Add task branching models and update CreateTaskRequest

- Add branched_from_task_id field to Task struct
- Make contract_id optional in CreateTaskRequest for anonymous tasks
- Add branched_from_task_id and conversation_history to CreateTaskRequest
- Add BranchTaskRequest struct for branching API
- Add BranchTaskResponse struct with task, message_count, daemon_id

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 43 insertions, 2 deletions

diff --git a/makima/src/db/models.rs b/makima/src/db/models.rs
index 291fad7..bf95a3a 100644
--- a/makima/src/db/models.rs
+++ b/makima/src/db/models.rs
@@ -519,6 +519,12 @@ pub struct Task {
     /// When the task was last interrupted due to daemon disconnect
     #[serde(skip_serializing_if = "Option::is_none")]
     pub interrupted_at: Option<DateTime<Utc>>,
+
+    // Task branching
+    /// Source task ID when this task was branched from another task's conversation.
+    /// Used to track the origin of "what if" explorations.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub branched_from_task_id: Option<Uuid>,
 }
 
 impl Task {
@@ -598,8 +604,8 @@ pub struct TaskListResponse {
 #[derive(Debug, Deserialize, ToSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct CreateTaskRequest {
-    /// Contract this task belongs to (required)
-    pub contract_id: Uuid,
+    /// Contract this task belongs to (optional for branched/anonymous tasks)
+    pub contract_id: Option<Uuid>,
     /// Name of the task
     pub name: String,
     /// Optional description
@@ -633,6 +639,10 @@ pub struct CreateTaskRequest {
     pub copy_files: Option<Vec<String>>,
     /// Checkpoint SHA to branch from (optional)
     pub checkpoint_sha: Option<String>,
+    /// Source task ID when branching from another task's conversation
+    pub branched_from_task_id: Option<Uuid>,
+    /// Conversation history to initialize the task with (JSON array of messages)
+    pub conversation_history: Option<serde_json::Value>,
 }
 
 /// Request payload for updating a task
@@ -681,6 +691,37 @@ pub struct SendMessageRequest {
     pub message: String,
 }
 
+/// Default for include_conversation field in BranchTaskRequest
+fn default_include_conversation() -> bool {
+    true
+}
+
+/// Request to branch a task from an existing task's conversation.
+/// Creates a new anonymous task that continues from the source task's state.
+#[derive(Debug, Deserialize, ToSchema)]
+#[serde(rename_all = "camelCase")]
+pub struct BranchTaskRequest {
+    /// The initial message/instructions for the branched task
+    pub message: String,
+    /// Optional name for the branched task (auto-generated if not provided)
+    pub name: Option<String>,
+    /// Whether to include conversation history from the source task (default: true)
+    #[serde(default = "default_include_conversation")]
+    pub include_conversation: bool,
+}
+
+/// Response from branching a task.
+#[derive(Debug, Serialize, ToSchema)]
+#[serde(rename_all = "camelCase")]
+pub struct BranchTaskResponse {
+    /// The newly created branched task
+    pub task: Task,
+    /// Number of conversation messages included from source task
+    pub message_count: usize,
+    /// Daemon ID if the task was started (None if no daemon available)
+    pub daemon_id: Option<Uuid>,
+}
+
 // =============================================================================
 // Daemon Types
 // =============================================================================