Phase 8: push and notifications

Implements PLAN.md Phase 8. internal/pushrules is the rule language: the
spec's default ruleset, all six condition kinds, glob and word-boundary
matching, intentional mentions switching off the legacy body rules, and
rule ordering as Synapse has it. internal/pushserver keeps the rules,
pushers and notifications and talks to push gateways.

Push rules are the m.push_rules account data, written only by the push
server; reads keep the user's own rules and the enabled/actions of each
default and take the rest from the current defaults, so new default rules
reach every user without a migration. PUT account_data/m.push_rules is
refused with 405.

The push server listens on the roomserver's emit stage and evaluates each
event on its own worker for every local member and an invite's target.
Notifications and per-room unread counts are stored in migration 0010;
counts are a seventh sync token stream, so /sync reports
unread_notifications and picks up count changes made after the event or by
a receipt from another device. m.read and m.read.private receipts clear
the counts; leaving a room clears it.

Pushers (http kind only) push through a bounded sender pool with retries,
honour event_id_only, drop push keys the gateway rejects, and go away with
their device. GET /notifications pages the history. New config section
push: enabled, include_content, gateway_timeout, notification_retention.

Account data writes now wake the user's blocked syncs.

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

server/internal/syncapi/syncapi.go

@@ -28,8 +28,9 @@
 //
 // Phase 4 of PLAN.md, with device lists from Phase 7: the keyserver writes
 // the device list stream, and this package works out which of its changes
-// concern whom (devicelists.go). What it does not do yet is notification
-// counts, which need push rules (Phase 8); docs/sync.md names that gap.
+// concern whom (devicelists.go). Notification counts, from Phase 8, are
+// the push server's: it writes them and their stream, and a sync reports
+// them per joined room (notifications.go).
 package syncapi
 
 import (
@@ -82,12 +83,24 @@ type Keys interface {
 	DeviceListChanges(ctx context.Context, userIDs []string, from, to int64) ([]storage.DeviceListChange, error)
 }
 
+// Push is the part of the push server a sync reads: the push rules it
+// reports as account data, the unread counts of each room, and which
+// rooms' counts moved. It is also told about read receipts, which are what
+// clear the counts. *pushserver.API satisfies it.
+type Push interface {
+	Document(ctx context.Context, localpart, userID string) ([]byte, error)
+	NotificationCounts(ctx context.Context, userID string, roomIDs []string) (map[string]storage.NotificationCounts, error)
+	NotificationCountChanges(ctx context.Context, userID string, from, to int64) ([]string, error)
+	ReceiptSet(ctx context.Context, userID, roomID, receiptType, threadID, eventID string)
+}
+
 // API is the syncapi component.
 type API struct {
 	serverName string
 	rooms      *roomserver.API
 	accounts   Accounts
 	keys       Keys
+	push       Push
 	store      storage.SyncStore
 	notifier   *Notifier
 	typing     *typingTracker
@@ -126,6 +139,10 @@ type Options struct {
 	// both device lists empty.
 	Keys Keys
 
+	// Push is the push server. Nil leaves the notification counts out of
+	// a sync, and m.push_rules is then whatever account data holds.
+	Push Push
+
 	// Store is the sync half of storage.
 	Store storage.SyncStore
 
@@ -206,6 +223,7 @@ func New(opts Options) (*API, error) {
 		rooms:           opts.Rooms,
 		accounts:        opts.Accounts,
 		keys:            opts.Keys,
+		push:            opts.Push,
 		store:           opts.Store,
 		notifier:        opts.Notifier,
 		typing:          newTypingTracker(opts.TypingTimeout, opts.Notifier, opts.Now),