$ca-task — task-board writer

The one blessed way to mutate <project-root>/.codearbiter/open-tasks.md (resolves D-1). Hand-editing the board is no longer the only path; this command keeps every entry schema-conformant and every transition dated. The board LOGIC lives in the pure _taskboardlib transforms; this command runs the thin writer hooks/taskwrite.py.

Verbs

Always put -- before user text (a desc or title) so a value beginning with - is not parsed as a flag. Resolve the interpreter once by presence — PY=python3; { command -v python3 >/dev/null 2>&1 && python3 --version >/dev/null 2>&1; } || PY=python — never python3 … || python …, which reruns the helper on any nonzero exit and reports the second run's code instead of the first's (#577) — then invoke "$PY" below.

• add — append a queued task. ID-less by default; pass --id <group>.<type> to mint a dotted ID now, --from <origin> for a harvest back-ref, --boundaries a,b for the security/trust boundaries it touches. The description must be nonblank and single-line; origin and boundary values must also stay on one line.
  • "$PY" "${PLUGIN_ROOT}/hooks/taskwrite.py" add [--id group.type] [--from origin] [--boundaries a,b] -- "<desc>"
• start — flip a task to in-progress and stamp the started date (so it can never be a dateless [~]). On an ID-less item, pass --as <group>.<type> to mint its dotted ID at pick-up. --date YYYY-MM-DD overrides today.
  • "$PY" "${PLUGIN_ROOT}/hooks/taskwrite.py" start [--as group.type] [--date YYYY-MM-DD] -- "<id|title>"
• done — flip an in-progress task to done and stamp the done date (--date overrides today). A queued task must be started first.
  • "$PY" "${PLUGIN_ROOT}/hooks/taskwrite.py" done [--date YYYY-MM-DD] -- "<id|title>"

A missing target, an already-matching state, an out-of-order transition, a malformed add field or --date, or an invalid GROUP.TYPE namespace is reported and writes nothing (exit 1). A queued done identifies the task as queued and tells the caller to start it first. Targeting by title is best-effort: prefer the dotted ID, and note that if two ID-less items share a title, start/done act on the first — give one an ID ($ca-task start --as <group>.<type> -- "<title>") to disambiguate.

When NOT to use

• Promoting workflow follow-ups in bulk → that is the harvest (includes/harvest.md), which calls this writer for you.
• Reading the board / counts → $ca-status (read-only).
• Archiving long-settled done items → deferred (D-2); done items stay in-place for now.
• Filing a separate chore(board) PR just to flip a task state → task-board transitions ([x] done-flip, [~] start-flip, new [ ] add) ride the work commit via commit-gate, co-located atomically with the code that completes, starts, or spawns the task (ADR-0008). A lagging board-only PR is the anti-pattern this design eliminates.

Hard gate

• MUST write the board only through taskwrite.py (the pure transforms), never a free-hand Edit that can malform the schema.
• start MUST stamp a started date — never leave a dateless [~].
• done MUST target an in-progress task — a queued task must go through start first.
• MUST NOT delete a task to "complete" it — mark it done so the record survives.