perf(rectification): evidence turns get Skill §5/§7 only; drop Mastra <available_skills> injection (R4)

T6 of TASK-rectification-grounding-20260927.
- skill-slice.ts: per-action slice rule as a code constant, keyed on heading
  titles (evidence: 「ConversationFocus 与意图承接」「批量证据与日期真实性」, i.e.
  §5/§7 of the 10.0.x layout); other actions and any bound Skill without those
  headings (9.0.0) get the whole body, so historical Cases still run with their
  exact bound Skill (BUG-621).
- The rectification Agent declares providesSkillDiscovery "on-demand"
  (rectificationSkillBoundProcessor): no <available_skills> block with a temp
  path and no "call the skill tool" system message; getSkill still loads the
  bound package.
- Measured on a real Agent + recording model (public AA case, estimate = CJK
  chars + other chars / 4): fixed overhead per call 12,002 → 6,471 tokens
  (step 0: 8,440 → 2,909). Skill text unchanged; no version bump.

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

frontend/src/lib/rectification-agentic/v9/agent-run-messages.ts

@@ -10,6 +10,7 @@ import type { V9CaseDossier } from "./tool-service";
 import { cachedSystemMessage } from "../../agent-generation-settings.ts";
 import { OPENING_COLLECT_DOMAINS } from "../user-copy";
 import { retryConstraintForAttempt } from "./host-fallback";
+import { sliceRectificationSkill } from "./skill-slice";
 import type { V9AgentRunOptions } from "./agent-run";
 
 function clockWindow(range: { start_time?: string | null; end_time?: string | null } | null | undefined): string | null {
@@ -54,9 +55,12 @@ export function buildAgentMessages(
   const timeContext = options.timeContext
     ?? `服务端当前时间（权威）：${new Date().toISOString()}。涉及“现在、今天、今年、未来几个月”等相对时间时，以此为准。`;
   const caseContext = `【服务端 Case ID】${options.caseId}。所有 rectification 工具调用的 caseId 必须原样使用此值。`;
+  // T6 (TASK-rectification-grounding-20260927): an evidence turn gets only
+  // the Skill sections it uses; other actions keep the whole bound body.
+  const boundSkill = sliceRectificationSkill(skillInstructions, options.action).text;
   const bootstrapContent = [
     "【服务器已绑定当前 Case 的精确 Skill】运行器已在本 attempt 内加载并核验下列指令；不要重复调用 skill。第一步必须调用 rectification-read-case。",
-    skillInstructions,
+    boundSkill,
     ...(attempt > 1 ? [retryConstraintForAttempt(previousErrorCode)] : []),
   ].join("\n\n");
   const bootstrap = cachedSystemMessage(bootstrapContent, options.generationModel)

frontend/src/lib/rectification-agentic/v9/skill-slice.ts

@@ -0,0 +1,71 @@
+/**
+ * Per-turn slice of the bound rectification Skill (TASK-rectification-
+ * grounding-20260927 T6).
+ *
+ * The runner used to send the whole bound SKILL.md body (about 10.7K
+ * characters for 10.0.31) on every model call. An evidence turn only uses
+ * §5 (ConversationFocus and intent) and §7 (batch evidence and date
+ * truthfulness); the rest describes the opening, case status table, fields
+ * that only exist in `full_diagnostics` (method_followup_plan,
+ * CaseConversationSummary, guided_collect_windows …), the candidate language
+ * of offer turns, and upstream sync. Other actions keep the whole body.
+ *
+ * The slice is keyed on `## N. <title>` heading titles, not on numbers:
+ * the 9.0.0 snapshot numbers its sections differently (its §5 is the
+ * candidate language). If any wanted title is missing, the whole body is
+ * sent unchanged, so a historical Case still runs with its exact bound Skill
+ * (BUG-621). All 10.0.x snapshots share the 10.0.31 headings.
+ */
+import type { RectificationAgentAction } from "./step-budget";
+
+/** Heading titles per action; evidence = §5 and §7 of the 10.0.x layout. */
+export const RECTIFICATION_SKILL_SECTIONS_BY_ACTION: Readonly<
+  Record<RectificationAgentAction, readonly string[] | "all">
+> = {
+  opening: "all",
+  read_only: "all",
+  evidence: ["ConversationFocus 与意图承接", "批量证据与日期真实性"],
+  rescore: "all",
+  accept: "all",
+  confirm: "all",
+};
+
+export type RectificationSkillSlice = Readonly<{
+  text: string;
+  /** Heading lines sent, or "all" when the whole body went out. */
+  sections: readonly string[] | "all";
+}>;
+
+function headingTitle(line: string): string | null {
+  const match = /^##\s+(?:\d+\.\s*)?(.+?)\s*$/.exec(line);
+  return match ? match[1] : null;
+}
+
+export function sliceRectificationSkill(
+  instructions: string,
+  action: RectificationAgentAction,
+): RectificationSkillSlice {
+  const wanted = RECTIFICATION_SKILL_SECTIONS_BY_ACTION[action];
+  if (wanted === "all") return { text: instructions, sections: "all" };
+  const preamble: string[] = [];
+  const sections: Array<{ title: string; lines: string[] }> = [];
+  for (const line of instructions.split("\n")) {
+    const title = line.startsWith("## ") ? headingTitle(line) : null;
+    if (title !== null) {
+      sections.push({ title, lines: [line] });
+      continue;
+    }
+    if (sections.length > 0) sections.at(-1)!.lines.push(line);
+    else preamble.push(line);
+  }
+  const picked = wanted.map((title) => sections.find((section) => section.title === title));
+  if (picked.some((section) => !section)) return { text: instructions, sections: "all" };
+  const title = preamble.find((line) => line.startsWith("# ")) ?? "";
+  const headings = picked.map((section) => section!.lines[0]!.trim());
+  const note = `（本轮是证据轮：以下只附本轮适用的 Skill 章节「${picked.map((section) => section!.title).join("」「")}」；其余章节不适用于本轮，按服务器投影与工具说明执行。）`;
+  const body = picked.map((section) => section!.lines.join("\n").trim()).join("\n\n");
+  return {
+    text: [title, note, body].filter(Boolean).join("\n\n"),
+    sections: headings,
+  };
+}

frontend/src/mastra/agentic-rectification.ts

@@ -1,4 +1,5 @@
 import { Agent } from "@mastra/core/agent";
+import type { Processor } from "@mastra/core/processors";
 import type { ResolvedLanguageModel } from "./model";
 import {
   resolveActiveSkillPackage,
@@ -56,8 +57,30 @@ export function getRectificationV9Agent(
     model: model.model,
     instructions: agenticRectificationInstructions,
     skills: [resolveSkillPackageRuntimePath(skillPackage)],
+    inputProcessors: [rectificationSkillBoundProcessor],
     tools: createRectificationV9AgentTools(ctx),
   });
 }
 
+/**
+ * R4 (TASK-rectification-grounding-20260927): Mastra's default skills
+ * processor added an `<available_skills>` block (with a temporary package
+ * path) and "call the `skill` tool" to every step, contradicting the runner's
+ * "do not call skill" and costing about 1K characters per call.
+ * `providesSkillDiscovery: "on-demand"` declares that the caller owns skill
+ * loading, which is true: the runner loads the exact bound Skill through
+ * `agent.getSkill` and quotes it (sliced per turn) in the bootstrap message.
+ * With this marker Mastra adds neither the system block nor the `skill` /
+ * `skill_search` tools (same mechanism as the consultation agents'
+ * `jyotishSkillBoundProcessor`).
+ */
+export const rectificationSkillBoundProcessor: Processor & { processInputStep: NonNullable<Processor["processInputStep"]> } = {
+  id: "rectification-skill-bound",
+  name: "Rectification Skill Bound",
+  providesSkillDiscovery: "on-demand",
+  processInputStep() {
+    // Nothing to inject: the bound Skill text rides in the runner's bootstrap message.
+  },
+};
+
 export { RECTIFICATION_V9_SKILL_NAME };