From 931147e852fc8f5eea6a5ee734f426c164a34ddb Mon Sep 17 00:00:00 2001
From: Henry Mercer <henrymercer@github.com>
Date: Fri, 15 May 2026 11:10:02 +0100
Subject: [PATCH] Improve OS types and docs

---
 pr-checks/sync.ts | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/pr-checks/sync.ts b/pr-checks/sync.ts
index 3faffc1d0..c810e7cbf 100755
--- a/pr-checks/sync.ts
+++ b/pr-checks/sync.ts
@@ -28,10 +28,21 @@ interface WorkflowInput {
 /** A partial mapping from known input names to input definitions. */
 type WorkflowInputs = Partial<Record<KnownInputName, WorkflowInput>>;
 
+/** An operating system identifier. */
+type OperatingSystemIdentifier = "ubuntu" | "macos" | "windows";
+
+/**
+ * Represents an operating system matrix entry for a generated PR check workflow.
+ *
+ * Either a string containing the OS identifier or an object containing the OS identifier and an
+ * optional runner image label.
+ */
 type OperatingSystem =
-  | string
+  | OperatingSystemIdentifier
   | {
-      os: string;
+      /** OS identifier. */
+      os: OperatingSystemIdentifier;
+      /** Optional runner image label. */
       "runner-image"?: string;
     };