feature: in-process LSP to interact with `opencode`

[nickjvandyke]

Opening the floor to ideas for an in-process LSP that interacts with opencode 😁

Validity

Pros

• Primary goal of this plugin is supplementing editor-first workflows, and LSPs are essentially first-class citizens in editors
• Familiar UX
• ?

Cons

• Slight departure from opencode-TUI-only experience; bit scattered
• LSPs are generally deterministic and reliable; LLMs, not as much
• ?

Handlers

• Code actions
  • Ask opencode to fix the diagnostic under the cursor
  • ?
• Hover
  • Ask opencode to explain the symbol under the cursor
    • I say "symbol" but really it works for anything, like literals
• Code lens/inlay hints
  • Some kind of useful contextual info?
• Completion
  • Inline
    • Not sure how much this adds over e.g. copilot.lua. opencode can probably gather more context for a better suggestion, but is that worth the speed tradeoff?
• ?

Describe alternatives you've considered

Manually prompting opencode with whatever the LSP handlers would do. Possibly via non-LSP keymaps.

Additional context

Presumably some ideas in https://github.com/SilasMarvin/lsp-ai, but I think we could do better with nvim and opencode specificity.

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Please offer ideas and feedback!