v1.11: opencode-style compaction port

- compaction.ts: usable/isOverflow/estimate/turns/select/buildPrompt/process
- compaction-prompt.ts: SUMMARY_TEMPLATE verbatim from opencode
- schema: messages.{compacted_at,summary,tail_start_id} + chats.needs_compaction
- inference: auto-trigger on overflow, pre-fetch compaction before next turn
- /compact slash command rewired to new path
- WS: chat_status working/idle around compaction + compacted frame
- frontend: SummaryCard + sonner toast on compacted
- 24 unit tests for pure functions

apps/web/src/api/client.ts

@@ -168,8 +168,11 @@ export const api = {
       request<void>(`/api/chats/${chatId}`, { method: 'DELETE' }),
     messages: (chatId: string) =>
       request<Message[]>(`/api/chats/${chatId}/messages`),
+    // v1.11: anchored-rolling compaction. POST awaits the LLM call inside
+    // the route's lifecycle; the new summary row arrives via the 'compacted'
+    // WS frame (useSessionStream refetches + toasts).
     compact: (chatId: string) =>
-      request<{ compact_message_id: string }>(`/api/chats/${chatId}/compact`, { method: 'POST' }),
+      request<{ ok: true }>(`/api/chats/${chatId}/compact`, { method: 'POST' }),
     stop: (chatId: string) =>
       request<{ stopped: boolean }>(`/api/chats/${chatId}/stop`, { method: 'POST' }),
     forceSend: (chatId: string, content: string) =>