Phase 7: E2EE support

Implements PLAN.md Phase 7: the server half of end-to-end encryption.
Devices upload identity, one-time and fallback keys; other devices query
and claim them, across servers too, and every one-time key is handed out
exactly once. Cross-signing, signature uploads, device list tracking and
server-side key backup complete the set.

internal/keyserver is the component. Keys are stored in canonical JSON
so that re-uploading the same key is a byte comparison, and signatures
uploaded later are kept apart from the key they sign and merged in on
read, so a key's own JSON stays what its owner uploaded. Device keys must
be for the caller's own device; cross-signing keys must be the
uploader's, carry the right usage and, for self- and user-signing keys,
be signed by the master key. Signatures are verified against the key as
stored. Replacing a master key asks for the password; a first upload or
an upload of the keys already stored does not, as the spec allows. A
signature of another user's master key is shown only to the user who
made it and never federated.

Every write that changes what /keys/query answers moves the device list
stream in the same transaction, one position per device, and wakes the
syncs of everyone sharing a room. The stream is the sixth field of a sync
token; older tokens still parse. The syncapi works out device_lists
changed and left from the stream and from membership moves in the
window, skipping invites and knocks, and reports
device_one_time_keys_count and device_unused_fallback_key_types, the
latter as [] when empty. GET /keys/changes uses the same logic.

Over federation: /user/keys/query, /user/keys/claim and
/user/devices/{userId}, and m.device_list_update and m.signing_key_update
both ways. Remote keys are not cached; an update about a remote user
sharing a room moves them in the stream so local clients re-query.
Device display names are not sent to other servers. With federation off,
remote users are reported in failures at once.

Deleting a device deletes its keys, through a new userapi
DeviceObserver. Key backup keeps the better copy of each session by the
spec's rule, never reuses a deleted version's number, and answers writes
to a stale version with M_WRONG_ROOM_KEYS_VERSION.

Storage is migration 0008 for sqlite and postgres, with a PocketBase
stub. The Complement target sets gain the key, device list, fallback,
cross-signing and backup tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/test/complement/README.md

@@ -45,7 +45,7 @@ as `WARP_FEDERATION_ENABLED`.
 
 The federation set leaves out partial-state joins (MSC3706,
 `TestPartialStateJoin*`), which Warp does not implement, and anything that
-needs application services (Phase 9) or device lists (Phase 7).
+needs application services (Phase 9).
 
 ## The test set
 

server/test/complement/run.sh

@@ -27,18 +27,19 @@ REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../../.." && pwd)"
 # stream tests: /sync in all its forms, /messages, /context, filters,
 # typing, receipts and to-device messaging. What is still out is anything
 # needing a later phase — the notification counts of the push rules
-# (Phase 8) and the device lists of the keyserver (Phase 7). Phase 6 added
-# the media tests: uploads, async uploads, downloads with their file names
-# and thumbnails. The remote-media tests are in the federation set, which
-# TestRemote.* already covers.
-CSAPI_TESTS='TestMedia.*|TestContent.*|TestLocalPngThumbnail|TestAsyncUpload.*|TestUploadLimit|TestRegistration|TestLogin|TestDeviceManagement|TestRoomCreate|TestRoomState|TestRoomAlias|TestRoomForget|TestMembership.*|TestRedaction.*|TestJoinRoom.*|TestLeaveRoom.*|TestKickRoom.*|TestBanRoom.*|TestPublicRoom.*|TestSync.*|TestMessages.*|TestContext.*|TestFilter.*|TestTyping.*|TestReceipt.*|TestToDevice.*|TestRoomCreationReportsEventsToMyself|TestLazyLoading.*|TestWriteMDirectAccountData'
+# (Phase 8). Phase 6 added the media tests: uploads, async uploads,
+# downloads with their file names and thumbnails. The remote-media tests
+# are in the federation set, which TestRemote.* already covers. Phase 7
+# added the keyserver's: key uploads, claims, changes, device lists,
+# fallback keys, cross-signing and key backup.
+CSAPI_TESTS='TestUploadKey.*|TestKeyClaimOrdering|TestKeyChanges.*|TestDeviceListUpdates.*|TestE2EKeyBackup.*|TestFallbackKeys.*|TestCrossSigning.*|TestMedia.*|TestContent.*|TestLocalPngThumbnail|TestAsyncUpload.*|TestUploadLimit|TestRegistration|TestLogin|TestDeviceManagement|TestRoomCreate|TestRoomState|TestRoomAlias|TestRoomForget|TestMembership.*|TestRedaction.*|TestJoinRoom.*|TestLeaveRoom.*|TestKickRoom.*|TestBanRoom.*|TestPublicRoom.*|TestSync.*|TestMessages.*|TestContext.*|TestFilter.*|TestTyping.*|TestReceipt.*|TestToDevice.*|TestRoomCreationReportsEventsToMyself|TestLazyLoading.*|TestWriteMDirectAccountData'
 
 # federation: Phase 5. Joins, leaves and invites across servers, keys,
 # transactions, missing events, server ACLs and the queries. Partial-state
 # joins (MSC3706, TestPartialStateJoin*) are not implemented and are left
-# out; so is anything needing an application service (Phase 9) or device
-# lists (Phase 7).
-FEDERATION_TESTS='TestFederation.*|TestJoinViaRoomIDAndServerName|TestJoinFederatedRoom.*|TestBannedUserCannotSendJoin|TestCannotSendNon.*Via.*|TestCannotSendKnockViaSend.*|TestOutboundFederation.*|TestInboundFederation.*|TestInboundCanReturnMissingEvents|TestRemoteAliasRequestsUnderstandUnicode|TestNetworkPartitionOrdering|TestACLs|TestGetMissingEventsGapFilling|TestEventAuth|TestUnbanViaInvite|TestJoinRoomWithFederation.*|TestRemote.*'
+# out; so is anything needing an application service (Phase 9). Phase 7
+# added device lists across servers.
+FEDERATION_TESTS='TestDeviceListUpdates.*|TestDeviceListsUpdateOverFederation.*|TestFederation.*|TestJoinViaRoomIDAndServerName|TestJoinFederatedRoom.*|TestBannedUserCannotSendJoin|TestCannotSendNon.*Via.*|TestCannotSendKnockViaSend.*|TestOutboundFederation.*|TestInboundFederation.*|TestInboundCanReturnMissingEvents|TestRemoteAliasRequestsUnderstandUnicode|TestNetworkPartitionOrdering|TestACLs|TestGetMissingEventsGapFilling|TestEventAuth|TestUnbanViaInvite|TestJoinRoomWithFederation.*|TestRemote.*'
 
 case "$COMPLEMENT_PROFILE" in
 	csapi)