diff --git a/.env.example b/.env.example
index 338bcf5cdf..bc15daead4 100644
--- a/.env.example
+++ b/.env.example
@@ -858,6 +858,12 @@ PROVIDER_LIMITS_SYNC_SPACING_MS=1500
 # (>= 3 retrievals = never compressed). 1 disables the ramp (binary skip at the threshold only).
 # Used by: open-sse/services/compression/engines/ccr/index.ts.  Default: 2.
 #COMPRESSION_CCR_RETRIEVAL_RAMP_FACTOR=2
+# CCR durable block store (#9061). The in-memory store loses blocks to LRU eviction, the TTL, a
+# restart, or a retrieve landing on another instance, while the model is told it can retrieve them
+# verbatim. Set to false to keep blocks in memory only, at the cost of that promise. Blocks over
+# 512KB and cloud runtimes are memory-only regardless.
+# Used by: open-sse/services/compression/engines/ccr/index.ts.  Default: true.
+#COMPRESSION_CCR_DURABLE_STORE=true
 # T08/H5 — usage-observed prefix freeze (OPT-IN, default off). When enabled, a system prompt seen
 # >= THRESHOLD times is treated as a stable cacheable prefix and preserved from compression even
 # for providers the static cache-aware heuristic does not recognize (freeze = preserve, never
diff --git a/docs/reference/ENVIRONMENT.md b/docs/reference/ENVIRONMENT.md
index a36f60b7be..221db58669 100644
--- a/docs/reference/ENVIRONMENT.md
+++ b/docs/reference/ENVIRONMENT.md
@@ -454,6 +454,7 @@ detection above).
 | `COMPRESSION_PIPELINE_BREAKER_THRESHOLD`        | `3`                                                 | `open-sse/services/compression/pipelineEngineBreaker.ts`    | Consecutive cross-request failures before an engine's breaker opens.                                                                                                    |
 | `COMPRESSION_PIPELINE_BREAKER_COOLDOWN_MS`      | `30000`                                             | `open-sse/services/compression/pipelineEngineBreaker.ts`    | Milliseconds an opened engine stays skipped before a half-open probe.                                                                                                   |
 | `COMPRESSION_CCR_RETRIEVAL_RAMP_FACTOR`         | `2`                                                 | `open-sse/services/compression/engines/ccr/index.ts`        | T08/H8 CCR retrieval-feedback ramp: each prior retrieval of a stored block raises its effective `minChars` linearly (frequently-retrieved content compresses less; `>=3` retrievals = never compressed). `1` disables the ramp (binary skip at the threshold only). |
+| `COMPRESSION_CCR_DURABLE_STORE`                 | `true`                                              | `open-sse/services/compression/engines/ccr/index.ts`        | CCR durable block store (#9061). Backs the in-memory store with SQLite so a block survives LRU eviction, the TTL, a restart, or a retrieve landing on another instance. Set `false` to keep blocks in memory only. Blocks over 512KB and cloud runtimes stay memory-only regardless. |
 | `COMPRESSION_PREFIX_FREEZE_ENABLED`             | `false`                                             | `open-sse/services/compression/prefixFreeze.ts`             | T08/H5 usage-observed prefix freeze master switch. **Opt-in (default off)** — when on, a system prompt observed `>=` the threshold is treated as a stable cacheable prefix and preserved from compression even for providers the static cache heuristic misses (freeze only *preserves*, never mutates). |
 | `COMPRESSION_PREFIX_FREEZE_THRESHOLD`           | `3`                                                 | `open-sse/services/compression/prefixFreeze.ts`             | Observations of a system prompt before it is treated as a frozen stable prefix.                                                                                         |
 | `OMNIROUTE_BOOTSTRAPPED`                        | `false`                                             | `src/app/(dashboard)/dashboard/page.tsx`                    | Set `true` by bootstrap script after initial setup. Controls setup wizard visibility.                                                                                   |
diff --git a/open-sse/services/compression/engines/ccr/index.ts b/open-sse/services/compression/engines/ccr/index.ts
index e52755129f..e854666182 100644
--- a/open-sse/services/compression/engines/ccr/index.ts
+++ b/open-sse/services/compression/engines/ccr/index.ts
@@ -37,6 +37,13 @@
  */
 
 import crypto from "node:crypto";
+import {
+  deleteAllCcrBlocks,
+  deleteCcrBlockRow,
+  loadCcrBlock,
+  persistCcrBlock,
+  touchCcrBlock,
+} from "../../../../../src/lib/db/ccrBlocks.ts";
 import { createCompressionStats } from "../../stats.ts";
 import { queryBlock, type CcrQuery } from "./ccrQuery.ts";
 import { injectCcrProtocolInstruction } from "./protocolInstruction.ts";
@@ -156,6 +163,150 @@ function buildStoreKey(hash: string, principalId?: string): string {
   return `${principalId ?? ANON} ${hash}`;
 }
 
+// ─── durable second tier (#9061) ──────────────────────────────────────────────
+
+/**
+ * The map above is the hot cache. It loses entries to cross-principal LRU eviction, to
+ * the TTL, to restarts, and to a retrieve landing on another instance, while
+ * `fidelityGateStep` waives fidelity checks for sampling engines on the grounds that
+ * their drop is "CCR-recoverable", and the protocol instruction promises the model a
+ * verbatim block. These helpers put the block on disk so that promise survives.
+ *
+ * Every one of them is best-effort: a store without a usable database (compression
+ * preview, unit tests, a read-only volume) degrades to today's in-memory behaviour
+ * rather than failing the request.
+ *
+ * Three guards keep this from changing what the deployment stores at rest more than it
+ * has to. They follow the call-log artifact path, which faced the same question:
+ *
+ *   1. Blocks over `MAX_DURABLE_BLOCK_BYTES` stay memory-only. `MAX_CCR_BLOCK_BYTES` is
+ *      2 MB, and 5,000 of those would be 10 GB of prompt text in SQLite. 512 KB is the
+ *      ceiling #1647 already set on call artifacts for this exact reason.
+ *   2. No durable tier on a cloud runtime, which has no local disk to write to.
+ *   3. `COMPRESSION_CCR_DURABLE_STORE=false` turns it off. The content is prompt text, and an
+ *      operator who does not want that on disk needs a switch that is not a rebuild.
+ *
+ * The switch defaults to on because the model is already told, by the CCR protocol
+ * instruction, that it can retrieve the block verbatim. Leaving it off by default would
+ * keep that promise hollow for everyone who never reads this file.
+ */
+const MAX_DURABLE_BLOCK_BYTES = 512 * 1024;
+
+/** Matches the detection call-log artifacts use (`callLogArtifacts.ts`). */
+const isCloudRuntime = typeof globalThis.caches === "object" && globalThis.caches !== null;
+
+function durableTierEnabled(): boolean {
+  return !isCloudRuntime && process.env.COMPRESSION_CCR_DURABLE_STORE !== "false";
+}
+
+const loggedDurableErrors = new Set<string>();
+
+function warnDurableError(operation: string, error: unknown): void {
+  if (process.env.NODE_ENV === "test") return;
+  if (loggedDurableErrors.has(operation)) return;
+  if (loggedDurableErrors.size >= 20) {
+    const first = loggedDurableErrors.values().next().value;
+    if (first !== undefined) loggedDurableErrors.delete(first);
+  }
+  loggedDurableErrors.add(operation);
+  const message = error instanceof Error ? error.message : String(error);
+  console.warn(`[ccr] durable ${operation} failed: ${message}`);
+}
+
+/**
+ * Writes are deferred off the request path. Measured on this repo, a synchronous
+ * `persistCcrBlock` costs 0.032 ms at the 600-char minimum block but 1.77 ms at 500 KB,
+ * past the 1 ms this engine declares in its metadata, and roughly 7x the sha256 it
+ * already pays over the same bytes. The block is in the map before the defer runs, so an
+ * in-process retrieve never waits for the disk; only a crash inside that tick loses the
+ * durable copy, and the client's next request re-stores it under the same hash.
+ *
+ * Persist and delete share this queue so they cannot reorder: `setImmediate` is FIFO, and
+ * a delete that overtook its own persist would resurrect the block it just removed.
+ */
+const MAX_PENDING_DURABLE_WRITES = 1_000;
+let pendingDurableWrites = 0;
+let droppedDurableWrites = 0;
+
+function deferDurable(operation: string, work: () => void, droppable = false): void {
+  // Backpressure. A burst faster than SQLite drains would otherwise queue without bound
+  // and hold every block's content live in the closure. Dropping a persist is safe: the
+  // block is still in the map, and the client re-stores it under the same hash on its
+  // next request. Deletes are never dropped, or a deleted block would come back.
+  if (droppable && pendingDurableWrites >= MAX_PENDING_DURABLE_WRITES) {
+    droppedDurableWrites++;
+    return;
+  }
+  pendingDurableWrites++;
+  setImmediate(() => {
+    pendingDurableWrites--;
+    try {
+      work();
+    } catch (error) {
+      warnDurableError(operation, error);
+    }
+  });
+}
+
+function persistEntry(entry: CcrEntry): void {
+  if (!durableTierEnabled()) return;
+  if (entry.bytes > MAX_DURABLE_BLOCK_BYTES) return;
+  const snapshot = { ...entry };
+  deferDurable("persist", () => persistCcrBlock(snapshot), true);
+}
+
+function forgetEntry(hash: string, principalId: string): void {
+  if (!durableTierEnabled()) return;
+  deferDurable("delete", () => deleteCcrBlockRow(principalId, hash));
+}
+
+/**
+ * Read a block the map no longer holds and put it back in the map, so the LRU/byte
+ * accounting keeps working from there. Returns null when there is no durable row, which
+ * is also what a missing database looks like.
+ */
+function rehydrateEntry(hash: string, principalId: string, now: number): CcrEntry | null {
+  if (!durableTierEnabled()) return null;
+  let row: ReturnType<typeof loadCcrBlock>;
+  try {
+    row = loadCcrBlock(principalId, hash, now);
+  } catch (error) {
+    warnDurableError("load", error);
+    return null;
+  }
+  if (!row) return null;
+
+  const entry: CcrEntry = {
+    hash: row.hash,
+    principalId: row.principalId,
+    content: row.content,
+    bytes: row.bytes,
+    chars: row.chars,
+    lines: row.lines,
+    contentType: row.contentType,
+    source: row.source as CcrEntrySource,
+    createdAt: row.createdAt,
+    lastAccessedAt: now,
+    expiresAt: row.expiresAt,
+  };
+
+  // Re-admit through the same budgets a fresh store would face. If the block no longer
+  // fits, it stays on disk and is served straight from the row instead of being cached.
+  if (enforcePrincipalBudget(entry.principalId, entry.bytes) && enforceGlobalBudget(entry.bytes)) {
+    const key = buildStoreKey(hash, principalId === ANON ? undefined : principalId);
+    ccrStore.set(key, entry);
+    ccrTotalBytes += entry.bytes;
+    principalBytesMap.set(entry.principalId, principalBytes(entry.principalId) + entry.bytes);
+  }
+
+  try {
+    touchCcrBlock(entry.principalId, hash, now);
+  } catch (error) {
+    warnDurableError("touch", error);
+  }
+  return entry;
+}
+
 function readLifecycleCounters(principalId: string): CcrLifecycleCounters {
   return (
     lifecycleByPrincipal.get(principalId) ?? {
@@ -203,7 +354,12 @@ function removeEntry(key: string, reason?: "expired" | "capacity"): boolean {
   if (remainingPrincipalBytes === 0) principalBytesMap.delete(entry.principalId);
   else principalBytesMap.set(entry.principalId, remainingPrincipalBytes);
   const counters = mutableLifecycleCounters(entry.principalId);
-  if (reason === "expired") counters.expiredEvictions++;
+  if (reason === "expired") {
+    counters.expiredEvictions++;
+    // Expiry is the one eviction that means the block is finished. Capacity eviction is
+    // not: that block stays on disk, which is the point of the durable tier (#9061).
+    forgetEntry(entry.hash, entry.principalId);
+  }
   if (reason === "capacity") counters.capacityEvictions++;
   return true;
 }
@@ -350,6 +506,7 @@ export function tryStoreBlock(
   ccrStore.set(key, entry);
   ccrTotalBytes += bytes;
   principalBytesMap.set(owner, principalBytes(owner) + bytes);
+  persistEntry(entry);
   return { stored: true, hash, metadata: publicMetadata(entry) };
 }
 
@@ -372,7 +529,12 @@ export function storeBlock(
 export function retrieveBlock(hash: string, principalId?: string, now = Date.now()): string | null {
   const key = buildStoreKey(hash, principalId);
   const entry = getActiveEntry(key, now);
-  if (!entry) return null;
+  if (!entry) {
+    // Miss in the hot cache is not proof the block is gone (#9061): LRU eviction, the TTL
+    // sweep, a restart, or another instance all land here while the row is still on disk.
+    const restored = rehydrateEntry(hash, principalId ?? ANON, now);
+    return restored ? restored.content : null;
+  }
   entry.lastAccessedAt = now;
   ccrStore.delete(key);
   ccrStore.set(key, entry);
@@ -435,6 +597,14 @@ export function resetCcrStore(): void {
   principalBytesMap.clear();
   ccrTotalBytes = 0;
   lifecycleByPrincipal.clear();
+  // Through the same queue as persist/delete, so a reset cannot overtake a write it was
+  // meant to clear.
+  deferDurable("reset", deleteAllCcrBlocks);
+}
+
+/** Resolves once the deferred durable writes queued so far have run. */
+export function flushCcrDurableWrites(): Promise<void> {
+  return new Promise((resolve) => setImmediate(resolve));
 }
 
 export function inspectCcrBlock(
@@ -469,7 +639,11 @@ export function listCcrBlocks(
 }
 
 export function deleteCcrBlock(hash: string, principalId?: string, _now = Date.now()): boolean {
-  return removeEntry(buildStoreKey(hash, principalId));
+  const removedFromCache = removeEntry(buildStoreKey(hash, principalId));
+  // An explicit delete must reach the durable tier too, otherwise the next retrieve
+  // rehydrates the block the caller just deleted.
+  forgetEntry(hash, principalId ?? ANON);
+  return removedFromCache;
 }
 
 export function getCcrStoreStats(principalId?: string, now = Date.now()): CcrStoreStats {
diff --git a/src/lib/db/ccrBlocks.ts b/src/lib/db/ccrBlocks.ts
new file mode 100644
index 0000000000..56d49c131a
--- /dev/null
+++ b/src/lib/db/ccrBlocks.ts
@@ -0,0 +1,143 @@
+/**
+ * Durable second tier for the CCR block store (#9061).
+ *
+ * The CCR engine's in-process `Map` stays the hot cache; this module is what makes its
+ * promise survive an eviction, a TTL sweep, a restart, or a retrieve that lands on
+ * another instance. Every function here is best-effort: the caller treats a throw as
+ * "not durable this time", never as a request failure.
+ */
+import { getDbInstance } from "./core";
+
+export interface CcrBlockRow {
+  principalId: string;
+  hash: string;
+  content: string;
+  bytes: number;
+  chars: number;
+  lines: number;
+  contentType: string;
+  source: string;
+  createdAt: number;
+  lastAccessedAt: number;
+  expiresAt: number;
+}
+
+interface CcrBlockDbRow {
+  content: string;
+  bytes: number;
+  chars: number;
+  lines: number;
+  content_type: string;
+  source: string;
+  created_at: number;
+  last_accessed_at: number;
+  expires_at: number;
+}
+
+/**
+ * Writes older than this are not worth a prune scan on every call.
+ * ponytail: counter-based throttle, swap for a scheduled sweep if the table ever grows
+ * fast enough that 200 writes of drift matters.
+ */
+const PRUNE_EVERY_N_WRITES = 200;
+let writesSincePrune = 0;
+
+export function persistCcrBlock(row: CcrBlockRow): void {
+  const db = getDbInstance();
+  db.prepare(
+    `INSERT OR REPLACE INTO ccr_blocks (
+       principal_id, hash, content, bytes, chars, lines,
+       content_type, source, created_at, last_accessed_at, expires_at
+     ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+  ).run(
+    row.principalId,
+    row.hash,
+    row.content,
+    row.bytes,
+    row.chars,
+    row.lines,
+    row.contentType,
+    row.source,
+    row.createdAt,
+    row.lastAccessedAt,
+    row.expiresAt
+  );
+
+  if (++writesSincePrune >= PRUNE_EVERY_N_WRITES) {
+    writesSincePrune = 0;
+    pruneExpiredCcrBlocks(Date.now());
+  }
+}
+
+/** Returns the block only while it is unexpired; an expired row is deleted and read as a miss. */
+export function loadCcrBlock(principalId: string, hash: string, now: number): CcrBlockRow | null {
+  const db = getDbInstance();
+  const row = db
+    .prepare(
+      `SELECT content, bytes, chars, lines, content_type, source,
+              created_at, last_accessed_at, expires_at
+         FROM ccr_blocks WHERE principal_id = ? AND hash = ?`
+    )
+    .get(principalId, hash) as CcrBlockDbRow | undefined;
+
+  if (!row) return null;
+  if (row.expires_at <= now) {
+    deleteCcrBlockRow(principalId, hash);
+    return null;
+  }
+
+  return {
+    principalId,
+    hash,
+    content: row.content,
+    bytes: row.bytes,
+    chars: row.chars,
+    lines: row.lines,
+    contentType: row.content_type,
+    source: row.source,
+    createdAt: row.created_at,
+    lastAccessedAt: row.last_accessed_at,
+    expiresAt: row.expires_at,
+  };
+}
+
+export function touchCcrBlock(principalId: string, hash: string, lastAccessedAt: number): void {
+  getDbInstance()
+    .prepare(`UPDATE ccr_blocks SET last_accessed_at = ? WHERE principal_id = ? AND hash = ?`)
+    .run(lastAccessedAt, principalId, hash);
+}
+
+export function deleteCcrBlockRow(principalId: string, hash: string): void {
+  getDbInstance()
+    .prepare(`DELETE FROM ccr_blocks WHERE principal_id = ? AND hash = ?`)
+    .run(principalId, hash);
+}
+
+/**
+ * Drops every durable block. Mirrors the engine's `resetCcrStore()` so that "reset" keeps
+ * meaning reset once the store has a second tier.
+ */
+export function deleteAllCcrBlocks(): void {
+  getDbInstance().prepare(`DELETE FROM ccr_blocks`).run();
+}
+
+/** Drops every block whose TTL has passed. Returns how many rows went. */
+export function pruneExpiredCcrBlocks(now: number): number {
+  const result = getDbInstance().prepare(`DELETE FROM ccr_blocks WHERE expires_at <= ?`).run(now);
+  return result.changes ?? 0;
+}
+
+export function countCcrBlocks(principalId?: string): number {
+  const db = getDbInstance();
+  const row = (
+    principalId === undefined
+      ? db.prepare(`SELECT COUNT(*) AS n FROM ccr_blocks`).get()
+      : db.prepare(`SELECT COUNT(*) AS n FROM ccr_blocks WHERE principal_id = ?`).get(principalId)
+  ) as { n: number } | undefined;
+  return row?.n ?? 0;
+}
+
+/** Test seam: the write throttle is module state and has to be resettable between tests. */
+export function resetCcrBlockPruneCounter(): void {
+  writesSincePrune = 0;
+}
diff --git a/src/lib/db/cleanup.ts b/src/lib/db/cleanup.ts
index fc866800b3..20d0358ce4 100644
--- a/src/lib/db/cleanup.ts
+++ b/src/lib/db/cleanup.ts
@@ -370,6 +370,29 @@ export async function cleanupCompressionRunTelemetry(): Promise<CleanupResult> {
   return result;
 }
 
+/**
+ * Clean up expired CCR blocks (#9061).
+ *
+ * Unlike the tables above, these rows carry their own expiry: the engine writes
+ * `expires_at` from the block's TTL, so this needs no retention-days setting of its own.
+ * It is the same sweep the engine does opportunistically, run on the operator's schedule
+ * so the table cannot sit on rows nobody will read again.
+ */
+export async function cleanupCcrBlocks(): Promise<CleanupResult> {
+  const result: CleanupResult = { deleted: 0, errors: 0 };
+
+  try {
+    const { pruneExpiredCcrBlocks } = await import("./ccrBlocks");
+    result.deleted = pruneExpiredCcrBlocks(Date.now());
+    console.log(`[Cleanup] Deleted ${result.deleted} expired ccr_blocks`);
+  } catch (err: unknown) {
+    console.error("[Cleanup] Error cleaning ccr_blocks:", err);
+    result.errors++;
+  }
+
+  return result;
+}
+
 /**
  * Run all cleanup functions if auto-cleanup is enabled.
  */
@@ -401,6 +424,7 @@ export async function runAutoCleanup(): Promise<{
     xpAuditLog: await cleanupXpAuditLog(),
     compressionRunTelemetry: await cleanupCompressionRunTelemetry(),
     proxyLogs: await cleanupProxyLogs(),
+    ccrBlocks: await cleanupCcrBlocks(),
   };
 
   const totalDeleted = Object.values(results).reduce((sum, r) => sum + r.deleted, 0);
diff --git a/src/lib/db/migrations/134_ccr_blocks.sql b/src/lib/db/migrations/134_ccr_blocks.sql
new file mode 100644
index 0000000000..a1dd4b87cb
--- /dev/null
+++ b/src/lib/db/migrations/134_ccr_blocks.sql
@@ -0,0 +1,31 @@
+-- CCR durable block store (#9061).
+--
+-- The CCR engine keeps blocks in a process-local Map. That map loses entries to
+-- cross-principal LRU eviction (5,000 entries / 64 MB global cap), to the 24h TTL, to
+-- process restarts, and to multi-instance deployments where the MCP retrieve call lands
+-- on an instance that never ran the compression. Meanwhile `fidelityGateStep.ts` waives
+-- fidelity verification for sampling engines *because* their drop is "CCR-recoverable",
+-- and the model is told by the CCR protocol instruction that it can retrieve the block
+-- verbatim.
+--
+-- This table is the second tier behind that Map: the Map stays the hot cache and keeps
+-- its LRU/byte-budget behaviour untouched, and a block evicted from it is still readable
+-- here. Scoping matches the in-memory store's compound key (principal + content hash).
+
+CREATE TABLE IF NOT EXISTS ccr_blocks (
+  principal_id     TEXT    NOT NULL,
+  hash             TEXT    NOT NULL,
+  content          TEXT    NOT NULL,
+  bytes            INTEGER NOT NULL,
+  chars            INTEGER NOT NULL,
+  lines            INTEGER NOT NULL,
+  content_type     TEXT    NOT NULL DEFAULT 'text/plain',
+  source           TEXT    NOT NULL DEFAULT 'compression',
+  created_at       INTEGER NOT NULL,
+  last_accessed_at INTEGER NOT NULL,
+  expires_at       INTEGER NOT NULL,
+  PRIMARY KEY (principal_id, hash)
+);
+
+-- Pruning scans by expiry.
+CREATE INDEX IF NOT EXISTS idx_ccr_blocks_expires ON ccr_blocks(expires_at);
diff --git a/src/lib/localDb.ts b/src/lib/localDb.ts
index 5ec050fbf3..1da3925b95 100755
--- a/src/lib/localDb.ts
+++ b/src/lib/localDb.ts
@@ -89,6 +89,7 @@ export {
   reorderCombos,
   deleteCombo,
 } from "./db/combos";
+export * from "./db/ccrBlocks";
 export * from "./db/compressionCacheStats";
 export * from "./db/compressionCombos";
 export * from "./db/compressionContextBudget";
diff --git a/tests/unit/ccr-durable-store-9061.test.ts b/tests/unit/ccr-durable-store-9061.test.ts
new file mode 100644
index 0000000000..dec112749e
--- /dev/null
+++ b/tests/unit/ccr-durable-store-9061.test.ts
@@ -0,0 +1,164 @@
+/**
+ * #9061. The CCR store's in-process Map loses blocks to LRU eviction, the TTL, a
+ * restart, or a retrieve landing on another instance, while `fidelityGateStep` waives
+ * fidelity checks for sampling engines because their drop is "CCR-recoverable" and the
+ * protocol instruction promises the model a verbatim block.
+ *
+ * The regression test is the restart: a fresh module instance has an empty Map, so a
+ * block stored before it must come back from the durable tier or not at all.
+ */
+import { describe, it, before, beforeEach, after } from "node:test";
+import assert from "node:assert/strict";
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+const tmpDir = mkdtempSync(join(tmpdir(), "omniroute-ccr-9061-"));
+process.env.DATA_DIR = tmpDir;
+
+const core = await import("../../src/lib/db/core.ts");
+core.resetDbInstance();
+
+const {
+  persistCcrBlock,
+  loadCcrBlock,
+  deleteCcrBlockRow,
+  deleteAllCcrBlocks,
+  pruneExpiredCcrBlocks,
+  countCcrBlocks,
+} = await import("../../src/lib/db/ccrBlocks.ts");
+
+const ccrPath = "../../open-sse/services/compression/engines/ccr/index.ts";
+const ccr = await import(ccrPath);
+
+const HOUR = 60 * 60 * 1000;
+
+function row(overrides: Record<string, unknown> = {}) {
+  const now = 1_000_000;
+  return {
+    principalId: "principal-a",
+    hash: "aaaaaaaaaaaaaaaaaaaaaaaa",
+    content: "the verbatim block",
+    bytes: 18,
+    chars: 18,
+    lines: 1,
+    contentType: "text/plain",
+    source: "compression",
+    createdAt: now,
+    lastAccessedAt: now,
+    expiresAt: now + HOUR,
+    ...overrides,
+  };
+}
+
+describe("ccrBlocks durable store (#9061)", () => {
+  beforeEach(() => {
+    deleteAllCcrBlocks();
+  });
+
+  after(() => {
+    core.resetDbInstance();
+  });
+
+  it("round-trips a block", () => {
+    persistCcrBlock(row());
+    const loaded = loadCcrBlock("principal-a", "aaaaaaaaaaaaaaaaaaaaaaaa", 1_000_000);
+    assert.equal(loaded?.content, "the verbatim block");
+    assert.equal(loaded?.contentType, "text/plain");
+    assert.equal(loaded?.source, "compression");
+  });
+
+  it("scopes by principal, so another cannot read the block", () => {
+    persistCcrBlock(row());
+    assert.equal(loadCcrBlock("principal-b", "aaaaaaaaaaaaaaaaaaaaaaaa", 1_000_000), null);
+  });
+
+  it("reads an expired block as a miss and drops the row", () => {
+    persistCcrBlock(row({ expiresAt: 1_000_000 }));
+    assert.equal(loadCcrBlock("principal-a", "aaaaaaaaaaaaaaaaaaaaaaaa", 1_000_001), null);
+    assert.equal(countCcrBlocks(), 0);
+  });
+
+  it("prunes only what has expired", () => {
+    persistCcrBlock(row({ hash: "a".repeat(24), expiresAt: 500 }));
+    persistCcrBlock(row({ hash: "b".repeat(24), expiresAt: 9_000_000 }));
+    assert.equal(pruneExpiredCcrBlocks(1_000_000), 1);
+    assert.equal(countCcrBlocks(), 1);
+  });
+
+  it("deletes a single block", () => {
+    persistCcrBlock(row());
+    deleteCcrBlockRow("principal-a", "aaaaaaaaaaaaaaaaaaaaaaaa");
+    assert.equal(countCcrBlocks(), 0);
+  });
+});
+
+describe("CCR engine survives losing its in-memory map (#9061)", () => {
+  before(() => {
+    ccr.resetCcrStore();
+  });
+
+  after(() => {
+    ccr.resetCcrStore();
+    core.resetDbInstance();
+  });
+
+  it("retrieves a block from a fresh module instance, the way a restart sees it", async () => {
+    const text = "x".repeat(2_000);
+    const stored = ccr.tryStoreBlock(text, "principal-a");
+    assert.equal(stored.stored, true);
+    await ccr.flushCcrDurableWrites();
+
+    // A fresh instance of the engine module has its own empty Map, the same state the
+    // process has after a restart, and the same state another instance starts in.
+    const restarted = await import(`${ccrPath}?restart=9061`);
+    assert.equal(
+      restarted.retrieveBlock(stored.hash, "principal-a"),
+      text,
+      "block must come back from the durable tier after the in-memory map is gone"
+    );
+  });
+
+  it("keeps the principal boundary across the restart", async () => {
+    const text = "y".repeat(2_000);
+    const stored = ccr.tryStoreBlock(text, "principal-a");
+    await ccr.flushCcrDurableWrites();
+    const restarted = await import(`${ccrPath}?restart=9061-scope`);
+    assert.equal(restarted.retrieveBlock(stored.hash, "principal-b"), null);
+  });
+
+  it("keeps an oversized block memory-only", async () => {
+    // 512KB is the ceiling call artifacts already use (#1647). Above it the block still
+    // works from the map, it just never reaches disk.
+    const text = "b".repeat(600 * 1024);
+    const stored = ccr.tryStoreBlock(text, "principal-a");
+    assert.equal(stored.stored, true);
+    await ccr.flushCcrDurableWrites();
+
+    assert.equal(ccr.retrieveBlock(stored.hash, "principal-a"), text, "map still serves it");
+    assert.equal(loadCcrBlock("principal-a", stored.hash, Date.now()), null, "but disk has no row");
+  });
+
+  it("writes nothing when COMPRESSION_CCR_DURABLE_STORE is false", async () => {
+    const previous = process.env.COMPRESSION_CCR_DURABLE_STORE;
+    process.env.COMPRESSION_CCR_DURABLE_STORE = "false";
+    try {
+      const stored = ccr.tryStoreBlock("c".repeat(2_000), "principal-a");
+      await ccr.flushCcrDurableWrites();
+      assert.equal(loadCcrBlock("principal-a", stored.hash, Date.now()), null);
+    } finally {
+      if (previous === undefined) delete process.env.COMPRESSION_CCR_DURABLE_STORE;
+      else process.env.COMPRESSION_CCR_DURABLE_STORE = previous;
+    }
+  });
+
+  it("does not resurrect a block that was explicitly deleted", async () => {
+    const text = "z".repeat(2_000);
+    const stored = ccr.tryStoreBlock(text, "principal-a");
+    ccr.deleteCcrBlock(stored.hash, "principal-a");
+    // Persist and delete share one FIFO queue; one flush covers both.
+    await ccr.flushCcrDurableWrites();
+    const restarted = await import(`${ccrPath}?restart=9061-deleted`);
+    assert.equal(restarted.retrieveBlock(stored.hash, "principal-a"), null);
+  });
+});