fix(ci): add zig parse snippet to prebuild validate

The six zig prebuild jobs failed at "Validate the .node loads and parses"
because snippets[GRAMMAR] was undefined and tree-sitter threw
"Input must be a function".

Co-authored-by: Cursor <cursoragent@cursor.com>

.github/workflows/build-tree-sitter-prebuilds.yml

@@ -477,11 +477,14 @@ jobs:
               proto:  "syntax = \"proto3\";\nmessage M { int32 id = 1; }",
               kotlin: "fun main() { println(\"hi\") }",
               swift:  "func greet() { print(\"hi\") }",
+              zig:    "pub fn main() void {}",
             };
+            const src = snippets[process.env.GRAMMAR];
+            if (!src) throw new Error("no validate snippet for grammar: " + process.env.GRAMMAR);
             const lang = require("node-gyp-build")(process.cwd());
             const Parser = require("tree-sitter");
             const p = new Parser(); p.setLanguage(lang);
-            const tree = p.parse(snippets[process.env.GRAMMAR]);
+            const tree = p.parse(src);
             if (!tree || !tree.rootNode || tree.rootNode.hasError) {
               throw new Error("parse failed/error: " + (tree && tree.rootNode && tree.rootNode.type));
             }

gitnexus/test/unit/prebuild-coverage.test.ts

@@ -175,3 +175,28 @@ describe('npm-dependency grammar prebuild coverage', () => {
     });
   }
 });
+
+describe('prebuild workflow validate snippets cover every REGISTRY grammar', () => {
+  // The "Validate the .node loads and parses" step looks up snippets[GRAMMAR].
+  // A missing key yields undefined, and tree-sitter's parse() throws
+  // "Input must be a function" — the six zig jobs on #3180.
+  const workflow = readFileSync(
+    path.join(GITNEXUS_ROOT, '..', '.github/workflows/build-tree-sitter-prebuilds.yml'),
+    'utf8',
+  );
+  const registry = [
+    ...workflow.matchAll(/^\s{12}(\w+):\s+\{\s+name:\s+'tree-sitter-/gm),
+  ].map((m) => m[1]);
+  const snippets = [...workflow.matchAll(/^\s{14}(\w+):\s+"/gm)].map((m) => m[1]);
+
+  it('REGISTRY and snippets are both non-empty (the regex still matches the workflow)', () => {
+    expect(registry.length).toBeGreaterThan(0);
+    expect(snippets.length).toBeGreaterThan(0);
+  });
+
+  it('every REGISTRY grammar has a parse snippet', () => {
+    expect(snippets.sort(), 'add a snippets.<grammar> entry when extending REGISTRY').toEqual(
+      [...registry].sort(),
+    );
+  });
+});