feat(model): add ARK SDK LLM and Embedding model support

[wucm667]

Description

Add native Volcengine ARK SDK integration for LLM and Embedding models, replacing the dependency on OpenAI-compatible HTTP endpoints for ARK services.

Changes

New files:

• model/ark.go — ARK SDK LLM implementation (chat completion, streaming, tool calls, reasoning content, thinking config)
• model/embedding.go — Embedder interface definition
• model/ark_embedding.go — ARK SDK embedding implementation
• model/convert.go — Shared conversion utilities extracted from openai.go
• model/ark_test.go — ARK LLM unit tests
• model/ark_embedding_test.go — ARK Embedding unit tests

Modified files:

• model/openai.go — Refactored to use shared utilities from convert.go
• agent/llmagent/agent.go — Support "ark" model provider via ModelProvider config
• configs/model.go — Add EmbeddingModelConfig struct
• configs/configs.go — Initialize EmbeddingModelConfig in global config
• common/defaults.go — Add embedding model defaults

Highlights

• ARK LLM: Uses volcengine-go-sdk/service/arkruntime directly, supporting AK/SK and API Key auth, thinking/reasoning config, streaming with tool call accumulation
• ARK Embedding: Implements Embedder interface with batch embedding, configurable dimensions
• Provider selection: agent/llmagent now routes to ARK or OpenAI model based on ModelProvider field (default: "openai")
• Refactor: Common logic (mapFinishReason, maybeAppendUserContent, convertFunctionParameters, etc.) extracted to model/convert.go for reuse

[Copilot]

Pull request overview

This PR adds native Volcengine ARK SDK integration for LLM and Embedding models, replacing reliance on OpenAI-compatible HTTP endpoints. The implementation introduces ARK-specific model providers while maintaining backward compatibility with the existing OpenAI implementation through a provider selection mechanism.

Changes:

• Introduces ARK SDK-based LLM and Embedding model implementations with support for API Key and AK/SK authentication
• Refactors shared conversion utilities from openai.go to model/convert.go for reuse across providers
• Adds provider-based routing in agent/llmagent to select between "ark" and "openai" (default) implementations

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
model/embedding.go	Defines the Embedder interface for text embedding models
model/convert.go	Extracts shared conversion utilities (finish reason mapping, function parameters, content extraction) for reuse
model/ark.go	Implements ARK SDK LLM with chat completion, streaming, tool calls, reasoning content support
model/ark_embedding.go	Implements ARK SDK embedding model with batch embedding and configurable dimensions
model/ark_test.go	Unit tests for ARK LLM covering authentication, generation, streaming, tool calls, and reasoning
model/ark_embedding_test.go	Unit tests for ARK embedding covering single/batch embedding, dimension override, and error handling
model/openai.go	Refactored to use shared utilities from convert.go, removing duplicate code
agent/llmagent/agent.go	Adds ModelProvider config field with switch-based routing to ARK or OpenAI models
configs/model.go	Adds EmbeddingModelConfig struct with dimension configuration and env variable mapping
configs/configs.go	Initializes EmbeddingModelConfig in global config structure
common/defaults.go	Defines embedding model default values (name, API base, dimensions)

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[sjy3]

please fix the ：model/ark.go:554:34: invalid operation: usage.PromptTokensDetails != nil (mismatched types "github.com/volcengine/volcengine-go-sdk/service/arkruntime/model".PromptTokensDetail and untyped nil)

[wucm667]

please fix the ：model/ark.go:554:34: invalid operation: usage.PromptTokensDetails != nil (mismatched types "github.com/volcengine/volcengine-go-sdk/service/arkruntime/model".PromptTokensDetail and untyped nil)

@sjy3 Fixed. PromptTokensDetails in the ARK SDK is a value type struct (PromptTokensDetail), not a pointer, so it cannot be compared with nil. Changed to check CachedTokens > 0 directly. Local CI verification passed (build, lint, tests all green).

[sjy3]

LGTM