test(#2126): resolve review findings — fold dedup, harness fidelity, malformed-parity lock

Adversarial review of the Phase 3 branch surfaced three verified defects; fix
all three in place (no defer):

- install-runtime-artifacts.test.cjs: finish the fold-triplication dedup started
  earlier (only enh-1511 had been collapsed). 11 B1-batch __foldDescribe blocks
  were byte-identical triplicates (~5.9k lines, ~49% of the file), tripling the
  subprocess-spawning installer suites under --test-concurrency — the same
  starvation that produced the temp-dir races this branch fixes. Byte-identity
  verified per block before removal; 230 distinct test/it titles preserved
  (origin/next: 230 -> 230), interleaved B3/B5/B6 singletons untouched.
- config-get-default.test.cjs: make runExpectError faithful to production. The
  throwing process.exit seam was caught by cmdConfigGet's "No config.json"
  guard and reclassified into a spurious 2nd error() with the wrong reason
  (CONFIG_PARSE_FAILED). Drive io.setJsonErrorMode + carry the original message
  on the sentinel so the guard re-throws (single fire), assert exitCount===1,
  and strengthen both probes to assert the typed reason (CONFIG_NO_FILE /
  CONFIG_KEY_NOT_FOUND).
- roadmap.test.cjs: lock the #2121/#2114 malformed_roadmap parity — a
  project-code-prefixed query against a checklist-only roadmap now surfaces the
  same diagnostic a bare query always did (fails on prior silent-empty behavior).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/roadmap.test.cjs

@@ -2121,6 +2121,39 @@ describe('bug #2114: roadmap get-phase resolves drifted prefixed headings by bar
     assert.strictEqual(payload30.found, true);
     assert.strictEqual(payload30.phase_name, 'Plain');
   });
+
+  test('prefixed query surfaces malformed_roadmap when only a checklist entry exists (parity with bare)', () => {
+    // #2121/#2114 route all three resolvers through the shared 3-source lookup, so a
+    // project-code-prefixed query now surfaces the SAME `malformed_roadmap` diagnostic a
+    // bare numeric query always did: a `**Phase PROJ-42:**` summary line with no matching
+    // `### Phase PROJ-42:` detail heading is malformed for BOTH query forms. Before the
+    // consolidation the prefixed form silently returned `{found:false}` with no diagnostic
+    // (the exact-prefix pass discarded its malformed candidate) — this test fails on that
+    // prior behavior and locks the unified, more-informative result.
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      [
+        '# Roadmap v1.0',
+        '',
+        '## Phases',
+        '',
+        '- [ ] **Phase PROJ-42: Checklist only, no header**',
+        '',
+      ].join('\n'),
+    );
+
+    const prefixed = runGsdTools('roadmap get-phase PROJ-42 --json', tmpDir);
+    assert.ok(prefixed.success, `command failed: ${prefixed.error || prefixed.output}`);
+    const pPayload = JSON.parse(prefixed.output);
+    assert.strictEqual(pPayload.found, false, 'malformed roadmap: phase must not be found');
+    assert.strictEqual(pPayload.error, 'malformed_roadmap', 'prefixed query must surface malformed_roadmap');
+    assert.ok(pPayload.message.includes('missing'), 'message must explain the missing detail section');
+
+    // Parity: the bare numeric form yields the same diagnostic against the same fixture.
+    const bare = runGsdTools('roadmap get-phase 42 --json', tmpDir);
+    assert.ok(bare.success, `command failed: ${bare.error || bare.output}`);
+    assert.strictEqual(JSON.parse(bare.output).error, 'malformed_roadmap', 'bare query surfaces the same diagnostic');
+  });
 });
 
 describe('roadmap annotate-dependencies', () => {