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, 6 insertions, 7 deletions

diff --git a/internal/lsp/debounce_throttle_more_test.go b/internal/lsp/debounce_throttle_more_test.go
index 22d1888..a3c4b11 100644
--- a/internal/lsp/debounce_throttle_more_test.go
+++ b/internal/lsp/debounce_throttle_more_test.go
@@ -11,11 +11,9 @@ func TestWaitForDebounce_WaitsRoughlyDebounce(t *testing.T) {
 	cfg := s.cfg
 	cfg.CompletionDebounceMs = 20
 	s.cfg = cfg
-	s.mu.Lock()
-	s.lastInput = time.Now()
-	s.mu.Unlock()
+	s.chatSvc().markActivity()
 	start := time.Now()
-	s.waitForDebounce(context.Background())
+	s.completionSvc().waitForDebounce(context.Background())
 	if elapsed := time.Since(start); elapsed < 15*time.Millisecond {
 		t.Fatalf("debounce did not wait long enough: %v", elapsed)
 	}
@@ -26,9 +24,10 @@ func TestWaitForThrottle_WaitsRoughlyInterval(t *testing.T) {
 	cfg := s.cfg
 	cfg.CompletionThrottleMs = 20
 	s.cfg = cfg
-	s.stateMu.Lock()
-	s.lastLLMCall = time.Now()
-	s.stateMu.Unlock()
+	cs := s.completionSvc()
+	cs.stateMu.Lock()
+	cs.lastLLMCall = time.Now()
+	cs.stateMu.Unlock()
 	start := time.Now()
 	if !s.waitForThrottle(context.Background()) {
 		t.Fatalf("waitForThrottle returned false")