Complete LSP server implementation with lifecycle and crash recovery

[dollfins]

Description

The LSP server integration (src/server.ts) is a stub with several issues:

1. Memory leak — handleServerMessage creates a new DiagnosticCollection on every message instead of reusing a single collection
2. No proper LSP protocol handling — Only handles publishDiagnostics but ignores initialization, capabilities, shutdown, etc.
3. No lifecycle management — The server is never started or stopped; it is defined but not used in extension.ts
4. No error recovery — If the server process crashes, there is no restart logic

Required Changes

Fix diagnostic collection leak

• Create the diagnostic collection once in the constructor
• Reuse it across all publishDiagnostics messages

Implement basic LSP lifecycle

• Handle initialize request with capabilities response
• Handle shutdown and exit notifications
• Properly track client-server state

Wire server into extension lifecycle

• Start the server in activate() when configured
• Stop the server in deactivate()
• Add a configuration option to enable/disable LSP mode

Add crash recovery

• Restart the server process if it exits unexpectedly
• Limit restart attempts to avoid infinite loops
• Log restart events to output channel

Acceptance Criteria

• No diagnostic collection leak (single collection reused)
• LSP server handles initialize/shutdown/exit correctly
• Server starts on extension activation when enabled
• Server stops on extension deactivation
• Server auto-restarts on crash (with limit)
• Tests verify basic LSP handshake

Complexity

High — requires understanding of LSP protocol, child process management, and integration with VS Code diagnostic APIs.

Points

200