Specify partial-update field presence and compatibility #125

Selected contract

Add task_patch beside the existing replacement-style task_update. Required top-level arguments are projectId, taskNumber, version, and a JSON object named patch. task_update keeps its current behavior during the compatibility window.

Presence matrix

Field	Omitted	null	Empty string	Supplied value
title	Preserve	Reject	Reject	Validate 1-160 characters and replace
description	Preserve	Reject	Clear	Validate at most 4000 characters and replace
status	Preserve	Reject	Reject	Validate enum and transition, then replace
priority	Preserve	Reject	Reject	Validate enum and replace
assignee	Preserve without re-resolution	Clear assignment	Reject	Resolve an authorized stable public reference and replace

Unknown or duplicate patch properties, non-string field values, and a non-object patch are rejected. An empty object is a validated no-op: write permission and exact version are still required, but version, timestamp, assignment, and live events remain unchanged. Any stale or invalid patch performs zero writes.

Example

{
  "projectId": "...",
  "taskNumber": 105,
  "version": 3,
  "patch": { "description": "Updated specification" }
}

This preserves title, status, priority, and the exact current assignee without resolving its display name.