fix(llm): stop leaking instruction prompts instead of processed text

Running a custom instruction (translate, summarise, rewrite, explain code,
free prompt) inserted the instruction's own wording instead of the result.
Two faults stacked:

The instruction was passed as the text to process, leaving the system-prompt
argument empty. `BASE_SYSTEM_PROMPTS` has no `custom` key, so resolution fell
back to `refine` without saying so, and the model dutifully polished the
instruction it had been handed. The transcript never reached it.

And only `{{text}}` was substituted, which none of the five built-in
instructions use — they carry `{{targetLanguage}}`, `{{userPrompt}}`, or no
placeholder at all. The substitution was a no-op from the day it was written:
the presets landed ten hours before the code that expected them.

- Instruction prompts now go to the system-prompt argument and the transcript
  to the text argument. Instructions that spell out `{{text}}` keep their old
  meaning, so hand-written ones still work.
- `renderInstructionPrompt` resolves `{{text}}`, `{{userPrompt}}` and
  `{{targetLanguage}}` in one place, and warns by name when a placeholder is
  left standing rather than letting it reach the model.
- `resolveSystemPrompt` no longer drops silently to `refine` for `custom`.
- Voice shortcuts no longer die at the `defaultLLMAction === 'none'` gate; an
  explicitly named instruction outranks the default. Without one, `none` still
  passes the transcript through untouched.
- `translate` receives its target language instead of relying on a default two
  call frames away. It is still always English — `AppConfig` has no key for it,
  and neither `language` (UI locale) nor `sttLanguage` (source language) can
  stand in. Choosing a target language needs a setting and is not in this fix.
- Chains ran instructions with placeholders intact; they share the same
  resolution now.
- The command screen's pipeline bench called `llm.generate`, which preload does
  not expose, so every run threw and the catch showed the input back as if it
  had succeeded. It uses `llm.process` now, over the same path production
  takes, and a failure reads as a failure.

Present since the feature shipped: the custom-instruction path has never
worked. Plain actions (refine, summarise, grammar, expand) were unaffected and
are now covered by tests so they stay that way.

apps/desktop/tests/main/services/ChainService.test.ts

@@ -0,0 +1,174 @@
+// tests/main/services/ChainService.test.ts
+// 체인 스텝이 지시문을 시스템 프롬프트로 넘기고 플레이스홀더를 치환하는지 잠근다.
+// 인자 자리는 원래 옳았으나 치환이 없어 {{targetLanguage}} 등이 그대로 새어나갔다.
+
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import type { LLMChain } from '@d3ro/core/types'
+
+vi.mock('../../../src/main/services/LoggerService', () => ({
+  getLogger: () => ({ info: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn() })
+}))
+
+const config = vi.hoisted(() => ({ values: {} as Record<string, unknown> }))
+
+vi.mock('../../../src/main/services/ConfigService', () => ({
+  configGet: vi.fn((key: string) => config.values[key]),
+  configSet: vi.fn((key: string, value: unknown) => {
+    config.values[key] = value
+  })
+}))
+
+const instructionStore = vi.hoisted(() => ({
+  byId: {} as Record<string, { id: string; name: string; prompt: string }>
+}))
+
+vi.mock('../../../src/main/services/CustomInstructionService', () => ({
+  getCustomInstructionService: () => ({
+    getById: (id: string) => instructionStore.byId[id] ?? null
+  })
+}))
+
+const mockLLM = vi.hoisted(() => ({
+  processText: vi.fn(),
+  cancelGeneration: vi.fn()
+}))
+
+vi.mock('../../../src/main/services/PremiumLLMService', () => ({
+  getPremiumLLMService: () => mockLLM
+}))
+
+let getChainService: typeof import('../../../src/main/services/ChainService')['getChainService']
+
+function chain(steps: Array<{ instructionId: string }>): LLMChain {
+  return {
+    id: 'chain-1',
+    name: '테스트 체인',
+    steps: steps.map((s) => ({ instructionId: s.instructionId, inputSource: 'previous' as const })),
+    createdAt: 0,
+    updatedAt: 0
+  }
+}
+
+beforeEach(async () => {
+  vi.resetModules()
+  vi.clearAllMocks()
+  config.values = {}
+  instructionStore.byId = {}
+  mockLLM.processText.mockResolvedValue('LLM 결과')
+
+  const mod = await import('../../../src/main/services/ChainService')
+  mod.resetChainServiceForTests()
+  getChainService = mod.getChainService
+})
+
+describe('ChainService.execute — 지시문 인자 전달', () => {
+  it('지시문을 시스템 프롬프트로, 스텝 입력을 처리 대상 텍스트로 넘긴다', async () => {
+    instructionStore.byId['builtin-summarize'] = {
+      id: 'builtin-summarize',
+      name: '요약',
+      prompt: '다음 텍스트의 핵심 내용을 3줄 이내로 요약해주세요.'
+    }
+    config.values.llmChains = [chain([{ instructionId: 'builtin-summarize' }])]
+
+    const svc = getChainService()
+    svc.initialize()
+    await svc.execute('chain-1', '오늘 배포 일정을 정했습니다')
+
+    expect(mockLLM.processText).toHaveBeenCalledTimes(1)
+    const [text, action, targetLanguage, systemPrompt] = mockLLM.processText.mock.calls[0]
+
+    expect(text).toBe('오늘 배포 일정을 정했습니다')
+    expect(action).toBe('custom')
+    expect(targetLanguage).toBeUndefined()
+    expect(systemPrompt).toBe('다음 텍스트의 핵심 내용을 3줄 이내로 요약해주세요.')
+  })
+
+  it('{{targetLanguage}}를 치환해 시스템 프롬프트로 넘긴다', async () => {
+    instructionStore.byId['builtin-translate'] = {
+      id: 'builtin-translate',
+      name: '번역',
+      prompt: '다음 텍스트를 {{targetLanguage}}로 번역해주세요.\n자연스럽고 정확한 번역만 출력하세요.'
+    }
+    config.values.llmChains = [chain([{ instructionId: 'builtin-translate' }])]
+
+    const svc = getChainService()
+    svc.initialize()
+    await svc.execute('chain-1', '안녕하세요')
+
+    const [text, , , systemPrompt] = mockLLM.processText.mock.calls[0]
+
+    expect(text).toBe('안녕하세요')
+    expect(systemPrompt).toBe(
+      '다음 텍스트를 English로 번역해주세요.\n자연스럽고 정확한 번역만 출력하세요.'
+    )
+    expect(systemPrompt).not.toContain('{{')
+  })
+
+  it('{{userPrompt}}를 스텝 입력으로 치환한다', async () => {
+    instructionStore.byId['builtin-free-prompt'] = {
+      id: 'builtin-free-prompt',
+      name: '자유 프롬프트',
+      prompt: '{{userPrompt}}'
+    }
+    config.values.llmChains = [chain([{ instructionId: 'builtin-free-prompt' }])]
+
+    const svc = getChainService()
+    svc.initialize()
+    await svc.execute('chain-1', '피보나치 짜줘')
+
+    const [text, , , systemPrompt] = mockLLM.processText.mock.calls[0]
+
+    expect(text).toBe('피보나치 짜줘')
+    expect(systemPrompt).toBe('피보나치 짜줘')
+  })
+
+  it('{{text}}를 쓰는 지시문은 치환 결과를 처리 대상 텍스트로 넘긴다', async () => {
+    instructionStore.byId['user-bullets'] = {
+      id: 'user-bullets',
+      name: '불릿 정리',
+      prompt: '아래를 불릿으로 정리해줘:\n{{text}}'
+    }
+    config.values.llmChains = [chain([{ instructionId: 'user-bullets' }])]
+
+    const svc = getChainService()
+    svc.initialize()
+    await svc.execute('chain-1', '가 나 다')
+
+    const [text, action, , systemPrompt] = mockLLM.processText.mock.calls[0]
+
+    expect(text).toBe('아래를 불릿으로 정리해줘:\n가 나 다')
+    expect(action).toBe('custom')
+    expect(systemPrompt).toBeUndefined()
+  })
+
+  it('두 번째 스텝은 이전 스텝 출력을 처리 대상 텍스트로 받는다', async () => {
+    instructionStore.byId['builtin-summarize'] = {
+      id: 'builtin-summarize',
+      name: '요약',
+      prompt: '요약해줘.'
+    }
+    instructionStore.byId['builtin-translate'] = {
+      id: 'builtin-translate',
+      name: '번역',
+      prompt: '{{targetLanguage}}로 번역해줘.'
+    }
+    config.values.llmChains = [
+      chain([{ instructionId: 'builtin-summarize' }, { instructionId: 'builtin-translate' }])
+    ]
+    mockLLM.processText.mockResolvedValueOnce('요약된 텍스트')
+
+    const svc = getChainService()
+    svc.initialize()
+    await svc.execute('chain-1', '긴 원문')
+
+    expect(mockLLM.processText).toHaveBeenCalledTimes(2)
+
+    const [firstText, , , firstSystem] = mockLLM.processText.mock.calls[0]
+    expect(firstText).toBe('긴 원문')
+    expect(firstSystem).toBe('요약해줘.')
+
+    const [secondText, , , secondSystem] = mockLLM.processText.mock.calls[1]
+    expect(secondText).toBe('요약된 텍스트')
+    expect(secondSystem).toBe('English로 번역해줘.')
+  })
+})