Keep the scaffolder test inside its own workspace

Two review findings on #581, both fair.

The scratch app symlinked the whole of the repo's node_modules, so the
scaffolder's output directory, `node_modules/.impeccable-live`, resolved to the
REPO's copy. Variants were written there and survived `afterEach`, which only
removed the temp dir; the next case reused the session id, and the scaffolder
keeps existing variant files, so a case could parse a previous case's source
against a fresh manifest. Now only `svelte` is linked, into a node_modules the
workspace owns, and each case gets its own session id. Svelte's own
dependencies still resolve, because node follows the link to its real path
before looking for them.

The comment also pointed at a `PROPS_SCRIPT_SHAPES` symbol that does not exist
in the test file. Dropped the name and kept the file reference.

Written with AI assistance (Claude Code).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

skill/scripts/live/svelte-ast.mjs

@@ -938,9 +938,9 @@ function collectFreeIdentifierRanges(node, scopes, emit) {
 // onto the template's own declaration: `var /** @type {...} */ (h1) = root()`.
 // That is a syntax error, so the browser's dynamic import of the variant dies
 // with "Unexpected token '('" and nothing renders. `@typedef` carries the same
-// shape without being a cast. Keep it a typedef; see PROPS_SCRIPT_SHAPES in
-// tests/live-svelte-props-script.test.mjs, which compiles what these builders
-// emit and parses the result.
+// shape without being a cast. Keep it a typedef;
+// tests/live-svelte-props-script.test.mjs compiles what these builders emit
+// and parses the result.
 export function buildPropsScriptV2(contract) {
   if (!contract || contract.length === 0) {
     return '<script>\n  /** @typedef {Record<string, never>} Props */\n  let {} = $props();\n</script>\n';

tests/live-svelte-props-script.test.mjs

@@ -122,11 +122,20 @@ describe('the real scaffolder writes variants that parse', () => {
 
   beforeEach(() => {
     scratch = fs.mkdtempSync(path.join(os.tmpdir(), 'impeccable-svelte-scaffold-'));
-    // The scaffolder resolves the compiler from the app root, so the staged app
-    // needs a package.json and a reachable svelte. Symlinking the repo's
-    // node_modules is what the static fixture sweep already does.
     fs.writeFileSync(path.join(scratch, 'package.json'), JSON.stringify({ name: 'app', type: 'module' }));
-    fs.symlinkSync(path.join(REPO_ROOT, 'node_modules'), path.join(scratch, 'node_modules'), 'dir');
+    // Only `svelte` is linked, into a node_modules this workspace owns.
+    // Symlinking the whole directory pointed `node_modules/.impeccable-live` at
+    // the REPO's node_modules, so the scaffolder wrote its variants there:
+    // afterEach cleaned the temp dir and left them behind, the next case reused
+    // the session id, and a stale variant could be parsed against a fresh
+    // manifest. Svelte's own dependencies still resolve, because node follows
+    // the link to its real path before looking for them.
+    fs.mkdirSync(path.join(scratch, 'node_modules'), { recursive: true });
+    fs.symlinkSync(
+      path.join(REPO_ROOT, 'node_modules', 'svelte'),
+      path.join(scratch, 'node_modules', 'svelte'),
+      'dir',
+    );
   });
 
   afterEach(() => {
@@ -138,10 +147,15 @@ describe('the real scaffolder writes variants that parse', () => {
     'markup with a free expression': ['<h1 class="hero-title">{headline}</h1>'],
   };
 
+  let caseIndex = 0;
   for (const [label, originalLines] of Object.entries(CASES)) {
     it(label, () => {
+      // Distinct per case as well: an id shared across cases is only safe while
+      // the output directory is genuinely per-case, and that coupling is the
+      // kind that quietly breaks again.
+      const sessionId = `testsession${caseIndex++}`;
       const result = scaffoldSvelteComponentSession({
-        id: 'testsession',
+        id: sessionId,
         count: 3,
         sourceFile: 'src/routes/+page.svelte',
         sourceStartLine: 1,
@@ -151,7 +165,7 @@ describe('the real scaffolder writes variants that parse', () => {
       });
       assert.equal(result.fallback, undefined, `scaffold fell back: ${result.reason}`);
 
-      const dir = path.join(scratch, 'node_modules', '.impeccable-live', 'testsession');
+      const dir = path.join(scratch, 'node_modules', '.impeccable-live', sessionId);
       const variants = fs.readdirSync(dir).filter((name) => /^v\d+\.svelte$/.test(name));
       assert.ok(variants.length > 0, 'scaffolder wrote no variant files');