fix(#3841): express the anchor semantically so the pretty payload still verifies

The remote matrix caught a regression I introduced in the previous commit. The
anchor check was implemented as a byte-prefix match against IDENTITY_RAW_PREFIX,
which describes the `--raw` wire format -- but `cmdRuntimeIdentity` without that
flag pretty-prints at indent 2, and the classifier is handed BOTH serializations.
Only the shell is restricted to `--raw`. The pre-existing test that runs the real
verb with no flag went red: `+ 'unparseable' - 'ok'`.

No local gate caught it. build:lib, eslint and lint:ci were green throughout,
because none of them execute tests.

The anchor now reproduces its two properties semantically instead of byte-wise,
and both hold for either serialization: the payload begins at the first byte of
stdout, and `packageName` serializes first. IDENTITY_RAW_PREFIX stays exported
with its own tests -- it is the wire contract for the shell, not a general
classifier predicate, and conflating those was the error.

Adds the two rows the matrix was missing: the default pretty serialization
verifies, and a pretty payload with `packageName` not first does not. The design
and matrix now record that they enumerated only the inputs the SHELL produces
and assumed the classifier's input set was the same.

Refs #3841

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/runtime-identity.test.cjs

@@ -190,6 +190,19 @@ describe('classifyIdentityProbe', () => {
     assert.equal(v.reason, 'unparseable');
   });
 
+  test('the default PRETTY serialization still verifies (not just --raw)', () => {
+    // The classifier is handed both serializations: the shell only ever sees
+    // `--raw`, but `runtime-identity` with no flag emits two-space-indented
+    // JSON. An anchor expressed as a compact byte prefix rejected this.
+    const pretty = JSON.stringify({ packageName: EXPECTED_PACKAGE_NAME, version: '9.9.9' }, null, 2);
+    assert.equal(classifyIdentityProbe({ stdout: `${pretty}\n`, exitCode: 0 }).reason, 'ok');
+  });
+
+  test('a pretty payload with packageName not first does not verify', () => {
+    const pretty = JSON.stringify({ note: 'x', packageName: EXPECTED_PACKAGE_NAME }, null, 2);
+    assert.equal(classifyIdentityProbe({ stdout: `${pretty}\n`, exitCode: 0 }).reason, 'unparseable');
+  });
+
   test('a foreign packageName is a mismatch wherever it appears in the object', () => {
     const stdout = '{"note":"x","packageName":"get-shit-done-cc"}';
     const v = classifyIdentityProbe({ stdout, exitCode: 0 });