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+# PQ integration in chat
+
+## Problem
+
+- Group size not known when joining
+- Communicate intent and current state of each conversation
+
+## Solution
+
+### Group size not known when joining
+
+- Add to XGrpInv GroupInvitation
+  - pros: easy
+  - cons: size can change before joining, but can ignore as it's still a good estimate
+
+or
+
+- Send before introductions
+  - new protocol message
+    - XGrpIntro :: GrpIntro -> ChatMsgEvent 'Json -- (GrpIntro is a box type with Int, for possible extension)
+  - or put into XGrpInfo
+    - XGrpInfo :: GroupProfile -> GroupStats -> ChatMsgEvent 'Json -- GroupData?
+    - can update profile between invitation if it happened before joining
+    - can later add logic to "verify" stats?
+    - may be over-complicated until since there "supposed" use cases are out-of-scope / not planned / not known
+
+- What should be default if it's not known? (e.g. admin has older version)
+  - On -> then off when member count reaches 20?
+
+### Communicate intent and current state of each conversation
+
+- Current state items
+  - RCEPQEnabled (see #3845) both for direct conversation and per member (regular event items, merged in UI)
+  - created when PQ changes for contact/member (e.g. received from agent on MsgMeta / SENT)
+  - experimental toggle is planned: it doesn't affect contacts/members with already enabled PQ
+    - contact enabled PQ always overrides toggle (can't downgrade)
+    - member enabled PQ also overrides, but can downgrade if group size increases past 20
+
+- New items communicating state of e2e encryption in conversation
+  - should be well pronounced in UI, not merged
+  - should always say that conversation is e2e encrypted
+  - in direct chats:
+    - reflect actual state of PQ at the time of creation
+    - created during connection handshake when receiving first info about PQ in MsgMeta / some other event (TBC agent api)
+    - will not update if state changes (e.g. upgrades), as toggle is planned to be removed, PQ can't be downgraded, all will support soon
+    - flag in contacts table "e2e_info_created" to only create it once?
+    - should create for legacy contacts or not?
+  - in groups:
+    - reflect intent (should say "PQ will be used for members who support") based on number of members (see above) + toggle
+    - created at the same time as feature items? race with history may be possible, but we don't observe it? need to double check or ignore
+    - if based on XGrpInv GroupInvitation (first option above), can create item even before joining
+    - also will not update (as conversation progresses and it will scroll far up anyway) even if group size changes and it's disabled
+    - flag in groups table "e2e_info_created" to only create it once? and state is only reflected by RCEPQEnabled items?
+    - or create new such item if group size increases and PQ is off / decreases and PQ is on?
+    - "large group" thresholds have to different for group size increasing (e.g. 20) and decreases (e.g. 15), to avoid constant switching on the border.
+
+- Example texts for "e2e encryption info" chat items:
+  - for direct conversations:
+    - with PQ (and also forward a couple releases when more clients have upgraded):
+      ```
+      Messages in this conversation are end-to-end encrypted.
+      Post-quantum encryption is enabled.
+      ```
+    - no PQ (experimental toggle disabled):
+      ```
+      -//- (e2ee)
+      Post-quantum encryption is not enabled. [Also possibly:] Enabling post-quantum encryption in experimental settings will enable it in this conversation if your contact supports it.
+      ```
+    - no PQ (experimental toggle enabled):
+      ```
+      -//-
+      Post-quantum encryption will be enabled when your contact upgrades.
+      ```
+      "upgrades" / "supports it" / "starts to support it"
+    - can be of different color, but seems unnecessary
+    - created once at the start of conversation
+    - created once for old contacts when PQ is enabled?
+  - for groups:
+    - with PQ (small group; toggle enabled or later, as above):
+      ```
+      -//-
+      Post-quantum encryption will be enabled for members who support it.
+      ```
+      can remove qualification later when most clients have upgraded
+    - no PQ (large group):
+      ```
+      -//-
+      Post-quantum encryption is not enabled (group is too large).
+      ```
+    - created each time group changes between small/large, or once?
+    - created for old groups when experimental toggle is first turned on, and first message is received?
+
+
+- Save PQ encryption on chat items (messages)?
+  - in meta for direct + group rcv
+  - in group_snd_item_statuses for group snd?
+  - display in chat item details (info)
+  - may be overkill if aggressive upgrade strategy is planned