fix(api): do the things the API says yes to

Three reports from somebody driving the app through the MCP connector,
all the same shape: an argument accepted, an OK returned, and nothing
done.

**project_id on an update never moved the task.** Both the REST handler
and the MCP tool read it, both checked the caller's rights on the
destination — which reads as "understood" — and then neither passed it
on, because store.TaskUpdate has no such field: a project change is a
move, since sort_order is per project. So the task stayed where it was
and the answer said OK. Moving a task between projects was impossible
except by creating it again and closing the old one, which is what the
person ended up doing. Both paths now go through one helper, so they
cannot drift apart again.

**An unknown #project vanished without a word.** The parser reads
"#3Dekoration" correctly; the lookup then fails, the task goes to the
Inbox, and the name is gone from the title with nothing anywhere saying
why. Still not an error — a thought should not be thrown away over a typo
— but quick-add now returns unknown_project, and the MCP tool returns a
note written for a model to relay. The old behaviour was kind in the web
interface, where you see the row appear in the wrong place and fix it. In
a chat nobody sees the row.

**Sub-tasks were unreachable over MCP.** create_task had no parent_id,
though the REST API has had it all along, so importing a parent with
seven children produced eight unrelated tasks with the parent's name
prefixed onto each. A sub-task joins its parent's project — the two
cannot disagree — and a second level is refused rather than silently
flattened.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/httpapi/mcp_handlers.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"strings"
@@ -57,7 +58,8 @@ func (s *Server) buildMCP() *mcp.Server {
 		InputSchema: mcp.Schema(map[string]any{
 			"text":        mcp.Str("The task as a sentence, parsed for date, time, priority, #project, @label and recurrence."),
 			"content":     mcp.Str("The task title, if not using `text`."),
-			"project_id":  mcp.Str("Which project. Defaults to the Inbox."),
+			"project_id":  mcp.Str("Which project. Defaults to the Inbox. Naming a project that does not exist is not an error — the task goes to the Inbox and the answer says so."),
+			"parent_id":   mcp.Str("Make this a sub-task of that task. It joins the parent's project. One level deep."),
 			"due_date":    mcp.Str("A date as YYYY-MM-DD."),
 			"priority":    mcp.Int("1 (highest) to 4 (none)."),
 			"description": mcp.Str("Longer notes on the task."),
@@ -253,6 +255,7 @@ func (s *Server) mcpCreateTask(ctx context.Context, userID string, args json.Raw
 		Text        string   `json:"text"`
 		Content     string   `json:"content"`
 		ProjectID   string   `json:"project_id"`
+		ParentID    string   `json:"parent_id"`
 		DueDate     string   `json:"due_date"`
 		Priority    int      `json:"priority"`
 		Description string   `json:"description"`
@@ -268,6 +271,11 @@ func (s *Server) mcpCreateTask(ctx context.Context, userID string, args json.Raw
 	task := &store.Task{CreatedBy: userID, Priority: 4}
 	labels := params.Labels
 
+	// Reported below rather than swallowed. "#Dekoration" used to vanish from the
+	// title while the task went to the Inbox, with nothing anywhere saying so —
+	// invisible in a chat, where nobody sees the row that was written.
+	unknownProject := ""
+
 	if text := strings.TrimSpace(params.Text); text != "" {
 		parsed := quickadd.Parse(text, time.Now().In(userLocation(user.Timezone)), user.Locale)
 		task.Content = parsed.Content
@@ -280,6 +288,8 @@ func (s *Server) mcpCreateTask(ctx context.Context, userID string, args json.Raw
 		if parsed.Project != "" && params.ProjectID == "" {
 			if id, err := s.db.ProjectByName(ctx, userID, parsed.Project); err == nil {
 				task.ProjectID = id
+			} else {
+				unknownProject = parsed.Project
 			}
 		}
 	}
@@ -305,6 +315,23 @@ func (s *Server) mcpCreateTask(ctx context.Context, userID string, args json.Raw
 	if params.ProjectID != "" {
 		task.ProjectID = params.ProjectID
 	}
+
+	// A sub-task belongs to its parent's project, whatever else was asked for:
+	// the two cannot disagree, and the parent is the more specific instruction.
+	// Without this the tools could not build a tree at all — an import of a
+	// parent with seven children arrived as eight unrelated tasks.
+	if params.ParentID != "" {
+		parent, err := s.db.GetTask(ctx, params.ParentID, userID)
+		if err != nil {
+			return nil, mcp.ArgError("no task with id %q to hang this under", params.ParentID)
+		}
+		if parent.ParentID != "" {
+			return nil, mcp.ArgError("sub-tasks are one level deep; %q is already a sub-task", params.ParentID)
+		}
+		task.ParentID = parent.ID
+		task.ProjectID = parent.ProjectID
+	}
+
 	if task.ProjectID == "" {
 		if task.ProjectID, err = s.db.InboxID(ctx, userID); err != nil {
 			return nil, err
@@ -319,10 +346,23 @@ func (s *Server) mcpCreateTask(ctx context.Context, userID string, args json.Raw
 	}
 
 	s.hub.Publish(task.ProjectID, "task.created", toTaskJSON(*task))
-	return map[string]any{
+
+	out := map[string]any{
 		"id": task.ID, "content": task.Content, "priority": task.Priority,
 		"due_date": task.DueDate, "project_id": task.ProjectID,
-	}, nil
+	}
+	if task.ParentID != "" {
+		out["parent_id"] = task.ParentID
+	}
+	if unknownProject != "" {
+		// Phrased for a model to relay: it says what happened and what to do,
+		// so the person is told rather than left with a task in the wrong place.
+		out["note"] = fmt.Sprintf(
+			"There is no project called %q, so this went to the Inbox. "+
+				"Create the project and move it, or say which project you meant.",
+			unknownProject)
+	}
+	return out, nil
 }
 
 func (s *Server) mcpUpdateTask(ctx context.Context, userID string, args json.RawMessage) (any, error) {
@@ -364,8 +404,11 @@ func (s *Server) mcpUpdateTask(ctx context.Context, userID string, args json.Raw
 	if params.Labels != nil {
 		update.SetLabels, update.Labels = true, *params.Labels
 	}
+	// Moved before the field update, and through the same helper the REST handler
+	// uses. This used to check the caller's rights on the destination and then
+	// drop the argument, so the task never moved and the answer still said OK.
 	if params.ProjectID != nil {
-		if _, err := store.RequireProjectRole(ctx, s.db, *params.ProjectID, userID, store.RoleEditor); err != nil {
+		if err := s.moveTaskToProject(ctx, params.TaskID, *params.ProjectID, userID); err != nil {
 			return nil, mcp.ArgError("no project with id %q that you can write to", *params.ProjectID)
 		}
 	}
@@ -379,9 +422,13 @@ func (s *Server) mcpUpdateTask(ctx context.Context, userID string, args json.Raw
 	}
 	s.hub.Publish(task.ProjectID, "task.updated", toTaskJSON(*task))
 
+	// project_id is in the answer because it is one of the things that can be
+	// changed here: a caller that asked for a move can see whether it happened
+	// rather than taking "OK" on trust.
 	return map[string]any{
 		"id": task.ID, "content": task.Content, "priority": task.Priority,
 		"due_date": task.DueDate, "labels": task.Labels,
+		"project_id": task.ProjectID,
 	}, nil
 }