Chat panel in the garden editor (#57)

The conversational surface, in the editor rather than on its own page. The
reason is the feedback loop: watching the canvas change as the agent works IS
the confirmation, which is exactly what makes "act freely without asking first"
tolerable. It also means the agent never has to guess which garden you mean.

Tool calls surface as they happen, in the app's own vocabulary — "Clearing a
bed", "Looking up a plant" — not raw tool names or JSON. That is the difference
between the panel feeling like it's doing something and feeling like it's hung,
which matters because a replant makes a dozen calls over tens of seconds. An
unknown tool degrades to readable words rather than showing snake_case at the
user, so the client can lag the server by a tool without looking broken.

The canvas refreshes as each step lands, not just at the end. Refreshing only on
completion would put the whole point of siting the chat here — watching it work
— behind the same wait that streaming exists to remove.

Undo sits on the turn itself, so the common case never involves opening the
History panel. It uses #49's useUndo, not a second implementation, which meant
giving that hook an UndoTarget: the chat knows a turn's change set id but not
its tally, and fabricating counts to satisfy the type would have produced a
confidently wrong "1 of 1 changes undone". describeUndo now says "Partly undone"
when it has no denominator rather than inventing one.

The panel is only offered when the instance actually has the assistant
configured, via a new /capabilities read. The routes 404 without a key, so
without this the client would have to probe for a 404 to find out — and a tab
that opens onto an apology is worse than no tab.

Streaming is hand-rolled over fetch rather than EventSource, which can only
issue GETs and this needs a POST body. The wire format is still SSE, so a proxy
that understands it doesn't buffer and the server wouldn't change if EventSource
became viable. Partial frames are buffered across chunks and a malformed frame
is skipped rather than killing a working stream.

Errors read as sentences, and as different sentences: a permission refusal, a
timeout and a model failure want different reactions. Every failure path
refreshes, because something may have landed before it failed — and says where
to look for it.

Closes #57

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

DESIGN.md

@@ -69,6 +69,7 @@ GET,POST /gardens/:id/journal PATCH,DELETE /journal/:id           (editor writes
 GET  /gardens/:id/journal/counts  ← entries per object, for the "has notes" indicator
 POST /agent/chat              ← SSE: step events, then the finished turn (editor only)
 GET,DELETE /gardens/:id/agent/history                             (the actor's own thread)
+GET  /capabilities            ← what this instance can do, so the UI offers only what works
 GET,POST /gardens/:id/shares  PATCH,DELETE /gardens/:id/shares/:userId    (invite by email)
 ```
 
@@ -118,7 +119,7 @@ React 19 + TypeScript + Vite + Tailwind 4 (`@tailwindcss/vite`), `@tanstack/reac
 - **Routes:** `/login`, `/register`, `/gardens` (list), `/gardens/:id` (editor, `?focus=objectId`), `/plants` (catalog). Auth guard on the router root via `/auth/me`.
 - **State:** TanStack Query for all server state (editor keyed on `gardens/:id/full`; optimistic mutations with version-conflict rollback). One small Zustand store for ephemeral editor state only: viewport, selection, focused object, active tool, in-flight drag.
 - **Editor components (`web/src/editor/`):** `GardenCanvas` (svg root + viewport g), `useViewport` (use-gesture pan/zoom/pinch), `ObjectShape`, `PlopMarker` (semantic-zoom branching), `Palette` (drag-to-place object kinds), `EditorRail` (the one side panel), `Inspector`, `HistoryPanel`, `PlantPicker`.
-- **One rail, tabs inside it.** The inspector, history, journal, and later the chat panel all want the same strip of screen; rather than each bolting on its own chrome they are tabs in `EditorRail` — so the canvas is one width instead of a different width per panel, and adding a panel is adding a tab. Selecting an object switches to the Inspector tab automatically, so the rail is never something you operate before you can edit; on a phone the same tabs render in the bottom sheet the inspector already used. Pure geometry helpers (local↔world transforms, unit formatting) in `web/src/lib/geometry.ts`, unit-tested.
+- **One rail, tabs inside it.** The inspector, history, journal and assistant all want the same strip of screen; rather than each bolting on its own chrome they are tabs in `EditorRail` — so the canvas is one width instead of a different width per panel, and adding a panel is adding a tab. Selecting an object switches to the Inspector tab automatically, so the rail is never something you operate before you can edit; on a phone the same tabs render in the bottom sheet the inspector already used. Pure geometry helpers (local↔world transforms, unit formatting) in `web/src/lib/geometry.ts`, unit-tested.
 
 ## Roadmap
 

internal/api/api.go

@@ -53,6 +53,12 @@ func New(cfg *config.Config, svc *service.Service) *gin.Engine {
 	// is set; see csrfGuard).
 	v1.Use(h.csrfGuard())
 	v1.GET("/healthz", healthz)
+	// What this instance can actually do, so the UI offers only what works. The
+	// agent routes 404 when unconfigured; without this the client would have to
+	// probe for a 404 to find that out, and a dead button is worse than no button.
+	v1.GET("/capabilities", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"agent": cfg.Agent.Ready()})
+	})
 
 	// Auth endpoints are exempt from requireAuth (you can't be logged in yet);
 	// /me is the one that needs a session. Feature routers in later issues attach

web/src/editor/ChatPanel.tsx

@@ -0,0 +1,218 @@
+import { useEffect, useRef, useState } from 'react'
+import { Alert } from '@/components/ui/Alert'
+import { Button } from '@/components/ui/Button'
+import { TextArea } from '@/components/ui/TextArea'
+import { cn } from '@/lib/cn'
+import {
+  describeStep,
+  streamChat,
+  useAgentHistory,
+  useAgentRefresh,
+  useClearAgentHistory,
+  type AgentStep,
+  type AgentTurn,
+} from '@/lib/agent'
+import { useUndo } from '@/lib/history'
+import { UndoButton } from './UndoButton'
+
+/**
+ * Talk to the garden assistant, in the editor beside the canvas.
+ *
+ * Here rather than on its own page because watching the garden change as the
+ * agent works IS the confirmation — which is what makes acting without asking
+ * first tolerable. It also means the agent never has to guess which garden you
+ * mean.
+ */
+export function ChatPanel({ gardenId, canEdit }: { gardenId: number; canEdit: boolean }) {
+  const history = useAgentHistory(gardenId, true)
+  const clear = useClearAgentHistory(gardenId)
+  const refresh = useAgentRefresh(gardenId)
+  const undo = useUndo(gardenId)
+
+  const [input, setInput] = useState('')
+  // The turn in flight: what we sent, the steps so far, and how it ended.
+  const [pending, setPending] = useState<{ message: string; steps: AgentStep[] } | null>(null)
+  const [error, setError] = useState<string | null>(null)
+  const abort = useRef<AbortController | null>(null)
+  const bottom = useRef<HTMLDivElement>(null)
+
+  // Abort an in-flight turn when the panel goes away, so a closed tab doesn't
+  // leave a read hanging.
+  useEffect(() => () => abort.current?.abort(), [])
+
+  // Follow the conversation as it grows, including mid-turn as steps arrive.
+  useEffect(() => {
+    bottom.current?.scrollIntoView({ behavior: 'smooth', block: 'end' })
+  }, [history.data, pending])
+
+  const send = () => {
+    const message = input.trim()
+    if (!message || pending) return
+    setInput('')
+    setError(null)
+    setPending({ message, steps: [] })
+
+    const controller = new AbortController()
+    abort.current = controller
+
+    void streamChat(
+      gardenId,
+      message,
+      {
+        onStep: (step) => {
+          setPending((p) => (p ? { ...p, steps: [...p.steps, step] } : p))
+          // Refresh as each step lands, not just at the end: the canvas updating
+          // under the conversation is the whole point of putting the chat here.
+          refresh()
+        },
+        onDone: (turn: AgentTurn) => {
+          setPending(null)
+          refresh()
+          if (turn.truncated) {
+            setError('That turned into more steps than I should take at once — check what changed before continuing.')
+          }
+        },
+        onError: (message) => {
+          setPending(null)
+          setError(message)
+          // Something may still have landed before it failed.
+          refresh()
+        },
+      },
+      controller.signal,
+    )
+  }
+
+  const messages = history.data ?? []
+
+  return (
+    <div className="flex h-full flex-col gap-3">
+      <div className="flex items-center justify-between gap-2">
+        <h2 className="text-sm font-semibold text-fg">Assistant</h2>
+        {messages.length > 0 && (
+          <button
+            type="button"
+            onClick={() => clear.mutate()}
+            disabled={clear.isPending}
+            className="rounded px-1.5 py-0.5 text-xs text-muted outline-none hover:text-fg focus-visible:ring-2 focus-visible:ring-accent/40"
+          >
+            Start over
+          </button>
+        )}
+      </div>
+
+      {!canEdit && (
+        <p className="rounded-md bg-border/40 px-2 py-1 text-xs text-muted">
+          You can only view this garden, so the assistant can't change anything in it.
+        </p>
+      )}
+
+      <div className="flex min-h-0 flex-1 flex-col gap-2 overflow-y-auto">
+        {history.isSuccess && messages.length === 0 && !pending && (
+          <p className="text-sm text-muted">
+            Ask for what you want and it'll do it — “change the garlic bed to cucumbers this year”, “fill the
+            north half of the west bed with beans”, “what's in here?”. Everything it does lands as one change you
+            can undo.
+          </p>
+        )}
+
+        {messages.map((m) => (
+          <Bubble key={m.id} role={m.role} body={m.body}>
+            {/* Undo on the turn itself, so the common case never involves
+                opening the History panel. Same hook #49 uses, not a second
+                implementation. */}
+            {m.role === 'assistant' && m.changeSetId != null && canEdit && (
+              <UndoButton changeSet={{ id: m.changeSetId }} undo={undo} className="mt-1 items-start" />
+            )}
+          </Bubble>
+        ))}
+
+        {pending && (
+          <>
+            <Bubble role="user" body={pending.message} />
+            <div className="rounded-lg border border-border px-2.5 py-2 text-sm">
+              <ol className="flex flex-col gap-0.5">
+                {pending.steps.map((s) => (
+                  <li key={s.index} className="text-xs text-muted">
+                    {describeStep(s)}…
+                  </li>
+                ))}
+              </ol>
+              <p className="mt-1 flex items-center gap-1.5 text-xs text-muted">
+                <span className="inline-block h-1.5 w-1.5 animate-pulse rounded-full bg-accent" />
+                {pending.steps.length === 0 ? 'Thinking…' : 'Working…'}
+              </p>
+            </div>
+          </>
+        )}
+
+        {error && <Alert>{error}</Alert>}
+        <div ref={bottom} />
+      </div>
+
+      <div className="flex flex-col gap-2 border-t border-border pt-2">
+        <TextArea
+          label="Message"
+          name="agentMessage"
+          rows={2}
+          placeholder="Change the garlic bed to cucumbers this year"
+          value={input}
+          disabled={!!pending}
+          onChange={(e) => setInput(e.target.value)}
+          onKeyDown={(e) => {
+            // Enter sends, Shift+Enter breaks the line — the convention every
+            // chat box uses, and typing a newline by accident mid-thought is a
+            // worse failure than the reverse.
+            if (e.key === 'Enter' && !e.shiftKey) {
+              e.preventDefault()
+              send()
+            }
+          }}
+        />
+        <div className="flex justify-end gap-2">
+          {pending && (
+            <Button
+              variant="ghost"
+              className="px-2 py-1 text-xs"
+              onClick={() => {
+                abort.current?.abort()
+                setPending(null)
+                refresh()
+              }}
+            >
+              Stop
+            </Button>
+          )}
+          <Button className="px-3 py-1.5 text-sm" disabled={!!pending || input.trim() === ''} onClick={send}>
+            {pending ? 'Working…' : 'Send'}
+          </Button>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+function Bubble({
+  role,
+  body,
+  children,
+}: {
+  role: 'user' | 'assistant'
+  body: string
+  children?: React.ReactNode
+}) {
+  const mine = role === 'user'
+  return (
+    <div className={cn('flex flex-col', mine ? 'items-end' : 'items-start')}>
+      <div
+        className={cn(
+          'max-w-[90%] whitespace-pre-wrap rounded-lg px-2.5 py-2 text-sm',
+          mine ? 'bg-accent/15 text-fg' : 'border border-border text-fg',
+        )}
+      >
+        {body}
+      </div>
+      {children}
+    </div>
+  )
+}

web/src/editor/UndoButton.tsx

@@ -1,6 +1,6 @@
 import { Button } from '@/components/ui/Button'
 import { cn } from '@/lib/cn'
-import type { ChangeSet, UndoOutcome, useUndo } from '@/lib/history'
+import type { UndoOutcome, UndoTarget, useUndo } from '@/lib/history'
 
 /**
  * Undo, plus what happened. Paired with useUndo so the history list and the
@@ -14,7 +14,7 @@ export function UndoButton({
   className,
   label = 'Undo',
 }: {
-  changeSet: ChangeSet
+  changeSet: UndoTarget
   undo: ReturnType<typeof useUndo>
   className?: string
   label?: string

web/src/lib/agent.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from 'vitest'
+import { describeStep } from './agent'
+
+describe('describeStep', () => {
+  // Raw tool names tell you the agent is busy; these tell you what it's busy
+  // DOING, which is the difference between the panel feeling alive and hung.
+  it("names tools in the app's own vocabulary", () => {
+    expect(describeStep({ index: 0, tools: ['clear_object'] })).toBe('Clearing a bed')
+    expect(describeStep({ index: 1, tools: ['find_plant'] })).toBe('Looking up a plant')
+  })
+
+  it('collapses repeats within one step', () => {
+    expect(describeStep({ index: 0, tools: ['fill_region', 'fill_region'] })).toBe('Filling a bed')
+  })
+
+  it('joins distinct tools', () => {
+    expect(describeStep({ index: 0, tools: ['clear_object', 'fill_region'] })).toBe('Clearing a bed, Filling a bed')
+  })
+
+  it('says something for a step with no tool calls', () => {
+    expect(describeStep({ index: 0, tools: [] })).toBe('Thinking')
+  })
+
+  // A tool added server-side before the client knows about it should degrade to
+  // something readable rather than showing snake_case at the user.
+  it('falls back readably for an unknown tool', () => {
+    expect(describeStep({ index: 0, tools: ['prune_orchard'] })).toBe('prune orchard')
+  })
+})

web/src/lib/agent.ts

@@ -0,0 +1,188 @@
+// The garden assistant's client (#57).
+//
+// The chat lives in the editor, not on its own page, because watching the canvas
+// change as the agent works IS the confirmation — which is what makes acting
+// without asking first tolerable. So this module's job is as much about
+// surfacing progress as it is about sending a message.
+
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
+import { z } from 'zod'
+import { API_BASE, api } from './api'
+import { gardenFullKey } from './objects'
+import { historyKey } from './history'
+
+const capabilitiesSchema = z.object({ agent: z.boolean() })
+
+/** Whether this instance has the assistant configured. Without it the panel
+ *  isn't rendered at all — a dead button is worse than no button. */
+export function useCapabilities() {
+  return useQuery({
+    queryKey: ['capabilities'] as const,
+    queryFn: async () => capabilitiesSchema.parse(await api.get('/capabilities')),
+    staleTime: Infinity, // server config; it doesn't change under a running page
+  })
+}
+
+export const agentMessageSchema = z.object({
+  id: z.number(),
+  conversationId: z.number(),
+  role: z.enum(['user', 'assistant']),
+  body: z.string(),
+  changeSetId: z.number().optional(),
+  createdAt: z.string(),
+})
+export type AgentMessage = z.infer<typeof agentMessageSchema>
+
+const historySchema = z.object({ messages: z.array(agentMessageSchema) })
+
+export function agentHistoryKey(gardenId: number) {
+  return ['gardens', gardenId, 'agent-history'] as const
+}
+
+/** The stored conversation, so a reload doesn't lose the thread — which is
+ *  exactly when someone reloads, to check whether a change actually landed. */
+export function useAgentHistory(gardenId: number, enabled: boolean) {
+  return useQuery({
+    queryKey: agentHistoryKey(gardenId),
+    enabled,
+    queryFn: async (): Promise<AgentMessage[]> =>
+      historySchema.parse(await api.get(`/gardens/${gardenId}/agent/history`)).messages,
+  })
+}
+
+export function useClearAgentHistory(gardenId: number) {
+  const qc = useQueryClient()
+  return useMutation({
+    mutationFn: async (): Promise<void> => {
+      await api.delete(`/gardens/${gardenId}/agent/history`)
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: agentHistoryKey(gardenId) }),
+  })
+}
+
+/** One completed turn, as the server reports it. */
+export interface AgentTurn {
+  reply: string
+  changeSetId?: number
+  steps: number
+  truncated?: boolean
+}
+
+/** A step the model just finished, named in the app's own vocabulary. */
+export interface AgentStep {
+  index: number
+  tools: string[]
+}
+
+// What each tool is doing, in words. Raw tool names ("fill_region") tell you the
+// agent is busy; these tell you what it's busy DOING, which is the difference
+// between the panel feeling alive and feeling hung.
+const TOOL_LABELS: Record<string, string> = {
+  list_gardens: 'Looking at your gardens',
+  describe_garden: 'Reading the garden',
+  create_object: 'Adding a bed',
+  move_object: 'Moving a bed',
+  place_planting: 'Planting',
+  fill_region: 'Filling a bed',
+  clear_object: 'Clearing a bed',
+  find_plant: 'Looking up a plant',
+  create_plant: 'Adding a plant to your catalog',
+  add_journal_entry: 'Writing a journal note',
+}
+
+export function describeStep(step: AgentStep): string {
+  if (step.tools.length === 0) return 'Thinking'
+  const labels = step.tools.map((t) => TOOL_LABELS[t] ?? t.replace(/_/g, ' '))
+  // Repeated tools in one step read as one action, not a list of identical ones.
+  return [...new Set(labels)].join(', ')
+}
+
+export interface StreamHandlers {
+  onStep: (step: AgentStep) => void
+  onDone: (turn: AgentTurn) => void
+  onError: (message: string) => void
+}
+
+/**
+ * Send a message and stream the reply.
+ *
+ * Hand-rolled rather than EventSource, which can only issue GETs — this needs a
+ * POST body. The wire format is still SSE so a proxy that understands it doesn't
+ * buffer, and so switching to EventSource later wouldn't change the server.
+ */
+export async function streamChat(
+  gardenId: number,
+  message: string,
+  handlers: StreamHandlers,
+  signal?: AbortSignal,
+): Promise<void> {
+  let res: Response
+  try {
+    res = await fetch(`${API_BASE}/agent/chat`, {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify({ gardenId, message }),
+      credentials: 'same-origin',
+      signal,
+    })
+  } catch {
+    handlers.onError('Could not reach the server.')
+    return
+  }
+  if (!res.ok || !res.body) {
+    handlers.onError(
+      res.status === 404
+        ? "This instance doesn't have the assistant configured."
+        : 'The assistant is not available right now.',
+    )
+    return
+  }
+
+  const reader = res.body.getReader()
+  const decoder = new TextDecoder()
+  let buffer = ''
+  for (;;) {
+    let chunk: ReadableStreamReadResult<Uint8Array>
+    try {
+      chunk = await reader.read()
+    } catch {
+      // An aborted read is the caller navigating away, not a failure worth
+      // reporting back to them.
+      if (signal?.aborted) return
+      handlers.onError('The connection dropped partway through.')
+      return
+    }
+    if (chunk.done) break
+    buffer += decoder.decode(chunk.value, { stream: true })
+
+    // SSE frames are separated by a blank line; anything after the last one is
+    // a partial frame to keep for the next chunk.
+    const frames = buffer.split('\n\n')
+    buffer = frames.pop() ?? ''
+    for (const frame of frames) {
+      const line = frame.split('\n').find((l) => l.startsWith('data:'))
+      if (!line) continue
+      let event: unknown
+      try {
+        event = JSON.parse(line.slice(5).trim())
+      } catch {
+        continue // a malformed frame shouldn't kill a working stream
+      }
+      const e = event as { step?: AgentStep; done?: AgentTurn; error?: string }
+      if (e.error) handlers.onError(e.error)
+      else if (e.step) handlers.onStep(e.step)
+      else if (e.done) handlers.onDone(e.done)
+    }
+  }
+}
+
+/** Refresh everything a turn may have changed: the canvas, the history list,
+ *  and the conversation itself. */
+export function useAgentRefresh(gardenId: number) {
+  const qc = useQueryClient()
+  return () => {
+    void qc.invalidateQueries({ queryKey: gardenFullKey(gardenId) })
+    void qc.invalidateQueries({ queryKey: historyKey(gardenId) })
+    void qc.invalidateQueries({ queryKey: agentHistoryKey(gardenId) })
+  }
+}

web/src/lib/history.test.ts

@@ -113,3 +113,29 @@ describe('totalChanges', () => {
     ).toBe(13)
   })
 })
+
+describe('describeUndo with an unknown total', () => {
+  // The chat panel offers Undo on a turn knowing only its change set id — the
+  // agent's reply carries the id, not the tally. Inventing a denominator to
+  // fill the sentence would be worse than not having one.
+  it("doesn't invent a denominator it was never given", () => {
+    const out = describeUndo(
+      { id: 5 },
+      {
+        changeSet: changeSet({ id: 6, counts: [{ entityType: 'planting', op: 'delete', n: 2 }] }),
+        conflicts: [{ entityType: 'object', entityId: 7, reason: 'changed', name: 'North Bed' }],
+      },
+    )
+    expect(out.tone).toBe('partial')
+    expect(out.message).toBe('Partly undone — “North Bed” was edited since, so it was left alone.')
+    expect(out.message).not.toMatch(/\d+ of \d+/)
+  })
+
+  it('still reports a clean undo the same way', () => {
+    const out = describeUndo(
+      { id: 5 },
+      { changeSet: changeSet({ id: 6, counts: [{ entityType: 'object', op: 'update', n: 1 }] }), conflicts: [] },
+    )
+    expect(out).toEqual({ tone: 'ok', message: 'Undone.' })
+  })
+})

web/src/lib/history.ts

@@ -171,7 +171,7 @@ 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 +197,19 @@ 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 +221,7 @@ 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 +234,9 @@ export function describeUndo(target: ChangeSet, result: RevertResult): UndoOutco
   if (applied === 0) {
     return { tone: 'error', message: `Nothing was undone — ${skipped}.` }
   }
-  const total = totalChanges(target)
-  return { tone: 'partial', message: `${applied} of ${total} changes undone — ${skipped}.` }
+  // Only claim a denominator when we have one. "2 of 3" from a caller that
+  // never knew the total would be a number invented to fill a sentence.
+  const total = target.counts ? target.counts.reduce((sum, c) => sum + c.n, 0) : 0
+  const scale = total > 0 ? `${applied} of ${total} changes undone` : 'Partly undone'
+  return { tone: 'partial', message: `${scale} — ${skipped}.` }
 }

web/src/pages/GardenEditorPage.tsx

@@ -5,6 +5,7 @@ import { Button } from '@/components/ui/Button'
 import { GardenCanvas } from '@/editor/GardenCanvas'
 import { EditorRail, type RailTab } from '@/editor/EditorRail'
 import { HistoryPanel } from '@/editor/HistoryPanel'
+import { ChatPanel } from '@/editor/ChatPanel'
 import { JournalPanel } from '@/editor/JournalPanel'
 import { Inspector } from '@/editor/Inspector'
 import { PlopInspector } from '@/editor/PlopInspector'
@@ -30,6 +31,7 @@ import {
 } from '@/lib/objects'
 import { toEditorPlanting } from '@/lib/plantings'
 import type { Plant } from '@/lib/plants'
+import { useCapabilities } from '@/lib/agent'
 import { useJournalCounts } from '@/lib/journal'
 import { attributableLots, lotsByPlant, useSeedLots, type SeedLot } from '@/lib/seedLots'
 import { useSeedTray } from '@/lib/seedTray'
@@ -64,6 +66,7 @@ export function GardenEditorPage() {
   const journalObjectId = useEditorStore((s) => s.journalObjectId)
   const setJournalObjectId = useEditorStore((s) => s.setJournalObjectId)
   const journalCounts = useJournalCounts(gid)
+  const capabilities = useCapabilities()
   const journalTotal = useMemo(
     () => [...(journalCounts.data?.values() ?? [])].reduce((a, b) => a + b, 0),
     [journalCounts.data],
@@ -385,6 +388,16 @@ export function GardenEditorPage() {
     },
   ]
 
+  // Only when the instance actually has the assistant configured. A tab that
+  // opens onto an apology is worse than no tab.
+  if (capabilities.data?.agent) {
+    railTabs.push({
+      id: 'chat',
+      label: 'Assistant',
+      render: () => <ChatPanel gardenId={gid} canEdit={canEdit} />,
+    })
+  }
+
   return (
     <div className="flex h-[calc(100vh-8rem)] flex-col gap-3 md:flex-row">
       <div className="shrink-0 md:w-40">
@@ -422,6 +435,15 @@ export function GardenEditorPage() {
         >
           History
         </Button>
+        {capabilities.data?.agent && (
+          <Button
+            variant="ghost"
+            className="mt-1 w-full text-sm"
+            onClick={() => setRailTab(railTab === 'chat' ? null : 'chat')}
+          >
+            💬 Assistant
+          </Button>
+        )}
       </div>
 
       <div className="relative flex min-h-0 flex-1 flex-col gap-2">