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, 2 insertions, 2 deletions

diff --git a/internal/lsp/completion_cache_test.go b/internal/lsp/completion_cache_test.go
index ff85906..ee51016 100644
--- a/internal/lsp/completion_cache_test.go
+++ b/internal/lsp/completion_cache_test.go
@@ -25,7 +25,7 @@ func TestCompletionCache_IgnoresWhitespaceBeforeCursor(t *testing.T) {
 	// First request with trailing spaces before cursor
 	line := "foo   "
 	p := CompletionParams{Position: Position{Line: 0, Character: len(line)}, TextDocument: TextDocumentIdentifier{URI: "file://x.go"}}
-	items, ok, _ := s.tryLLMCompletion(p, "", line, "", "", "", false, "")
+	items, ok, _ := s.completion.tryLLMCompletion(p, "", line, "", "", "", false, "")
 	if !ok || len(items) == 0 || fake.calls != 1 {
 		t.Fatalf("expected first call to invoke LLM; ok=%v len=%d calls=%d", ok, len(items), fake.calls)
 	}
@@ -33,7 +33,7 @@ func TestCompletionCache_IgnoresWhitespaceBeforeCursor(t *testing.T) {
 	// Same logical context but with a different amount of trailing whitespace
 	line2 := "foo             "
 	p2 := CompletionParams{Position: Position{Line: 0, Character: len(line2)}, TextDocument: TextDocumentIdentifier{URI: "file://x.go"}}
-	items2, ok2, _ := s.tryLLMCompletion(p2, "", line2, "", "", "", false, "")
+	items2, ok2, _ := s.completion.tryLLMCompletion(p2, "", line2, "", "", "", false, "")
 	if !ok2 || len(items2) == 0 {
 		t.Fatalf("expected cache hit to still return items")
 	}