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) =>

apps/web/src/api/types.ts

@@ -145,6 +145,19 @@ export interface Message {
   // v1.8.2: per-message metadata; see MessageMetadata. null for the vast
   // majority of messages.
   metadata: MessageMetadata | null;
+  // v1.11: anchored rolling compaction fields. Optional on the wire so that
+  // older API responses (or test fixtures) parse without explicit nulls.
+  //   summary       — true on the assistant row that holds the active
+  //                   anchored summary. Render via SummaryCard.
+  //   tail_start_id — first preserved tail message the summary covers up to
+  //                   (exclusive). Diagnostic only on the client.
+  //   compacted_at  — set on rows that are "behind the curtain" of the
+  //                   current summary. Returned by the GET endpoint so the
+  //                   UI can show history, but the server-side inference
+  //                   assembly filters these out.
+  summary?: boolean;
+  tail_start_id?: string | null;
+  compacted_at?: string | null;
 }
 
 export interface ModelInfo {
@@ -305,6 +318,11 @@ export type WsFrame =
     }
   | { type: 'messages_deleted'; message_ids: string[]; chat_id?: string }
   | { type: 'chat_renamed'; chat_id: string; name: string }
+  // v1.11: published by services/compaction.ts after the new anchored
+  // summary row lands. Carries the new summary row id for diagnostics; the
+  // session-stream handler ignores the id and re-fetches the full message
+  // list (the cohort of compacted_at-stamped rows changed too).
+  | { type: 'compacted'; session_id: string; chat_id: string; summary_message_id: string }
   // v1.8.2: `reason` discriminates structured failures (the UI prefers it
   // over `error` text when present).
   | { type: 'error'; message_id?: string; chat_id?: string; error: string; reason?: ErrorReason };

apps/web/src/components/MessageBubble.tsx

@@ -537,7 +537,70 @@ function CompactCard({ message, sessionChats }: { message: Message; sessionChats
   );
 }
 
+// v1.11 anchored rolling summary. Inserted by services/compaction.ts as a
+// role='assistant', summary=true row. Distinct from legacy CompactCard
+// (which renders the kind='compact' system rows produced by v1.10 /compact).
+// Collapsed by default; header shows the timestamp; body renders the
+// summary markdown when expanded. Copy button matches CompactCard's affordance.
+function SummaryCard({ message }: { message: Message }) {
+  const [expanded, setExpanded] = useState(false);
+  const [copied, setCopied] = useState(false);
+
+  // Use finished_at when available (that's when the summary actually landed);
+  // fall back to created_at for any row missing it. Both are ISO strings.
+  const ts = message.finished_at ?? message.created_at;
+  const headerTs = ts ? new Date(ts).toLocaleString() : '';
+
+  async function handleCopy() {
+    try {
+      await navigator.clipboard.writeText(message.content);
+      setCopied(true);
+      setTimeout(() => setCopied(false), 1200);
+      toast.success('Summary copied to clipboard');
+    } catch {
+      toast.error('Copy failed');
+    }
+  }
+
+  return (
+    <div className="rounded-lg border border-primary/30 bg-primary/5 text-sm">
+      <div className="flex items-center gap-2 px-3 py-2">
+        <button
+          type="button"
+          onClick={() => setExpanded(!expanded)}
+          className="flex items-center gap-1.5 flex-1 min-w-0 text-left text-muted-foreground hover:text-foreground"
+        >
+          {expanded ? <ChevronDown size={14} /> : <ChevronRight size={14} />}
+          <span className="text-xs font-medium truncate">
+            Compacted summary — {headerTs}
+          </span>
+        </button>
+        <button
+          type="button"
+          onClick={() => void handleCopy()}
+          className="p-1 rounded hover:bg-muted text-muted-foreground"
+          aria-label="Copy summary"
+          title="Copy summary"
+        >
+          {copied ? <Check size={12} /> : <Copy size={12} />}
+        </button>
+      </div>
+      {expanded && (
+        <div className="px-3 pb-3 text-xs leading-relaxed border-t pt-2">
+          <MarkdownBody content={message.content} />
+        </div>
+      )}
+    </div>
+  );
+}
+
 export function MessageBubble({ message, sessionChats, capHitInfo }: Props) {
+  // v1.11: anchored rolling summary row. Checked BEFORE the kind==='compact'
+  // branch because summary=true never coexists with kind='compact' (new
+  // compactions emit role='assistant' rows with kind='message'+summary=true).
+  if (message.summary) {
+    return <SummaryCard message={message} />;
+  }
   if (message.kind === 'compact') {
     return <CompactCard message={message} sessionChats={sessionChats} />;
   }

apps/web/src/hooks/useSessionStream.ts

@@ -1,5 +1,7 @@
 import { useEffect, useRef, useState } from 'react';
+import { toast } from 'sonner';
 import type { Message, WsFrame } from '@/api/types';
+import { api } from '@/api/client';
 import { sessionEvents } from './sessionEvents';
 
 // session_renamed frame removed from WsFrame — it was declared but never
@@ -161,6 +163,12 @@ function applyFrame(state: State, frame: WsFrame): State {
         : state.messages;
       return { ...state, messages: next, error: frame.error };
     }
+    case 'compacted': {
+      // v1.11: side effects (refetch + toast) live in ws.onmessage; the
+      // reducer just no-ops so TS exhaustiveness is satisfied without
+      // duplicating async work inside a synchronous reducer.
+      return state;
+    }
   }
 }
 
@@ -196,6 +204,25 @@ export function useSessionStream(sessionId: string | undefined) {
       ws.onmessage = (ev) => {
         try {
           const frame = JSON.parse(typeof ev.data === 'string' ? ev.data : '') as WsFrame;
+          // v1.11: on a compaction completion, re-fetch the message list so
+          // the new summary row + the cohort of compacted_at-stamped older
+          // rows render correctly. We dispatch the fresh list as a synthetic
+          // 'snapshot' frame so the reducer's existing path handles state
+          // replacement (no need for a parallel "refetched" path).
+          // The toast is purely UX feedback; missing it would still leave
+          // the chat in a valid state.
+          if (frame.type === 'compacted') {
+            toast.success('Context compacted to free space');
+            void api.messages
+              .list(frame.session_id)
+              .then((messages) => {
+                setState((s) => applyFrame(s, { type: 'snapshot', messages }));
+              })
+              .catch((err: unknown) => {
+                console.warn('compacted refetch failed', err);
+              });
+            return;
+          }
           setState((s) => applyFrame(s, frame));
         } catch (err) {
           console.warn('bad ws frame', err);