Fix Matrix E2EE: stop double-login and make cross-signing bootstrap reachable

Two bugs prevented Pete's device from ever cross-signing itself:

1. Double login / split-brain: New() did a manual mx.Login() AND set
   ch.LoginAs, so cryptohelper.Init() logged in a second time on a fresh
   crypto store, minting a separate device. device.json recorded one device
   while the olm account belonged to another, and every cold start leaked an
   orphan device. Pete's outgoing events were attributed to a device whose
   keys no client could verify. Removed ch.LoginAs (auth is already handled by
   the manual login + isTokenValid re-login path).

2. Unreachable bootstrap: the reset gate used
   IsDeviceTrusted(mach.OwnIdentity()), but OwnIdentity() hard-codes
   Trust=TrustStateVerified, so it always returns true and the bootstrap/reset
   branch was never entered. Replaced with GetOwnVerificationStatus(), which
   actually checks whether the current device key is signed by our
   self-signing key.

internal/matrix/client.go

@@ -13,8 +13,8 @@ import (
 	"log/slog"
 	"net/http"
 	"os"
-	"strings"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -142,30 +142,45 @@ func New(cfg config.MatrixConfig) (*Client, error) {
 			"room", evt.RoomID, "event_id", evt.ID, "sender", evt.Sender, "err", err)
 	}
 
-	// LoginAs enables the cryptohelper to re-login if the token expires
+	// IMPORTANT: do NOT set ch.LoginAs here. We already performed an explicit
-	ch.LoginAs = &mautrix.ReqLogin{
+	// password login above (or restored a saved token), so mx is fully
-		Type: mautrix.AuthTypePassword,
+	// authenticated against device.json's device. When LoginAs is set AND the
-		Identifier: mautrix.UserIdentifier{
+	// crypto store is fresh, cryptohelper.Init() performs a SECOND login
-			Type: mautrix.IdentifierTypeUser,
+	// (StoreCredentials=true), minting a separate device and pinning the olm
-			User: cfg.UserID,
+	// account to it — while device.json still records the first device. That
-		},
+	// split-brain is exactly the "device never verifies" bug: the device the
-		Password:                 cfg.Password,
+	// token authenticates as is not the device the crypto account belongs to,
-		InitialDeviceDisplayName: cfg.DisplayName,
+	// and each cold start leaks another orphan device. Token-expiry recovery is
-	}
+	// already handled by the isTokenValid() check + re-login path above.
-
 	if err := ch.Init(context.Background()); err != nil {
 		return nil, fmt.Errorf("crypto helper init: %w", err)
 	}
 
 	mx.Crypto = ch
 
-	// Bootstrap cross-signing only if not already set up.
+	// Ensure our CURRENT device is cross-signed. We bootstrap (generate + upload
+	// fresh cross-signing keys, then self-sign) whenever either no keys exist yet,
+	// or keys exist on the server but our device is not signed by them. The latter
+	// is exactly the post-wipe state: when crypto.db is deleted the private
+	// self-signing key is lost (it is never persisted locally without an SSSS
+	// passphrase, and we discard the random recovery key), so the lingering server
+	// master key is useless to us and must be replaced.
+	//
+	// CRITICAL: do NOT gate this on IsDeviceTrusted(mach.OwnIdentity()).
+	// OwnIdentity() hard-codes Trust=id.TrustStateVerified, and ResolveTrustContext
+	// short-circuits on that, so the call is a tautology that ALWAYS returns true —
+	// it makes this branch unreachable and the device never gets signed.
+	// GetOwnVerificationStatus does a real check: is our own device key signed by
+	// our self-signing key?
 	mach := ch.Machine()
-	existingKeys, err := mach.GetOwnCrossSigningPublicKeys(context.Background())
+	hasKeys, deviceCrossSigned, err := mach.GetOwnVerificationStatus(context.Background())
 	if err != nil {
-		slog.Warn("cross-signing: failed to fetch existing keys", "err", err)
+		slog.Warn("cross-signing: failed to check verification status", "err", err)
+	}
+	if !hasKeys || !deviceCrossSigned {
+		if hasKeys {
+			slog.Warn("cross-signing: keys exist but current device is not cross-signed, resetting cross-signing")
 		}
-	if existingKeys == nil || existingKeys.MasterKey == "" {
 		_, _, err = mach.GenerateAndUploadCrossSigningKeys(context.Background(), func(ui *mautrix.RespUserInteractive) interface{} {
 			return map[string]interface{}{
 				"type": mautrix.AuthTypePassword,
@@ -195,7 +210,7 @@ func New(cfg config.MatrixConfig) (*Client, error) {
 			slog.Info("cross-signing: master key signed")
 		}
 	} else {
-		slog.Info("cross-signing: already configured, skipping bootstrap")
+		slog.Info("cross-signing: already configured and current device cross-signed, skipping bootstrap")
 	}
 
 	slog.Info("E2EE initialized",