Fix unreachable code detection persisting after incremental edits (#62783)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

src/compiler/binder.ts

@@ -1091,6 +1091,11 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
         // and set it before we descend into nodes that could actually be part of an assignment pattern.
         inAssignmentPattern = false;
 
+        // Clear Unreachable flag from previous binding (for incremental scenarios)
+        if (isPotentiallyExecutableNode(node)) {
+            (node as Mutable<Node>).flags &= ~NodeFlags.Unreachable;
+        }
+
         if (currentFlow === unreachableFlow) {
             if (canHaveFlowNode(node)) {
                 node.flowNode = undefined;