feat(provider): add OpenCode Go

[zhangmo8]

Summary

• add OpenCode Go as a built-in provider using the documented Go API endpoints
• fetch Go models from the live /models endpoint and route documented /messages models through the Anthropic runtime
• cover provider registration, model mapping, OpenAI-compatible routing, Anthropic routing, and Anthropic behavior presets

Validation

• pnpm run format
• pnpm run i18n
• pnpm run lint
• pnpm exec vitest run test/main/presenter/configPresenter/defaultProviders.test.ts test/main/presenter/llmProviderPresenter/basicApiKeyProviders.test.ts --pool=forks

Closes #1896

Summary by CodeRabbit

• New Features
  • Added built-in support for the OpenCode Go provider, including provider details, model discovery, and mixed routing for chat and messages models.
  • Certain models now automatically use the appropriate runtime based on their endpoint type.
• Documentation
  • Added feature plan, specification, and task-tracking docs for the new provider.
• Tests
  • Expanded coverage for provider setup, model mapping/classification, routing behavior, and improved fetch mocking isolation.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds an opencode-go built-in provider, wires mixed OpenAI-compatible and Anthropic routing, maps live /models metadata, and adds tests plus feature documentation.

Changes

OpenCode Go Provider

Layer / File(s)	Summary
Provider registration and strategy types src/main/presenter/configPresenter/providers.ts, src/main/presenter/llmProviderPresenter/providerRegistry.ts	Adds opencode-go to DEFAULT_PROVIDERS, extends model-source and route strategy unions, and registers the provider with its check and credential settings.
Routing and model mapping implementation src/main/presenter/llmProviderPresenter/providers/aiSdkProvider.ts	Adds the OpenCode Go Anthropic model allowlist, updates route selection, and implements model fetching/classification for OpenCode Go models.
Tests for provider definition, model mapping, and routing test/main/presenter/configPresenter/defaultProviders.test.ts, test/main/presenter/llmProviderPresenter/basicApiKeyProviders.test.ts	Adds coverage for provider metadata, model mapping from /models, and routing through OpenAI-compatible and Anthropic runtimes.
Feature planning documentation docs/features/opencode-go-provider/plan.md, docs/features/opencode-go-provider/spec.md, docs/features/opencode-go-provider/tasks.md	Adds planning, specification, and task-tracking docs for the OpenCode Go provider work.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant AiSdkProvider
  participant OpenAICompatibleRuntime
  participant AnthropicRuntime

  Client->>AiSdkProvider: request with modelId
  AiSdkProvider->>AiSdkProvider: resolveRouteDecision(modelId)
  alt modelId in OPENCODE_GO_ANTHROPIC_MODEL_IDS
    AiSdkProvider->>AnthropicRuntime: route via apiType anthropic, baseUrl
    AnthropicRuntime-->>Client: response
  else other model
    AiSdkProvider->>OpenAICompatibleRuntime: route via chat/completions
    OpenAICompatibleRuntime-->>Client: response
  end

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Possibly related issues

• [feature] OpenCode Go provider #1896: Implements the same OpenCode Go provider, live model discovery, and mixed OpenAI/Anthropic routing.

Possibly related PRs

• ThinkInAIXYZ/deepchat#1560: Shares the same model-fetching pipeline and model-metadata handling in aiSdkProvider.ts.
• ThinkInAIXYZ/deepchat#1788: Extends the same provider registration and routing infrastructure to add another provider entry.

Suggested reviewers: zerob13

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding OpenCode Go as a provider.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/opencode-go-provider

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