Vendor OpenClaw source as Adolf fork baseline

Adolf is a fork/vendored clone of github.com/openclaw/openclaw (v2026.6.11),
free to diverge. Tree copied sans upstream .git; upstream remote added for
future syncs. Node pinned to 24 (.nvmrc); engines already require >=22.19.
Preserves docs/ARCHITECTURE.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LeqyaxJF2nbRXJtae2kNB2

packages/ai/src/providers/anthropic-server-fallback.ts

@@ -0,0 +1,83 @@
+import type { AssistantMessageDiagnostic } from "../types.js";
+
+/** Anthropic beta that re-serves safety refusals on an allowed fallback model. */
+export const ANTHROPIC_SERVER_SIDE_FALLBACK_BETA = "server-side-fallback-2026-06-01";
+
+// Anthropic documents claude-opus-4-8 as the allowed fallback for claude-fable-5.
+export const CLAUDE_FABLE_5_FALLBACK_MODEL = "claude-opus-4-8";
+
+// Fallback-served turns bill at the serving model's rates.
+export const CLAUDE_FABLE_5_FALLBACK_MODEL_COST = {
+  input: 5,
+  output: 25,
+  cacheRead: 0.5,
+  cacheWrite: 6.25,
+} as const;
+
+export function buildAnthropicServerSideFallbacks(): Array<{ model: string }> {
+  return [{ model: CLAUDE_FABLE_5_FALLBACK_MODEL }];
+}
+
+export type AnthropicFallbackBoundary = {
+  fromModel: string | null;
+  toModel: string | null;
+};
+
+function readBoundaryModel(value: unknown): string | null {
+  if (!value || typeof value !== "object") {
+    return null;
+  }
+  const model = (value as { model?: unknown }).model;
+  return typeof model === "string" && model.trim() ? model : null;
+}
+
+/** Reads a `fallback` content block marking where one model's output gives way to the next. */
+export function readAnthropicFallbackBoundary(block: unknown): AnthropicFallbackBoundary | null {
+  if (!block || typeof block !== "object") {
+    return null;
+  }
+  const record = block as { type?: unknown; from?: unknown; to?: unknown };
+  if (record.type !== "fallback") {
+    return null;
+  }
+  return {
+    fromModel: readBoundaryModel(record.from),
+    toModel: readBoundaryModel(record.to),
+  };
+}
+
+/**
+ * Drops pre-fallback thinking/tool calls while preserving the text prefix that
+ * the serving model continued. Dropped tool calls must never execute or replay.
+ */
+export function applyAnthropicFallbackBoundary(params: {
+  output: {
+    content: Array<{ type: string }>;
+    responseModel?: string;
+    diagnostics?: AssistantMessageDiagnostic[];
+  };
+  boundary: AnthropicFallbackBoundary;
+  provider: string;
+}): void {
+  const { output, boundary } = params;
+  const survivors = output.content.filter((block) => block.type === "text");
+  for (const survivor of survivors) {
+    delete (survivor as { textSignature?: string }).textSignature;
+  }
+  output.content.splice(0, output.content.length, ...survivors);
+  if (boundary.toModel) {
+    output.responseModel = boundary.toModel;
+  }
+  output.diagnostics = [
+    ...(output.diagnostics ?? []),
+    {
+      type: "provider_fallback",
+      timestamp: Date.now(),
+      details: {
+        provider: params.provider,
+        fromModel: boundary.fromModel,
+        toModel: boundary.toModel,
+      },
+    },
+  ];
+}