refactor: remove legacy autoflush code paths (bd-xsl9)

Remove dual code paths in the autoflush system. FlushManager is now the
only code path for auto-flush operations.

Changes:
- Remove legacy globals: isDirty, needsFullExport, flushTimer
- Remove flushToJSONL() wrapper function (was backward-compat shim)
- Simplify markDirtyAndScheduleFlush/FullExport to just call FlushManager
- Update tests to use FlushManager or flushToJSONLWithState directly

FlushManager handles all flush state internally in its run() goroutine,
eliminating the need for global state. Sandbox mode and tests that do
not need flushing get a no-op when FlushManager is nil.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/direct_mode_test.go

@@ -28,17 +28,15 @@ func TestFallbackToDirectModeEnablesFlush(t *testing.T) {
 	origDBPath := dbPath
 	origAutoImport := autoImportEnabled
 	origAutoFlush := autoFlushEnabled
-	origIsDirty := isDirty
-	origNeedsFull := needsFullExport
 	origFlushFailures := flushFailureCount
 	origLastFlushErr := lastFlushError
+	origFlushManager := flushManager
 
-	flushMutex.Lock()
-	if flushTimer != nil {
-		flushTimer.Stop()
-		flushTimer = nil
+	// Shutdown any existing FlushManager
+	if flushManager != nil {
+		_ = flushManager.Shutdown()
+		flushManager = nil
 	}
-	flushMutex.Unlock()
 
 	defer func() {
 		if store != nil && store != origStore {
@@ -54,17 +52,14 @@ func TestFallbackToDirectModeEnablesFlush(t *testing.T) {
 		dbPath = origDBPath
 		autoImportEnabled = origAutoImport
 		autoFlushEnabled = origAutoFlush
-		isDirty = origIsDirty
-		needsFullExport = origNeedsFull
 		flushFailureCount = origFlushFailures
 		lastFlushError = origLastFlushErr
 
-		flushMutex.Lock()
-		if flushTimer != nil {
-			flushTimer.Stop()
-			flushTimer = nil
+		// Restore FlushManager
+		if flushManager != nil {
+			_ = flushManager.Shutdown()
 		}
-		flushMutex.Unlock()
+		flushManager = origFlushManager
 	}()
 
 	tmpDir := t.TempDir()
@@ -112,8 +107,6 @@ func TestFallbackToDirectModeEnablesFlush(t *testing.T) {
 	daemonStatus = DaemonStatus{}
 	autoImportEnabled = false
 	autoFlushEnabled = true
-	isDirty = false
-	needsFullExport = false
 
 	if err := fallbackToDirectMode("test fallback"); err != nil {
 		t.Fatalf("fallbackToDirectMode failed: %v", err)
@@ -131,14 +124,7 @@ func TestFallbackToDirectModeEnablesFlush(t *testing.T) {
 	}
 
 	// Force a full export and flush synchronously
-	markDirtyAndScheduleFullExport()
-	flushMutex.Lock()
-	if flushTimer != nil {
-		flushTimer.Stop()
-		flushTimer = nil
-	}
-	flushMutex.Unlock()
-	flushToJSONL()
+	flushToJSONLWithState(flushState{forceDirty: true, forceFullExport: true})
 
 	jsonlPath := findJSONLPath()
 	data, err := os.ReadFile(jsonlPath)