feat(kanban/dashboard): board archive/restore/hard-delete UX + per-stage timestamps

[nnnet]

Summary

Two related dashboard improvements bundled into one PR:

1. Board lifecycle in the dashboard — archive/restore/hard-delete via UI with safety rails (hard-delete only reachable on already-archived boards).
2. Per-stage timestamps on cards — cards show "created_age / in-stage_age ago" instead of only created_at.

1. Board lifecycle UX

New backend endpoints

• POST /boards/{slug}/archive — soft archive (board dir moved to boards/_archived/<slug>-<ts>/); recoverable.
• POST /boards/{slug}/restore — un-archive.
• DELETE /boards/{slug}?delete=true — hard-delete (default delete=false is archive for backwards compat).
• cascade=true query — opt-in to operate on non-empty boards (refuses with HTTP 409 + task_count otherwise). Default is refuse — accidental clicks on a populated board do not silently wipe data.

Dashboard

• Toolbar: [+ New board] [Archive] — Archive is the panel toggle. No Delete button on toolbar (was a source of foot-guns).
• Archive viewer header has a new [ToArchive] action that moves the currently active board into the archive (cascade for non-empty). Hidden for default (cannot be archived).
• Archive viewer rows for archived boards show [Restore] and a new [Delete] — Delete is the only path to permanent hard-delete and is only reachable here, after the board is already archived. Two-step confirm.
• After archive/hard-delete: optimistic local filter removes the slug from the selector immediately + loadBoardList() refetches.

Backend hardening

• hard_delete_board auto-switches the current pointer to default if the deleted board was active. Previously returned HTTP 409 "switch first" — pure friction since the dashboard always intends to remove the current board.
• kanban_db.connect() refuses to auto-resurrect a deleted board. Previously path.parent.mkdir(parents=True, exist_ok=True) silently recreated boards/<slug>/ if any stale caller (frontend with cached ?board=<gone> query, dispatcher tick before list refresh, current pointer not cleared) opened a connection to the gone slug. Now raises FileNotFoundError for non-default boards whose parent dir doesn't exist. Callers that wrap connect() in try/except (dispatcher tick, _board_counts) degrade gracefully.
• Selector filter: GET /boards defaults to include_archived=False.

Dispatcher safety (verified)

• list_boards(include_archived=False) excludes archived boards from _tick_once iteration — archived boards are quiescent.
• Tasks with status='archived' are skipped by both the promoter (WHERE status='todo') and the claim path (WHERE status='ready').
• restore_task sets status='todo' — next tick promotes to ready, tick after claims. No state loss across archive→restore.

2. Per-stage timestamps on cards

Backend

• _task_dict() emits entered_status_at (unix seconds) — time the task entered its current status. Derived from existing task_events audit log (kinds: promoted → ready, claimed → running, completed → done, blocked → blocked, archived → archived, restored/claim_rejected → todo rollback).
• Batch query (_batch_entered_status_at) avoids N+1 on the board list endpoint. Index idx_events_task makes lookup O(log n) per task.
• No DB schema change — the data was already in task_events.

Frontend

• Card age label: "3h / 12m ago" when entered_status_at !== created_at (single ago suffix). Falls back to plain "3h ago" when the task never moved (status=todo without transitions).
• Edge cases handled: timeAgo() special strings like "just now" / "yesterday" render without a trailing ago ("3h / just now").

Tests

• tests/plugins/kanban/test_board_archive_api.py — 540 lines, comprehensive: archive default-refusal, restore, cascade rules, hard-delete refusal-by-default, selector filter, switch-then-archive flow.
• tests/plugins/kanban/test_dashboard_stage_entered_time.py — 323 lines, one test per status type + batch query correctness + edge cases.
• tests/plugins/test_kanban_dashboard_plugin.py — added bundle regression incl. node --check syntax guard (subprocess.run; pytest.skip if node not on PATH).

Bundle patching note

plugins/kanban/dashboard/dist/index.js is hand-patched (no build step in this tree). Every edit was validated with node --check plus a mock-load that asserts register() is called. The new test_dashboard_bundle_syntax_valid enforces this in CI so a future patch can't accidentally break the IIFE.

Test plan

• pytest tests/plugins/kanban/ tests/plugins/test_kanban_dashboard_plugin.py passes
• Archive a non-empty board via UI → appears in Archive viewer → Restore → board back in selector with all tasks
• Hard-delete the same board from archive row → board + all tasks wiped, doesn't reappear after refresh
• On a board with movement, cards show two timestamps via slash; on fresh todo tasks, only one

[teknium1]

Thanks @nnnet — closing this one. 2767 LOC including a regenerated dist bundle is too cross-cutting for mechanical salvage. The archive/restore/hard-delete UX is good direction but the bundle conflicts and the per-stage timestamps schema decision deserve a focused fresh PR. Appreciate the work.