operation %d: modify operation missing both title and descri

Error message

operation %d: modify operation missing both title and description fields

What it means

A modify operation with an ID that is empty on both editable fields (title and description) is rejected: it would be a no-op or an accidental wipe. applySubtaskOperations requires at least one non-empty field to know what to change.

Source

Thrown at backend/pkg/providers/subtask_patch.go:78

				opLogger.Error(err.Error())
				return nil, err
			}
			if _, ok := idToIdx[*op.ID]; !ok {
				err := fmt.Errorf("operation %d: subtask with id %d not found for removal", i, *op.ID)
				opLogger.Error(err.Error())
				return nil, err
			}
			removed[*op.ID] = true
			opLogger.WithField("subtask_id", *op.ID).Debug("marked subtask for removal")

		case tools.SubtaskOpModify:
			if op.ID == nil {
				err := fmt.Errorf("operation %d: modify operation missing required id field", i)
				opLogger.Error(err.Error())
				return nil, err
			}
			if op.Title == "" && op.Description == "" {
				err := fmt.Errorf("operation %d: modify operation missing both title and description fields", i)
				opLogger.Error(err.Error())
				return nil, err
			}
			idx, ok := idToIdx[*op.ID]
			if !ok {
				err := fmt.Errorf("operation %d: subtask with id %d not found for modification", i, *op.ID)
				opLogger.Error(err.Error())
				return nil, err
			}
			// Only update fields that are provided
			if op.Title != "" {
				result[idx].Title = op.Title
				opLogger.WithField("new_title", op.Title).Debug("updated subtask title")
			}
			if op.Description != "" {
				result[idx].Description = op.Description
				opLogger.WithField("new_description_len", len(op.Description)).Debug("updated subtask description")
			}

View on GitHub (pinned to ea665308ba)

Solutions

Retry the refiner call and instruct the model to only emit modify ops that change something.
Filter out empty modify operations client-side before applying the patch.
Add prompt guidance: omit modify operations that make no changes.
Treat this as a no-op and skip the operation if you control the caller.

Example fix

// before
{"op":"modify","id":2,"title":"","description":""} // no change
// after: either drop the op or provide real content
{"op":"modify","id":2,"description":"Enumerate subdomains with amass"}

Defensive patterns

Strategy: validation

Validate before calling

for i, op := range ops {
    if op.Op == tools.SubtaskOpModify && op.Title == "" && op.Description == "" {
        return fmt.Errorf("op %d: modify is a no-op", i)
    }
}

Type guard

func modifiesSomething(op tools.SubtaskOperation) bool {
    return op.Title != "" || op.Description != ""
}

Try / catch

patched, err := applySubtaskOperations(ctx, logger, ops, subtasks)
if err != nil && strings.Contains(err.Error(), "missing both title and description") {
    // drop no-op modify ops and reapply the rest
    ops = filterNoopModifies(ops)
    patched, err = applySubtaskOperations(ctx, logger, ops, subtasks)
}

Prevention

Instruct the model to emit modify ops only with actual changes.
Pre-filter empty modify operations before applying patches.
Prompt the model to remove unchanged subtasks from its output entirely.

When it happens

Trigger: LLM emits {"op":"modify","id":2} (or with "title":"","description":"") — the patch carries no actual change, so validation fails.

Common situations: Model echoing back a subtask unchanged; prompt asking for 'review and update' causing empty updates; template/serialization dropping optional empty strings leaving a bare modify.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of vxcontrol/pentagi@ea665308ba (2026-09-01). Data as JSON: /api/errors/f1bbe2e1813fe4ce. Report an issue: GitHub.