Add branch_task endpoint for task branching

Implement POST /api/v1/mesh/tasks/{id}/branch endpoint that:
- Creates a new anonymous task from an existing task's conversation
- Sets branched_from_task_id to track the source task
- Optionally includes conversation history for context continuation
- Automatically starts on available daemon if one is connected
- Uses continue_from_task_id to inherit worktree from source
- Records history event for branching operation

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

1 files changed, 254 insertions, 3 deletions

diff --git a/makima/src/server/handlers/mesh.rs b/makima/src/server/handlers/mesh.rs
index 275dc3c..b6eadf1 100644
--- a/makima/src/server/handlers/mesh.rs
+++ b/makima/src/server/handlers/mesh.rs
@@ -9,9 +9,10 @@ use axum::{
 use uuid::Uuid;
 
 use crate::db::models::{
-    CreateTaskRequest, DaemonDirectory, DaemonDirectoriesResponse, DaemonListResponse,
-    SendMessageRequest, Task, TaskEventListResponse, TaskListResponse, TaskOutputEntry,
-    TaskOutputResponse, TaskWithSubtasks, UpdateTaskRequest,
+    BranchTaskRequest, BranchTaskResponse, CreateTaskRequest, DaemonDirectory,
+    DaemonDirectoriesResponse, DaemonListResponse, SendMessageRequest, Task,
+    TaskEventListResponse, TaskListResponse, TaskOutputEntry, TaskOutputResponse,
+    TaskWithSubtasks, UpdateTaskRequest,
 };
 use crate::db::repository::{self, RepositoryError};
 use crate::server::auth::Authenticated;
@@ -3304,3 +3305,253 @@ pub async fn branch_from_checkpoint(
     )
         .into_response()
 }
+
+// =============================================================================
+// Task Branching
+// =============================================================================
+
+/// Branch a task, creating a new anonymous task from an existing task's conversation.
+///
+/// Creates a new task that:
+/// - Has no contract_id (anonymous task)
+/// - Has branched_from_task_id pointing to the source task
+/// - Optionally includes conversation history from the source task
+/// - Can be started on an available daemon
+#[utoipa::path(
+    post,
+    path = "/api/v1/mesh/tasks/{id}/branch",
+    params(
+        ("id" = Uuid, Path, description = "Source task ID to branch from")
+    ),
+    request_body = BranchTaskRequest,
+    responses(
+        (status = 201, description = "Task branched successfully", body = BranchTaskResponse),
+        (status = 400, description = "Invalid request", body = ApiError),
+        (status = 401, description = "Unauthorized", body = ApiError),
+        (status = 404, description = "Source task not found", body = ApiError),
+        (status = 503, description = "Database not configured", body = ApiError),
+        (status = 500, description = "Internal server error", body = ApiError),
+    ),
+    security(
+        ("bearer_auth" = []),
+        ("api_key" = [])
+    ),
+    tag = "Mesh"
+)]
+pub async fn branch_task(
+    State(state): State<SharedState>,
+    Authenticated(auth): Authenticated,
+    Path(source_task_id): Path<Uuid>,
+    Json(req): Json<BranchTaskRequest>,
+) -> impl IntoResponse {
+    let Some(ref pool) = state.db_pool else {
+        return (
+            StatusCode::SERVICE_UNAVAILABLE,
+            Json(ApiError::new("DB_UNAVAILABLE", "Database not configured")),
+        )
+            .into_response();
+    };
+
+    // Get the source task (must belong to the same owner)
+    let source_task = match repository::get_task_for_owner(pool, source_task_id, auth.owner_id).await {
+        Ok(Some(task)) => task,
+        Ok(None) => {
+            return (
+                StatusCode::NOT_FOUND,
+                Json(ApiError::new("NOT_FOUND", "Source task not found")),
+            )
+                .into_response();
+        }
+        Err(e) => {
+            tracing::error!("Failed to get source task: {}", e);
+            return (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(ApiError::new("DB_ERROR", e.to_string())),
+            )
+                .into_response();
+        }
+    };
+
+    // Build conversation history if requested
+    let (conversation_history, message_count) = if req.include_conversation {
+        match repository::get_task_output(pool, source_task_id, Some(500)).await {
+            Ok(events) => {
+                let entries: Vec<TaskOutputEntry> = events
+                    .into_iter()
+                    .filter_map(TaskOutputEntry::from_task_event)
+                    .collect();
+                let count = entries.len();
+
+                // Convert entries to a JSON array for conversation_history
+                let history_json = serde_json::to_value(&entries).unwrap_or(serde_json::Value::Null);
+                (Some(history_json), count)
+            }
+            Err(e) => {
+                tracing::warn!("Failed to get task output for branching: {}", e);
+                (None, 0)
+            }
+        }
+    } else {
+        (None, 0)
+    };
+
+    // Generate task name if not provided
+    let task_name = req.name.unwrap_or_else(|| {
+        format!("{} (branch)", source_task.name)
+    });
+
+    // Create the branched task (anonymous - no contract_id)
+    let create_req = CreateTaskRequest {
+        contract_id: None, // Anonymous task
+        name: task_name,
+        description: Some(format!("Branched from task: {}", source_task.name)),
+        plan: req.message,
+        parent_task_id: None,
+        is_supervisor: false,
+        priority: source_task.priority,
+        repository_url: source_task.repository_url.clone(),
+        base_branch: source_task.base_branch.clone(),
+        target_branch: None, // Branched tasks don't auto-merge
+        merge_mode: None,
+        target_repo_path: source_task.target_repo_path.clone(),
+        completion_action: Some("none".to_string()), // Don't auto-complete
+        continue_from_task_id: Some(source_task_id), // Continue from source task's worktree
+        copy_files: None,
+        checkpoint_sha: None,
+        branched_from_task_id: Some(source_task_id),
+        conversation_history,
+    };
+
+    let task = match repository::create_task_for_owner(pool, auth.owner_id, create_req).await {
+        Ok(task) => task,
+        Err(e) => {
+            tracing::error!("Failed to create branched task: {}", e);
+            return (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(ApiError::new("DB_ERROR", e.to_string())),
+            )
+                .into_response();
+        }
+    };
+
+    // Record history event for task branching
+    let _ = repository::record_history_event(
+        pool,
+        auth.owner_id,
+        None, // No contract for anonymous tasks
+        Some(task.id),
+        "task",
+        Some("branched"),
+        None,
+        serde_json::json!({
+            "name": &task.name,
+            "sourceTaskId": source_task_id,
+            "sourceTaskName": &source_task.name,
+            "messageCount": message_count,
+        }),
+    ).await;
+
+    // Try to find an available daemon to start the task
+    let daemon_id = state.daemon_connections
+        .iter()
+        .find(|d| d.value().owner_id == auth.owner_id)
+        .map(|d| d.value().id);
+
+    // If a daemon is available, start the task
+    if let Some(target_daemon_id) = daemon_id {
+        // Update task with daemon assignment
+        let update_req = UpdateTaskRequest {
+            status: Some("starting".to_string()),
+            daemon_id: Some(target_daemon_id),
+            ..Default::default()
+        };
+
+        if let Ok(Some(updated_task)) = repository::update_task_for_owner(pool, task.id, auth.owner_id, update_req).await {
+            // Send SpawnTask command to daemon
+            let command = DaemonCommand::SpawnTask {
+                task_id: task.id,
+                task_name: updated_task.name.clone(),
+                plan: updated_task.plan.clone(),
+                repo_url: updated_task.repository_url.clone(),
+                base_branch: updated_task.base_branch.clone(),
+                target_branch: updated_task.target_branch.clone(),
+                parent_task_id: None,
+                depth: 0,
+                is_orchestrator: false,
+                target_repo_path: updated_task.target_repo_path.clone(),
+                completion_action: updated_task.completion_action.clone(),
+                continue_from_task_id: updated_task.continue_from_task_id,
+                copy_files: None,
+                contract_id: None,
+                is_supervisor: false,
+                resume_session: message_count > 0, // Resume if we have conversation history
+                conversation_history: updated_task.conversation_state.clone(),
+            };
+
+            if let Err(e) = state.send_daemon_command(target_daemon_id, command).await {
+                tracing::warn!(
+                    task_id = %task.id,
+                    daemon_id = %target_daemon_id,
+                    error = %e,
+                    "Failed to send SpawnTask command for branched task, task created but not started"
+                );
+                // Task was created but not started - return without daemon_id
+                return (
+                    StatusCode::CREATED,
+                    Json(BranchTaskResponse {
+                        task,
+                        message_count,
+                        daemon_id: None,
+                    }),
+                )
+                    .into_response();
+            }
+
+            tracing::info!(
+                task_id = %task.id,
+                source_task_id = %source_task_id,
+                daemon_id = %target_daemon_id,
+                message_count = message_count,
+                "Branched task created and started"
+            );
+
+            // Broadcast task update notification
+            state.broadcast_task_update(TaskUpdateNotification {
+                task_id: task.id,
+                owner_id: Some(auth.owner_id),
+                version: updated_task.version,
+                status: "starting".to_string(),
+                updated_fields: vec!["status".to_string(), "daemon_id".to_string()],
+                updated_by: "system".to_string(),
+            });
+
+            return (
+                StatusCode::CREATED,
+                Json(BranchTaskResponse {
+                    task: updated_task,
+                    message_count,
+                    daemon_id: Some(target_daemon_id),
+                }),
+            )
+                .into_response();
+        }
+    }
+
+    // No daemon available or failed to start - return task without daemon_id
+    tracing::info!(
+        task_id = %task.id,
+        source_task_id = %source_task_id,
+        message_count = message_count,
+        "Branched task created (no daemon available to start)"
+    );
+
+    (
+        StatusCode::CREATED,
+        Json(BranchTaskResponse {
+            task,
+            message_count,
+            daemon_id: None,
+        }),
+    )
+        .into_response()
+}