tasks: card 47 — an archive button on the card

The tray works but the gesture is a drag across the whole board. Puts
the same glyph on the card's footer row, on backlog/to-do/done only,
arming on the first click as the other two-step actions do.

tasks/backlog/47-an-archive-button-on-the-card.md

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+# 47 — An archive button on the card, where the card is
+
+**Status:** Backlog
+**Priority:** Medium — archiving works, but only by dragging a card the
+length of the board to a tray at the far corner
+**Type:** Feature
+
+Today the only way to archive a card is to drag it onto the activity bar.
+That is a long gesture for a common tidy-up, it is awkward on a trackpad,
+and it is invisible to anyone who has not discovered it. Put the same
+action on the card itself: an archive chip at the right-hand end of the
+footer row, arming on the first click and firing on the second.
+
+## Context
+
+- The tray is `#tray` in `manager/core/board.html:587`, rendered at
+  `:1581` with the glyph **`⌸`** (it swaps to `↓` while a card is over
+  the bar). That glyph is the one the card's chip must wear — the whole
+  point is that the two are visibly the same action.
+- The rule about which cards may be archived already exists and is
+  already enforced server-side: `ARCHIVE_FROM = {"backlog", "to-do",
+  "done"}` in `manager/core/taskfiles.py:111`, with `archive_task()`
+  refusing anything else at `:123` ("archive takes cards from backlog,
+  to-do or done only"). `AGENTS.md` says the same in prose: cards in the
+  working stages cannot be archived — finish or walk them back first.
+- The routes exist: `POST /api/archive` and `/api/unarchive`
+  (`manager/core/httpd.py:200`, `:211`), with `state.LAST_ARCHIVED`
+  behind the ⌘Z undo the toast promises.
+- The arm-then-fire pattern is built and general:
+  `actLabel(rest, confirm, busy)` and `armAction()` (`board.html:1191`
+  onwards) drive it, and the stylesheet already anticipates a chip using
+  it — `button.chip2.armed` is styled at `:240` alongside the hover
+  actions.
+- The footer row is where `.chip2` lives: CI, copilot, PR, drive, and the
+  `$` local-command chips.
+
+**Affected areas:** `manager/core/board.html` — the card's footer row and
+its click handling. No server change: the API and its guard are done.
+
+## What to build
+
+- **An archive chip at the right-hand end of the card's footer row**,
+  wearing `⌸`. Quiet in its resting state — this is a tidy-up, not a
+  destination — and taking the `--alarm` register when armed, exactly as
+  the hover actions do.
+- **Only on `backlog/`, `to-do/` and `done/` cards.** On in-progress and
+  review cards it is not there at all, rather than present-and-refusing:
+  the board's habit is to offer what it will do. `ARCHIVE_FROM` is the
+  list; read it from the state the board already has rather than
+  hard-coding a second copy in the page.
+- **Arm on the first click, archive on the second**, through the same
+  helper the other two-step actions use. Nothing about archiving should
+  invent its own confirmation.
+- **The undo stays the promise it is.** The existing toast — ⌘Z brings it
+  back — must fire from this path too, because it is the sentence that
+  makes a one-click archive safe.
+- **The tray's count follows**, since it is the same action reaching the
+  same place.
+
+**Out of scope** — tempting neighbours left alone:
+
+- The drag-to-the-bar gesture, which keeps working exactly as it does.
+- Archiving from in-progress or review, by any route.
+- Bulk archive, or archiving from the card sheet.
+- What archiving does in git — that is card 44, and see Notes.
+
+## Acceptance
+
+- [ ] Given a card in `backlog/`, `to-do/` or `done/`, when it is
+      rendered, then its footer row ends with a `⌸` chip.
+- [ ] Given a card in `in-progress/` or `review/`, no such chip appears.
+- [ ] Clicking the chip once arms it visibly and archives nothing;
+      clicking again archives the card, and it leaves the column.
+- [ ] An armed chip disarms itself the way the other armed actions do,
+      rather than staying armed until the page is reloaded.
+- [ ] The toast after archiving names ⌘Z, and ⌘Z brings the card back to
+      the stage it came from.
+- [ ] The archive tray's count goes up by one.
+- [ ] Edge case: a card archived from the board by someone else — or by
+      hand on disk — while the chip is armed does not leave a stale armed
+      chip behind or fire a second archive.
+- [ ] Dragging a card to the bar still archives it.
+
+## Notes
+
+Worth doing after — or at least knowing about — **card 44**: archiving
+does not commit, so in team mode an archive leaves an uncommitted
+deletion, which is precisely the condition `sync` refuses to run over.
+That bug is survivable while archiving costs a deliberate drag across the
+whole board. This card makes it one click on every card in three
+columns, which is the same bug reached far more often.
+
+**Risks** — the footer row is described in `AGENTS.md` as carrying tool
+chips, which are "destinations, not statuses", while actions live in the
+status pill's slot on hover. An action chip in the footer is a
+deliberate exception to that division: the pill's slot is capped at two
+actions and already spent on most of these cards, and the card asks for
+this control to sit bottom-right. If it reads as noise on a full board,
+the fallback is to reveal it on hover like the other actions rather than
+to move it back into the pill.