Retry clean rebuild and preserve PCH mtimes

Launcher/Build-Installer.ps1

@@ -253,7 +253,7 @@ foreach ($required in @('ToolkitFingerprint','TranslationFingerprint','NativeToo
 
 $manifest = [ordered]@{
     SchemaVersion = 2
-    ProductVersion = '0.2.15'
+    ProductVersion = '0.2.17'
     ExpectedGameId = $pins.GameId
     ExpectedDolSha256 = $pins.DolSha256
     ExpectedRelSha256 = $pins.RelSha256

Launcher/WiiCompiled.Setup/ProductRepairService.cs

@@ -233,12 +233,13 @@ internal sealed class ProductRepairService
                 retroOutput = Path.Combine(scratchRoot, "retro-output");
                 _reporter.Progress(InstallStages.BuildBase,
                     "Recompiling Mario Kart Wii and Retro Rewind with the installed toolkit...", 5);
-                await builder.BuildAsync(_installation.Root, BuildProfile.Both, retroOutput,
-                    requestedPayloadMode, payloadSnapshot?.Directory, cancellationToken,
-                    toolkitComponents, forceCleanBuild,
-                    progress: new BuildProgressWindow(_reporter, InstallStages.BuildBase, 5, 92),
-                    retroRewindPackageDirectory: compileInputs.RetroRewindRoot,
-                    baseOutputDirectory: baseOutput);
+                await BuildWithCleanRetryAsync(forceCleanBuild, clean =>
+                    builder.BuildAsync(_installation.Root, BuildProfile.Both, retroOutput,
+                        requestedPayloadMode, payloadSnapshot?.Directory, cancellationToken,
+                        toolkitComponents, clean,
+                        progress: new BuildProgressWindow(_reporter, InstallStages.BuildBase, 5, 92),
+                        retroRewindPackageDirectory: compileInputs.RetroRewindRoot,
+                        baseOutputDirectory: baseOutput));
                 LocalBuildService.WriteFingerprint(baseOutput, BuildProfile.Base, toolkitFingerprint,
                     dolSha, relSha, "", RetroWfcPayloadMode.NotApplicable);
                 LocalBuildService.WriteFingerprint(retroOutput, BuildProfile.RetroRewind,
@@ -251,10 +252,11 @@ internal sealed class ProductRepairService
                 baseOutput = Path.Combine(scratchRoot, "base-output");
                 _reporter.Progress(InstallStages.BuildBase,
                     "Recompiling Mario Kart Wii with the installed toolkit...", 5);
-                await builder.BuildAsync(_installation.Root, BuildProfile.Base, baseOutput,
-                    RetroWfcPayloadMode.NotApplicable, null, cancellationToken,
-                    toolkitComponents, forceCleanBuild,
-                    progress: new BuildProgressWindow(_reporter, InstallStages.BuildBase, 5, 92));
+                await BuildWithCleanRetryAsync(forceCleanBuild, clean =>
+                    builder.BuildAsync(_installation.Root, BuildProfile.Base, baseOutput,
+                        RetroWfcPayloadMode.NotApplicable, null, cancellationToken,
+                        toolkitComponents, clean,
+                        progress: new BuildProgressWindow(_reporter, InstallStages.BuildBase, 5, 92)));
                 LocalBuildService.WriteFingerprint(baseOutput, BuildProfile.Base, toolkitFingerprint,
                     dolSha, relSha, "", RetroWfcPayloadMode.NotApplicable);
             }
@@ -265,11 +267,12 @@ internal sealed class ProductRepairService
                 retroOutput = Path.Combine(scratchRoot, "retro-output");
                 _reporter.Progress(InstallStages.BuildRetro,
                     "Recompiling Retro Rewind for the canonical Code.pul...", 5);
-                await builder.BuildAsync(_installation.Root, BuildProfile.RetroRewind, retroOutput,
-                    requestedPayloadMode, payloadSnapshot?.Directory, cancellationToken,
-                    toolkitComponents, forceCleanBuild,
-                    progress: new BuildProgressWindow(_reporter, InstallStages.BuildRetro, 5, 92),
-                    retroRewindPackageDirectory: compileInputs.RetroRewindRoot);
+                await BuildWithCleanRetryAsync(forceCleanBuild, clean =>
+                    builder.BuildAsync(_installation.Root, BuildProfile.RetroRewind, retroOutput,
+                        requestedPayloadMode, payloadSnapshot?.Directory, cancellationToken,
+                        toolkitComponents, clean,
+                        progress: new BuildProgressWindow(_reporter, InstallStages.BuildRetro, 5, 92),
+                        retroRewindPackageDirectory: compileInputs.RetroRewindRoot));
                 LocalBuildService.WriteFingerprint(retroOutput, BuildProfile.RetroRewind,
                     toolkitFingerprint, dolSha, relSha, compileInputs.CodePulSha256,
                     requestedPayloadMode, compileInputs.CompileInputsSha256,
@@ -465,6 +468,20 @@ internal sealed class ProductRepairService
         transaction.Commit();
     }
 
+    private async Task BuildWithCleanRetryAsync(bool forceCleanBuild, Func<bool, Task> build)
+    {
+        try
+        {
+            await build(forceCleanBuild);
+        }
+        catch (InvalidOperationException ex) when (!forceCleanBuild)
+        {
+            _reporter.Diagnostic(
+                $"Incremental recompilation failed ({ex.Message}); retrying with a clean build.");
+            await build(true);
+        }
+    }
+
     private void EnsureSufficientRepairDiskSpace()
     {
         const long localBuildAllowance = 14L * 1024 * 1024 * 1024;

Launcher/WiiCompiled.Setup/Program.cs

@@ -121,7 +121,7 @@ internal static class PlatformChecks
 internal static class ProductInfo
 {
     public const string Name = "WiiCompiled";
-    public const string Version = "0.2.15";
+    public const string Version = "0.2.17";
 
     /// <summary>
     /// The setup executable is copied into the installation under this name. It is the launcher and

Launcher/WiiCompiled.Setup/SelfTests.cs

@@ -109,6 +109,9 @@ internal static class SelfTests
             Directory.CreateDirectory(Path.Combine(staged, "runtime", "src"));
             File.WriteAllText(Path.Combine(installed, "runtime", "src", "same.cpp"), "int same();");
             File.WriteAllText(Path.Combine(staged, "runtime", "src", "same.cpp"), "int same();");
+            var installedSameStamp = new DateTime(2026, 1, 2, 3, 4, 5, DateTimeKind.Utc);
+            File.SetLastWriteTimeUtc(Path.Combine(installed, "runtime", "src", "same.cpp"),
+                installedSameStamp);
             File.WriteAllText(Path.Combine(installed, "runtime", "src", "edited.cpp"), "int old();");
             File.WriteAllText(Path.Combine(staged, "runtime", "src", "edited.cpp"), "int new_();");
             File.WriteAllText(Path.Combine(staged, "runtime", "src", "added.cpp"), "int added();");
@@ -117,8 +120,10 @@ internal static class SelfTests
 
             WorkspaceTimestamps.MarkChangedFiles(installed, staged, _ => { });
 
-            if (File.GetLastWriteTimeUtc(Path.Combine(staged, "runtime", "src", "same.cpp")).Year != 2000)
-                throw new Exception("An unchanged workspace file lost its normalized timestamp.");
+            if (File.GetLastWriteTimeUtc(Path.Combine(staged, "runtime", "src", "same.cpp")) !=
+                installedSameStamp)
+                throw new Exception("An unchanged workspace file did not inherit the installed " +
+                                    "timestamp; clang would reject the previous build's PCHs.");
             if (File.GetLastWriteTimeUtc(Path.Combine(staged, "runtime", "src", "edited.cpp")).Year == 2000)
                 throw new Exception("A changed workspace file kept its normalized timestamp; " +
                                     "Ninja would never recompile it.");

Launcher/WiiCompiled.Setup/WiiCompiled.Setup.csproj

@@ -7,7 +7,7 @@
     <AssemblyName>WiiCompiled.Setup</AssemblyName>
     <RootNamespace>WiiCompiled.Setup</RootNamespace>
     <ApplicationManifest>app.manifest</ApplicationManifest>
-    <Version>0.2.15</Version>
+    <Version>0.2.17</Version>
     <Authors>patchzy</Authors>
     <Product>WiiCompiled</Product>
     <Description>Command-line installer and launcher for WiiCompiled</Description>

Launcher/WiiCompiled.Setup/WorkspaceTimestamps.cs

@@ -18,8 +18,12 @@ internal static class WorkspaceTimestamps
         {
             cancellationToken.ThrowIfCancellationRequested();
             var relative = Path.GetRelativePath(stagedWorkspace, stagedFile);
-            if (FileUnchanged(Path.Combine(installedWorkspace, relative), stagedFile))
+            var installedFile = Path.Combine(installedWorkspace, relative);
+            if (FileUnchanged(installedFile, stagedFile))
             {
+                // Clang validates PCH dependency mtimes by equality, so an unchanged file must
+                // keep the exact timestamp the previous build recorded, not the normalized one.
+                InheritTimestamp(installedFile, stagedFile);
                 unchanged++;
                 continue;
             }
@@ -30,6 +34,17 @@ internal static class WorkspaceTimestamps
                    $"{unchanged} unchanged file(s) keep the incremental build cache valid.");
     }
 
+    private static void InheritTimestamp(string installedFile, string stagedFile)
+    {
+        try
+        {
+            File.SetLastWriteTimeUtc(stagedFile, File.GetLastWriteTimeUtc(installedFile));
+        }
+        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
+        {
+        }
+    }
+
     private static bool FileUnchanged(string installedFile, string stagedFile)
     {
         try