From 597d40a301e80a558f95a3eeb733c91d13cb4017 Mon Sep 17 00:00:00 2001
From: Chrison Simtian <csimon@chrison.dev>
Date: Mon, 29 Jun 2026 19:28:17 +1200
Subject: [PATCH] Lift the four stable extension interfaces into Fallout.Core
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First step of the de-statification / plugin-SDK groundwork: move the small,
already-pure extension abstractions down into Fallout.Core (public), so the
stable contracts live at the center next to ITargetModel.

Moved (namespaces unchanged -> zero consumer/implementer edits):
- IBuildExtension, IOnBuildFinished (extracted from BuildExtensionAttributeBase.cs)
- IHostTheme (Fallout.Common.Execution.Theming)
- IBuildServer (Fallout.Common.CI)

All four are pure abstractions (string/float/void members only), so they clear
Core's purity bar. Implementers stay in Build/Common and see the interfaces via
the existing Build/Common -> Core reference; IHostTheme's internal members
remain accessible because the shared AssemblyInfo grants Core's
InternalsVisibleTo to Build and Common. The interfaces keep their legacy
Fallout.Common.* namespaces, so they remain in the architecture naming-drift
baseline by full name — the ratchet stays green with no baseline change.

Deliberately NOT included (separate follow-ups): the IOn* lifecycle interfaces
(need ExecutableTarget -> ITargetModel re-typing across ~21 implementers) and
IOnTargetSummaryUpdated (blocked by IFalloutBuild).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .../BuildExtensionAttributeBase.cs             | 10 ----------
 .../CICD => Fallout.Core/CI}/IBuildServer.cs   |  0
 src/Fallout.Core/Execution/IBuildExtension.cs  | 18 ++++++++++++++++++
 .../Execution}/Theming/IHostTheme.cs           |  0
 4 files changed, 18 insertions(+), 10 deletions(-)
 rename src/{Fallout.Build/CICD => Fallout.Core/CI}/IBuildServer.cs (100%)
 create mode 100644 src/Fallout.Core/Execution/IBuildExtension.cs
 rename src/{Fallout.Build => Fallout.Core/Execution}/Theming/IHostTheme.cs (100%)

diff --git a/src/Fallout.Build/Execution/Extensibility/BuildExtensionAttributeBase.cs b/src/Fallout.Build/Execution/Extensibility/BuildExtensionAttributeBase.cs
index ad53bb3e4..5d2a46d59 100644
--- a/src/Fallout.Build/Execution/Extensibility/BuildExtensionAttributeBase.cs
+++ b/src/Fallout.Build/Execution/Extensibility/BuildExtensionAttributeBase.cs
@@ -4,11 +4,6 @@
 
 namespace Fallout.Common.Execution;
 
-public interface IBuildExtension
-{
-    float Priority { get; }
-}
-
 [AttributeUsage(AttributeTargets.Class)]
 public abstract class BuildExtensionAttributeBase : Attribute, IBuildExtension
 {
@@ -52,8 +47,3 @@ public interface IOnTargetFailed : IBuildExtension
 {
     void OnTargetFailed(ExecutableTarget target);
 }
-
-public interface IOnBuildFinished : IBuildExtension
-{
-    void OnBuildFinished();
-}
diff --git a/src/Fallout.Build/CICD/IBuildServer.cs b/src/Fallout.Core/CI/IBuildServer.cs
similarity index 100%
rename from src/Fallout.Build/CICD/IBuildServer.cs
rename to src/Fallout.Core/CI/IBuildServer.cs
diff --git a/src/Fallout.Core/Execution/IBuildExtension.cs b/src/Fallout.Core/Execution/IBuildExtension.cs
new file mode 100644
index 000000000..d4d821aa6
--- /dev/null
+++ b/src/Fallout.Core/Execution/IBuildExtension.cs
@@ -0,0 +1,18 @@
+namespace Fallout.Common.Execution;
+
+/// <summary>
+/// Root marker for a build extension — the stable seam the plugin SDK builds lifecycle
+/// listeners on. Higher <see cref="Priority"/> runs earlier.
+/// </summary>
+public interface IBuildExtension
+{
+    float Priority { get; }
+}
+
+/// <summary>
+/// Build extension invoked once the build has finished (whatever the outcome).
+/// </summary>
+public interface IOnBuildFinished : IBuildExtension
+{
+    void OnBuildFinished();
+}
diff --git a/src/Fallout.Build/Theming/IHostTheme.cs b/src/Fallout.Core/Execution/Theming/IHostTheme.cs
similarity index 100%
rename from src/Fallout.Build/Theming/IHostTheme.cs
rename to src/Fallout.Core/Execution/Theming/IHostTheme.cs