feat(opencode): add Claude Code ACP runtime

[stocky789]

Issue for this PR

Related to #5182, #20002, and #24038.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds Claude Code as an OpenCode runtime through @agentclientprotocol/claude-agent-acp.

Selecting Claude Code from /models starts an ACP session in the current workspace and maps Claude's streamed text, reasoning, tool calls, permissions, questions, usage, compaction, and configuration updates into OpenCode's existing session and TUI. Claude-specific slash commands and effort/fast state are shown only while this runtime is selected.

Claude Code continues to own authentication and model execution; OpenCode does not read or manage subscription credentials.

This is a draft for architecture review and refactoring before it is marked ready.

How did you verify your code works?

• Installed and exercised the branch with an isolated HOME and fixture workspace.
• Verified Claude model selection and the /effort and /fast command surfaces in the TUI.
• bun typecheck passes in packages/opencode, packages/tui, and packages/app.
• Focused tests: 141 pass / 5 fail in packages/opencode; 19 pass in packages/tui; 7 pass in packages/app.
• Built the standalone Linux executable and verified all Claude ACP models are listed.

Known draft blockers: the five failing tests cover Windows-path handling when run on Linux, and an actual Claude prompt through the standalone executable currently exits with ACP connection closed. Both need to be resolved before this is ready for review.

Screenshots / recordings

Captured from the installed branch in an isolated fixture workspace.

Before — upstream dev has no Claude Code model result

After — Claude Code models in /models

Claude-specific slash commands

Claude /effort levels

Claude /fast toggle

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

The search results show only PR #41901 (the current PR) as the only exact match for Claude Code ACP runtime implementation. The other results like #29789 (Dynamic workflows) and #20491 (Kiro provider) are different features.

No duplicate PRs found

[stocky789]

Superseded by a replacement draft using the existing stocky789:claude-acp branch. No implementation change.