fix(claude): forward client-negotiated thinking-binding-controls and thinking-display-updates betas (#12989)

* fix(claude): forward client-negotiated thinking-binding-controls and thinking-display-updates betas

Gateways drops anthropic-beta tokens not on FORWARDABLE_CLIENT_BETAS, so
@ai-sdk/anthropic Fable 5.1 requests carrying thinking.block_binding were
rejected upstream with thinking.adaptive.block_binding: Extra inputs are
not permitted even when the client negotiated
thinking-binding-controls-2026-08-01 correctly. Same class for
thinking.display updates (thinking-display-updates-2026-08-18).

Regression guard: tests/unit/thinking-binding-controls-beta-forward.test.ts

* chore(changelog): fragment for #12989

* chore: trim comments

changelog.d/fixes/12989-thinking-binding-controls-beta-forward.md

@@ -0,0 +1 @@
+- **fix(claude):** forward client-negotiated `thinking-binding-controls-2026-08-01` and `thinking-display-updates-2026-08-18` betas so Fable 5.1 `thinking.block_binding` / `thinking.display` requests are no longer rejected upstream with `Extra inputs are not permitted` ([#12989](https://github.com/diegosouzapw/OmniRoute/pull/12989))

open-sse/config/anthropicHeaders.ts

@@ -65,6 +65,10 @@ export const FORWARDABLE_CLIENT_BETAS = Object.freeze([
   // gate (#9505), so a client that sent it must keep it through the merge —
   // otherwise its effort negotiation is silently dropped.
   "effort-2025-11-24",
+  // Fable 5.1 betas (@ai-sdk/anthropic sends both automatically): without them
+  // upstream rejects `thinking.block_binding` / `thinking.display` with 400.
+  "thinking-binding-controls-2026-08-01",
+  "thinking-display-updates-2026-08-18",
 ]);
 
 /**

tests/unit/thinking-binding-controls-beta-forward.test.ts

@@ -0,0 +1,69 @@
+/**
+ * Fable 5.1 sends `thinking.block_binding` + `thinking-binding-controls-2026-08-01`
+ * (and `thinking.display` + `thinking-display-updates-2026-08-18`) automatically.
+ * The gateway stripped both betas, so upstream 400'd with `Extra inputs are not
+ * permitted`. Both must be forwarded when the client negotiates them.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { ANTHROPIC_BETA_API_KEY, mergeClientAnthropicBeta, FORWARDABLE_CLIENT_BETAS } =
+  await import("../../open-sse/config/anthropicHeaders.ts");
+
+const BINDING_CONTROLS = "thinking-binding-controls-2026-08-01";
+const DISPLAY_UPDATES = "thinking-display-updates-2026-08-18";
+
+// ── allowlist membership ────────────────────────────────────────────────────
+
+test("FORWARDABLE_CLIENT_BETAS must include thinking-binding-controls beta", () => {
+  assert.ok(FORWARDABLE_CLIENT_BETAS.includes(BINDING_CONTROLS));
+});
+
+test("FORWARDABLE_CLIENT_BETAS must include thinking-display-updates beta", () => {
+  assert.ok(FORWARDABLE_CLIENT_BETAS.includes(DISPLAY_UPDATES));
+});
+
+// ── client-negotiated beta forwarding ───────────────────────────────────────
+
+test("mergeClientAnthropicBeta must forward client-negotiated thinking-binding-controls beta", () => {
+  const out = mergeClientAnthropicBeta(
+    ANTHROPIC_BETA_API_KEY,
+    `claude-code-20250219,${BINDING_CONTROLS}`
+  );
+  const tokens = out.split(",").map((s) => s.trim());
+  assert.ok(tokens.includes(BINDING_CONTROLS), `client beta dropped: ${out}`);
+});
+
+test("mergeClientAnthropicBeta must forward client-negotiated thinking-display-updates beta", () => {
+  const out = mergeClientAnthropicBeta(
+    ANTHROPIC_BETA_API_KEY,
+    `claude-code-20250219,${DISPLAY_UPDATES}`
+  );
+  const tokens = out.split(",").map((s) => s.trim());
+  assert.ok(tokens.includes(DISPLAY_UPDATES), `client beta dropped: ${out}`);
+});
+
+test("mergeClientAnthropicBeta forwards both betas together without duplication", () => {
+  const out = mergeClientAnthropicBeta(
+    `${ANTHROPIC_BETA_API_KEY},${BINDING_CONTROLS}`,
+    `claude-code-20250219,${BINDING_CONTROLS},${DISPLAY_UPDATES}`
+  );
+  const tokens = out.split(",").map((s) => s.trim());
+  assert.ok(tokens.includes(BINDING_CONTROLS), `binding-controls missing: ${out}`);
+  assert.ok(tokens.includes(DISPLAY_UPDATES), `display-updates missing: ${out}`);
+  assert.equal(
+    tokens.filter((t) => t.toLowerCase() === BINDING_CONTROLS).length,
+    1,
+    `binding-controls duplicated: ${out}`
+  );
+});
+
+// ── guard: allowlist still closed ───────────────────────────────────────────
+
+test("mergeClientAnthropicBeta still ignores non-allowlisted client betas", () => {
+  const out = mergeClientAnthropicBeta(
+    ANTHROPIC_BETA_API_KEY,
+    "some-random-future-beta-2099-01-01"
+  );
+  assert.ok(!out.includes("some-random-future-beta"), `unknown beta leaked: ${out}`);
+});