feat: chat — saisie auto-agrandissante, accusé de réception ✓✓, vignette de tuile #192 (BUG-109)

backend/schemas.py

@@ -172,6 +172,17 @@ class ChatHistoryResponse(BaseModel):
     """Response for ``GET /api/file/{vault}/chat``."""
 
     messages: list[ChatMessageItem] = Field(description="Messages, chronological")
+    read: dict[str, float] = Field(
+        default_factory=dict,
+        description="{username: last read unix ts} per participant (#192)",
+    )
+
+
+class ChatReadResponse(BaseModel):
+    """Response for ``POST /api/chat/read`` (#192 read receipts)."""
+
+    read: dict[str, float] = Field(description="{username: last read unix ts}")
+    status: str = Field(description="'ok'")
 
 
 class ChatMessageResponse(BaseModel):