MSC4257: Profiles Arent Auth: Move profile contents to a separate event

proposals/4257-profiles-arent-auth.md

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+# MSC4257: Move profiles to a separate event
+
+Profile updates being part of membership, makes all kinds of operations a pain in the ass,
+be it calculating auth events, or figuring out if someone changed their displayname or joined.
+
+What if we made them a separate event instead, and simplified the redaction rules for membership events?
+
+
+## Proposal
+
+We could move profiles (display names/avatars) to a separate event. This would make calculating event auth
+chains faster, as there's far less noise to consider. Additionally, it'd allow telling membership edges
+appart in code a decent amount faster. This MSC's purpose is to be a middle step between current day
+Matrix and Profiles as Rooms. This also doesn't break historical profiles, as needed in some contexts.
+Additionally, this could be used together with MSC 4133 to optionally override fields per room, unless
+specified otherwise in the field's MSC.
+
+An example of an `m.room.member` event after this MSC could look like this:
+```json5
+{
+    "content": {
+        "is_direct": false, // Should this be moved to a different event? Or only be valid when membership==invite?
+        "membership": "join"
+    },
+    "event_id": "$aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+    "origin_server_ts": 1737828697089,
+    "sender": "@bob:example.com",
+    "state_key": "@bob:example.com",
+    "type": "m.room.member",
+    "unsigned": {
+        "age": 4
+    }
+}
+```
+
+An example of an `m.room.member.profile` event after this MSC could look like this:
+```
+{
+    "content": {
+        "displayname": "Alice",
+        "avatar_url": "mxc://example.com/abcdefg",
+        "m.pronouns.en": "she/her"
+    },
+    "event_id": "$aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab",
+    "origin_server_ts": 1737828697090,
+    "sender": "@bob:example.com",
+    "state_key": "@bob:example.com",
+    "type": "m.room.member.profile",
+    "unsigned": {
+        "age": 4
+    }
+}
+```
+
+This change would make event auth faster, as profile updates no longer need to be considered.
+Additionally: the profile event is only allowed to be sent by the user specified in the state key,
+except in the case that the content being sent is an empty json set`{}`, or in the case of a redaction.
+
+## Potential issues
+
+This is going to require a separate room version, I think? Especially given this changes the redaction
+rules for m.room.member events as additional fields are technically no longer required.
+
+## Alternatives
+
+None yet.
+
+## Security considerations
+
+I do not think this MSC has any security ramifications.
+
+## Unstable prefix
+
+`gay.rory.room.member.profile`, relevant if used in older room versions.
+
+## Dependencies
+
+None.