test(#3149): correct stale tdd_mode assertion and drop a marker-token collision

Two failures from the remote runner on 654b2cc10, both introduced here.

1. tests/mcp-catalog-parity.install.test.cjs greps emitted workflow files
   for the bare substring 'gsd:section' and treats its presence in a
   composed file as an un-stripped marker. debug.md's new Step 0 prose
   documented the field by writing that token literally, so the emitted
   file tripped the gate even though the parser correctly ignored it as
   prose. Reworded to 'applicability-section markers'. Same class as
   DEFECT.PROMPT-INJECTION-SCAN-COLLISION.

2. tests/debug-session-management.test.cjs asserted debug.md contains the
   literal 'config-get workflow.tdd_mode'. That call is gone. The
   invariant it protected -- tdd_mode comes from the workflow.tdd_mode
   key, never a bare top-level one -- is unchanged, and now has a
   stronger behavioral home: init-debug.test.cjs row A9 asserts a bare
   key is ignored and the canonical key is honored, whatever the read
   mechanism.

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

tests/init-debug.test.cjs

@@ -157,6 +157,26 @@ describe('init.debug resolves identically to the three calls it replaces (matrix
     assert.equal(viaInit.tdd_mode, true, 'the root value must be inherited, not lost');
     assert.equal(String(viaInit.tdd_mode), viaConfigGet.output.trim());
   });
+
+  test('honors workflow.tdd_mode, ignores a bare top-level tdd_mode (row A9)', () => {
+    // The invariant tests/debug-session-management.test.cjs used to guard by
+    // grepping debug.md for `config-get workflow.tdd_mode`. Asserted here
+    // behaviorally instead, which is strictly stronger: a bare top-level key
+    // must NOT be honored, whatever the read mechanism.
+    writeConfig(tmpDir, { tdd_mode: true });
+    assert.equal(
+      runJson(['init', 'debug'], tmpDir).tdd_mode,
+      false,
+      'a bare top-level tdd_mode key must be ignored — the canonical key is workflow.tdd_mode'
+    );
+
+    writeConfig(tmpDir, { workflow: { tdd_mode: true } });
+    assert.equal(
+      runJson(['init', 'debug'], tmpDir).tdd_mode,
+      true,
+      'the canonical workflow.tdd_mode key must be honored'
+    );
+  });
 });
 
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