Agent: what a day of live use asked for

Twenty-one prompts against the live assistant found one fabricated success,
a model that believed it was 2025, and a describe_garden that was ~450 plop
entries per turn. This is the set of fixes, each traceable to a finding:

- The gardener's LOCAL day travels with the turn (`today` on POST /agent/chat,
  sent by the UI like plantedAt) into the system prompt and every dated tool
  default. Left to guess, the model dated journal entries a year back; left to
  the server, a 9 pm fill landed on UTC's tomorrow.
- describe_garden groups plops by plant — count, where, planted date, days to
  maturity — and lists ids only for groups of ≤ 8; list_plantings spells a big
  group out on demand and remove_plantings acts on one plant in a bed ("take
  the beets out, leave the garlic"), which used to mean 116 single removals.
- New tools: move_planting (keeps the planting date; across beds via the new
  MovePlanting, which is why the store's UPDATE now writes object_id),
  update_plant, read_history, copy_garden (the "<garden> — <year>" plan
  convention). fill_region takes an explicit local rectangle and a seedLotId;
  place_planting's radius defaults to one plant (spacing/2) instead of a guess.
- The system prompt states the date and the gardener's units, forbids claiming
  a change no tool made, says it cannot undo and points at the Undo button,
  asks before clearing beds on an ambiguous sentence, and stops narrating its
  own plantings into the journal.
- A mutation aimed at ANOTHER garden inside a turn is recorded under that
  garden as its own change set, not filed into the open scope.
- UI: the thread scrolls inside the Assistant panel so the composer stays
  put; every tool has a step label; wide tables stay inside the bubble.

Co-Authored-By: Claude Fable 5 <[email protected]>

internal/agent/doc.go

@@ -29,8 +29,15 @@
 //
 // # Unconfigured instances
 //
-// With no API key the assistant is simply not offered: the chat route isn't
-// registered and the capability isn't advertised — the same shape as OIDC
-// 404ing when unconfigured. An instance without a key starts and serves the app
-// exactly as it did before.
+// With no API key the assistant is simply not offered: the chat route answers
+// 503 and /capabilities says agent:false, so the UI never shows the tab. (The
+// route is always registered — a Settings change can turn the assistant on
+// without a restart, which a missing route couldn't do.) An instance without a
+// key starts and serves the app exactly as it did before.
+//
+// # The gardener's day
+//
+// A turn carries the person's local date (from the client) into the prompt and
+// every dated tool default. The model is never the source of a date: left to
+// guess, it wrote the year it remembered from training.
 package agent