequest -Uri $manifestUrl -UseBasicParsing | Out-Null
+            Invoke-WebRequest -Uri $stableManifestUrl -UseBasicParsing | Out-Null
             break
         } catch {
             if ($attempt -eq 19) { throw }
@@ -113,8 +130,31 @@ try {
         }
     }
 
+    $freshStableHome = Join-Path $root "fresh-stable-home"
+    $freshStableBin = Join-Path $root "fresh-stable-bin"
+    $stableManifest | Out-File -LiteralPath $stableManifestPath -Encoding utf8
+    $env:HERDR_HOME = $freshStableHome
+    $env:Path = $oldProcessPath
+    & $installerPath `
+        -ManifestUrl $stableManifestUrl `
+        -InstallDir $freshStableBin
+    $freshStableRelease = Get-ChildItem -LiteralPath (Join-Path $freshStableHome "packages\standalone\releases") -Directory |
+        Where-Object { $_.Name.StartsWith("0.0.1-") } |
+        Select-Object -First 1
+    if ($null -eq $freshStableRelease) {
+        throw "fresh installer did not default to the stable Windows package"
+    }
+
+    $legacyStableManifest | Out-File -LiteralPath $stableManifestPath -Encoding utf8
+    $env:HERDR_HOME = Join-Path $root "unused\..\home"
+    $env:Path = $oldProcessPath
+    & $installerPath `
+        -ManifestUrl $stableManifestUrl `
+        -InstallDir $installDir `
+        -ExpectedBuildId "installer-test"
+
     # Keep the existing positional web-installer contract, including Retain in slot five.
-    & "$PSScriptRoot\..\website\install.ps1" "preview" $manifestUrl $installDir "installer-test" 3
+    & $installerPath "preview" $previewManifestUrl $installDir "installer-test" 3
 
     $localInstallDir = Join-Path $root "local-bin"
     $env:HERDR_HOME = Join-Path $root "local-home"
@@ -136,7 +176,7 @@ try {
     $badLocalChecksumRejected = $false
     try {
         & $installerPath `
-            -ManifestUrl "$manifestUrl/unused" `
+            -ManifestUrl "$previewManifestUrl/unused" `
             -InstallDir $localInstallDir `
             -LocalPackagePath $archive `
             -LocalPackageFormat "zip" `
@@ -153,7 +193,7 @@ try {
     }
 
     & $installerPath `
-        -ManifestUrl "$manifestUrl/unused" `
+        -ManifestUrl "$previewManifestUrl/unused" `
         -InstallDir $localInstallDir `
         -LocalPackagePath $archive `
         -LocalPackageFormat "zip" `
@@ -188,13 +228,14 @@ try {
     }
     Remove-Item -LiteralPath (Join-Path $releaseDir.FullName "conpty\conpty.dll") -Force
 
-    $badManifest = $manifest | ConvertFrom-Json
+    $badManifest = $previewManifest | ConvertFrom-Json
     $badManifest.assets."windows-x86_64".url = "http://127.0.0.1:$port/missing.zip"
-    $badManifest | ConvertTo-Json -Depth 5 | Out-File -LiteralPath $manifestPath -Encoding utf8
+    $badManifest | ConvertTo-Json -Depth 5 | Out-File -LiteralPath $previewManifestPath -Encoding utf8
     $downloadFailed = $false
     try {
         & "$PSScriptRoot\..\website\install.ps1" `
-            -ManifestUrl $manifestUrl `
+            -Channel preview `
+            -ManifestUrl $previewManifestUrl `
             -InstallDir $installDir `
             -ExpectedBuildId "installer-test"
     } catch {
@@ -210,7 +251,7 @@ try {
         throw "failed repair removed the existing release"
     }
 
-    $manifest | Out-File -LiteralPath $manifestPath -Encoding utf8
+    $previewManifest | Out-File -LiteralPath $previewManifestPath -Encoding utf8
     $stagedConpty = Join-Path $releasesDir ".staging.$($releaseDir.Name).$PID\conpty\conpty.dll"
 
     $transientLockState = @{ Handle = $null; Acquired = $false; Released = $false }
@@ -245,8 +286,9 @@ try {
     }.GetNewClosure()
     $transientLockBreakpoint = Set-PSBreakpoint -Script $installerPath -Variable "backupDir" -Mode Write -Action $lockStagedFileTransiently
     try {
-        & "$PSScriptRoot\..\website\install.ps1" `
-            -ManifestUrl $manifestUrl `
+        & $installerPath `
+            -Channel preview `
+            -ManifestUrl $previewManifestUrl `
             -InstallDir $installDir `
             -ExpectedBuildId "installer-test"
         if (-not $transientLockState.Acquired) {
@@ -285,8 +327,9 @@ try {
     try {
         $swapFailed = $false
         try {
-            & "$PSScriptRoot\..\website\install.ps1" `
-                -ManifestUrl $manifestUrl `
+            & $installerPath `
+                -Channel preview `
+                -ManifestUrl $previewManifestUrl `
                 -InstallDir $installDir `
                 -ExpectedBuildId "installer-test"
         } catch {
@@ -317,7 +360,8 @@ try {
     }
 
     & "$PSScriptRoot\..\website\install.ps1" `
-        -ManifestUrl $manifestUrl `
+        -Channel preview `
+        -ManifestUrl $previewManifestUrl `
         -InstallDir $installDir `
         -ExpectedBuildId "installer-test"
     if (-not (Test-Path -LiteralPath (Join-Path $installDir "conpty\conpty.dll") -PathType Leaf)) {
@@ -329,7 +373,8 @@ try {
     Move-Item -LiteralPath $x64HostDir -Destination $junctionTarget
     New-Item -ItemType Junction -Path $x64HostDir -Target $junctionTarget | Out-Null
     & "$PSScriptRoot\..\website\install.ps1" `
-        -ManifestUrl $manifestUrl `
+        -Channel preview `
+        -ManifestUrl $previewManifestUrl `
         -InstallDir $installDir `
         -ExpectedBuildId "installer-test"
     $repairedHostDir = Get-Item -LiteralPath (Join-Path $installDir "conpty\x64") -Force
@@ -340,7 +385,8 @@ try {
     $rejected = $false
     try {
         & "$PSScriptRoot\..\website\install.ps1" `
-            -ManifestUrl $manifestUrl `
+            -Channel preview `
+            -ManifestUrl $previewManifestUrl `
             -InstallDir $installDir `
             -ExpectedBuildId "different-build"
     } catch {
@@ -352,8 +398,67 @@ try {
     if (-not $rejected) {
         throw "installer accepted a manifest that did not match the updater-selected build"
     }
+
+    $stableManifest | Out-File -LiteralPath $stableManifestPath -Encoding utf8
+    & "$PSScriptRoot\..\website\install.ps1" `
+        -Channel stable `
+        -ManifestUrl $stableManifestUrl `
+        -InstallDir $installDir
+    $stableReleaseDir = Get-ChildItem -LiteralPath (Join-Path $herdrHome "packages\standalone\releases") -Directory |
+        Where-Object { $_.Name.StartsWith("0.0.1-") } |
+        Select-Object -First 1
+    if ($null -eq $stableReleaseDir) {
+        throw "installer did not install the stable Windows package"
+    }
+    foreach ($relative in $required) {
+        if (-not (Test-Path -LiteralPath (Join-Path $installDir $relative) -PathType Leaf)) {
+            throw "stable installer did not activate required file $relative"
+        }
+    }
+
+    $customPreviewManifestPath = Join-Path $webRoot "candidate.json"
+    $customPreviewManifest = $previewManifest | ConvertFrom-Json
+    $customPreviewManifest.PSObject.Properties.Remove("channel")
+    $customPreviewManifest | ConvertTo-Json -Depth 5 | Out-File -LiteralPath $customPreviewManifestPath -Encoding utf8
+    $fakeBin = Join-Path $root "fake-existing"
+    New-Item -ItemType Directory -Force -Path $fakeBin | Out-Null
+    @'
+@echo off
+if "%1"=="channel" if "%2"=="show" (
+  echo preview
+  exit /b 0
+)
+exit /b 1
+'@ | Out-File -LiteralPath (Join-Path $fakeBin "herdr.cmd") -Encoding ascii
+
+    $preserveHome = Join-Path $root "preserve-home"
+    $preserveBin = Join-Path $root "preserve-bin"
+    $env:HERDR_HOME = $preserveHome
+    $env:Path = "$fakeBin;$oldProcessPath"
+    & "$PSScriptRoot\..\website\install.ps1" `
+        -ManifestUrl "http://127.0.0.1:$port/candidate.json" `
+        -InstallDir $preserveBin `
+        -ExpectedBuildId "installer-test"
+    $preservedPreview = Get-ChildItem -LiteralPath (Join-Path $preserveHome "packages\standalone\releases") -Directory |
+        Where-Object { $_.Name.StartsWith("0.0.0-preview.installer-test-") } |
+        Select-Object -First 1
+    if ($null -eq $preservedPreview) {
+        throw "installer did not preserve the existing preview channel"
+    }
+
+    & "$PSScriptRoot\..\website\install.ps1" `
+        -Channel stable `
+        -ManifestUrl $stableManifestUrl `
+        -InstallDir $preserveBin
+    $explicitStable = Get-ChildItem -LiteralPath (Join-Path $preserveHome "packages\standalone\releases") -Directory |
+        Where-Object { $_.Name.StartsWith("0.0.1-") } |
+        Select-Object -First 1
+    if ($null -eq $explicitStable) {
+        throw "explicit stable channel did not override the existing preview channel"
+    }
 } finally {
     $env:HERDR_HOME = $oldHerdrHome
+    $env:Path = $oldProcessPath
     if ($null -ne $server -and -not $server.HasExited) {
         Stop-Process -Id $server.Id -Force -ErrorAction SilentlyContinue
     }