feat: fork-agent-redesign — 新增 AgentTool fork 参数与 spec 设计文档

为 AgentTool 引入 fork 布尔参数，支持子代理从父对话上下文中 fork 出独立分支，
继承完整历史、系统提示和模型配置。重构 inputSchema 条件逻辑以适配 fork 模式。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/builtin-tools/src/tools/AgentTool/__tests__/prompt.test.ts

@@ -0,0 +1,69 @@
+import { describe, expect, test } from 'bun:test'
+import { readFileSync } from 'fs'
+import { join, dirname } from 'path'
+import { fileURLToPath } from 'url'
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+const promptSource = readFileSync(join(__dirname, '..', 'prompt.ts'), 'utf-8')
+
+describe('prompt.ts fork-related text verification', () => {
+  test('does not contain "omit `subagent_type`" guidance', () => {
+    expect(promptSource).not.toMatch(/omit.*subagent_type/)
+  })
+
+  test('contains `fork: true` in at least 3 locations (shared + whenToFork + forkExamples)', () => {
+    const matches = promptSource.match(/fork: true/g)
+    expect(matches).not.toBeNull()
+    expect(matches!.length).toBeGreaterThanOrEqual(3)
+  })
+
+  test('all forkEnabled references are ternary conditions, not negated', () => {
+    const lines = promptSource.split('\n')
+    for (const line of lines) {
+      if (
+        line.includes('forkEnabled') &&
+        !line.includes('const forkEnabled') &&
+        !line.includes('forkEnabled =')
+      ) {
+        expect(line).not.toContain('!forkEnabled')
+      }
+    }
+  })
+
+  test('uses "non-fork" terminology instead of "fresh agent"', () => {
+    expect(promptSource).toContain('non-fork')
+    // "fresh agent" should not appear in fork-aware conditional text
+    const freshAgentMatches = promptSource.match(/fresh agent/g)
+    if (freshAgentMatches) {
+      // Only allowed in comments explaining behavior, not in prompt text
+      const linesWithFreshAgent = promptSource
+        .split('\n')
+        .filter(line => line.includes('fresh agent'))
+        .map(line => line.trim())
+      for (const line of linesWithFreshAgent) {
+        // "fresh agent" in the context of "starts fresh" (not fork-aware) is ok
+        // but "fresh agent" in forkEnabled conditional should not appear
+        expect(line).not.toMatch(/fresh agent.*subagent_type/)
+      }
+    }
+  })
+
+  test('background task condition does not include !forkEnabled', () => {
+    // The condition for showing background task instructions should not exclude fork
+    const bgCondition = promptSource.match(
+      /!isEnvTruthy.*isInProcessTeammate[\s\S]*?run_in_background/,
+    )
+    if (bgCondition) {
+      expect(bgCondition[0]).not.toContain('!forkEnabled')
+    }
+  })
+
+  test('fork example includes fork: true parameter', () => {
+    // The first fork example should have fork: true
+    const forkExampleBlock = promptSource.match(
+      /name: "ship-audit"[\s\S]*?Under 200 words/,
+    )
+    expect(forkExampleBlock).not.toBeNull()
+    expect(forkExampleBlock![0]).toContain('fork: true')
+  })
+})