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, 3 insertions, 3 deletions

diff --git a/internal/lsp/provider_native_success_test.go b/internal/lsp/provider_native_success_test.go
index 5bfe434..9951372 100644
--- a/internal/lsp/provider_native_success_test.go
+++ b/internal/lsp/provider_native_success_test.go
@@ -26,7 +26,7 @@ func TestProviderNativeCompletion_Success(t *testing.T) {
 	current := "fmt."
 	p := CompletionParams{TextDocument: TextDocumentIdentifier{URI: "file:///x.go"}, Position: Position{Line: 0, Character: len(current)}}
 	plan := completionPlan{current: current, params: p, funcCtx: "func f(){}", docStr: "doc", cacheKey: "k"}
-	items, ok := s.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000")
+	items, ok := s.completion.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000")
 	if !ok || len(items) == 0 {
 		t.Fatalf("expected provider-native items")
 	}
@@ -53,7 +53,7 @@ func TestProviderNativeCompletion_IndentWithDoubleOpen(t *testing.T) {
 	current := "  >>!do>" // leading indent + double-open marker
 	p := CompletionParams{TextDocument: TextDocumentIdentifier{URI: "file:///x.go"}, Position: Position{Line: 0, Character: len(current)}}
 	plan := completionPlan{current: current, params: p, funcCtx: "func f(){}", docStr: "doc", cacheKey: "k"}
-	items, ok := s.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000")
+	items, ok := s.completion.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000")
 	if !ok || len(items) == 0 {
 		t.Fatalf("expected provider-native items")
 	}
@@ -91,7 +91,7 @@ func TestProviderNativeCompletion_UsesPromptTemplate(t *testing.T) {
 	// Cursor at line 1, char 1 -> before should be "AAA\nB"
 	p := CompletionParams{TextDocument: TextDocumentIdentifier{URI: uri}, Position: Position{Line: 1, Character: 1}}
 	plan := completionPlan{current: current, params: p, funcCtx: "func f(){}", docStr: "doc", cacheKey: "k"}
-	if _, ok := s.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000"); !ok {
+	if _, ok := s.completion.tryProviderNativeCompletion(context.Background(), plan, spec, s.llmClient, "0000"); !ok {
 		t.Fatalf("expected provider-native path")
 	}
 	if cap.lastPrompt == "" {