board: 19 → in-progress (istos)

2026-07-30 09:22:13 +02:00
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 # 19 — Boards sync through origin/main: push on move, pull on a beat
 **Status:** In Progress
 **Assignee:** istos
 **Priority:** High — this is the multi-user feature; 18 without it is bookkeeping
 **Type:** Feature
 **Depends on:** 18 — the claim commit is what gets pushed, and its
 same-commit atomicity is what makes the races below resolve correctly
 One machine's `tasks/` is the truth today; everyone else's is stale
 until someone remembers to push and pull. Make origin/main the truth
 and every board a converging replica: board-made moves push
 immediately, every board pulls on a short beat, remote moves appear in
 the ticker attributed to their author, and losing a same-card race is
 a toast, not a mystery.
 ## Context
 - `watch.py` polls the stage directories every 2s — remote changes
  that arrive via pull are already noticed and narrated; today they
  would read "disk", this card upgrades them to the commit author.
 - Task 14 (landed) already points fresh agent branches at
  origin/main; this card gives the *board state* the same treatment.
 - The precondition that makes pulling safe is bench's own discipline:
  code work lives in worktrees and PRs, so the main checkout stays
  clean and fast-forwardable. Team mode assumes — and the docs must
  say — that local main advances only through the board and origin.
 - Push publishes every local-ahead commit, not just the board's —
  the piggyback hazard below is the sharpest edge in this card.
 **Affected areas:** a new small `sync.py` (or a sibling thread beside
 `watch.py`), `config.py` (settings), `state.py`/ticker attribution,
 AGENTS.md (team-mode discipline).
 ## What to build
 - **Gate**: `BOARD_SYNC=1` (default off; implies `BOARD_COMMIT_MOVES`).
  Off = today's behaviour exactly.
 - **Push, event-driven**: after each board-made task commit, push. On
  non-fast-forward: fetch, rebase the board commits, push again. If
  the rebase conflicts on a task file, the local move loses: revert
  it, re-read the remote version, and toast who took it
  ("07 claimed by elena — your move was undone").
 - **Piggyback guard**: before any auto-push, every local-ahead commit
  on main must be `board: `-prefixed. Anything else → no push, one
  clear ticker warning naming the stray commit. Never publish a
  human's unpushed work as a side effect.
 - **Pull, periodic**: fetch + fast-forward-only merge every
  `BOARD_SYNC_INTERVAL` (default ~30s) and once at startup. Never
  pull into a non-clean tree or past a divergence — narrate and wait
  for a human instead. The watcher then narrates arrived moves with
  the commit author's name instead of "disk".
 - **Offline**: unreachable origin degrades to local-only silently
  sane — commits queue, a quiet ticker note says sync is behind,
  next successful fetch catches up. No errors every 30s.
 **Out of scope** — tempting neighbours left alone:
 - Reacting to synced state with side effects — replicas render only
  (task 20 owns the etiquette).
 - Syncing `local/state/` — liveness stays per-board by design.
 - Any transport other than git via origin; any branch other than main.
 ## Acceptance
 - [ ] Given two clones with `BOARD_SYNC=1`, when A moves a card, then
      within one beat B's board shows the move and B's ticker
      attributes it to A's git name.
 - [ ] Given both move the same card in one window, then exactly one
      claim survives on origin, the loser's board reverts with the
      take-over toast, and both converge to the same file bytes.
 - [ ] Given a human's non-board commit sitting on local main, when
      the board would push, then it refuses with the named warning
      and the human's commit stays private.
 - [ ] Edge case — origin unreachable: boards keep working locally,
      one quiet ticker note, full convergence after connectivity
      returns; no error spam.
 - [ ] With the gate off, no fetch, no push, no behaviour change.
 ## Open questions
 - None.
 ## Notes
 Middle card of the multi-user arc (18 claim → 19 sync → 20 etiquette).
 Git is the lock server and main the linearizer: push races are the
 concurrency control, which is why the claim must ride in the move's
 own commit (18) and why replicas must not react (20).
 **Risks**
 - ff-only pulls plus the piggyback guard mean a divergent main stalls
  sync until a human resolves it — correct, but the stall must be
  loudly visible or two halves of a team quietly stop converging.
 - A 30s beat × N boards is N fetches/min against origin — fine for
  GitHub, worth a doc line for rate-limited setups.
 - Reverting a lost move while the user is mid-drag needs care in the
  UI — the board re-reads disk on every render, which should make
  this safe, but test the race deliberately.