feat(#92): IMP-92 u1~u5 AI fallback config validation (model ping + operational error classification)

Replaces #84 UI-noise removal plan with positive operational-alert contract.
Five-axis stack lands together: (1) default model literal moved to current
Opus-family ID, (2) Anthropic SDK error classifier mapping exceptions to
quota/billing/auth/other, (3) api_error_kind plumbed through ai_repair_status
summary + per-record retention, (4) Step 0 preflight ping gated under
ai_fallback_enabled (default OFF preserved) with fail-fast on invalid
model/key, (5) frontend formatter rewritten to surface only operational
quota/billing/auth toasts (non-operational paths return null per
feedback_auto_pipeline_first silent-pipeline policy).

u1 - default model literal claude-opus-4-6-20250415 -> claude-opus-4-7
     (src/config.py + tests/test_phase_z2_ai_fallback_config.py lock mirror)
u2 - classify_operational_error type+status_code dispatch + Step 12
     api_error_kind stamp on except path (src/phase_z2_ai_fallback/client.py
     + src/phase_z2_ai_fallback/step12.py + tests/phase_z2_ai_fallback/test_step12.py)
u3 - _summarize_ai_repair_status aggregates api_error_kinds {quota,billing,
     auth,other}; error_records[i].api_error_kind retained per-record
     (src/phase_z2_pipeline.py + tests/test_imp47b_failure_surface.py)
u4 - _run_step0_ai_preflight + Step0PreflightError; preflight only fires
     when ai_fallback_enabled=true; one-token ping; invalid key/model =>
     setup failure before Step 1 (src/phase_z2_pipeline.py +
     tests/phase_z2/test_pipeline_step0_preflight.py NEW)
u5 - AiRepairStatus.api_error_kinds? interface + formatAiRepairHumanReview
     Message rewritten: operational quota/billing/auth -> Korean copy
     verbatim from issue body (tie-break quota -> billing -> auth);
     validation/coverage_violated/unsupported_kind/generic-other/legacy
     payload -> null (Front/client/src/services/designAgentApi.ts +
     Front/client/tests/imp47b_human_review_toast.test.tsx)

Guardrails respected:
- feedback_demo_env_toggle_policy: default OFF preserved; preflight skipped
  when ai_fallback_enabled=false (test_preflight_skipped_when_disabled
  asserts anthropic.Anthropic() not called).
- feedback_auto_pipeline_first: non-operational AI failures stay silent;
  only quota/billing/auth reach user toast.
- feedback_ai_isolation_contract: AI remains fallback-only; no normal-path
  migration; MDX preserved.
- project_imp46_carveout_caveat: cache_key/fingerprints fields untouched on
  every record; no overlap with #62 cache region.
- feedback_no_hardcoding: zero MDX-sample-specific literals; classifier
  dispatch by SDK type, not by string parsing.
- feedback_artifact_status_naming: operational toast scoped to alert axis,
  not overall PASS signal.

Tests:
- Targeted u1+u2+u3+u4: 63 passed
- u5 vitest (Front/): 10/10 passed
- tests/phase_z2_ai_fallback dir regression: 240 passed
- tests/phase_z2 dir regression: 323 passed
- IMP-92-adjacent (-k "imp47b or ai_fallback or preflight or step12 or step0"): 299 passed (808 deselected)
- u1 baseline lock (test_client_mock.py): 8 passed
Zero failures, zero regressions outside scope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Front/client/src/services/designAgentApi.ts

@@ -235,6 +235,15 @@ export interface AiRepairStatus {
     unsupported_kind: number;
     error: number;
   };
+  // IMP-92 u3 — per-kind operational error aggregates plumbed from Step 12
+  // (u2 classify_operational_error). Optional for backward compatibility
+  // with pre-u3 payloads — u5 formatter treats absence as silent.
+  api_error_kinds?: {
+    quota: number;
+    billing: number;
+    auth: number;
+    other: number;
+  };
   unsupported_kind_records: Array<{
     unit_index?: number | null;
     source_section_ids: string[];
@@ -244,6 +253,8 @@ export interface AiRepairStatus {
     unit_index?: number | null;
     source_section_ids: string[];
     error: string;
+    // IMP-92 u3 — per-record operational error kind (quota|billing|auth|other|null).
+    api_error_kind?: string | null;
   }>;
   coverage_status: string;
   dropped_section_ids: string[];
@@ -267,23 +278,32 @@ export interface RunMeta {
   ai_repair_status: AiRepairStatus | null;
 }
 
+// IMP-92 u5 — Operational-only AI repair message formatter.
+//
+// Per the #84 operational-vs-non-operational replacement-plan contract, this
+// returns a user-visible toast string ONLY when ai_repair_status carries one
+// of the three actionable Anthropic API error kinds plumbed by u3
+// (quota / billing / auth). Non-operational AI failures (validation,
+// coverage_violated, unsupported_kind, or generic "other" API errors) return
+// null so the auto-pipeline stays silent per feedback_auto_pipeline_first.
+// Messages mirror the issue body copy contract exactly (429/402/401 →
+// quota/billing/auth Korean strings).
 export function formatAiRepairHumanReviewMessage(
   ai: AiRepairStatus | null | undefined,
 ): string | null {
-  if (!ai || !ai.human_review_required) return null;
-  if (ai.status === "error") {
-    const n = ai.counts?.error ?? ai.error_records?.length ?? 0;
-    return `AI 재구성 호출 실패 (${n}건) — 다른 frame 선택 또는 수동 편집 필요`;
+  if (!ai) return null;
+  const kinds = ai.api_error_kinds;
+  if (!kinds) return null;
+  if (kinds.quota > 0) {
+    return `API quota 부족 — 충전 필요 (${kinds.quota}건)`;
   }
-  if (ai.status === "coverage_violated") {
-    const dropped = (ai.dropped_section_ids || []).join(", ");
-    return `AI 재구성 후 콘텐츠 누락 (dropped: ${dropped || "?"}) — 다른 frame 선택 또는 수동 편집 필요`;
+  if (kinds.billing > 0) {
+    return `API billing 문제 — 결제 정보 확인 (${kinds.billing}건)`;
   }
-  if (ai.status === "unsupported_kind") {
-    const n = ai.counts?.unsupported_kind ?? ai.unsupported_kind_records?.length ?? 0;
-    return `AI 제안 형식 미지원 (${n}건) — 다른 frame 선택 또는 수동 편집 필요`;
+  if (kinds.auth > 0) {
+    return `API key 무효 — .env 확인 (${kinds.auth}건)`;
   }
-  return `AI 재구성 human_review 필요 (status: ${ai.status})`;
+  return null;
 }
 
 export interface LoadRunResult {