refactor(javascript): centralize source coordinate operations

src/domain/javascript/javascriptSourceCoordinates.ts

@@ -1,4 +1,28 @@
 import { z } from "zod";
+import type {
+  JavaScriptSourcePoint,
+  JavaScriptSourceRange,
+} from "./javascriptStaticAnalysisTypes.js";
+
+/** Compare parser coordinates by line, then UTF-16 column. */
+export const compareJavaScriptSourcePoints = (
+  left: JavaScriptSourcePoint,
+  right: JavaScriptSourcePoint,
+): number => left.line - right.line || left.column - right.column;
+
+/** Include equal endpoints without implying runtime reachability. */
+export const javascriptSourceRangeContains = (
+  outer: JavaScriptSourceRange,
+  inner: JavaScriptSourceRange,
+): boolean =>
+  compareJavaScriptSourcePoints(outer.start, inner.start) <= 0 &&
+  compareJavaScriptSourcePoints(outer.end, inner.end) >= 0;
+
+/** Exact artifact-local coordinate key; callers supply the artifact identity. */
+export const javascriptSourceRangeKey = (
+  range: JavaScriptSourceRange,
+): string =>
+  `${range.start.line}:${range.start.column}-${range.end.line}:${range.end.column}`;
 
 const sourcePointSchema = z.strictObject({
   line: z.number().int().min(1),
@@ -9,11 +33,7 @@ const sourcePointSchema = z.strictObject({
 export const javascriptSourceRangeSchema = z
   .strictObject({ start: sourcePointSchema, end: sourcePointSchema })
   .superRefine((range, context) => {
-    if (
-      range.end.line < range.start.line ||
-      (range.end.line === range.start.line &&
-        range.end.column < range.start.column)
-    )
+    if (compareJavaScriptSourcePoints(range.end, range.start) < 0)
       context.addIssue({
         code: "custom",
         path: ["end"],