Agent: undo for real, past seasons, and tools that correct the record

Six tools the live assistant kept needing and a prompt that knows about them:

- undo_change wraps RevertChangeSet(source=agent). A revert is its own change
  set, so Run reports the last one as the turn's handle when the turn changed
  nothing else — an undo-only reply keeps its "Undo this", which is now a redo.
- describe_garden takes a year: the season view (GardenFull(year)), pulled
  plops included, with removed/removedAt per group and per plop; list_years
  says which years have records. Rotation questions finally have data.
- update_planting corrects a plop's date, count, label, radius or seed lot in
  place; remove_planting, remove_plantings and clear_object take a removedAt so
  a harvest can be backdated.
- update_journal_entry / delete_journal_entry correct a note instead of
  stacking a contradicting one.
- update_garden renames/resizes/re-units a garden and rewrites its notes — and
  the notes now go into the system prompt as the gardener's standing facts, so
  "remember we're in zone 6a" persists across conversations.

describe_garden also reports the garden's notes, version and grid, which the
new tools need. Prompt, CLAUDE.md and DESIGN.md updated to match; UI step
labels for the new tools.

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

CLAUDE.md

@@ -173,10 +173,22 @@ Conventions that follow from it:
   garden made the old per-plop describe ~450 entries on every turn. A tool that
   needs individual ids uses `list_plantings`; bulk work takes (object, plant)
   — `remove_plantings`, `ClearPlantings`. Don't add a tool that lists plops.
-- **The assistant can't undo and must not pretend to.** Asked to "undo the
-  beets", the live model replied "Done!" and changed nothing. The prompt now
-  forbids claiming a change no tool made and points at the Undo button; keep
-  both rules when editing `systemPrompt`.
+  With a `year` it is the season view (`GardenFull(year)`: every plop whose
+  time in the ground overlapped the year, pulled ones included, with `removed`
+  / `removedAt` per group) — that is how "what was here last year?" is answered.
+- **The assistant undoes through `undo_change`, never by claiming.** Asked to
+  "undo the beets", the live model once replied "Done!" and changed nothing.
+  `undo_change` wraps `RevertChangeSet(source=agent)`; the prompt still forbids
+  claiming a change no tool made. A revert is its own change set (it points at
+  what it undid), so it never joins the turn's scope — `Run` reports the last
+  revert as the turn's `ChangeSetID` when the turn made no other change, so the
+  reply's "Undo this" is a redo. Keep that fallback: without it an undo-only
+  turn is the one change in the conversation with no undo button.
+- **Garden notes are the assistant's memory.** `systemPrompt` quotes
+  `Garden.Notes` (owner-written, `%q`) as standing context, and `update_garden`
+  is how the model adds "we're in zone 6a" to them. Notes are replaced whole,
+  so the tool description tells the model to merge; don't add a second store
+  for "things the assistant remembers".
 
 - **Request deadlines are extended through `responseController(c)`, never
   `http.NewResponseController(c.Writer)`.** A controller built in a handler