fix(javascript): keep empty URL path segments significant (#3792)

* fix(javascript): keep empty URL path segments significant

ESM imports and HTML script references were joined with POSIX path
rules, which collapse '//' before applying '..'. URL resolution removes
the empty segment instead, so './assets//../app.js' names assets/app.js,
not app.js, and the graph linked the importer and renderer to the wrong
file. URL references refused every '//' even when dot segments cancel it.

Resolve ESM, HTML (including document base) and URL references through
one URL dot-segment helper. A remaining empty segment stays unavailable,
references above the artifact root are still rejected, and CommonJS keeps
filesystem path semantics.

Fixes #3307

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(javascript): resolve HTML base and reference as one URL path

The base href was turned into a canonical path before the script
reference was applied. A base empty segment that the reference's '..'
would remove was rejected early, and an above-root '..' from the base
became a removable segment that the reference's '..' could cancel.

Keep one URL path state through base and reference resolution, with
above-root escapes held apart from removable segments, and reject empty
segments only in the final path. Remove the superseded htmlBaseDirectory.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/application/javascript/JavaScriptArtifactPathResolution.test.ts

@@ -2495,20 +2495,61 @@ describe("url-reference directory and empty-segment semantics", () => {
     });
   });
 
-  it.each(["./nested//worker.js", "./nested//../worker.js"])(
-    "does not collapse empty URL path segments: %s",
-    (declaredPath) => {
+  it.each([
+    ["./nested//worker.js", null],
+    ["./nested//../worker.js", "dist/nested/worker.js"],
+  ])(
+    "keeps empty URL path segments significant: %s",
+    (declaredPath, resolvedPath) => {
+      // A dot segment removes the preceding empty segment, never `nested`.
+      expect(new URL(declaredPath, "file:///root/dist/app.mjs").pathname).toBe(
+        resolvedPath === null
+          ? "/root/dist/nested//worker.js"
+          : `/root/${resolvedPath}`,
+      );
+      for (const context of ["url-reference", "html-reference"] as const)
+        expect(
+          resolve({
+            declaredPath,
+            sourcePath: "dist/app.mjs",
+            context,
+            files: fileMap([
+              file("dist/worker.js", "root"),
+              file("dist/nested/worker.js", "root"),
+            ]),
+          }),
+          context,
+        ).toMatchObject({ resolved_path: resolvedPath });
       expect(
         resolve({
           declaredPath,
           sourcePath: "dist/app.mjs",
-          context: "url-reference",
+          context: "module-specifier",
+          moduleKind: "import",
           files: fileMap([
             file("dist/worker.js", "root"),
             file("dist/nested/worker.js", "root"),
           ]),
         }),
-      ).toMatchObject({ resolved_path: null });
+      ).toMatchObject({ resolved_path: resolvedPath });
+      // CommonJS keeps filesystem path semantics.
+      expect(
+        resolve({
+          declaredPath,
+          sourcePath: "dist/app.mjs",
+          context: "module-specifier",
+          moduleKind: "require",
+          files: fileMap([
+            file("dist/worker.js", "root"),
+            file("dist/nested/worker.js", "root"),
+          ]),
+        }),
+      ).toMatchObject({
+        resolved_path:
+          declaredPath === "./nested//worker.js"
+            ? "dist/nested/worker.js"
+            : "dist/worker.js",
+      });
     },
   );