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

crates/domain/src/chat_draft.rs

@@ -0,0 +1,84 @@
+//! Persisted custom chat draft model.
+
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+use crate::ids::{LayoutId, NodeId, ProjectId};
+
+/// Maximum draft text size persisted by IdeA.
+pub const CHAT_DRAFT_MAX_BYTES: usize = 100 * 1024;
+
+/// Stable scope for one custom chat draft.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ChatDraftKey {
+    /// Project owning the layout.
+    pub project_id: ProjectId,
+    /// Named layout containing the chat cell.
+    pub layout_id: LayoutId,
+    /// Layout node hosting the chat cell.
+    pub node_id: NodeId,
+}
+
+impl ChatDraftKey {
+    /// Builds a draft key.
+    #[must_use]
+    pub const fn new(project_id: ProjectId, layout_id: LayoutId, node_id: NodeId) -> Self {
+        Self {
+            project_id,
+            layout_id,
+            node_id,
+        }
+    }
+}
+
+/// Durable text draft for one custom chat composer.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ChatDraft {
+    /// Stable draft scope.
+    pub key: ChatDraftKey,
+    /// Draft text. Attachments are deliberately excluded.
+    pub text: String,
+    /// Last update time, epoch milliseconds.
+    pub updated_at_ms: u64,
+}
+
+impl ChatDraft {
+    /// Builds validated draft metadata.
+    ///
+    /// # Errors
+    /// Returns [`ChatDraftError::TooLarge`] when `text` exceeds the maximum
+    /// persisted draft size.
+    pub fn new(
+        key: ChatDraftKey,
+        text: impl Into<String>,
+        updated_at_ms: u64,
+    ) -> Result<Self, ChatDraftError> {
+        let text = text.into();
+        if text.len() > CHAT_DRAFT_MAX_BYTES {
+            return Err(ChatDraftError::TooLarge {
+                max: CHAT_DRAFT_MAX_BYTES,
+                actual: text.len(),
+            });
+        }
+        Ok(Self {
+            key,
+            text,
+            updated_at_ms,
+        })
+    }
+}
+
+/// Chat draft validation errors.
+#[derive(Debug, Clone, PartialEq, Eq, Error)]
+pub enum ChatDraftError {
+    /// Draft content exceeds the persisted size limit.
+    #[error("chat draft exceeds {max} bytes: {actual}")]
+    TooLarge {
+        /// Maximum allowed bytes.
+        max: usize,
+        /// Actual text bytes.
+        actual: usize,
+    },
+}