refactor(rectification): split runV9AgentTurn into prepare / attempt / retry / finish

Move-only (TASK-rectification-code-split-20260926 T3/T4). No behavior,
receipt, billing, Skill or scoring change.

- agent-run.ts: 1400 -> 135 lines; runV9AgentTurn 1046 -> 25 lines, no
  nested functions. It keeps the public types, the budget constants and the
  phase order: agent-run-prepare.ts (reliability, session, year re-ask, Skill
  identity, delivered guard, reserve, turn row / replay),
  agent-run-retry.ts (attempt loop), agent-run-attempt.ts (the old nested
  streamAttempt), agent-run-finish.ts (billing settle, receipts, interview,
  finalize), agent-run-support.ts (outcome types, retry classification, turn
  receipt writers), agent-run-messages.ts (buildAgentMessages /
  buildOpeningBrief, re-exported).
- One token changed with the move: the attempt passes its own
  `previousErrorCode` argument to buildAgentMessages instead of reading the
  enclosing `lastAttemptError`; the loop passes that same value (clears the
  old unused-parameter warning).
- Tests: whole-source contracts read tests/rectification-agent-run-surface.ts;
  behavioral runV9AgentTurn tests unchanged. agent-run growth caps added.

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

frontend/tests/rectification-agentic-entry.test.ts

@@ -17,6 +17,7 @@ import { deriveRectificationChatView } from "../src/lib/rectification-chat-view.
 import { completedReceiptFromPersisted } from "../src/lib/rectification-chat-messages.ts";
 import { RectificationQuestionGapNotices } from "../src/components/rectification-question-gap-notices.tsx";
 import { rectificationAgentRouteSurface } from "./rectification-agent-route-surface.ts";
+import { rectificationAgentRunSurface } from "./rectification-agent-run-surface.ts";
 
 const component = readFileSync(
   new URL("../src/components/conversational-birth-time-rectification.tsx", import.meta.url),
@@ -288,10 +289,8 @@ test("candidate acceptance is non-billable, mutually exclusive, and continues th
 });
 
 test("usage completes or releases without hiding settlement failures", () => {
-  const run = readFileSync(
-    new URL("../src/lib/rectification-agentic/v9/agent-run.ts", import.meta.url),
-    "utf8",
-  );
+  // 原值: 读 lib/rectification-agentic/v9/agent-run.ts 单文件。新值: rectificationAgentRunSurface（agent-run.ts + 拆出的 agent-run-*.ts，见 rectification-agent-run-surface.ts）。原因: TASK-rectification-code-split-20260926 只搬不改，整文件断言跟着代码走；切片断言另行改写。
+  const run = rectificationAgentRunSurface;
   assert.match(run, /billing\.complete\(/);
   assert.match(run, /billing\.release\(/);
   assert.match(run, /usage_settlement_failed/);