chore(#2453): resolve the uniform-router-param conflict and clear the warning floor (#2489)

npx eslint . reported 0 errors, 53 warnings. The floor eroded the signal: a
genuinely new warning had to be spotted against noise, so 'lint is clean' was not
usable as a check. This takes it to zero.

Fifty of the 53 were one category in gsd-core/bin/gsd-tools.cjs — all unused
ARGUMENTS (error x30, cwd x10, raw x7, args x3), never unused variables. They are
the Command Routing Hub's uniform handler signature, function routeX({ args, cwd,
raw, error }), declared identically whether or not a handler uses all four
members. argsIgnorePattern: '^_' is structurally in conflict with that convention:
satisfying it would mean _-prefixing ~50 parameters and making the signature
non-uniform across the table. Option 1 of #2453: disable args checking for that
file only, keeping varsIgnorePattern intact so genuinely dead variables (the #2379
class) still surface — verified by injecting an unused variable, which still warns.

This is the config decision #732 explicitly deferred ('Severities stay warn (no
config change in this pass)').

The remaining three predate the issue's count of 51 and are real defects, not
suppressions:

- tests/workflow-compat.test.cjs — the step-9 lookahead used (?=\*\*10\.|\z).
  \z is a Perl/Ruby end-of-input anchor with NO meaning in JavaScript; it matched
  a literal 'z', so the lazy span silently stopped at the first z whenever **10.
  was absent, truncating the captured step and letting the assertion pass against
  a partial block. Corrected to $.
- tests/debugger-prevention.test.cjs — an unused RegExp built one line above the
  one actually used. Removed.
- tests/installer-migrations.test.cjs — try/finally inside a test body, which
  CONTRIBUTING prohibits ('verbose, masks test failures, not an approved
  pattern'); the unused t was the symptom. Converted to t.after().

Closes #2453

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

eslint.config.mjs

@@ -419,4 +419,33 @@ export default tseslint.config(
     languageOptions: { sourceType: 'commonjs', globals: { ...globals.node } },
     rules: { 'local/no-source-grep': 'error' },
   },
+
+  // ── #2453 Command Routing Hub: uniform handler signature ────────────────────
+  // Every route handler in gsd-tools.cjs is declared with the SAME destructured
+  // signature — `function routeX({ args, cwd, raw, error })` — whether or not it
+  // uses all four members. That uniformity is the point: it is the dispatch
+  // contract, so a handler can be moved or added without re-deriving which
+  // members exist.
+  //
+  // `argsIgnorePattern: '^_'` is structurally in conflict with that convention:
+  // satisfying it would mean `_`-prefixing ~50 parameters, which makes the
+  // signature non-uniform across the table and defeats the contract. So args
+  // checking is disabled HERE ONLY.
+  //
+  // `varsIgnorePattern` is deliberately left intact: genuinely dead *variables*
+  // (the #2379 case — unused `require()` results) must still surface. This
+  // narrows the exemption to the one category the convention actually forces.
+  //
+  // Decision deferred by #732 ("Severities stay `warn` (no config change in this
+  // pass)"), resolved by #2453 option 1.
+  {
+    files: ['gsd-core/bin/gsd-tools.cjs'],
+    rules: {
+      'no-unused-vars': ['warn', {
+        args: 'none',
+        varsIgnorePattern: '^_',
+        caughtErrors: 'none',
+      }],
+    },
+  },
 );