fix(gateway): preserve Fable 1M picker selection

src/claude/model-info.ts

@@ -143,14 +143,19 @@ export function buildAnthropicModelInfos(
   // the auto-context widening that let a 372K route carry the marker (and be
   // over-filled) is the #854 defect and does not come back. Guards (audit R1#11):
   // same dedupe set, never double-suffix.
-  const push1mVariant = (base: AnthropicModelInfo, contextWindow: number | undefined, maxInputTokens?: number) => {
+  const push1mVariant = (
+    base: AnthropicModelInfo,
+    contextWindow: number | undefined,
+    maxInputTokens?: number,
+    selectorId?: string,
+  ) => {
     // The [1m] marker makes Claude Code account 1e6 tokens for the row, so it
     // may only name models whose AUTHORITATIVE effective window is >= 1M —
     // never the auto-context widening, which would mark a 372K route and have
     // Claude Code over-fill it (the #854 defect).
     if (contextWindow === undefined || contextWindow < ONE_MILLION) return;
     if (base.id.includes("[1m]")) return;
-    const id = `${base.id}[1m]`;
+    const id = selectorId ?? `${base.id}[1m]`;
     if (seen.has(id)) return;
     seen.add(id);
     // The marker fixes Claude Code's accounting at 1e6, but a model may accept less input
@@ -220,7 +225,15 @@ export function buildAnthropicModelInfos(
     out.push(info);
     // Anthropic passthrough guard (audit 021 #3): never auto-widen canonical claude
     // routes — only a genuine >=1M window earns the variant row there.
-    push1mVariant(info, m.contextWindow, routedMaxInput);
+    // Claude Code groups canonical Fable ids before it compares the [1m] marker. This
+    // reversible alias only separates picker families; it is not an OpenAI-native route.
+    // The Messages ingress restores the canonical Anthropic id before passthrough.
+    const oneMillionSelector = idStyle === "readable"
+      && m.provider === "anthropic"
+      && listedModelId.startsWith("claude-fable-")
+      ? `${claudeCodeNativeAlias(listedModelId)}[1m]`
+      : undefined;
+    push1mVariant(info, m.contextWindow, routedMaxInput, oneMillionSelector);
     // The whole model is passed, not a (provider, id) pair: a combo row lives in its own
     // namespace with no config.providers entry, so the caller classifies it from the
     // aggregated supportsServiceTier the row already carries.

src/server/claude-messages.ts

@@ -12,6 +12,7 @@ import { enforceAnthropicImageLimits, sniffImageDimensions } from "../adapters/a
 import { normalizeAnthropicImages } from "../adapters/anthropic-image-normalize";
 import { AnthropicRequestError, anthropicToResponsesTranslation, extractOcxEffortDirective, extractOcxRouteDirective, resolveInboundModel, type ClaudeCacheKeySource } from "../claude/inbound";
 import { resolveDesktop3pAlias } from "../claude/desktop-3p";
+import { claudeCodeNativeAlias } from "../claude/alias";
 import { recordDesktopRequest } from "../claude/desktop-health";
 import { stripOneMillionMarker } from "../claude/context-windows";
 import { captureClaudeInbound } from "../claude/inbound-debug";
@@ -79,6 +80,13 @@ function decodeClaudeFastSelector(raw: string, cc?: OcxConfig["claudeCode"]): st
   return decodedBase === bare ? exact : `${decodedBase}--fast`;
 }
 
+/** Restore the reversible Fable picker alias before Anthropic passthrough checks. */
+function decodeFablePickerAlias(raw: string, cc?: OcxConfig["claudeCode"]): string {
+  const decoded = resolveInboundModel(raw, cc);
+  if (!decoded.startsWith("claude-fable-")) return raw;
+  return claudeCodeNativeAlias(decoded) === raw ? decoded : raw;
+}
+
 function isRec(v: unknown): v is Rec {
   return !!v && typeof v === "object" && !Array.isArray(v);
 }
@@ -649,6 +657,9 @@ async function handleClaudeMessagesWithBudget(
         effortOverride = extractOcxEffortDirective(anthropicBody);
       }
     }
+    if (isRec(anthropicBody) && typeof anthropicBody.model === "string") {
+      anthropicBody.model = decodeFablePickerAlias(anthropicBody.model, config.claudeCode);
+    }
     if (isRec(anthropicBody) && typeof anthropicBody.model === "string") {
       requestedModel = anthropicBody.model;
       // Decode for Fast only. A Claude alias is `claude-ocx-<provider>--<model>`, so it
@@ -1079,6 +1090,8 @@ export async function handleClaudeCountTokens(
     model = stripOneMillionMarker(countRoute);
     raw.model = model;
   }
+  model = decodeFablePickerAlias(model, config.claudeCode);
+  raw.model = model;
   // Fast-only: count_tokens never parsed an effort row, so it must not start. It returns a
   // token estimate and sends no tier, so only the IDENTITY is corrected - without this the
   // synthetic id reaches native passthrough as a model Anthropic has never heard of.

tests/claude-integration/claude-model-info.test.ts

@@ -44,6 +44,22 @@ describe("anthropic-flavor ModelInfo discovery entries (devlog 130 B4b)", () =>
     expect(info!.capabilities.effort.max.supported).toBe(true);
   });
 
+  test("readable Fable rows keep base and 1M selections distinct in Claude Code", () => {
+    const infos = buildAnthropicModelInfos([], [{
+      provider: "anthropic",
+      id: "claude-fable-5-1",
+      contextWindow: 1_000_000,
+      maxInputTokens: 1_000_000,
+    }], undefined, "readable");
+
+    expect(infos.map(info => info.id)).toEqual([
+      "claude-fable-5-1",
+      "claude-ocx-native--claude-fable-5-1[1m]",
+    ]);
+    expect(infos[1]!.display_name).toBe("claude-fable-5-1 (anthropic) · 1M");
+    expect(infos[1]!.max_input_tokens).toBe(1_000_000);
+  });
+
   test("native effective ladder only advertises clamp-identity rungs (audit R4#1)", () => {
     for (const slug of ["gpt-5.5", "gpt-5.4", "gpt-5.6-sol"]) {
       for (const rung of nativeEffectiveLadder(slug)) {

tests/claude-integration/claude-native-passthrough.test.ts

@@ -206,6 +206,47 @@ test("count_tokens passes through with native credentials", async () => {
   }
 });
 
+test("Fable 1M picker alias preserves native passthrough on both Messages endpoints", async () => {
+  const captured: Captured[] = [];
+  const upstream = mockAnthropicUpstream(captured);
+  saveConfig(cfg(upstream.url.toString().replace(/\/$/, "")));
+  const server = startServer(0);
+  const pickerModel = "claude-ocx-native--claude-fable-5-1";
+  try {
+    const messagesWithoutMarker = await fetch(new URL("/v1/messages", server.url), {
+      method: "POST",
+      headers: OAUTH_HEADERS,
+      body: JSON.stringify({ ...claudeBody(), model: pickerModel }),
+    });
+    expect(messagesWithoutMarker.status).toBe(200);
+    await messagesWithoutMarker.text();
+
+    const messagesWithMarker = await fetch(new URL("/v1/messages", server.url), {
+      method: "POST",
+      headers: OAUTH_HEADERS,
+      body: JSON.stringify({ ...claudeBody(), model: `${pickerModel}[1m]` }),
+    });
+    expect(messagesWithMarker.status).toBe(200);
+    await messagesWithMarker.text();
+
+    const countTokens = await fetch(new URL("/v1/messages/count_tokens", server.url), {
+      method: "POST",
+      headers: OAUTH_HEADERS,
+      body: JSON.stringify({ model: `${pickerModel}[1m]`, messages: [{ role: "user", content: "hi" }] }),
+    });
+    expect(countTokens.status).toBe(200);
+    expect(await countTokens.json()).toEqual({ input_tokens: 4242 });
+
+    expect(captured).toHaveLength(3);
+    expect(captured[0]!.body.model).toBe("claude-fable-5-1");
+    expect(captured[1]!.body.model).toBe("claude-fable-5-1");
+    expect(captured[2]!.body.model).toBe("claude-fable-5-1");
+  } finally {
+    await server.stop(true);
+    upstream.stop(true);
+  }
+});
+
 test("exposed native passthrough requires dedicated admission and never forwards admission credentials", async () => {
   const admissionSecret = "sk-ant-api03-key";
   const providerBearer = "sk-ant-oat01-provider";