fix(sourcemaps)!: preserve nullable source declarations

Accept absent map-level sourcesContent and preserve null source-name slots alongside known originals and aligned content. Represent unnamed local declarations explicitly, retain leaf-local and flattened indices, and preserve declared indexed-section order across consumers.

Account for added indices before browser output allocation. Accept legacy retained rows without indices. Consolidate public CLI/MCP source-map fixtures and update the stale named-source-only assertion.

BREAKING CHANGE: Browser source-map original and mapping rows expose null for unavailable source names instead of inventing an unknown-source string. New index fields are optional when reading older retained evidence.

Refs #2023, #2024

src/application/javascript/JavaScriptArtifactAnalysis.ts

@@ -539,6 +539,7 @@ const collectSourceMapOriginals = (
   maps: readonly Readonly<Record<string, unknown>>[],
 ): JavaScriptSourceMapObservation => {
   const sources: JavaScriptSourceMapOriginal[] = [];
+  let declarationIndex = 0;
   for (const map of maps) {
     const names = map.sources;
     if (!Array.isArray(names))
@@ -556,7 +557,7 @@ const collectSourceMapOriginals = (
       );
     const root = typeof map.sourceRoot === "string" ? map.sourceRoot : null;
     for (const [index, raw] of names.entries()) {
-      if (typeof raw !== "string")
+      if (raw !== null && typeof raw !== "string")
         return invalidSourceMap(
           file,
           "Source map contains a non-string source name.",
@@ -564,7 +565,12 @@ const collectSourceMapOriginals = (
       const rawContent = Array.isArray(contents) ? contents[index] : undefined;
       const content = typeof rawContent === "string" ? rawContent : null;
       sources.push({
-        reference: resolveJavaScriptSourceMapReference(raw, root, file.path),
+        source_index: index,
+        declaration_index: declarationIndex++,
+        reference:
+          typeof raw === "string"
+            ? resolveJavaScriptSourceMapReference(raw, root, file.path)
+            : null,
         content,
         content_sha256: content === null ? null : sha256(content),
       });