refactor(rectification): split the chat component into hooks, parameter functions and blocks

Move-only (TASK-rectification-code-split-20260926 T1/T4). No behavior, API,
copy, DB, Skill or scoring change.

- rectification-agentic-chat.tsx: 2043 -> 737 lines; component body
  1625 -> 630; useState 35 -> 12, useRef 16 -> 9, effects 9 -> 5,
  useCallback 12 -> 6.
- Snapshot sync -> hooks/use-rectification-case-snapshot.ts; board layout
  and live label clock -> two small hooks.
- send / submitStructuredChoice / acceptCandidate bodies ->
  lib/rectification-chat-{turn,choice,accept}-run.ts parameter functions
  (bodies verbatim, deps destructured to the same names); copy/regenerate,
  question repair, pure transcript and snapshot helpers and the per-render
  view derivation -> lib/rectification-chat-*.ts (no React hooks).
- Question-gap blocks and the read-only range line ->
  components/rectification-question-gap-notices.tsx.
- Dependency arrays kept exactly as before (lint warnings +3, listed in
  PROGRESS); no dep added to appease the linter.
- Tests: whole-source contracts read tests/rectification-chat-surface.ts
  (container + split files, like home-surface.ts); slices of moved code now
  call the extracted functions or render the extracted block, each with a
  原值/新值/原因 comment. New tests/rectification-growth-contract.test.ts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017eEAG8HD3mm8gsKXgk8uU8

frontend/tests/rectification-answer-choice.test.ts

@@ -53,6 +53,7 @@ import {
   fakeAccounting,
   receiptHandlers,
 } from "./rectification-v9-test-support.ts";
+import { rectificationChatSurface } from "./rectification-chat-surface.ts";
 
 const ACTION_ID = "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa";
 const QUESTION_ID = "question-1";
@@ -1477,7 +1478,8 @@ test("the public agent route treats structured choice as a non-model command", (
   assert.match(route, /SKIP_PROBE_ACTION/);
   assert.doesNotMatch(route, /action === "skip_probe"[\s\S]{0,80}paused/);
   assert.match(route, /export const maxDuration = 240/);
-  const chat = readFileSync(new URL("../src/components/rectification-agentic-chat.tsx", import.meta.url), "utf8");
+  // 原值: 读 rectification-agentic-chat.tsx 单文件。新值: rectificationChatSurface（容器 + 拆出的 hook / 参数函数 / 块，见 rectification-chat-surface.ts）。原因: TASK-rectification-code-split-20260926 只搬不改，整文件断言跟着代码走；切片断言另行改为调用函数。
+  const chat = rectificationChatSurface;
   assert.match(chat, /isPersistedFocusId\(focusId\)/);
   assert.match(chat, /focusId,/);
   assert.match(chat, /shouldContinueAfterStructuredChoice\(payload\?\.nextAction, payload\)/);