[FEATURE]: Export LSP functionality through @opencode-ai/plugin for custom tools #4410

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Problem

We have very specific requirements for code changes and have built a custom tool in .opencode/tool/ for this purpose. Currently, the LSP module (packages/opencode/src/lsp/index.ts) is only available to opencode's built-in tools and cannot be accessed by custom tools created via @opencode-ai/plugin.

Built-in tools like edit, write and lsp_diagnostics use LSP functions to validate code changes:

await LSP.touchFile(filePath, true)  
const diagnostics = await LSP.diagnostics()

The lsp_diagnostics tool would be a good candidate to work around this issue, but packages/opencode/src/tool/lsp-diagnostics.txt says "do not use". When creating custom tools in .opencode/tool/, users can only import from @opencode-ai/plugin, which doesn't expose LSP functionality.

Use Case

If my reading of the source is correct, custom tools that modify code files need to:

1. Notify the language server of file changes via LSP.touchFile()
2. Retrieve diagnostics to validate changes via LSP.diagnostics()
3. Format diagnostic output using LSP.Diagnostic.pretty()

Proposed Solution

Export LSP functionality through @opencode-ai/plugin to enable custom tools to:

• Call LSP.touchFile(filepath, waitForDiagnostics) to notify language servers of file changes
• Call LSP.diagnostics() to retrieve validation errors and warnings
• Access LSP.Diagnostic.pretty() for formatting diagnostic output
• Optionally access LSP.hover() for hover information

Alternative Workarounds

• Fork opencode and add tools directly to the codebase
• Update and use the lsp_diagnostics tool
• Use built-in edit/write tools instead of custom editing tools (this violates our requirements)