feat(tasks): align Task edit UI's AC editor with Task Draft

[ChenNima]

Summary

The real Task edit form rendered acceptance criteria as a legacy Markdown <Textarea>, while the Task Draft panel used a structured-rows editor (one row per item with a required toggle). Every other editable field on the form was already aligned with the draft panel — only the AC editor had drifted.

This PR closes that gap:

• Extracts the structured AC editor into a shared controlled component so the draft panel and the real-task panel render identical UI by construction (they can no longer drift).
• Persists real-task AC edits through the existing replaceAcceptanceCriteria service via a small extension to updateTaskFieldsAction — no new service, REST endpoint, or schema change.
• Uses client-side change detection so editing a non-AC field (title, description, priority, storyPoints) does not trigger the destructive replace — existing dev/admin verification marks survive.
• Empty-clear guard: if a user wipes all criteria, the form blocks Save with the existing required-AC i18n message rather than letting the server throw.

OpenSpec change align-task-edit-ui-with-draft is included and archived in this PR.

Changed files

File	Change
src/components/acceptance-criteria-editor.tsx	New. Shared controlled AcceptanceCriteriaEditor + AcceptanceCriteriaItemDraft type + acCriteriaChanged(original, edited) change-detection helper.
src/components/__tests__/acceptance-criteria-editor.test.ts	New. 12 unit tests for acCriteriaChanged: identical, whitespace-only, length, description text, required flip, mid-list flip, reorder, add/remove, empty↔populated.
src/app/(dashboard)/projects/[uuid]/proposals/[proposalUuid]/task-draft-detail-panel.tsx	Replaces ~60 lines of inline AC editor JSX with <AcceptanceCriteriaEditor>. Behavior preserved (empty-row filtering on save remains in handleSave).
src/app/(dashboard)/projects/[uuid]/tasks/task-detail-panel.tsx	Removes legacy <Textarea> + editAcceptanceCriteria string state. Adds editCriteriaItems seeded from task.acceptanceCriteriaItems, mounts the shared editor, and conditionally spreads acceptanceCriteriaItems into updateTaskFieldsAction only when acCriteriaChanged is true. Empty-set guard short-circuits with the i18n required-AC message.
src/app/(dashboard)/projects/[uuid]/tasks/[taskUuid]/actions.ts	Extends UpdateTaskFieldsInput with optional acceptanceCriteriaItems. After updateTask(...), when the field is provided (!== undefined) routes it to replaceAcceptanceCriteria. Auth/scoping/error-handling preserved; required-AC error surfaced verbatim.
messages/en.json, messages/zh.json	Adds acceptanceCriteria.atLeastOneRequired for the empty-clear inline error in both locales.
openspec/changes/archive/2026-06-07-align-task-edit-ui-with-draft/	OpenSpec change archive (proposal/design/spec/tasks).
openspec/specs/task-edit-ui/spec.md	New long-term spec for the task-edit-ui capability, emitted by openspec archive.

Test plan

• npx tsc --noEmit → exit 0
• pnpm test -- src/components/__tests__/acceptance-criteria-editor.test.ts → 12/12 pass
• npx eslint on the touched files → exit 0 (warnings only, all pre-existing)
• Manual: open a task with passed-AC and edit the title — verify Save preserves the green AC marks
• Manual: open a task and add/edit/remove a criterion — verify Save replaces the set and resets verification marks
• Manual: open a task, delete every criterion in the editor, click Save — verify the inline "at least one acceptance criterion required" message appears and no server call is made
• Manual: confirm the draft panel's AC editor still works identically

Out of scope / follow-ups

• docs/design.pen update for the new Task panel AC editor — Pencil MCP bridge to VS Code was unreachable during this work; will be picked up in a small follow-up once Pencil connectivity is restored.
• Removing the legacy task.acceptanceCriteria Markdown column — left in the model since it requires a migration; noted as future cleanup.

🤖 Generated with Claude Code

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	97.41% (🎯 95%)	2449 / 2514
🔵	Statements	96.36% (🎯 95%)	2676 / 2777
🔵	Functions	96.03% (🎯 93%)	508 / 529
🔵	Branches	89.37% (🎯 85%)	1641 / 1836

File Coverage

No changed files found.

Generated in workflow #709 for commit 2a0fc06 by the Vitest Coverage Report Action