Refactor lsp.Server God Object: extract chat and completion subsystems

The Server type accumulated two large, tangled feature subsystems (in-editor
chat and code completion) alongside its core LSP dispatch role. Pull them into
cohesive types that own their state and logic while delegating shared
infrastructure back to Server via a back-reference.

- Add completionService (completion_service.go): owns the completion
  cache/throttle state (completionState) and all completion request-handling
  logic (handleCompletion, plan/jobs/execute, provider-native path,
  post-processing, message building, prefix heuristics). Methods moved off
  Server in handlers_completion.go to completionService.
- Add chatService (chat_service.go + chat_handlers.go): owns the input-activity
  clock (lastInput, with its own mutex instead of Server.mu) and all in-editor
  chat logic (detection, transcript history, message building, edit
  application, inline prompts) plus the slash-command handlers
  (chat_commands.go).
- Server now holds chat/completion fields, wires them in NewServer, and
  delegates (dispatch table, didChange, debounce gate) to them. Thin Server
  shims preserve the existing completion-state API for callers/tests.

Pure refactor: no behavior or LSP protocol changes. Tests adjusted only to
reach the relocated methods/state via the services. All tests pass with -race;
coverage 86.1%.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 13 insertions, 12 deletions

diff --git a/internal/lsp/chat_commands.go b/internal/lsp/chat_commands.go
index 11e5a28..480643a 100644
--- a/internal/lsp/chat_commands.go
+++ b/internal/lsp/chat_commands.go
@@ -11,27 +11,27 @@ type chatCommandResult struct {
 	message string
 }
 
-func (s *Server) chatCommandResponse(uri string, lineIdx int, prompt string) (chatCommandResult, bool) {
-	trimmed := strings.TrimSpace(s.stripTrailingTrigger(prompt))
+func (c *chatService) chatCommandResponse(uri string, lineIdx int, prompt string) (chatCommandResult, bool) {
+	trimmed := strings.TrimSpace(c.stripTrailingTrigger(prompt))
 	if trimmed == "" || !strings.HasPrefix(trimmed, "/") {
 		return chatCommandResult{}, false
 	}
 
 	switch {
 	case strings.HasPrefix(trimmed, "/reload"):
-		return s.handleReloadCommand(), true
+		return c.handleReloadCommand(), true
 	case strings.HasPrefix(trimmed, "/help"):
-		return s.handleHelpCommand(), true
+		return c.handleHelpCommand(), true
 	case strings.HasPrefix(trimmed, "/disable"):
-		return s.handleDisableCompletionCommand(), true
+		return c.handleDisableCompletionCommand(), true
 	case strings.HasPrefix(trimmed, "/enable"):
-		return s.handleEnableCompletionCommand(), true
+		return c.handleEnableCompletionCommand(), true
 	default:
 		return chatCommandResult{message: fmt.Sprintf("Unknown command %q. Try /help?>", trimmed)}, true
 	}
 }
 
-func (s *Server) handleHelpCommand() chatCommandResult {
+func (c *chatService) handleHelpCommand() chatCommandResult {
 	lines := []string{
 		"Available slash commands:",
 		"- /reload?> reload configuration from file (ignores env overrides)",
@@ -41,7 +41,8 @@ func (s *Server) handleHelpCommand() chatCommandResult {
 	return chatCommandResult{message: strings.Join(lines, "\n")}
 }
 
-func (s *Server) handleReloadCommand() chatCommandResult {
+func (c *chatService) handleReloadCommand() chatCommandResult {
+	s := c.srv
 	if s.configStore == nil {
 		return chatCommandResult{message: "Reload unavailable: no config store"}
 	}
@@ -57,16 +58,16 @@ func (s *Server) handleReloadCommand() chatCommandResult {
 	return chatCommandResult{message: summary}
 }
 
-func (s *Server) handleDisableCompletionCommand() chatCommandResult {
-	prev := s.setCompletionsDisabled(true)
+func (c *chatService) handleDisableCompletionCommand() chatCommandResult {
+	prev := c.srv.setCompletionsDisabled(true)
 	if prev {
 		return chatCommandResult{message: "Auto-completions were already disabled."}
 	}
 	return chatCommandResult{message: "Auto-completions disabled. Use /enable?> to restore."}
 }
 
-func (s *Server) handleEnableCompletionCommand() chatCommandResult {
-	prev := s.setCompletionsDisabled(false)
+func (c *chatService) handleEnableCompletionCommand() chatCommandResult {
+	prev := c.srv.setCompletionsDisabled(false)
 	if !prev {
 		return chatCommandResult{message: "Auto-completions are already enabled."}
 	}