test(pi): scope mapping assertions to the table, not whole file

The pi tokens (subagent, pi-subagents, Task, TODO.md) also appear in the
surrounding prose, so matching the whole file passed even with the mapping
table deleted — the exact regression this test exists to catch. Filter to
table rows (lines starting with '|') so the assertion fails when the table
is gone and passes on dev.

Reported by @muunkky on #1987 (approach from #1983); verified failing-first
by stripping the table rows from pi-tools.md.

tests/pi/test-pi-extension.mjs

@@ -122,7 +122,16 @@ test('pi tools reference documents pi-specific mappings', async () => {
   assert.equal(existsSync(piToolsPath), true, 'pi-tools.md should exist');
   const text = await readFile(piToolsPath, 'utf8');
 
-  for (const expected of ['subagent', 'pi-subagents', 'Task', 'TODO.md']) {
-    assert.match(text, new RegExp(expected));
-  }
+  // Assert against the mapping-table rows only. The surrounding prose mentions
+  // these same tokens, so matching the whole file would still pass if the table
+  // were deleted — the exact regression this test exists to catch.
+  const rows = text.split('\n').filter((line) => line.startsWith('|'));
+  assert.ok(
+    rows.some((row) => /subagent/i.test(row)),
+    'mapping table documents subagent dispatch',
+  );
+  assert.ok(
+    rows.some((row) => /todo|task/i.test(row)),
+    'mapping table documents task tracking',
+  );
 });