the picker stopped overruling the default

a new chat offered fable. not displayed it — SELECTED it, sent it, and the
server honoured the choice it was given. the composer's fallback was
providerModels[0], the first entry in the catalogue, which is not a default but
an ordering accident. the file already carried a comment about the day fable was
added above opus and every resumed session came back claiming fable; the same
accident then quietly defeated the whole server-side default.

so the fallback prefers the platform's default and uses catalogue order only
when that model is not in the provider's list at all — which is every opencode
model, where there is no officer-wide default to prefer.

and a test, because a comment cannot hold a constant mirrored across two
packages. it asserts the client's copy equals the server's, and that the value
names a tier rather than the bare harness. both of the ways this default has
been defeated are now failures a test catches: a drifted mirror, and a stored
harness read as a choice.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

src/workspaces/officerdev/src/apps/Chat/components/ModelSelector.tsx

@@ -3,6 +3,7 @@ import { CirclePlay, ClipboardList, FolderOpen } from 'lucide-react';
 import { toneText } from '@/components/Data';
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select';
 import type { ModelOption } from 'state/useModels';
+import { CHAT_DEFAULT_MODEL } from '../types';
 import { getProviderDisplayName } from 'state/useModels';
 import type { ChatMessage } from '../types';
 import { UsagePopover } from './UsagePopover';
@@ -88,7 +89,18 @@ export function ModelSelector({
 
   const activeProvider = availableModels.find((m) => m.id === displayModel)?.provider ?? providers[0];
   const providerModels = availableModels.filter((m) => m.provider === activeProvider);
-  const fallbackModelId = providerModels[0]?.id ?? null;
+  /*
+    The platform's default first, and the catalogue's order only as a last resort.
+
+    `providerModels[0]` is not a default — it is whichever entry happens to be listed first, and the
+    comment below records what that cost once already. It cost it again on 2026-08-25: with the server
+    defaulting to Sonnet, this line selected `fable`, sent it, and the server honoured the choice it was
+    given. A default the client can silently overrule is not a default.
+
+    Falls back to the first entry only when the platform default is not in this provider's list at all —
+    which is every OpenCode model, where there is no Officer-wide default to prefer.
+  */
+  const fallbackModelId = providerModels.find((m) => m.id === CHAT_DEFAULT_MODEL)?.id ?? providerModels[0]?.id ?? null;
 
   /*
     Pick a default only for a chat that has not started.

src/workspaces/officerdev/src/apps/Chat/types.ts

@@ -1,3 +1,18 @@
+/**
+ * What an unstarted chat offers when nothing else has been chosen.
+ *
+ * **Mirrors `CHAT_DEFAULT_MODEL` in `src/servers/api/chat/websocket.ts` and must not drift from it.** Same
+ * arrangement as `COMMANDER_DEFAULT_MODEL` in `apps/CommandHQ/types.ts`, and for the same reason: the
+ * server decides, but the picker has to show the same answer or it silently sends a different one.
+ *
+ * The composer used to fall back to `providerModels[0]` — the first entry in the catalogue. That is not a
+ * default, it is an ordering accident, and the file already carried a comment about the day `fable` was
+ * added above `opus` and every resumed session came back claiming fable. The same accident then defeated
+ * the server-side default entirely: the client selected fable, SENT fable, and the server honoured what it
+ * was told.
+ */
+export const CHAT_DEFAULT_MODEL = 'claude-code/sonnet';
+
 export type Attachment =
   | { type: 'webpage'; url: string; title: string; content: string; attachmentId: string; loading?: boolean }
   | { type: 'image'; filename: string; dataUrl: string; attachmentId: string; loading?: boolean }