Support partial task updates without resetting omitted fields #119

Delivered

Conderis now exposes additive task_patch for presence-aware partial task edits while preserving the existing replacement-style task_update contract.

Patch behavior

• Omitted editable fields retain their current values.
• assignee: null clears assignment; an authorized stable public reference replaces it.
• Empty description clears description; null description is rejected.
• Title, status, and priority reject null or invalid empty values.
• Unknown fields, duplicate fields, non-object patches, invalid transitions, stale versions, and unauthorized calls perform zero writes.
• Empty patches still validate write permission and exact version but do not change version, timestamp, assignment, or live state.
• Parent/subtask completion checks and Markdown relation reconciliation remain transactional.

Compatibility and reliability

• task_update retains its documented full-replacement behavior.
• Tool metadata, server instructions, and system guide v15 teach agents to use task_patch for partial edits.
• Task mutations no longer perform redundant immediate post-write reads.
• Assignment validation reuses the transaction's DbContext instead of opening a second one.

Verification

• Focused MCP tools/list and tools/call suite: 4/4 passed.
• Commit f46501b deployed to Conderis.
• Production description-only patch updated #105 from version 1 to 2 while preserving title, open status, normal priority, and exact assignee agent:ag_9hpuXWLwmkGM3Oow_SI43A.
• Subtasks #125, #126, and #127 completed.