fix(anthropic): resolve model aliases for anthropic_native provider

[xuandung38]

Problem

When an agent is configured with a short model alias (e.g. "opus", "sonnet", "haiku") and uses the anthropic_native provider, the alias is sent verbatim to the Anthropic API, resulting in a HTTP 404 not_found_error:

LLM call failed (iteration 1): HTTP 404: anthropic: {"type":"error","error":{"type":"not_found_error","message":"model: opus"}}

Short aliases are only valid for the Claude CLI provider, which handles them internally. The AnthropicProvider lacked equivalent resolution.

Solution

Added resolveAnthropicModel() in internal/providers/anthropic.go — a small helper that expands short aliases to full Anthropic model IDs before the API call. Both Chat() and ChatStream() now go through this resolver.

Alias map:

Alias	Resolved model ID
opus	claude-opus-4-6
sonnet	claude-sonnet-4-6
haiku	claude-haiku-4-5-20251001

Full model IDs (e.g. claude-sonnet-4-5-20250929) are passed through unchanged — no breaking change.

Files changed

• internal/providers/anthropic.go — added claudeModelAliases map + resolveAnthropicModel(), updated Chat()
• internal/providers/anthropic_stream.go — updated ChatStream() to use the resolver