diff --git a/apps/server/src/index.ts b/apps/server/src/index.ts
index 58d463d..7e88fdb 100644
--- a/apps/server/src/index.ts
+++ b/apps/server/src/index.ts
@@ -19,6 +19,7 @@ import { registerSkillsRoutes } from './routes/skills.js';
 import { createInferenceRunner } from './services/inference.js';
 import { createBroker } from './services/broker.js';
 import { listSkills } from './services/skills.js';
+import * as compaction from './services/compaction.js';
 
 async function main() {
   const config = loadConfig();
@@ -81,6 +82,11 @@ async function main() {
       publish: (sessionId, frame) => {
         broker.publish(sessionId, frame as unknown as Record<string, unknown> & { type: string });
       },
+      // v1.11: broker handle for compaction.process to publish 'compacted'
+      // frames on the per-session channel. Inference's regular publish path
+      // is bound to (sessionId, InferenceFrame); compaction publishes a
+      // different frame shape, so it goes through the raw broker.
+      broker,
     },
     (user, frame) => {
       broker.publishUser(user, frame as unknown as Record<string, unknown> & { type: string });
@@ -90,9 +96,13 @@ async function main() {
     enqueueInference: (sessionId, chatId, assistantId, user) => {
       inference.enqueue(sessionId, chatId, assistantId, user);
     },
-    enqueueCompact: (sessionId, chatId, compactId, user) => {
-      inference.enqueueCompact(sessionId, chatId, compactId, user);
-    },
+    // v1.11: synchronous compaction. Awaits the LLM call inside the route's
+    // request lifecycle; the new summary row arrives via the WS 'compacted'
+    // frame published from inside compaction.process. We let the error
+    // bubble up so the route can reply 500 — manual /compact failures
+    // should be loud (the user just clicked a button).
+    runCompaction: (chatId) =>
+      compaction.process({ sql, config, log: app.log, broker, chatId }),
     cancelInference: async (sessionId, chatId) => {
       return inference.cancel(sessionId, chatId);
     },
diff --git a/apps/server/src/routes/chats.ts b/apps/server/src/routes/chats.ts
index b845c48..5d0c45f 100644
--- a/apps/server/src/routes/chats.ts
+++ b/apps/server/src/routes/chats.ts
@@ -316,7 +316,8 @@ export function registerChatRoutes(
       }
       const rows = await sql<Message[]>`
         SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq,
-               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata
+               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata,
+               summary, tail_start_id, compacted_at
         FROM messages
         WHERE chat_id = ${req.params.id}
         ORDER BY created_at ASC, id ASC
diff --git a/apps/server/src/routes/messages.ts b/apps/server/src/routes/messages.ts
index 4c0e666..bfaf148 100644
--- a/apps/server/src/routes/messages.ts
+++ b/apps/server/src/routes/messages.ts
@@ -49,7 +49,12 @@ const AskUserInputArgs = z.object({
 
 interface MessageHandlers {
   enqueueInference: (sessionId: string, chatId: string, assistantMessageId: string, user: string) => void;
-  enqueueCompact: (sessionId: string, chatId: string, compactMessageId: string, user: string) => void;
+  // v1.11: returns a promise that resolves after compaction.process finishes
+  // (await the LLM call). Throws on failure — the route surfaces a 500.
+  // Replaces the v1.10 enqueueCompact (which fired-and-forgot a kind='compact'
+  // streaming row). The new anchored-rolling strategy inserts a single
+  // summary=true assistant row only after the LLM responds.
+  runCompaction: (chatId: string) => Promise<void>;
   publishUserMessage: (
     sessionId: string,
     chatId: string,
@@ -81,9 +86,15 @@ export function registerMessageRoutes(
         reply.code(404);
         return { error: 'session not found' };
       }
+      // v1.11: returns ALL messages including compacted ones. The UI
+      // distinguishes via the new `summary` flag (renders an accordion
+      // SummaryCard) and shows compacted_at-stamped rows inline for context.
+      // Internal inference assembly filters compacted_at IS NULL separately —
+      // see services/inference.ts loadContext + services/compaction.ts.
       const rows = await sql<Message[]>`
         SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq,
-               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata
+               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata,
+               summary, tail_start_id, compacted_at
         FROM messages
         WHERE session_id = ${req.params.id}
         ORDER BY created_at ASC, id ASC
@@ -251,29 +262,30 @@ export function registerMessageRoutes(
     }
   );
 
+  // v1.11: manual /compact. Was a streaming kind='compact' row inserted by
+  // this handler; now delegates to the anchored-rolling compaction service.
+  // Synchronous (we await the LLM call) — callers either await or rely on
+  // the 'compacted' WS frame to refresh their view. The response carries
+  // no body of interest; the new summary row arrives via the WS frame.
   app.post<{ Params: { id: string } }>(
     '/api/chats/:id/compact',
     async (req, reply) => {
-      const chatRows = await sql<Chat[]>`
-        SELECT id, session_id FROM chats WHERE id = ${req.params.id} AND status = 'open'
+      const chatRows = await sql<{ id: string }[]>`
+        SELECT id FROM chats WHERE id = ${req.params.id} AND status = 'open'
       `;
       if (chatRows.length === 0) {
         reply.code(404);
         return { error: 'chat not found' };
       }
-      const chat = chatRows[0]!;
-      const sessionId = chat.session_id;
-
-      const [compactMsg] = await sql<{ id: string }[]>`
-        INSERT INTO messages (session_id, chat_id, role, content, kind, status, created_at)
-        VALUES (${sessionId}, ${chat.id}, 'system', '', 'compact', 'streaming', clock_timestamp())
-        RETURNING id
-      `;
-
-      handlers.enqueueCompact(sessionId, chat.id, compactMsg!.id, 'default');
-
-      reply.code(202);
-      return { compact_message_id: compactMsg!.id };
+      try {
+        await handlers.runCompaction(chatRows[0]!.id);
+      } catch (err) {
+        req.log.error({ err, chatId: chatRows[0]!.id }, 'manual compaction failed');
+        reply.code(500);
+        return { error: err instanceof Error ? err.message : 'compaction failed' };
+      }
+      reply.code(200);
+      return { ok: true };
     }
   );
 
diff --git a/apps/server/src/routes/ws.ts b/apps/server/src/routes/ws.ts
index 88c854e..e25efd2 100644
--- a/apps/server/src/routes/ws.ts
+++ b/apps/server/src/routes/ws.ts
@@ -21,9 +21,12 @@ export function registerWebSocket(
         return;
       }
 
+      // v1.11: snapshot includes compaction fields so MessageBubble can
+      // render the SummaryCard for summary=true rows on first connect.
       const messages = await sql<Message[]>`
         SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq,
-               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata
+               tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata,
+               summary, tail_start_id, compacted_at
         FROM messages
         WHERE session_id = ${sessionId}
         ORDER BY created_at ASC, id ASC
diff --git a/apps/server/src/schema.sql b/apps/server/src/schema.sql
index 9be9395..801a487 100644
--- a/apps/server/src/schema.sql
+++ b/apps/server/src/schema.sql
@@ -179,3 +179,25 @@ INSERT INTO settings (key, value) VALUES ('theme_mode', '"dark"') ON CONFLICT (k
 ALTER TABLE projects ADD COLUMN IF NOT EXISTS default_system_prompt TEXT NOT NULL DEFAULT '';
 ALTER TABLE projects ADD COLUMN IF NOT EXISTS default_web_search_enabled BOOLEAN NOT NULL DEFAULT false;
 ALTER TABLE sessions ADD COLUMN IF NOT EXISTS web_search_enabled BOOLEAN;
+
+-- v1.11: anchored rolling compaction.
+--   compacted_at  — marks rows that are "behind the curtain" of the latest
+--                   summary. Inference assembly filters compacted_at IS NULL;
+--                   the API GET still returns all rows so the UI can show
+--                   history with the summary card inline.
+--   summary       — true on the assistant row that IS the anchored summary.
+--                   Exactly one row per chat is the "current" summary
+--                   (every prior summary row is itself compacted_at-stamped
+--                   when superseded, leaving one live anchor).
+--   tail_start_id — points at the first preserved message that the summary
+--                   covers up to (exclusive). Lets the UI/debug reason about
+--                   the boundary without re-deriving from compacted_at.
+--   needs_compaction — flag on chats (not sessions) because chat history is
+--                   per-chat; sessions have 1:N chats. Set true post-overflow,
+--                   cleared by compaction.process at the start of the next
+--                   inference turn.
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS compacted_at TIMESTAMPTZ;
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS summary BOOLEAN NOT NULL DEFAULT FALSE;
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS tail_start_id UUID REFERENCES messages(id) ON DELETE SET NULL;
+ALTER TABLE chats ADD COLUMN IF NOT EXISTS needs_compaction BOOLEAN NOT NULL DEFAULT FALSE;
+CREATE INDEX IF NOT EXISTS idx_messages_chat_compacted ON messages (chat_id, compacted_at);
diff --git a/apps/server/src/services/__tests__/compaction.test.ts b/apps/server/src/services/__tests__/compaction.test.ts
new file mode 100644
index 0000000..a239ee8
--- /dev/null
+++ b/apps/server/src/services/__tests__/compaction.test.ts
@@ -0,0 +1,258 @@
+import { describe, it, expect } from 'vitest';
+import {
+  usable,
+  isOverflow,
+  estimate,
+  turns,
+  select,
+  buildPrompt,
+  type CompactionMessage,
+} from '../compaction.js';
+import { SUMMARY_TEMPLATE } from '../compaction-prompt.js';
+
+// ---- fixture ----------------------------------------------------------------
+// Tiny constructor for the message shape `compaction.ts` consumes. Default
+// values match the post-CP1 schema (summary=false, kind='message', complete).
+// Tests that need a summary row pass `summary: true`.
+
+let counter = 0;
+function mkMsg(
+  role: CompactionMessage['role'],
+  content: string,
+  overrides: Partial<CompactionMessage> = {},
+): CompactionMessage {
+  counter += 1;
+  return {
+    id: `m${counter}`,
+    role,
+    content,
+    kind: 'message',
+    summary: false,
+    status: 'complete',
+    tool_calls: null,
+    tool_results: null,
+    metadata: null,
+    created_at: new Date(counter * 1000).toISOString(),
+    ...overrides,
+  };
+}
+
+// ---- usable -----------------------------------------------------------------
+
+describe('usable', () => {
+  it('returns 0 when contextLimit is 0', () => {
+    expect(usable(0)).toBe(0);
+  });
+
+  it('returns 0 when contextLimit is below the 20k buffer', () => {
+    // Math.max(0, x - 20000) clamps the subtraction so we never report
+    // negative headroom. A 10k-context model reports 0 usable, which makes
+    // isOverflow short-circuit to false (correct — we can't size the
+    // compaction with no headroom).
+    expect(usable(10_000)).toBe(0);
+    expect(usable(19_999)).toBe(0);
+    expect(usable(20_000)).toBe(0);
+  });
+
+  it('subtracts the 20k buffer from a normal-sized context window', () => {
+    expect(usable(100_000)).toBe(80_000);
+    expect(usable(32_768)).toBe(12_768);
+  });
+});
+
+// ---- isOverflow -------------------------------------------------------------
+
+describe('isOverflow', () => {
+  it('returns false when usable is 0 (unknown / sub-buffer context)', () => {
+    expect(isOverflow({ prompt_tokens: 999_999, completion_tokens: 0 }, 0)).toBe(false);
+    expect(isOverflow({ prompt_tokens: 0, completion_tokens: 999_999 }, 10_000)).toBe(false);
+  });
+
+  it('returns false at 50% of usable', () => {
+    // usable(100k) = 80k → 50% = 40k.
+    expect(isOverflow({ prompt_tokens: 30_000, completion_tokens: 10_000 }, 100_000)).toBe(false);
+  });
+
+  it('returns false just under usable', () => {
+    expect(isOverflow({ prompt_tokens: 79_000, completion_tokens: 999 }, 100_000)).toBe(false);
+  });
+
+  it('returns true exactly at usable (>=, not strict >)', () => {
+    expect(isOverflow({ prompt_tokens: 80_000, completion_tokens: 0 }, 100_000)).toBe(true);
+  });
+
+  it('returns true above usable', () => {
+    expect(isOverflow({ prompt_tokens: 50_000, completion_tokens: 40_000 }, 100_000)).toBe(true);
+  });
+});
+
+// ---- estimate ---------------------------------------------------------------
+
+describe('estimate', () => {
+  it('returns a tiny value for an empty array (JSON.stringify([]) is "[]")', () => {
+    // Math.ceil('[]'.length / 4) = 1. Documented here so the next reader
+    // doesn't think "0" is the expected baseline — char-count/4 will never
+    // be exactly 0 for any JSON-serializable input.
+    expect(estimate([])).toBe(1);
+  });
+
+  it('scales roughly with content length', () => {
+    const tiny = estimate([mkMsg('user', 'hi')]);
+    const big = estimate([mkMsg('user', 'x'.repeat(4000))]);
+    expect(big).toBeGreaterThan(tiny);
+    expect(big).toBeGreaterThanOrEqual(1000); // 4000 chars / 4 = 1000 floor
+  });
+
+  it('is deterministic across repeated calls', () => {
+    const msgs = [mkMsg('user', 'one'), mkMsg('assistant', 'two')];
+    expect(estimate(msgs)).toBe(estimate(msgs));
+  });
+});
+
+// ---- turns ------------------------------------------------------------------
+
+describe('turns', () => {
+  it('returns [] for an empty message list', () => {
+    expect(turns([])).toEqual([]);
+  });
+
+  it('returns one turn for a single user message', () => {
+    const u = mkMsg('user', 'hi');
+    const result = turns([u]);
+    expect(result).toHaveLength(1);
+    expect(result[0]).toEqual({ start: 0, end: 1, id: u.id });
+  });
+
+  it('returns two turns for user/assistant/user/assistant', () => {
+    const u1 = mkMsg('user', 'q1');
+    const a1 = mkMsg('assistant', 'a1');
+    const u2 = mkMsg('user', 'q2');
+    const a2 = mkMsg('assistant', 'a2');
+    const result = turns([u1, a1, u2, a2]);
+    expect(result).toEqual([
+      { start: 0, end: 2, id: u1.id },
+      { start: 2, end: 4, id: u2.id },
+    ]);
+  });
+
+  it('extends the final turn end to include trailing non-user messages', () => {
+    // Spec wording: "user/assistant + trailing system → trailing included
+    // in last turn's range". Single-turn variant: [user, assistant, system]
+    // should produce one turn with end=3 (covers all three indices).
+    const u = mkMsg('user', 'q');
+    const a = mkMsg('assistant', 'a');
+    const s = mkMsg('system', 'note');
+    const result = turns([u, a, s]);
+    expect(result).toEqual([{ start: 0, end: 3, id: u.id }]);
+  });
+
+  it('skips user rows flagged as summary (anchored-rolling rows)', () => {
+    // Defense-in-depth — process() pre-filters summary rows, but turns()
+    // also skips them so a misuse from another caller doesn't create a
+    // bogus turn boundary on the summary row itself.
+    const u1 = mkMsg('user', 'q1');
+    const a1 = mkMsg('assistant', 'a1');
+    const sum = mkMsg('user', 'rolled-up', { summary: true });
+    const u2 = mkMsg('user', 'q2');
+    const result = turns([u1, a1, sum, u2]);
+    expect(result.map((t) => t.id)).toEqual([u1.id, u2.id]);
+  });
+});
+
+// ---- select -----------------------------------------------------------------
+
+describe('select', () => {
+  it('returns empty head + undefined tail for an empty message list', () => {
+    const result = select([], 100_000);
+    expect(result.head).toEqual([]);
+    expect(result.tail_start_id).toBeUndefined();
+  });
+
+  it('full-preserves when there are fewer turns than tail_turns', () => {
+    // 1 turn but tail_turns=2: keep === turn0 → keep.start === 0 →
+    // sentinel-return path that signals "no compaction this round".
+    const u = mkMsg('user', 'only');
+    const a = mkMsg('assistant', 'a');
+    const result = select([u, a], 100_000, 2);
+    expect(result.head).toEqual([u, a]);
+    expect(result.tail_start_id).toBeUndefined();
+  });
+
+  it('keeps the last tail_turns turns when they all fit the budget', () => {
+    // 3 turns, all small. tail_turns=2 means keep the last 2; head =
+    // messages[0..turn2.start] = just turn1's content.
+    const u1 = mkMsg('user', 'q1');
+    const a1 = mkMsg('assistant', 'a1');
+    const u2 = mkMsg('user', 'q2');
+    const a2 = mkMsg('assistant', 'a2');
+    const u3 = mkMsg('user', 'q3');
+    const a3 = mkMsg('assistant', 'a3');
+    const msgs = [u1, a1, u2, a2, u3, a3];
+    const result = select(msgs, 100_000, 2);
+    // Turn boundaries: [0,2), [2,4), [4,6). slice(-2) = turns at 2 and 4.
+    // Walking backward: u3 fits, then u2 fits → keep={start:2, id:u2.id}.
+    expect(result.tail_start_id).toBe(u2.id);
+    expect(result.head).toEqual([u1, a1]);
+  });
+
+  it('splits a turn mid-stream when the whole turn would overflow the budget', () => {
+    // tail_turns=1 so we look only at the most recent turn. Stuff it past
+    // 8k of content (max preserve budget) and the splitter walks forward
+    // looking for the largest suffix that fits.
+    const u1 = mkMsg('user', 'q1');
+    const a1 = mkMsg('assistant', 'a1');
+    const u2 = mkMsg('user', 'q2 with a giant payload');
+    const huge = mkMsg('assistant', 'X'.repeat(40_000)); // ~10k tokens
+    const smallTail = mkMsg('assistant', 'short answer');
+    const msgs = [u1, a1, u2, huge, smallTail];
+    const result = select(msgs, 100_000, 1);
+    // The split walks from turn.start+1 forward; the first index whose
+    // [i, end) slice fits the budget becomes the new keep. We don't assert
+    // a specific id (depends on character math), only that compaction was
+    // triggered (tail_start_id set, head non-empty) and that the head
+    // doesn't include the final small message.
+    expect(result.tail_start_id).toBeDefined();
+    expect(result.head.length).toBeGreaterThan(0);
+    expect(result.head).not.toContain(smallTail);
+  });
+
+  it('full-preserves when no split point fits', () => {
+    // Single oversized turn; splitTurn walks but each suffix is still too
+    // big. After the loop, keep is undefined → full-preserve sentinel.
+    // Force this with a sub-buffer context so budget is the floor (2k),
+    // and a single 40k-char message.
+    const u = mkMsg('user', 'oversized');
+    const a = mkMsg('assistant', 'Y'.repeat(40_000));
+    const result = select([u, a], 30_000, 1);
+    // usable(30k) = 10k → budget = min(8k, max(2k, floor(10k*0.25))) =
+    // min(8k, max(2k, 2500)) = 2500. 40k chars ≈ 10k tokens. Can't fit.
+    expect(result.tail_start_id).toBeUndefined();
+    expect(result.head).toEqual([u, a]);
+  });
+});
+
+// ---- buildPrompt ------------------------------------------------------------
+
+describe('buildPrompt', () => {
+  it('opens with the "create new" anchor when previousSummary is undefined', () => {
+    const out = buildPrompt(undefined, []);
+    expect(out.startsWith('Create a new anchored summary')).toBe(true);
+    expect(out).toContain(SUMMARY_TEMPLATE);
+    expect(out).not.toContain('<previous-summary>');
+  });
+
+  it('opens with the "update" anchor and embeds previousSummary verbatim', () => {
+    const prev = '## Goal\n- finish v1.11 compaction';
+    const out = buildPrompt(prev, []);
+    expect(out.startsWith('Update the anchored summary')).toBe(true);
+    expect(out).toContain('<previous-summary>');
+    expect(out).toContain(prev);
+    expect(out).toContain('</previous-summary>');
+    expect(out).toContain(SUMMARY_TEMPLATE);
+  });
+
+  it('appends extra context strings after the template (reserved for plugin injection)', () => {
+    const out = buildPrompt(undefined, ['extra-context-line']);
+    expect(out.endsWith('extra-context-line')).toBe(true);
+  });
+});
diff --git a/apps/server/src/services/compaction-prompt.ts b/apps/server/src/services/compaction-prompt.ts
new file mode 100644
index 0000000..6bf96cb
--- /dev/null
+++ b/apps/server/src/services/compaction-prompt.ts
@@ -0,0 +1,40 @@
+// v1.11: anchored rolling summary template. Verbatim port from opencode
+// (packages/opencode/src/session/compaction.ts SUMMARY_TEMPLATE). Kept in a
+// separate module so the long template literal doesn't bloat compaction.ts.
+
+export const SUMMARY_TEMPLATE = `Output exactly the Markdown structure shown inside <template> and keep the section order unchanged. Do not include the <template> tags in your response.
+<template>
+## Goal
+- [single-sentence task summary]
+
+## Constraints & Preferences
+- [user constraints, preferences, specs, or "(none)"]
+
+## Progress
+### Done
+- [completed work or "(none)"]
+
+### In Progress
+- [current work or "(none)"]
+
+### Blocked
+- [blockers or "(none)"]
+
+## Key Decisions
+- [decision and why, or "(none)"]
+
+## Next Steps
+- [ordered next actions or "(none)"]
+
+## Critical Context
+- [important technical facts, errors, open questions, or "(none)"]
+
+## Relevant Files
+- [file or directory path: why it matters, or "(none)"]
+</template>
+
+Rules:
+- Keep every section, even when empty.
+- Use terse bullets, not prose paragraphs.
+- Preserve exact file paths, commands, error strings, and identifiers when known.
+- Do not mention the summary process or that context was compacted.`;
diff --git a/apps/server/src/services/compaction.ts b/apps/server/src/services/compaction.ts
new file mode 100644
index 0000000..e954bb6
--- /dev/null
+++ b/apps/server/src/services/compaction.ts
@@ -0,0 +1,503 @@
+// v1.11: anchored rolling compaction. Ported algorithms (not Effect-TS code)
+// from opencode (packages/opencode/src/session/{compaction,overflow}.ts).
+//
+// What's different from BooCode's legacy /compact:
+//   - Operates per-chat (chats have N:1 to sessions; history is per-chat).
+//   - Detects overflow automatically after each inference completion using
+//     llama-swap's reported n_ctx; flags chats.needs_compaction=true.
+//   - On the next turn (or manual /compact) we summarize the *head* (messages
+//     prior to a preserved tail of N user-turns) into a single
+//     summary=true assistant row. Older messages get compacted_at-stamped so
+//     inference assembly filters them out; the GET endpoint still returns
+//     them so the UI can show history with the summary card inline.
+//   - The summary is *anchored rolling* — exactly one live summary=true row
+//     per chat. Subsequent compactions read the prior summary as
+//     previousSummary, ask the LLM to update-merge it, then mark the prior
+//     summary row compacted_at too (it stays in the UI but isn't sent to the
+//     LLM again).
+
+import type { FastifyBaseLogger } from 'fastify';
+import type { Sql } from '../db.js';
+import type { Config } from '../config.js';
+import type { Broker } from './broker.js';
+import { SUMMARY_TEMPLATE } from './compaction-prompt.js';
+
+const COMPACTION_BUFFER = 20_000;
+const MIN_PRESERVE_RECENT_TOKENS = 2_000;
+const MAX_PRESERVE_RECENT_TOKENS = 8_000;
+const DEFAULT_TAIL_TURNS = 2;
+
+// Subset of Message fields compaction touches. Selecting only what's needed
+// keeps process() independent of api.ts mutations and reduces DB egress.
+export interface CompactionMessage {
+  id: string;
+  role: 'user' | 'assistant' | 'system' | 'tool';
+  content: string;
+  kind: 'message' | 'compact';
+  summary: boolean;
+  status: 'streaming' | 'complete' | 'failed' | 'cancelled';
+  tool_calls: Array<{ id: string; name: string; args: Record<string, unknown> }> | null;
+  tool_results: { tool_call_id: string; output: unknown; truncated: boolean; error?: string } | null;
+  metadata: { kind?: string } | null;
+  created_at: string;
+}
+
+// === overflow ===
+
+// Tokens we hold in reserve for the model's response so a near-full context
+// can still produce a useful turn. Mirrors opencode's COMPACTION_BUFFER.
+// Returns 0 when the context limit is unknown (caller treats 0 as "do not
+// trigger overflow"); avoids dividing-by-zero downstream.
+export function usable(contextLimit: number): number {
+  if (!contextLimit || contextLimit <= 0) return 0;
+  return Math.max(0, contextLimit - COMPACTION_BUFFER);
+}
+
+export interface Usage {
+  prompt_tokens: number;
+  completion_tokens: number;
+}
+
+// True when the assistant just used >= usable() tokens. Unknown limit → false
+// (we never auto-trigger compaction without a budget — better to keep
+// inference flowing than to fall into a compaction we can't size properly).
+export function isOverflow(usage: Usage, contextLimit: number): boolean {
+  const budget = usable(contextLimit);
+  if (budget <= 0) return false;
+  return (usage.prompt_tokens + usage.completion_tokens) >= budget;
+}
+
+// === selection ===
+
+interface Turn {
+  start: number;
+  end: number;
+  id: string;
+}
+
+// Char-count / 4 token estimate. Matches opencode's Token.estimate (which
+// also goes through JSON.stringify). Adequate for tail-fitting math; we
+// don't need a real tokenizer here — the 20k buffer absorbs the slop.
+export function estimate(messages: CompactionMessage[]): number {
+  return Math.ceil(JSON.stringify(messages).length / 4);
+}
+
+// Walk messages, return one Turn per user message that is NOT a summary row.
+// end = next-user-start; final turn ends at messages.length.
+export function turns(messages: CompactionMessage[]): Turn[] {
+  const result: Turn[] = [];
+  for (let i = 0; i < messages.length; i++) {
+    const m = messages[i]!;
+    if (m.role !== 'user') continue;
+    if (m.summary) continue;
+    result.push({ start: i, end: messages.length, id: m.id });
+  }
+  for (let i = 0; i < result.length - 1; i++) {
+    result[i]!.end = result[i + 1]!.start;
+  }
+  return result;
+}
+
+// Inside a turn that doesn't fit whole, walk forward from start+1 looking for
+// the largest suffix that fits the remaining budget. Returns the keep-start
+// index (the first preserved message) or undefined if no suffix fits.
+function splitTurn(
+  messages: CompactionMessage[],
+  turn: Turn,
+  budget: number,
+): { start: number; id: string } | undefined {
+  if (budget <= 0) return undefined;
+  if (turn.end - turn.start <= 1) return undefined;
+  for (let start = turn.start + 1; start < turn.end; start++) {
+    const size = estimate(messages.slice(start, turn.end));
+    if (size > budget) continue;
+    return { start, id: messages[start]!.id };
+  }
+  return undefined;
+}
+
+export interface SelectResult {
+  head: CompactionMessage[];
+  tail_start_id: string | undefined;
+}
+
+// Choose the boundary between the "head" (to be summarized) and the "tail"
+// (preserved verbatim). Strategy:
+//   1. Reserve a budget for the recent tail. Default ranges [2k, 8k] tokens
+//      with 25% of usable() as the target.
+//   2. Take the last `tail_turns` user-turns; greedily fit from newest back.
+//   3. If the next-older turn doesn't fit whole, split it mid-turn.
+//   4. If we couldn't keep anything OR everything fit (keep.start === 0),
+//      return full-preserve (no compaction this round).
+export function select(
+  messages: CompactionMessage[],
+  contextLimit: number,
+  tailTurns: number = DEFAULT_TAIL_TURNS,
+): SelectResult {
+  if (tailTurns <= 0) return { head: messages, tail_start_id: undefined };
+  const budget = Math.min(
+    MAX_PRESERVE_RECENT_TOKENS,
+    Math.max(MIN_PRESERVE_RECENT_TOKENS, Math.floor(usable(contextLimit) * 0.25)),
+  );
+
+  const all = turns(messages);
+  if (all.length === 0) return { head: messages, tail_start_id: undefined };
+  const recent = all.slice(-tailTurns);
+
+  let total = 0;
+  let keep: { start: number; id: string } | undefined;
+  for (let i = recent.length - 1; i >= 0; i--) {
+    const turn = recent[i]!;
+    const size = estimate(messages.slice(turn.start, turn.end));
+    if (total + size <= budget) {
+      total += size;
+      keep = { start: turn.start, id: turn.id };
+      continue;
+    }
+    const remaining = budget - total;
+    const split = splitTurn(messages, turn, remaining);
+    if (split) keep = split;
+    break;
+  }
+
+  if (!keep || keep.start === 0) {
+    return { head: messages, tail_start_id: undefined };
+  }
+  return {
+    head: messages.slice(0, keep.start),
+    tail_start_id: keep.id,
+  };
+}
+
+// === prompt assembly ===
+
+// Build the final user message that asks the model to (re)produce the
+// anchored summary. `context` is reserved for future plugin injection;
+// callers pass [] today.
+export function buildPrompt(
+  previousSummary: string | undefined,
+  context: string[],
+): string {
+  const anchor = previousSummary
+    ? [
+        'Update the anchored summary below using the conversation history above.',
+        'Preserve still-true details, remove stale details, and merge in the new facts.',
+        '<previous-summary>',
+        previousSummary,
+        '</previous-summary>',
+      ].join('\n')
+    : 'Create a new anchored summary from the conversation history above.';
+  return [anchor, SUMMARY_TEMPLATE, ...context].join('\n\n');
+}
+
+// === OpenAI conversion (compaction-local; intentionally does NOT call
+// inference.ts buildMessagesPayload because that uses the legacy "find latest
+// kind='compact' marker and skip everything before it" shortcircuit, which
+// would silently drop pre-legacy-compact history before the LLM sees it.
+// Compaction wants to send the entire head, full stop.) ===
+
+interface OpenAiMessage {
+  role: 'system' | 'user' | 'assistant' | 'tool';
+  content: string | null;
+  tool_calls?: Array<{
+    id: string;
+    type: 'function';
+    function: { name: string; arguments: string };
+  }>;
+  tool_call_id?: string;
+}
+
+function isCapHitSentinel(m: CompactionMessage): boolean {
+  return m.role === 'system' && m.metadata != null && m.metadata.kind === 'cap_hit';
+}
+
+function buildHeadPayload(head: CompactionMessage[]): OpenAiMessage[] {
+  const out: OpenAiMessage[] = [];
+  for (const m of head) {
+    if (isCapHitSentinel(m)) continue;
+    if (m.role === 'assistant' && (m.status === 'streaming' || m.status === 'cancelled')) continue;
+    if (m.kind === 'compact') {
+      // Legacy compact row — pass through as system context. The new
+      // anchored summary will subsume it, but the LLM should see it during
+      // the bridging round so it can carry forward the still-true bits.
+      out.push({ role: 'system', content: m.content });
+      continue;
+    }
+    if (m.summary) {
+      // Defense in depth: process() filters these out of the select-input
+      // already. If one slips through, render it as assistant content so we
+      // never crash here.
+      out.push({ role: 'assistant', content: m.content });
+      continue;
+    }
+    if (m.role === 'tool') {
+      const tr = m.tool_results;
+      if (!tr) continue;
+      const outputText = tr.error
+        ? `error: ${tr.error}`
+        : typeof tr.output === 'string'
+          ? tr.output
+          : JSON.stringify(tr.output);
+      out.push({ role: 'tool', content: outputText, tool_call_id: tr.tool_call_id });
+      continue;
+    }
+    if (m.role === 'assistant') {
+      const msg: OpenAiMessage = {
+        role: 'assistant',
+        content: m.content && m.content.length > 0 ? m.content : null,
+      };
+      if (m.tool_calls && m.tool_calls.length > 0) {
+        msg.tool_calls = m.tool_calls.map((tc) => ({
+          id: tc.id,
+          type: 'function' as const,
+          function: { name: tc.name, arguments: JSON.stringify(tc.args) },
+        }));
+      }
+      out.push(msg);
+      continue;
+    }
+    out.push({ role: 'user', content: m.content });
+  }
+  return out;
+}
+
+// === llama-swap call ===
+
+// Non-streaming completion. Opencode streams; for a one-shot summary call a
+// single POST is less code and the latency hit is acceptable (the user
+// doesn't see this directly — useSessionStream emits the toast + refetches
+// on the 'compacted' frame).
+interface CompletionResult {
+  content: string;
+  promptTokens: number;
+  completionTokens: number;
+  nCtx: number | null;
+}
+
+async function callLlamaSwap(
+  config: Config,
+  model: string,
+  messages: OpenAiMessage[],
+  log: FastifyBaseLogger,
+): Promise<CompletionResult> {
+  const res = await fetch(`${config.LLAMA_SWAP_URL}/v1/chat/completions`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ model, messages, stream: false }),
+  });
+  if (!res.ok) {
+    const text = await res.text().catch(() => '');
+    throw new Error(`llama-swap returned ${res.status}: ${text.slice(0, 200)}`);
+  }
+  const json = (await res.json()) as {
+    choices?: Array<{ message?: { content?: string } }>;
+    usage?: { prompt_tokens?: number; completion_tokens?: number };
+    timings?: { n_ctx?: number };
+  };
+  const content = json.choices?.[0]?.message?.content ?? '';
+  const promptTokens = json.usage?.prompt_tokens ?? 0;
+  const completionTokens = json.usage?.completion_tokens ?? 0;
+  const nCtx = typeof json.timings?.n_ctx === 'number' ? json.timings.n_ctx : null;
+  log.debug({ promptTokens, completionTokens, nCtx, chars: content.length }, 'compaction llm complete');
+  return { content, promptTokens, completionTokens, nCtx };
+}
+
+// === entry point ===
+
+export interface ProcessInput {
+  sql: Sql;
+  config: Config;
+  log: FastifyBaseLogger;
+  broker: Broker;
+  chatId: string;
+}
+
+// Runs one round of anchored rolling compaction on `chatId`. No-ops cleanly
+// (clearing needs_compaction) when there's nothing reasonable to compact.
+// Throws on LLM failure — callers decide whether to log+swallow or surface.
+export async function process(input: ProcessInput): Promise<void> {
+  const { sql, config, log, broker, chatId } = input;
+
+  // 1. Resolve chat → session for model + WS publish channel.
+  const chatRows = await sql<{ id: string; session_id: string }[]>`
+    SELECT id, session_id FROM chats WHERE id = ${chatId}
+  `;
+  if (chatRows.length === 0) {
+    log.warn({ chatId }, 'compaction: chat not found');
+    return;
+  }
+  const chat = chatRows[0]!;
+  const sessionId = chat.session_id;
+
+  const sessRows = await sql<{ id: string; model: string }[]>`
+    SELECT id, model FROM sessions WHERE id = ${sessionId}
+  `;
+  if (sessRows.length === 0) {
+    log.warn({ chatId, sessionId }, 'compaction: session not found');
+    return;
+  }
+  const session = sessRows[0]!;
+
+  // 2. All currently-active messages in this chat (compacted_at IS NULL).
+  // ORDER BY (created_at, id) matches loadContext in inference.ts so the
+  // turns() boundary logic sees the same sequence the LLM will.
+  const messages = await sql<CompactionMessage[]>`
+    SELECT id, role, content, kind, summary, status, tool_calls, tool_results, metadata, created_at
+    FROM messages
+    WHERE chat_id = ${chatId} AND compacted_at IS NULL
+    ORDER BY created_at ASC, id ASC
+  `;
+  if (messages.length === 0) {
+    await sql`UPDATE chats SET needs_compaction = false WHERE id = ${chatId}`;
+    return;
+  }
+
+  // 3. Find the prior anchored summary (newest summary=true row). Its content
+  // becomes previousSummary — the anchor in the prompt. Filter it out of the
+  // select-input so we don't double-encode (it's already in the anchor text).
+  const previousSummary = messages.filter((m) => m.summary).at(-1)?.content;
+  const forSelect = messages.filter((m) => !m.summary);
+
+  // 4. Resolve a recent context limit. llama-swap reports timings.n_ctx per
+  // completion; we cache it on messages.ctx_max. Use the most recent value
+  // from any message in this chat (oldest assumption is the same model is
+  // still running). When unknown, fall back to model.context_limit-less
+  // defaults via the buffer-only path (see usable()).
+  const ctxRows = await sql<{ ctx_max: number | null }[]>`
+    SELECT ctx_max FROM messages
+    WHERE chat_id = ${chatId} AND ctx_max IS NOT NULL
+    ORDER BY created_at DESC LIMIT 1
+  `;
+  const contextLimit = ctxRows[0]?.ctx_max ?? 0;
+
+  // 5. Decide head / tail.
+  const sel = select(forSelect, contextLimit);
+  if (!sel.tail_start_id || sel.head.length === 0) {
+    // Full preserve — nothing to compact this round. Clear the flag so we
+    // don't loop. (Could happen when the chat is short or the budget swung
+    // wider after a model context bump.)
+    await sql`UPDATE chats SET needs_compaction = false WHERE id = ${chatId}`;
+    log.info({ chatId, contextLimit, msgCount: messages.length }, 'compaction: nothing to compact');
+    return;
+  }
+
+  // 6. Build the OpenAI request: head as user/assistant/tool turns + a final
+  // user message carrying buildPrompt(previousSummary, []). No system prompt
+  // — matches opencode (`system: []`); the template + anchor are sufficient.
+  const headPayload = buildHeadPayload(sel.head);
+  const finalUser: OpenAiMessage = { role: 'user', content: buildPrompt(previousSummary, []) };
+  const payload = [...headPayload, finalUser];
+
+  log.info(
+    {
+      chatId,
+      contextLimit,
+      headLen: sel.head.length,
+      tailStartId: sel.tail_start_id,
+      hadPrevSummary: previousSummary !== undefined,
+    },
+    'compaction: invoking model',
+  );
+
+  // 6a. Flip the chat dot amber for the duration of the LLM call + DB writes.
+  // Same { type: 'chat_status', status: 'working', at } shape inference.ts
+  // emits at runner enqueue. publishUser → broadcasts on the per-user channel
+  // (all devices / tabs see it) since chat_status is a user-channel frame in
+  // BooCode (see useChatStatus.ts, which is the consumer).
+  broker.publishUser('default', {
+    type: 'chat_status',
+    chat_id: chatId,
+    status: 'working',
+    at: new Date().toISOString(),
+  });
+
+  // try/finally so the dot ALWAYS drops back to idle, even if the LLM call
+  // throws or a downstream DB write fails. The succeeded flag gates the
+  // 'compacted' frame + final log: we only signal completion to the UI when
+  // the new summary row actually landed.
+  let succeeded = false;
+  let newId = '';
+  let result: CompletionResult | undefined;
+  try {
+    // 7. Single completion (no tools). Throws on llama-swap failure.
+    result = await callLlamaSwap(config, session.model, payload, log);
+
+    // 8. Insert the new anchored summary row. role='assistant' per spec; the
+    // UI distinguishes via summary=true. tail_start_id points at the first
+    // preserved tail message so debug surfaces / future tools can reason
+    // about the boundary without re-deriving from compacted_at.
+    const insertRows = await sql<{ id: string }[]>`
+      INSERT INTO messages (
+        session_id, chat_id, role, content, kind, status,
+        summary, tail_start_id,
+        tokens_used, ctx_used, ctx_max,
+        created_at, finished_at
+      )
+      VALUES (
+        ${sessionId}, ${chatId}, 'assistant', ${result.content}, 'message', 'complete',
+        true, ${sel.tail_start_id},
+        ${result.completionTokens}, ${result.promptTokens}, ${result.nCtx},
+        clock_timestamp(), clock_timestamp()
+      )
+      RETURNING id
+    `;
+    newId = insertRows[0]!.id;
+
+    // 9. Mark every prior live message (head + prior summary) as compacted.
+    // Bound by "created_at strictly less than tail_start_id's created_at" so
+    // the preserved tail stays compacted_at=NULL. Exclude the new summary
+    // row we just inserted (it's "now", which is >= tail_start_id's
+    // created_at anyway, but defensive).
+    await sql`
+      UPDATE messages
+      SET compacted_at = clock_timestamp()
+      WHERE chat_id = ${chatId}
+        AND compacted_at IS NULL
+        AND id != ${newId}
+        AND created_at < (SELECT created_at FROM messages WHERE id = ${sel.tail_start_id})
+    `;
+
+    // 10. Clear the flag and bump the chat's updated_at so the sidebar
+    // reflects recent activity.
+    await sql`
+      UPDATE chats
+      SET needs_compaction = false, updated_at = clock_timestamp()
+      WHERE id = ${chatId}
+    `;
+
+    succeeded = true;
+  } finally {
+    // Always restore the dot. Status='idle' (not 'error') even on failure —
+    // the caller logs/re-surfaces the error separately; the dot doesn't
+    // need to stay red across reloads for a transient compaction blip.
+    broker.publishUser('default', {
+      type: 'chat_status',
+      chat_id: chatId,
+      status: 'idle',
+      at: new Date().toISOString(),
+    });
+  }
+
+  // 11. Tell the client. useSessionStream subscribes to the per-session WS
+  // channel; the handler refetches messages (so the new summary row + the
+  // compacted_at-stamped older rows render correctly) and fires a sonner
+  // toast. Order matters: idle must precede 'compacted' so the dot is
+  // already green by the time the refetch toast appears.
+  if (succeeded) {
+    broker.publish(sessionId, {
+      type: 'compacted',
+      session_id: sessionId,
+      chat_id: chatId,
+      summary_message_id: newId,
+    });
+    log.info(
+      {
+        chatId,
+        newId,
+        completionTokens: result?.completionTokens,
+        promptTokens: result?.promptTokens,
+      },
+      'compaction: complete',
+    );
+  }
+}
diff --git a/apps/server/src/services/inference.ts b/apps/server/src/services/inference.ts
index dd23623..9767cdd 100644
--- a/apps/server/src/services/inference.ts
+++ b/apps/server/src/services/inference.ts
@@ -21,6 +21,8 @@ import {
 import { PathScopeError, resolveProjectRoot } from './path_guard.js';
 import { maybeAutoNameChat } from './auto_name.js';
 import { getAgentById } from './agents.js';
+import * as compaction from './compaction.js';
+import type { Broker } from './broker.js';
 
 const BASE_SYSTEM_PROMPT = (projectPath: string) =>
   `You are BooCode Chat, a code investigation assistant. The user is working on a project located at ${projectPath}. Use the file-read tools (view_file, list_dir, grep, find_files) to investigate code when needed. Be concise. Cite file paths and line numbers when discussing code. Do not hallucinate file contents — read the file first. Tool results may be truncated; if so, narrow your query rather than guessing.`;
@@ -147,6 +149,12 @@ export interface InferenceContext {
   log: FastifyBaseLogger;
   publish: FramePublisher;
   publishUser: (frame: UserStreamFrame) => void;
+  // v1.11: passed through so compaction.process can publish 'compacted'
+  // frames on the same session WS channel useSessionStream subscribes to.
+  // Compaction is the only path that needs the raw broker handle (regular
+  // inference goes through `publish`); keeping a separate field avoids
+  // tempting other code paths into bypassing the session-id binding.
+  broker: Broker;
 }
 
 // Resolution order: base prompt < agent.system_prompt < user prompt, where
@@ -260,17 +268,48 @@ async function loadContext(
   if (projectRows.length === 0) return null;
   const project = projectRows[0]!;
 
+  // v1.11: filter compacted messages out of the inference assembly. The GET
+  // /api/sessions/:id/messages endpoint still returns everything (so the UI
+  // can show history with the summary card inline); only LLM payloads skip
+  // compacted rows. compacted_at IS NULL keeps the active summary + tail.
   const history = await sql<Message[]>`
     SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, status, last_seq,
            tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata
     FROM messages
-    WHERE chat_id = ${chatId}
+    WHERE chat_id = ${chatId} AND compacted_at IS NULL
     ORDER BY created_at ASC, id ASC
   `;
 
   return { session, project, history };
 }
 
+// v1.11: shared helper used after both finalizeCompletion and executeToolPhase
+// persist their token counts. Reads tokens off the just-UPDATEd row (which
+// the caller returns from RETURNING), runs compaction.isOverflow, and flips
+// chats.needs_compaction. The next runAssistantTurn invocation acts on it.
+// Silent on missing tokens — llama-swap occasionally omits usage on truncated
+// streams, and we'd rather miss one overflow than crash the inference path.
+async function maybeFlagForCompaction(
+  ctx: InferenceContext,
+  chatId: string,
+  updated: { tokens_used: number | null; ctx_used: number | null; ctx_max: number | null } | undefined,
+): Promise<void> {
+  if (!updated) return;
+  const promptTokens = updated.ctx_used;
+  const completionTokens = updated.tokens_used;
+  const contextLimit = updated.ctx_max;
+  if (typeof promptTokens !== 'number') return;
+  if (typeof completionTokens !== 'number') return;
+  if (typeof contextLimit !== 'number') return;
+  const overflow = compaction.isOverflow(
+    { prompt_tokens: promptTokens, completion_tokens: completionTokens },
+    contextLimit,
+  );
+  if (!overflow) return;
+  await ctx.sql`UPDATE chats SET needs_compaction = true WHERE id = ${chatId}`;
+  ctx.log.info({ chatId, promptTokens, completionTokens, contextLimit }, 'inference: flagged for compaction');
+}
+
 async function* sseLines(stream: ReadableStream<Uint8Array>): AsyncGenerator<string> {
   const reader = stream.getReader();
   const decoder = new TextDecoder('utf-8');
@@ -758,6 +797,10 @@ async function executeToolPhase(
     WHERE id = ${assistantMessageId}
     RETURNING tokens_used, ctx_used, ctx_max, finished_at
   `;
+  // v1.11: flag for compaction if this turn pushed us over the usable budget.
+  // We never compact mid-loop (the recursive runAssistantTurn keeps tools
+  // flowing); the flag fires on the NEXT turn's pre-fetch hook above.
+  await maybeFlagForCompaction(ctx, chatId, updated);
   const [toolSessRow] = await ctx.sql<{ project_id: string; name: string; updated_at: string }[]>`
     UPDATE sessions SET updated_at = clock_timestamp()
     WHERE id = ${sessionId}
@@ -889,6 +932,9 @@ async function finalizeCompletion(
     WHERE id = ${assistantMessageId}
     RETURNING tokens_used, ctx_used, ctx_max, finished_at
   `;
+  // v1.11: flag for compaction on the terminal turn too. Catches the common
+  // case of a turn that hit the limit without invoking tools.
+  await maybeFlagForCompaction(ctx, chatId, updated);
   const [completeSessRow] = await ctx.sql<{ project_id: string; name: string; updated_at: string }[]>`
     UPDATE sessions SET updated_at = clock_timestamp()
     WHERE id = ${sessionId}
@@ -927,6 +973,29 @@ async function runAssistantTurn(
 ): Promise<void> {
   const { sessionId, chatId } = args;
 
+  // v1.11: if the prior turn flagged this chat for compaction, run it first
+  // so loadContext below reads the post-compaction history. We swallow
+  // compaction failures (clearing the flag so we don't loop) and proceed
+  // with the un-compacted history — a slow turn that hits the model's
+  // hard limit is recoverable; a dead session is not.
+  const chatFlag = await ctx.sql<{ needs_compaction: boolean }[]>`
+    SELECT needs_compaction FROM chats WHERE id = ${chatId}
+  `;
+  if (chatFlag[0]?.needs_compaction) {
+    try {
+      await compaction.process({
+        sql: ctx.sql,
+        config: ctx.config,
+        log: ctx.log,
+        broker: ctx.broker,
+        chatId,
+      });
+    } catch (err) {
+      ctx.log.warn({ err, chatId }, 'auto-compaction failed; clearing flag and proceeding');
+      await ctx.sql`UPDATE chats SET needs_compaction = false WHERE id = ${chatId}`;
+    }
+  }
+
   const loaded = await loadContext(ctx.sql, sessionId, chatId);
   if (!loaded) {
     ctx.log.warn({ sessionId }, 'inference: session or project missing');
@@ -1237,81 +1306,6 @@ async function insertCapHitSentinel(
   });
 }
 
-const COMPACT_SYSTEM_PROMPT =
-  'Summarize the preceding conversation into a dense but complete context paragraph. Preserve all key facts, decisions, file paths, code patterns, and action items. Do not add any new information. Output only the summary paragraph.';
-
-async function runCompact(
-  ctx: InferenceContext,
-  sessionId: string,
-  chatId: string,
-  compactMessageId: string
-): Promise<void> {
-  const loaded = await loadContext(ctx.sql, sessionId, chatId);
-  if (!loaded) return;
-  const { session, project, history } = loaded;
-
-  const messagesForSummary = buildMessagesPayload(session, project,
-    history.filter((m) => m.id !== compactMessageId)
-  );
-  messagesForSummary.push({
-    role: 'system',
-    content: COMPACT_SYSTEM_PROMPT,
-  });
-
-  ctx.publish(sessionId, {
-    type: 'message_started',
-    message_id: compactMessageId,
-    chat_id: chatId,
-    role: 'assistant',
-  });
-
-  let content = '';
-  try {
-    const result = await streamCompletion(
-      ctx,
-      session.model,
-      messagesForSummary,
-      { tools: null },
-      (delta) => {
-        content += delta;
-        ctx.publish(sessionId, {
-          type: 'delta',
-          message_id: compactMessageId,
-          chat_id: chatId,
-          content: delta,
-        });
-      }
-    );
-    content = result.content;
-  } catch (err) {
-    const errMsg = err instanceof Error ? err.message : String(err);
-    await ctx.sql`
-      UPDATE messages SET status = 'failed', content = ${content}, finished_at = clock_timestamp()
-      WHERE id = ${compactMessageId}
-    `;
-    ctx.publish(sessionId, {
-      type: 'error',
-      message_id: compactMessageId,
-      chat_id: chatId,
-      error: errMsg,
-    });
-    return;
-  }
-
-  const preCompactCount = history.filter((m) => m.id !== compactMessageId && m.kind !== 'compact').length;
-  const summary = `[Context compacted — ${preCompactCount} messages summarized]\n\n${content}`;
-
-  await ctx.sql`
-    UPDATE messages SET content = ${summary}, status = 'complete', finished_at = clock_timestamp()
-    WHERE id = ${compactMessageId}
-  `;
-  ctx.publish(sessionId, {
-    type: 'message_complete',
-    message_id: compactMessageId,
-    chat_id: chatId,
-  });
-}
-
 interface InferenceRegistration {
   controller: AbortController;
   completed: Promise<void>;
@@ -1328,6 +1322,10 @@ export function createInferenceRunner(
       const callCtx: InferenceContext = {
         ...ctx,
         publishUser: (frame) => publishUserFn(user, frame),
+        // v1.11: broker comes in via ctx (set at registration time). Repeated
+        // here so the destructure carries it onto the per-call ctx without
+        // having to add it to every enqueue/cancel signature individually.
+        broker: ctx.broker,
       };
       // v1.8 mobile-tabs: announce working before the async loop starts so
       // every device subscribed to the user channel sees the amber dot.
@@ -1357,20 +1355,6 @@ export function createInferenceRunner(
       })();
     },
 
-    enqueueCompact(sessionId: string, chatId: string, compactMessageId: string, user: string) {
-      const callCtx: InferenceContext = {
-        ...ctx,
-        publishUser: (frame) => publishUserFn(user, frame),
-      };
-      void (async () => {
-        try {
-          await runCompact(callCtx, sessionId, chatId, compactMessageId);
-        } catch (err) {
-          callCtx.log.error({ err }, 'unhandled compact error');
-        }
-      })();
-    },
-
     async cancel(_sessionId: string, chatId: string): Promise<boolean> {
       const reg = registry.get(chatId);
       if (!reg) return false;
diff --git a/apps/server/src/types/api.ts b/apps/server/src/types/api.ts
index 3751c0b..54f5a04 100644
--- a/apps/server/src/types/api.ts
+++ b/apps/server/src/types/api.ts
@@ -159,6 +159,12 @@ export interface Message {
   // v1.8.2: per-message metadata. See MessageMetadata for the discriminated
   // shapes currently in use.
   metadata: MessageMetadata | null;
+  // v1.11: anchored rolling compaction. Optional so consumers that SELECT
+  // the pre-v1.11 column set still type-check. See compaction.ts +
+  // schema.sql for semantics.
+  summary?: boolean;
+  tail_start_id?: string | null;
+  compacted_at?: string | null;
 }
 
 export interface ModelInfo {
diff --git a/apps/web/src/api/client.ts b/apps/web/src/api/client.ts
index 6a7b50b..0335886 100644
--- a/apps/web/src/api/client.ts
+++ b/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) =>
diff --git a/apps/web/src/api/types.ts b/apps/web/src/api/types.ts
index 5d719fd..9784382 100644
--- a/apps/web/src/api/types.ts
+++ b/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 };
diff --git a/apps/web/src/components/MessageBubble.tsx b/apps/web/src/components/MessageBubble.tsx
index 4efa392..018bd8d 100644
--- a/apps/web/src/components/MessageBubble.tsx
+++ b/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} />;
   }
diff --git a/apps/web/src/hooks/useSessionStream.ts b/apps/web/src/hooks/useSessionStream.ts
index 07d85df..1ccdf8a 100644
--- a/apps/web/src/hooks/useSessionStream.ts
+++ b/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);