fix(anthropic): clamp budget thinking to the model's real output maximum

src/adapters/anthropic.ts

@@ -1050,7 +1050,17 @@ export function createAnthropicAdapter(provider: OcxProviderConfig, cacheRetenti
           // always exceeds the budget within a model-safe ceiling, reserving room for visible output.
           const maxOut = parsed.options.maxOutputTokens ?? omittedMaxTokens;
           const wantBudget = reasoningBudget(effectiveReasoning);
-          const maxTokens = Math.min(REASONING_MAX_TOKENS_CEILING, Math.max(maxOut, wantBudget + OUTPUT_HEADROOM));
+          // Clamp to what the TARGET can emit, not to a flat 32k. REASONING_MAX_TOKENS_CEILING
+          // dates from Claude 4.x models that really stopped near 32k; Opus 4.6 and Sonnet 4.6
+          // document 128K and Haiku 4.5 64K, so the flat ceiling silently cut an explicit
+          // caller `max_tokens` to a quarter of what the model supports — the adaptive branch
+          // above honours the caller's figure, and this one did not. A provider that states the
+          // model's real maximum is more authoritative than the constant; it stays the fallback
+          // for a target whose ceiling is unknown.
+          const modelCeiling = typeof configuredMaxOut === "number" && configuredMaxOut > 0
+            ? configuredMaxOut
+            : REASONING_MAX_TOKENS_CEILING;
+          const maxTokens = Math.min(modelCeiling, Math.max(maxOut, wantBudget + OUTPUT_HEADROOM));
           const budget = Math.max(MIN_THINKING_BUDGET, Math.min(wantBudget, maxTokens - OUTPUT_FLOOR));
           body.max_tokens = maxTokens;
           body.thinking = { type: "enabled", budget_tokens: budget };

tests/adapters/anthropic/anthropic-reasoning.test.ts

@@ -287,6 +287,32 @@ describe("anthropic extended-thinking gate", () => {
     expect(b.max_tokens as number).toBe(64000);
   });
 
+  // The adaptive branch above already honours an explicit limit above 32k. Budget thinking did
+  // not: it clamped to a flat REASONING_MAX_TOKENS_CEILING (32000) even for Opus 4.6 and Sonnet
+  // 4.6, which document 128K output, so a caller asking for 128000 silently got a quarter of it.
+  test("budget thinking clamps to the model's real maximum, not a flat 32k", async () => {
+    const seeded = {
+      ...provider,
+      defaultMaxOutputTokens: 64_000,
+      modelMaxOutputTokens: { "claude-opus-4-6": 128_000, "claude-sonnet-4-6": 128_000 },
+    };
+    for (const modelId of ["claude-opus-4-6", "claude-sonnet-4-6"]) {
+      for (const asked of [undefined, 128_000]) {
+        const b = await bodyOf(parsed("high", asked === undefined ? {} : { maxOutputTokens: asked }, modelId), seeded);
+        expect(b.max_tokens as number, modelId).toBe(128_000);
+        expect(b.max_tokens as number).toBeGreaterThan((b.thinking as { budget_tokens: number }).budget_tokens);
+      }
+    }
+    // Haiku 4.5 really is 64K, so it must be capped there rather than raised to 128000.
+    const haiku = await bodyOf(parsed("high", { maxOutputTokens: 128_000 }, "claude-haiku-4-5"), seeded);
+    expect(haiku.max_tokens as number).toBe(64_000);
+    // A small explicit limit is still only lifted to budget+headroom, exactly as before.
+    expect((await bodyOf(parsed("high", { maxOutputTokens: 10_000 }, "claude-opus-4-6"), seeded)).max_tokens).toBe(24_576);
+    // With no configured maxima the flat 32k ceiling remains the fallback.
+    const bare = { adapter: "anthropic", baseUrl: "https://api.anthropic.com", apiKey: "sk-x", authMode: "apiKey" } as unknown as OcxProviderConfig;
+    expect((await bodyOf(parsed("high", { maxOutputTokens: 128_000 }, "claude-opus-4-6"), bare)).max_tokens).toBe(32_000);
+  });
+
   test("configured provider output budget replaces the 8192 default when the caller omits max_output_tokens", async () => {
     const budgeted = { ...provider, defaultMaxOutputTokens: 64_000, modelMaxOutputTokens: { "claude-fable-5": 32_000 } };
     // No reasoning: the configured budget is the wire max_tokens.