feat(workflow): add opt-in TDD pipeline mode (#2119)

* feat(workflow): add opt-in TDD pipeline mode (workflow.tdd_mode)

Add workflow.tdd_mode config key (default: false) that enables
red-green-refactor as a first-class phase execution mode. When
enabled, the planner aggressively applies type: tdd to eligible
tasks and the executor enforces RED/GREEN/REFACTOR gate sequence
with fail-fast on unexpected GREEN before RED. An end-of-phase
collaborative review checkpoint verifies gate compliance.

Closes #1871

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(test): allowlist plan-phase.md in prompt injection scan

plan-phase.md exceeds 50K chars after TDD mode integration.
This is legitimate orchestration complexity, not prompt stuffing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* ci: trigger CI run

* ci: trigger CI run

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

tests/prompt-injection-scan.test.cjs

@@ -53,7 +53,7 @@ const ALLOWLIST = new Set([
   'get-shit-done/bin/lib/security.cjs',        // The security module itself
   'get-shit-done/workflows/discuss-phase.md',  // Large workflow (~50K) with power mode + i18n
   'get-shit-done/workflows/execute-phase.md',  // Large orchestration workflow (~51K) with wave execution + code-review gate
-  'get-shit-done/workflows/plan-phase.md',      // Large orchestration workflow (~52K) with pattern mapper + TDD mode
+  'get-shit-done/workflows/plan-phase.md',      // Large orchestration workflow (~51K) with TDD mode integration
   'hooks/gsd-prompt-guard.js',                  // The prompt guard hook
   'tests/security.test.cjs',                    // Security tests
   'tests/prompt-injection-scan.test.cjs',       // This file

tests/tdd-mode.test.cjs

@@ -0,0 +1,105 @@
+/**
+ * GSD Tools Tests — workflow.tdd_mode config key
+ *
+ * Validates that the tdd_mode workflow toggle is a first-class config key
+ * with correct default, round-trip behavior, and presence in VALID_CONFIG_KEYS.
+ *
+ * Requirements: #1871
+ */
+
+const { test, describe, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+const { runGsdTools, createTempProject, cleanup } = require('./helpers.cjs');
+
+// ─── helpers ──────────────────────────────────────────────────────────────────
+
+function readConfig(tmpDir) {
+  const configPath = path.join(tmpDir, '.planning', 'config.json');
+  return JSON.parse(fs.readFileSync(configPath, 'utf-8'));
+}
+
+// ─── VALID_CONFIG_KEYS ──────────────────────────────────────────────────────
+
+describe('workflow.tdd_mode in VALID_CONFIG_KEYS', () => {
+  test('workflow.tdd_mode is a recognized config key', () => {
+    const { VALID_CONFIG_KEYS } = require('../get-shit-done/bin/lib/config.cjs');
+    assert.ok(
+      VALID_CONFIG_KEYS.has('workflow.tdd_mode'),
+      'workflow.tdd_mode should be in VALID_CONFIG_KEYS'
+    );
+  });
+});
+
+// ─── config default value ───────────────────────────────────────────────────
+
+describe('workflow.tdd_mode default value', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('defaults to false in new project config', () => {
+    // Ensure config is created with defaults
+    const result = runGsdTools('config-ensure-section', tmpDir, { HOME: tmpDir });
+    assert.ok(result.success, `config-ensure-section failed: ${result.error}`);
+
+    const config = readConfig(tmpDir);
+    assert.strictEqual(
+      config.workflow.tdd_mode,
+      false,
+      'workflow.tdd_mode should default to false'
+    );
+  });
+});
+
+// ─── config round-trip (set / get) ─────────────────────────────────────────
+
+describe('workflow.tdd_mode config round-trip', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+    // Create a config file first
+    runGsdTools('config-ensure-section', tmpDir, { HOME: tmpDir });
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('config-set workflow.tdd_mode true round-trips via config-get', () => {
+    const setResult = runGsdTools('config-set workflow.tdd_mode true', tmpDir);
+    assert.ok(setResult.success, `config-set failed: ${setResult.error}`);
+
+    const getResult = runGsdTools('config-get workflow.tdd_mode', tmpDir);
+    assert.ok(getResult.success, `config-get failed: ${getResult.error}`);
+    assert.strictEqual(getResult.output, 'true');
+  });
+
+  test('config-set workflow.tdd_mode false round-trips via config-get', () => {
+    // First set to true, then back to false
+    runGsdTools('config-set workflow.tdd_mode true', tmpDir);
+
+    const setResult = runGsdTools('config-set workflow.tdd_mode false', tmpDir);
+    assert.ok(setResult.success, `config-set failed: ${setResult.error}`);
+
+    const getResult = runGsdTools('config-get workflow.tdd_mode', tmpDir);
+    assert.ok(getResult.success, `config-get failed: ${getResult.error}`);
+    assert.strictEqual(getResult.output, 'false');
+  });
+
+  test('persists in config.json as boolean', () => {
+    runGsdTools('config-set workflow.tdd_mode true', tmpDir);
+
+    const config = readConfig(tmpDir);
+    assert.strictEqual(config.workflow.tdd_mode, true);
+    assert.strictEqual(typeof config.workflow.tdd_mode, 'boolean');
+  });
+});