feat: implement thinking configuration resolution and variant mapping

src/core/request/thinking.ts

@@ -0,0 +1,56 @@
+type RawBody = {
+  variant?: unknown
+  providerOptions?: {
+    variant?: unknown
+    modelVariant?: unknown
+    thinkingConfig?: {
+      thinkingBudget?: unknown
+    }
+  }
+}
+
+export type ThinkingVariant = 'low' | 'medium' | 'high' | 'max'
+
+export function resolveThinkingConfig(
+  model: string,
+  body: unknown,
+  defaults: { budget: number } = { budget: 20000 }
+): { enabled: boolean; budget: number; variant?: string } {
+  const b = (body || {}) as RawBody
+
+  const rawVariant =
+    (typeof b.variant === 'string' && b.variant) ||
+    (typeof b.providerOptions?.variant === 'string' && b.providerOptions.variant) ||
+    (typeof b.providerOptions?.modelVariant === 'string' && b.providerOptions.modelVariant) ||
+    undefined
+
+  const explicitBudget = b.providerOptions?.thinkingConfig?.thinkingBudget
+  const budgetFromBody =
+    typeof explicitBudget === 'number' && Number.isFinite(explicitBudget) && explicitBudget > 0
+      ? explicitBudget
+      : undefined
+
+  const budgetFromVariant = variantToBudget(rawVariant)
+  const enabled =
+    model.endsWith('-thinking') ||
+    budgetFromBody !== undefined ||
+    b.providerOptions?.thinkingConfig !== undefined ||
+    budgetFromVariant !== undefined
+
+  return {
+    enabled,
+    budget: budgetFromBody ?? budgetFromVariant ?? defaults.budget,
+    variant: rawVariant
+  }
+}
+
+function variantToBudget(rawVariant: string | undefined): number | undefined {
+  if (!rawVariant) return undefined
+
+  const v = rawVariant.toLowerCase()
+  if (v === 'low') return 8192
+  if (v === 'medium') return 16384
+  // "high" is the documented name, but "max" is kept as backward compat
+  if (v === 'high' || v === 'max') return 32768
+  return undefined
+}

test/thinking.test.js

@@ -0,0 +1,30 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+
+import { resolveThinkingConfig } from '../dist/core/request/thinking.js'
+
+test('resolveThinkingConfig: model suffix enables thinking with default budget', () => {
+  const r = resolveThinkingConfig('claude-sonnet-4-5-thinking', {})
+  assert.equal(r.enabled, true)
+  assert.equal(r.budget, 20000)
+})
+
+test('resolveThinkingConfig: explicit thinkingConfig takes precedence', () => {
+  const r = resolveThinkingConfig('claude-sonnet-4-5', {
+    providerOptions: { thinkingConfig: { thinkingBudget: 12345 } }
+  })
+  assert.equal(r.enabled, true)
+  assert.equal(r.budget, 12345)
+})
+
+test('resolveThinkingConfig: variant low/medium/high maps to budgets', () => {
+  assert.equal(resolveThinkingConfig('claude-sonnet-4-5', { variant: 'low' }).budget, 8192)
+  assert.equal(resolveThinkingConfig('claude-sonnet-4-5', { variant: 'medium' }).budget, 16384)
+  assert.equal(resolveThinkingConfig('claude-sonnet-4-5', { variant: 'high' }).budget, 32768)
+})
+
+test('resolveThinkingConfig: max is accepted as backward-compatible alias of high', () => {
+  const r = resolveThinkingConfig('claude-sonnet-4-5', { providerOptions: { variant: 'max' } })
+  assert.equal(r.enabled, true)
+  assert.equal(r.budget, 32768)
+})