feat(chat): persistance bornee du brouillon custom chat par projet/layout (#182)

crates/backend/src/dto.rs

@@ -3100,6 +3100,42 @@ impl From<TerminalSession> for TerminalSessionDto {
 // Structured chat sessions (§17 — D4)
 // ---------------------------------------------------------------------------
 
+/// Request scoped to one persisted custom chat draft.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ChatDraftScopeRequestDto {
+    /// Project id.
+    pub project_id: String,
+    /// Named layout id.
+    pub layout_id: String,
+    /// Layout node id.
+    pub node_id: String,
+}
+
+/// Request for saving one custom chat draft.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SaveChatDraftRequestDto {
+    /// Project id.
+    pub project_id: String,
+    /// Named layout id.
+    pub layout_id: String,
+    /// Layout node id.
+    pub node_id: String,
+    /// Draft text. Empty text clears the draft.
+    pub text: String,
+}
+
+/// Response for reading one custom chat draft.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ReadChatDraftResponseDto {
+    /// Draft text, or `null` when absent.
+    pub text: Option<String>,
+    /// Last update time, epoch milliseconds, or `null` when absent.
+    pub updated_at_ms: Option<u64>,
+}
+
 /// Structured attachment intent sent by the chat frontend.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]