removal protocol

docs/rfcs/2025-10-20-chat-relays.md

@@ -21,7 +21,7 @@ par With each relay
     O ->> R: 5. Contact request<br>(x.grp.relay.inv)
     R ->> RSMP: 6. Create relay link
     RSMP -->> R:
-    R ->> O: 7. Accept request<br>(x.grp.relay.acpt)
+    R ->> O: 7. Accept request<br>(x.grp.relay.acpt<br>incl. relay link)
     O ->> OSMP: 8. Update short link<br>(add relay link)
     OSMP -->> O:
     O ->> R: 9. Notify relay link added<br>(x.grp.info)
@@ -34,10 +34,17 @@ O -->> O: 13. Share group short link<br>(social, out-of-band)
 
 note over OSMP, M: New member connects
 
-M ->> OSMP: 1. Retrieve short link data
+M ->> OSMP: 14. Retrieve short link data
 OSMP -->> M:
-M ->> R: 2. Connect via relay link(s)
+M -->> M: 15. Prepare group record,<br>save relay links
+M ->> R: 16. Connect via relay link(s)
 R -->> M:
+
+note over O, M: Message forwarding
+
+O ->> R: 17. Send message
+R ->> M: 18. Forward message
+M -->> M: 19. Deduplicate message
 ```
 
 Notes:
@@ -61,3 +68,89 @@ Notes:
   - Link is recoverable from profile, e.g. for purpose of restoring connection with group via new chat relays.
 
   Overall it just seems a natural and convenient way to store group link for all members, rather than having it separately.
+
+- Owner should reject contact requests to their group link.
+
+- Chat relay should reject contact requests to its relay link until chat relay confirms it is attached to the group link data.
+
+
+## Protocol for removing chat relay from group, restoring connection to group
+
+```mermaid
+sequenceDiagram
+  participant OSMP as Owner's<br>SMP server
+  participant O as Owner
+  participant R as Chat relay
+  participant RSMP as Chat relays'<br>SMP server(s)
+  participant M as Member
+
+note over OSMP, M: Scenario 1. Owner deletes chat relay, notifies relay
+
+par Owner to chat relay
+    O ->> R: 1a. Delete chat relay<br>(x.grp.mem.del)
+    par Chat relay to SMP
+        R ->> RSMP: 2a. Delete relay link
+    and Chat relay to members
+        R ->> M: 2b. Forward relay is deleted
+        M -->> M: 3. Delete connections with relay
+    end
+and Owner to SMP
+    O ->> OSMP: 1b. Remove relay link<br>(update group link data)
+    OSMP -->> O:
+and
+    O -->> O: 1c. Delete connection with relay
+end
+
+note over OSMP, M: Scenario 2. Owner deletes chat relay, fails to notify relay
+
+par Owner to chat relay
+    O --x R: 1a. Fail to notify relay
+and Owner to SMP
+    O ->> OSMP: 1b. Remove relay link<br>(update group link data)
+    OSMP -->> O:
+and
+    O -->> O: 1c. Delete connection with relay
+end
+loop Chat relay periodic checks
+    R ->> OSMP: 2. Retrieve short link data for served gorup
+    OSMP -->> R:
+    R --x R: 3. Check relay link added
+end
+par Chat relay to SMP
+    destroy RSMP
+    R ->> RSMP: 4a. Delete relay link 
+and Chat relay to members
+    destroy R
+    R ->> M: 4b. Notify relay is deleted
+    M -->> M: 5. Delete connections with relay
+end
+
+note over OSMP, M: Last relay is deleted
+
+O --x M: Owner can't send messages to members
+M -->> M: Attempt to restore<br>connection to group (manual)
+M ->> OSMP: Retrieve short link data
+OSMP -->> M:
+M --x M: Members can't restore connection to group
+
+note over OSMP, M: Restore connection to group
+
+create participant NR as New chat relay
+O <<-->> NR: 1. Add new relay, relay creates and sends link
+O <<-->> OSMP: 2. Update short link<br>(add relay link)
+M -->> M: 3. Attempt to restore<br>connection to group (manual)
+M ->> OSMP: 4. Retrieve short link data
+OSMP -->> M:
+M ->> NR: 5. Connect via relay link
+NR -->> M:
+O ->> NR: 6. Send message
+NR ->> M: 7. Forward message
+M -->> M: 8. Deduplicate message
+```
+
+Notes:
+
+- New relay doesn't have group history.
+  - We can prohibit to remove last relay without adding new one.
+  - Relays can synchronize history.
+  - Can be considered after MVP.