fix(pi): Claude Code billing rejection and missing claude-opus-5

packages/pi/README.md

@@ -2,7 +2,7 @@
 
 Pi package for CortexKit Anthropic OAuth support. It overrides Pi's built-in `anthropic` provider with a CortexKit provider extension backed by the shared `@cortexkit/anthropic-auth-core` package.
 
-The Pi provider catalog includes Claude Fable 5 (`claude-fable-5`), limited-access Claude Mythos 5 (`claude-mythos-5`), Claude Opus 4.8, Claude Opus 4.5, Claude Sonnet 4.5, and Claude Sonnet 5 (`claude-sonnet-5`). Fable/Mythos reasoning uses Anthropic adaptive thinking with `thinking.display: "summarized"` and `output_config.effort`; the package does not send rejected manual `thinking.budget_tokens` for those models.
+The Pi provider catalog includes Claude Fable 5 (`claude-fable-5`), limited-access Claude Mythos 5 (`claude-mythos-5`), Claude Opus 5 (`claude-opus-5`), Claude Opus 4.8, Claude Opus 4.5, Claude Sonnet 4.5, and Claude Sonnet 5 (`claude-sonnet-5`). Fable/Mythos reasoning uses Anthropic adaptive thinking with `thinking.display: "summarized"` and `output_config.effort`; the package does not send rejected manual `thinking.budget_tokens` for those models.
 
 This package is part of the CortexKit Anthropic Auth monorepo, which supports both OpenCode (`@cortexkit/opencode-anthropic-auth`) and Pi (`@cortexkit/pi-anthropic-auth`) through the same shared core logic.
 

packages/pi/src/convert.ts

@@ -391,7 +391,24 @@ export async function buildAnthropicRequest(
     { type: 'text', text: CLAUDE_CODE_IDENTITY },
   ]
   if (context.systemPrompt?.trim()) {
-    system.push({ type: 'text', text: sanitize(context.systemPrompt) })
+    // Anthropic validates system[] for OAuth requests using Claude Code
+    // billing. Third-party system content alongside the identity block is
+    // rejected with 400 "You're out of extra usage". Keep only the billing
+    // header and identity in system[], and relocate Pi's prompt to the first
+    // user message, where it is functionally equivalent.
+    const prompt = sanitize(context.systemPrompt)
+    const firstUser = messages.find((m) => m.role === 'user')
+    const content = firstUser?.content
+    if (firstUser && typeof content === 'string') {
+      firstUser.content = `${prompt}\n\n${content}`
+    } else if (firstUser && Array.isArray(content)) {
+      content.unshift({ type: 'text', text: prompt })
+    }
+    // No else: with no user message, messages[] is necessarily empty
+    // (convertMessages emits only user/assistant, and trailing assistants are
+    // stripped above), so the request is already invalid. Pushing the prompt
+    // into system[] there would recreate the rejected three-entry shape for
+    // no benefit, so the prompt is dropped instead.
   }
 
   const body: AnthropicRequestBody = {

packages/pi/src/index.ts

@@ -80,6 +80,15 @@ export default function cortexKitPiAnthropicAuth(pi: ExtensionAPI) {
         contextWindow: CLAUDE_FABLE_MYTHOS_5_CONTEXT_WINDOW,
         maxTokens: CLAUDE_FABLE_MYTHOS_5_MAX_OUTPUT_TOKENS,
       })),
+      {
+        id: 'claude-opus-5',
+        name: 'Claude Opus 5',
+        reasoning: true,
+        input: textImageInput(),
+        cost: { input: 5, output: 25, cacheRead: 0.5, cacheWrite: 6.25 },
+        contextWindow: 1_000_000,
+        maxTokens: 128_000,
+      },
       {
         id: 'claude-opus-4-8',
         name: 'Claude Opus 4.8',

packages/pi/src/tests/convert.test.ts

@@ -33,10 +33,14 @@ function toolResultMsg(toolCallId: string, text: string): Message {
 
 const defaultCache = { enabled: false, mode: 'hybrid' as const }
 
-async function buildMessages(messages: Message[]) {
+// systemPrompt is opt-in. buildAnthropicRequest relocates a non-empty prompt
+// onto the first user message, so tests that assert raw conversion output pass
+// no prompt and observe messages unchanged. The relocation itself is covered by
+// the "Claude Code system[] shape" block below.
+async function buildMessages(messages: Message[], systemPrompt?: string) {
   const context = {
     messages,
-    systemPrompt: 'test',
+    systemPrompt,
     tools: [],
   }
   const { body } = await buildAnthropicRequest(
@@ -326,6 +330,76 @@ describe('convertMessages — empty base64 image guard', () => {
   })
 })
 
+describe('buildAnthropicRequest — Claude Code system[] shape', () => {
+  // Anthropic rejects OAuth requests carrying Claude Code billing headers when
+  // third-party system content sits in system[] alongside the identity block.
+  // These cases pin the resulting shape: system[] holds only the billing header
+  // and the identity block, and Pi's prompt rides on the first user message.
+  async function buildBody(messages: Message[], systemPrompt?: string) {
+    const { body } = await buildAnthropicRequest(
+      'claude-sonnet-4-20250514',
+      { messages, systemPrompt, tools: [] } as any,
+      undefined,
+      defaultCache,
+    )
+    return body
+  }
+
+  test('keeps system[] to the billing header and identity block', async () => {
+    const body = await buildBody([userMsg('hello')], 'PI PROMPT')
+    expect(body.system).toHaveLength(2)
+    expect(JSON.stringify(body.system)).not.toContain('PI PROMPT')
+  })
+
+  test('prepends the prompt to a string first user message', async () => {
+    const body = await buildBody([userMsg('hello')], 'PI PROMPT')
+    expect(body.messages[0]).toEqual({
+      role: 'user',
+      content: 'PI PROMPT\n\nhello',
+    })
+  })
+
+  test('prepends a text block when the first user message is structured', async () => {
+    const body = await buildBody(
+      [
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: 'see image' },
+            { type: 'image', mimeType: 'image/png', data: 'aGVsbG8=' },
+          ],
+          timestamp: 0,
+        } as Message,
+      ],
+      'PI PROMPT',
+    )
+    const content = body.messages[0]?.content as Array<Record<string, unknown>>
+    expect(content).toHaveLength(3)
+    expect(content[0]).toEqual({ type: 'text', text: 'PI PROMPT' })
+  })
+
+  test('drops the prompt when there is no user message to carry it', async () => {
+    const body = await buildBody([assistantMsg('only assistant')], 'PI PROMPT')
+    // convertMessages emits only user/assistant and trailing assistants are
+    // stripped, so a conversation with no user message converts to empty.
+    // system[] must stay at two entries even on this path.
+    expect(body.messages).toHaveLength(0)
+    expect(body.system).toHaveLength(2)
+    expect(JSON.stringify(body.system)).not.toContain('PI PROMPT')
+  })
+
+  test('leaves the identity block as the last system entry for cache anchoring', async () => {
+    const body = await buildBody([userMsg('hello')], 'PI PROMPT')
+    expect(String(body.system?.at(-1)?.text)).toContain('Claude Code')
+  })
+
+  test('leaves system[] and messages untouched when no prompt is set', async () => {
+    const body = await buildBody([userMsg('hello')])
+    expect(body.system).toHaveLength(2)
+    expect(body.messages[0]).toEqual({ role: 'user', content: 'hello' })
+  })
+})
+
 describe('buildAnthropicRequest — Fable/Mythos thinking', () => {
   test('maps Pi reasoning to output_config effort for Claude Fable 5', async () => {
     const { body } = await buildAnthropicRequest(

packages/pi/src/tests/index.test.ts

@@ -44,4 +44,23 @@ describe('cortexKitPiAnthropicAuth provider registration', () => {
       maxTokens: 128_000,
     })
   })
+
+  test('exposes Claude Opus 5 in the Pi Anthropic catalog', () => {
+    const { pi, providers } = mockPi()
+
+    cortexKitPiAnthropicAuth(pi)
+
+    const opus5 = providers
+      .get('anthropic')
+      ?.models?.find((model) => model.id === 'claude-opus-5')
+    expect(opus5).toMatchObject({
+      id: 'claude-opus-5',
+      name: 'Claude Opus 5',
+      reasoning: true,
+      input: ['text', 'image'],
+      cost: { input: 5, output: 25, cacheRead: 0.5, cacheWrite: 6.25 },
+      contextWindow: 1_000_000,
+      maxTokens: 128_000,
+    })
+  })
 })