Chat panel in the garden editor (#57) (#71)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

web/src/lib/history.ts

@@ -113,9 +113,10 @@ export function useRevertChangeSet(gardenId: number) {
   })
 }
 
-/** How many rows a change set touched, for "3 changes" in the list. */
-export function totalChanges(cs: ChangeSet): number {
-  return cs.counts.reduce((sum, c) => sum + c.n, 0)
+/** How many rows a change set touched, for "3 changes" in the list. Undefined
+ *  counts total zero, which callers read as "no denominator to quote". */
+export function totalChanges(cs: { counts?: ChangeCount[] }): number {
+  return (cs.counts ?? []).reduce((sum, c) => sum + c.n, 0)
 }
 
 const ENTITY_NOUNS: Record<ChangeCount['entityType'], [string, string]> = {
@@ -171,7 +172,7 @@ export function useUndo(gardenId: number) {
   const revert = useRevertChangeSet(gardenId)
   const [outcomes, setOutcomes] = useState<Record<number, UndoOutcome>>({})
 
-  const undo = (cs: ChangeSet) => {
+  const undo = (cs: UndoTarget) => {
     setOutcomes((prev) => ({ ...prev, [cs.id]: { tone: 'pending', message: 'Undoing…' } }))
     revert.mutate(cs.id, {
       onSuccess: (result) => {
@@ -197,6 +198,19 @@ export function useUndo(gardenId: number) {
   }
 }
 
+/**
+ * What undo needs to know about a change set.
+ *
+ * `counts` is optional because the chat panel offers Undo on a turn knowing only
+ * its change set id — the agent's reply carries the id, not the tally. Fabricating
+ * counts to satisfy a type would produce a confidently wrong "1 of 1 changes
+ * undone"; leaving them out lets describeUndo say what it actually knows.
+ */
+export interface UndoTarget {
+  id: number
+  counts?: ChangeCount[]
+}
+
 export interface UndoOutcome {
   tone: 'pending' | 'ok' | 'partial' | 'error'
   message: string
@@ -208,7 +222,7 @@ export interface UndoOutcome {
  * useful thing to report: a bare failure would be a lie about the two that did
  * apply, and a bare success would hide the one that didn't.
  */
-export function describeUndo(target: ChangeSet, result: RevertResult): UndoOutcome {
+export function describeUndo(target: UndoTarget, result: RevertResult): UndoOutcome {
   const skipped = result.conflicts.map(describeConflict).join('; ')
   const applied = result.changeSet ? totalChanges(result.changeSet) : 0
   if (result.conflicts.length === 0) {
@@ -221,6 +235,9 @@ export function describeUndo(target: ChangeSet, result: RevertResult): UndoOutco
   if (applied === 0) {
     return { tone: 'error', message: `Nothing was undone — ${skipped}.` }
   }
+  // Only claim a denominator when we have one. "2 of 3" from a caller that
+  // never knew the total would be a number invented to fill a sentence.
   const total = totalChanges(target)
-  return { tone: 'partial', message: `${applied} of ${total} changes undone — ${skipped}.` }
+  const scale = total > 0 ? `${applied} of ${total} changes undone` : 'Partly undone'
+  return { tone: 'partial', message: `${scale} — ${skipped}.` }
 }