Agent Skills: docx and pptx skills fail with 'stream ended without producing Message'

[tarik0]

Description

When using the Agent Skills beta feature via the container.skills parameter, the docx and pptx skills fail silently, causing the stream to end without producing a Message.

Environment

• SDK: @anthropic-ai/sdk (TypeScript)
• Model: claude-sonnet-4-5-20250929
• Beta headers: code-execution-2025-08-25,skills-2025-10-02

Working Skills

• pdf ✅
• xlsx ✅

Broken Skills

• docx ❌
• pptx ❌

Reproduction

// This works
const response = await client.messages.stream({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 4096,
  container: {
    skills: [{ type: 'anthropic', skill_id: 'pdf', version: 'latest' }]
  },
  tools: [{ type: 'code_execution_20250825', name: 'code_execution' }],
  messages: [{ role: 'user', content: 'Hello' }]
}, {
  headers: { 'anthropic-beta': 'code-execution-2025-08-25,skills-2025-10-02' }
});

// This fails with "stream ended without producing a Message with role=assistant"
const response = await client.messages.stream({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 4096,
  container: {
    skills: [{ type: 'anthropic', skill_id: 'docx', version: 'latest' }]
  },
  tools: [{ type: 'code_execution_20250825', name: 'code_execution' }],
  messages: [{ role: 'user', content: 'Hello' }]
}, {
  headers: { 'anthropic-beta': 'code-execution-2025-08-25,skills-2025-10-02' }
});

Test Matrix

Skills	Result
['pdf']	✅ Works
['xlsx']	✅ Works
['docx']	❌ Fails
['pptx']	❌ Fails
['pdf', 'xlsx']	✅ Works
['pdf', 'docx']	❌ Fails
['pdf', 'pptx']	❌ Fails
['pdf', 'xlsx', 'docx', 'pptx']	❌ Fails
[] (empty)	✅ Works

Expected Behavior

All documented Anthropic skills (pdf, xlsx, docx, pptx) should work as described in the Skills Guide.

Actual Behavior

Only pdf and xlsx skills work. Including docx or pptx in the skills array causes the API to fail without a proper error message.