When removing an account, wait for the last account reference has gone away before removing the files.

The intent to remove the account is stored in the database. At startup, if
there are any such referenes, they are applied by removing the account
directories and the entry in the database. This ensures the account directory
is properly removed, even on incomplete shutdown.

Don't add an account when its directory already exits.

store/account_test.go

@@ -2,6 +2,8 @@ package store
 
 import (
 	"context"
+	"errors"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -411,3 +413,72 @@ func TestNextMessageID(t *testing.T) {
 	tcheck(t, err, "closing account")
 	acc.WaitClosed()
 }
+
+func TestRemove(t *testing.T) {
+	log := mlog.New("store", nil)
+	os.RemoveAll("../testdata/store/data")
+	mox.ConfigStaticPath = filepath.FromSlash("../testdata/store/mox.conf")
+	mox.MustLoadConfig(true, false)
+	err := Init(ctxbg)
+	tcheck(t, err, "init")
+	defer func() {
+		err := Close()
+		tcheck(t, err, "close")
+	}()
+	defer Switchboard()()
+
+	// Note: we are not removing the account from the config file. Nothing currently
+	// has a problem with that.
+
+	// Ensure account exists.
+	acc, err := OpenAccount(log, "mjl", false)
+	tcheck(t, err, "open account")
+
+	// Mark account removed. It will only be removed when we close the account.
+	err = acc.Remove(context.Background())
+	tcheck(t, err, "remove account")
+
+	p := filepath.Join(mox.DataDirPath("accounts"), "mjl")
+	_, err = os.Stat(p)
+	tcheck(t, err, "stat account dir")
+
+	err = acc.Close()
+	tcheck(t, err, "closing account")
+	acc.WaitClosed()
+	acc = nil
+
+	if _, err := os.Stat(p); err == nil || !errors.Is(err, fs.ErrNotExist) {
+		t.Fatalf(`got stat err %v for account directory, expected "does not exist"`, err)
+	}
+
+	// Recreate files and directories. We will reinitialize store/ without closing our
+	// account reference. This will apply the account removal. We only drop our (now
+	// broken) account reference when done.
+	acc, err = OpenAccount(log, "mjl", false)
+	tcheck(t, err, "open account")
+	defer func() {
+		acc.Close() // Ignore errors.
+		acc.WaitClosed()
+		CheckConsistencyOnClose = true
+	}()
+
+	// Init below will remove the directory, we are no longer consistent.
+	CheckConsistencyOnClose = false
+
+	err = acc.Remove(context.Background())
+	tcheck(t, err, "remove account")
+
+	_, err = os.Stat(p)
+	tcheck(t, err, "stat account dir")
+
+	err = Close()
+	tcheck(t, err, "close store")
+	err = Init(ctxbg)
+	tcheck(t, err, "init store")
+	if _, err := os.Stat(p); err == nil || !errors.Is(err, fs.ErrNotExist) {
+		t.Fatalf(`got stat err %v for account directory, expected "does not exist"`, err)
+	}
+	exists, err := bstore.QueryDB[AccountRemove](ctxbg, AuthDB).Exists()
+	tcheck(t, err, "checking for account removals")
+	tcompare(t, exists, false)
+}