context and sequence diagrams of sending a message

docs/flow.md

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+## Sending a message
+
+```mermaid
+sequenceDiagram
+    participant Alice PC
+    participant Alice Connection 1
+    participant Alice Phone
+    participant Alice Connection 2
+    participant Alice
+    participant Room
+    participant Bob
+    participant Bob Connection 1
+    participant Bob PC
+    
+    Alice PC->>Alice Connection 1: `PRIVMSG Room :Hello!`
+    Alice Connection 1->>+Alice: PlayerCommand::SendMessage
+    Alice->Alice: Check permissions
+    Alice->>+Room: /send Room Hello!
+    Alice-->>Alice Connection 1: fulfil promise
+    Alice->>-Alice Connection 2: Updates::NewMessage
+    Alice Connection 2->>Alice Phone: `:Alice PRIVMSG Room :Hello!`
+    Room->>+Bob: Updates::NewMessage
+    deactivate Room;
+    Bob->>+Bob Connection 1: Updates::NewMessage
+    deactivate Bob;
+    Bob Connection 1->>-Bob PC: `:Alice PRIVMSG Room :Hello!`
+
+```
+
+## Context
+
+```mermaid
+C4Context
+    System_Ext(AlicePC, "Alice PC", "Alice's PC")
+    BiRel(AlicePC, AliceConn1, "IRC")
+    System_Ext(AlicePh, "Alice Phone", "Alice's phone")
+    BiRel(AlicePh, AliceConn2, "XMPP")
+    Boundary(Node, "Node", "Single server process") { 
+        System(AliceConn1, "Alice Connection 1", "Projection nto an IRC socket")
+        
+        System(AliceConn2, "Alice Connection 2", "Projection onto an XMPP socket")
+        BiRel(AliceConn1, Alice, "Cmds & updates")
+        BiRel(AliceConn2, Alice, "Cmds & updates")
+        
+
+        Boundary(Core, "Core", "Core chat entities") {
+            System(Alice, "Alice", "Player actor")
+            System(Room1, "#room")
+            BiRel(Alice, Room1, "")
+            System(Bob, "Bob", "Player actor")
+            BiRel(Bob, Room1, "")
+
+            System(Players, "Player Registry", "")
+            Rel(Players, Alice, "References")
+            Rel(Players, Bob, "References")
+            Rel(Players, Rooms, "")
+            System(Rooms, "Room Registry", "")
+            Rel(Rooms, Room1, "")
+        }
+
+        System(BobConn1, "Bob Connection 1", "Projection onto an IRC socket")  
+        BiRel(BobConn1, Bob, "Cmds & updates")
+    }
+    System_Ext(BobPC, "Bob PC", "Bob's PC")
+    BiRel(BobPC, BobConn1, "IRC")
+    UpdateLayoutConfig($c4ShapeInRow="3", $c4BoundaryInRow="1")
+```