feat: add workflow.discuss_mode assumptions config (#637)

Add codebase-first assumption-driven alternative to the interview-style
discuss-phase. New `workflow.discuss_mode: "assumptions"` config routes
to a separate workflow that spawns a gsd-assumptions-analyzer agent to
read 5-15 codebase files, surface assumptions with evidence, and ask
only for corrections (~2-4 interactions vs ~15-20).

- New gsd-assumptions-analyzer agent for deep codebase analysis
- New discuss-phase-assumptions.md workflow (15 steps)
- Command-level routing via dual @reference + process gate
- Identical CONTEXT.md output — downstream agents unaffected
- Existing discuss-phase.md workflow untouched (zero diff)
- Mode-aware plan-phase gate and progress display
- User documentation and integration tests
- Update agent count and list in copilot-install tests (17 → 18)

Closes #637

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/discuss-mode.test.cjs

@@ -0,0 +1,101 @@
+/**
+ * Discuss Mode Config Tests
+ *
+ * Validates workflow.discuss_mode config, routing, and assumptions workflow integration.
+ */
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert');
+const fs = require('fs');
+const path = require('path');
+
+describe('workflow.discuss_mode config', () => {
+  test('config template includes discuss_mode default', () => {
+    const template = JSON.parse(
+      fs.readFileSync(path.join(__dirname, '..', 'get-shit-done', 'templates', 'config.json'), 'utf8')
+    );
+    assert.strictEqual(template.workflow.discuss_mode, 'discuss');
+  });
+
+  test('discuss-phase command references both workflow files', () => {
+    const command = fs.readFileSync(
+      path.join(__dirname, '..', 'commands', 'gsd', 'discuss-phase.md'), 'utf8'
+    );
+    assert.ok(command.includes('discuss-phase-assumptions.md'), 'should reference assumptions workflow');
+    assert.ok(command.includes('discuss-phase.md'), 'should reference discuss workflow');
+    assert.ok(command.includes('workflow.discuss_mode'), 'should reference config key');
+  });
+
+  test('discuss-phase command argument-hint includes --text', () => {
+    const command = fs.readFileSync(
+      path.join(__dirname, '..', 'commands', 'gsd', 'discuss-phase.md'), 'utf8'
+    );
+    assert.ok(command.includes('--text'), 'argument-hint should include --text');
+  });
+
+  test('assumptions workflow file exists and has required steps', () => {
+    const workflow = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'discuss-phase-assumptions.md'), 'utf8'
+    );
+    const requiredSteps = [
+      'initialize', 'check_existing', 'load_prior_context',
+      'deep_codebase_analysis', 'present_assumptions', 'correct_assumptions',
+      'write_context', 'write_discussion_log', 'auto_advance'
+    ];
+    for (const step of requiredSteps) {
+      assert.ok(workflow.includes(`<step name="${step}"`), `missing step: ${step}`);
+    }
+  });
+
+  test('assumptions workflow produces same CONTEXT.md sections', () => {
+    const workflow = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'discuss-phase-assumptions.md'), 'utf8'
+    );
+    const sections = ['<domain>', '<decisions>', '<canonical_refs>', '<code_context>', '<specifics>', '<deferred>'];
+    for (const section of sections) {
+      assert.ok(workflow.includes(section), `missing CONTEXT.md section: ${section}`);
+    }
+  });
+
+  test('plan-phase gate references discuss_mode config', () => {
+    const planPhase = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'plan-phase.md'), 'utf8'
+    );
+    assert.ok(planPhase.includes('workflow.discuss_mode'), 'should reference config key');
+    assert.ok(planPhase.includes('assumptions mode'), 'should mention assumptions mode');
+  });
+
+  test('assumptions workflow handles --auto flag', () => {
+    const workflow = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'discuss-phase-assumptions.md'), 'utf8'
+    );
+    assert.ok(workflow.includes('--auto'), 'should handle --auto');
+    assert.ok(workflow.includes('auto-select'), 'should auto-select in --auto mode');
+    assert.ok(workflow.includes('auto_advance'), 'should support auto_advance');
+  });
+
+  test('assumptions workflow handles --text flag', () => {
+    const workflow = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'discuss-phase-assumptions.md'), 'utf8'
+    );
+    assert.ok(workflow.includes('text_mode'), 'should reference text_mode config');
+    assert.ok(workflow.includes('--text'), 'should handle --text flag');
+  });
+
+  test('progress workflow references discuss_mode', () => {
+    const progress = fs.readFileSync(
+      path.join(__dirname, '..', 'get-shit-done', 'workflows', 'progress.md'), 'utf8'
+    );
+    assert.ok(progress.includes('workflow.discuss_mode'), 'should read discuss_mode config');
+    assert.ok(progress.includes('Discuss mode'), 'should display discuss mode');
+  });
+
+  test('documentation file exists', () => {
+    const docPath = path.join(__dirname, '..', 'docs', 'workflow-discuss-mode.md');
+    assert.ok(fs.existsSync(docPath), 'docs/workflow-discuss-mode.md should exist');
+    const doc = fs.readFileSync(docPath, 'utf8');
+    assert.ok(doc.includes('assumptions'), 'doc should mention assumptions');
+    assert.ok(doc.includes('discuss'), 'doc should mention discuss');
+    assert.ok(doc.includes('config-set'), 'doc should show how to configure');
+  });
+});