diff --git a/backend/src/config.ts b/backend/src/config.ts
index ee7193d7..87160468 100644
--- a/backend/src/config.ts
+++ b/backend/src/config.ts
@@ -251,6 +251,7 @@ export function loadConfig(env: Record<string, string | undefined>): AppConfig {
     secretRoots,
     maxImportBytes: positiveImportLimit(env.THT_WORKSPACE_MAX_IMPORT_BYTES, 10 * 1024 * 1024),
     maxImportEntries: positiveImportLimit(env.THT_WORKSPACE_MAX_IMPORT_ENTRIES, 32),
+    dataRoot: env.THT_DATA_ROOT,
   };
   const settingsFile = env.SETTINGS_FILE ?? "data/settings.json";
   const internalQdrantUrl = internalServiceUrl(
diff --git a/backend/src/workspaces/annotations-sync.ts b/backend/src/workspaces/annotations-sync.ts
new file mode 100644
index 00000000..1592308e
--- /dev/null
+++ b/backend/src/workspaces/annotations-sync.ts
@@ -0,0 +1,174 @@
+import { createHash, randomBytes } from "node:crypto";
+import {
+  closeSync,
+  constants as fsConstants,
+  fchmodSync,
+  fstatSync,
+  fsyncSync,
+  lstatSync,
+  mkdirSync,
+  openSync,
+  readFileSync,
+  renameSync,
+  unlinkSync,
+  writeFileSync,
+} from "node:fs";
+import { dirname, isAbsolute, join } from "node:path";
+import { parseAnnotationsYaml } from "./annotations.js";
+
+export interface AnnotationsSyncInput {
+  dataRoot: string;
+  workspaceId: string;
+  commit: string;
+  blobId: string;
+  contents: Buffer;
+}
+
+export interface AnnotationsSyncResult {
+  path: string;
+  manifestPath: string;
+  contentDigest: string;
+}
+
+interface AnnotationsOwnershipManifest {
+  workspace: string;
+  commit: string;
+  blobId: string;
+  contentDigest: string;
+  destination: string;
+}
+
+export function annotationsSyncRoot(dataRoot: string, workspaceId: string, commit: string): string {
+  return join(dataRoot, "sessions", workspaceId, "revisions", commit, "artifacts");
+}
+
+function sha256(value: Buffer | string): string {
+  return `sha256:${createHash("sha256").update(value).digest("hex")}`;
+}
+
+function ensureDirectory(path: string): void {
+  mkdirSync(path, { recursive: true, mode: 0o700 });
+  const entry = lstatSync(path);
+  if (!entry.isDirectory() || entry.isSymbolicLink()) {
+    throw new Error("annotations sync directory is unavailable");
+  }
+}
+
+function syncDirectory(directory: string): void {
+  if (process.platform === "win32") return;
+  const fd = openSync(directory, "r");
+  try { fsyncSync(fd); } finally { closeSync(fd); }
+}
+
+function writeAtomicFile(path: string, contents: string | Buffer, mode: number): void {
+  ensureDirectory(dirname(path));
+  const staging = `${path}.tmp-${process.pid}-${Date.now()}-${randomBytes(6).toString("hex")}`;
+  const fd = openSync(
+    staging,
+    fsConstants.O_WRONLY | fsConstants.O_CREAT | fsConstants.O_EXCL | fsConstants.O_NOFOLLOW,
+    0o600,
+  );
+  let closed = false;
+  try {
+    writeFileSync(fd, contents);
+    fsyncSync(fd);
+    fchmodSync(fd, mode);
+    closeSync(fd);
+    closed = true;
+    renameSync(staging, path);
+    syncDirectory(dirname(path));
+  } catch (error) {
+    if (!closed) try { closeSync(fd); } catch { /* preserve original failure */ }
+    try { unlinkSync(staging); } catch { /* best effort */ }
+    throw error;
+  }
+}
+
+function readTrustedFile(path: string): Buffer {
+  const entry = lstatSync(path);
+  if (!entry.isFile() || entry.isSymbolicLink()) throw new Error("annotations sync file is invalid");
+  const fd = openSync(path, fsConstants.O_RDONLY | fsConstants.O_NOFOLLOW);
+  try {
+    const before = fstatSync(fd);
+    if (!before.isFile() || before.nlink !== 1) throw new Error("annotations sync file is invalid");
+    const contents = readFileSync(fd);
+    const after = fstatSync(fd);
+    if (before.dev !== after.dev || before.ino !== after.ino || before.size !== after.size || before.nlink !== after.nlink) {
+      throw new Error("annotations sync file changed while reading");
+    }
+    return contents;
+  } finally {
+    closeSync(fd);
+  }
+}
+
+function parseManifest(source: string): AnnotationsOwnershipManifest {
+  const parsed = JSON.parse(source) as Record<string, unknown>;
+  if (
+    typeof parsed.workspace !== "string"
+    || typeof parsed.commit !== "string"
+    || typeof parsed.blobId !== "string"
+    || typeof parsed.contentDigest !== "string"
+    || typeof parsed.destination !== "string"
+  ) {
+    throw new Error("annotations ownership manifest is invalid");
+  }
+  return parsed as unknown as AnnotationsOwnershipManifest;
+}
+
+/**
+ * Atomically synchronize a curated annotation blob to its immutable revision-qualified runtime
+ * root and write an adjacent ownership manifest. Idempotent: an existing destination is re-verified
+ * against the exact blob/digest and fails closed on any mismatch. Never follows symlinks.
+ */
+export function syncAnnotations(input: AnnotationsSyncInput): AnnotationsSyncResult {
+  if (!isAbsolute(input.dataRoot)) throw new Error("annotations sync data root must be absolute");
+  if (!/^[a-z][a-z0-9-]{2,62}$/.test(input.workspaceId) || input.workspaceId === "workspace-docs") {
+    throw new Error("annotations sync workspace id is invalid");
+  }
+  if (!/^[0-9a-f]{40}$/.test(input.commit)) throw new Error("annotations sync commit is invalid");
+  if (!/^[0-9a-f]{40}$/.test(input.blobId)) throw new Error("annotations sync blob id is invalid");
+  parseAnnotationsYaml(input.contents.toString("utf8"));
+
+  const root = annotationsSyncRoot(input.dataRoot, input.workspaceId, input.commit);
+  const directory = join(root, "mschema");
+  const path = join(directory, "annotations.yaml");
+  const manifestPath = join(directory, "annotations.ownership.json");
+  const contentDigest = sha256(input.contents);
+  const manifest: AnnotationsOwnershipManifest = {
+    workspace: input.workspaceId,
+    commit: input.commit,
+    blobId: input.blobId,
+    contentDigest,
+    destination: path,
+  };
+
+  let existingContents: Buffer | undefined;
+  try {
+    existingContents = readTrustedFile(path);
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code !== "ENOENT") throw error;
+    existingContents = undefined;
+  }
+
+  if (existingContents !== undefined) {
+    if (sha256(existingContents) !== contentDigest) {
+      throw new Error("annotations sync destination does not match the pinned revision");
+    }
+    const existingManifest = parseManifest(readTrustedFile(manifestPath).toString("utf8"));
+    if (
+      existingManifest.workspace !== manifest.workspace
+      || existingManifest.commit !== manifest.commit
+      || existingManifest.blobId !== manifest.blobId
+      || existingManifest.contentDigest !== manifest.contentDigest
+      || existingManifest.destination !== manifest.destination
+    ) {
+      throw new Error("annotations ownership manifest does not match the pinned revision");
+    }
+    return { path, manifestPath, contentDigest };
+  }
+
+  writeAtomicFile(path, input.contents, 0o400);
+  writeAtomicFile(manifestPath, `${JSON.stringify(manifest)}\n`, 0o600);
+  return { path, manifestPath, contentDigest };
+}
diff --git a/backend/src/workspaces/registry.ts b/backend/src/workspaces/registry.ts
index 2f05e04a..82e71e64 100644
--- a/backend/src/workspaces/registry.ts
+++ b/backend/src/workspaces/registry.ts
@@ -4,6 +4,7 @@ import { mkdir, readdir, readFile, rename, rm, writeFile } from "node:fs/promise
 import { isAbsolute, join } from "node:path";
 import { buildInstallationContract, renderWorkspaceDocs } from "./contracts.js";
 import { parseAnnotationsYaml } from "./annotations.js";
+import { syncAnnotations } from "./annotations-sync.js";
 import { assertCatalogMatchesDescriptor, parseWorkspaceCatalogYaml, type WorkspaceCatalog, type WorkspaceCatalogEntry } from "./catalog.js";
 import {
   GitWorkspaceRepository,
@@ -585,6 +586,15 @@ export class WorkspaceRegistry {
         const annotations = await this.repository.annotationsObject(safeHead, id);
         if (annotations !== undefined) {
           parseAnnotationsYaml(annotations.contents.toString("utf8"));
+          if (this.config.dataRoot !== undefined) {
+            syncAnnotations({
+              dataRoot: this.config.dataRoot,
+              workspaceId: id,
+              commit: safeHead,
+              blobId: annotations.blobId,
+              contents: annotations.contents,
+            });
+          }
         }
         const collection = workspace.semantic_index.vector_store.collection;
         const owner = collectionOwners.get(collection);
diff --git a/backend/src/workspaces/types.ts b/backend/src/workspaces/types.ts
index e10909bb..b703ae8b 100644
--- a/backend/src/workspaces/types.ts
+++ b/backend/src/workspaces/types.ts
@@ -8,6 +8,8 @@ export interface WorkspaceRegistryConfig {
   secretRoots: readonly string[];
   maxImportBytes: number;
   maxImportEntries: number;
+  /** Absolute runtime data root; when set, activation also syncs curated annotations per revision. */
+  dataRoot?: string;
 }
 
 export type WorkspaceErrorCode =
diff --git a/backend/test/annotations-sync.test.ts b/backend/test/annotations-sync.test.ts
new file mode 100644
index 00000000..e93a4652
--- /dev/null
+++ b/backend/test/annotations-sync.test.ts
@@ -0,0 +1,116 @@
+import { chmodSync, lstatSync, mkdirSync, mkdtempSync, readFileSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, expect, test } from "vitest";
+import { syncAnnotations } from "../src/workspaces/annotations-sync.js";
+
+const temporaryRoots: string[] = [];
+
+afterEach(() => {
+  temporaryRoots.splice(0).forEach((root) => rmSync(root, { recursive: true, force: true }));
+});
+
+function input(overrides: Partial<{
+  dataRoot: string; workspaceId: string; commit: string; blobId: string; contents: Buffer;
+}> = {}) {
+  return {
+    dataRoot: overrides.dataRoot ?? "",
+    workspaceId: overrides.workspaceId ?? "research",
+    commit: overrides.commit ?? "a".repeat(40),
+    blobId: overrides.blobId ?? "b".repeat(40),
+    contents: overrides.contents ?? Buffer.from("tables: {}\n"),
+  };
+}
+
+test("writes the revision-qualified annotations file and ownership manifest", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const target = input({ dataRoot });
+
+  const result = syncAnnotations(target);
+
+  expect(readFileSync(result.path, "utf8")).toBe("tables: {}\n");
+  const manifest = JSON.parse(readFileSync(result.manifestPath, "utf8"));
+  expect(manifest).toMatchObject({
+    workspace: "research",
+    commit: "a".repeat(40),
+    blobId: "b".repeat(40),
+    contentDigest: result.contentDigest,
+    destination: result.path,
+  });
+  expect(result.path).toContain("/revisions/" + "a".repeat(40) + "/artifacts/mschema/annotations.yaml");
+  expect(lstatSync(result.path).mode & 0o777).toBe(0o400);
+});
+
+test("is idempotent for the exact same blob and manifest", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const target = input({ dataRoot });
+
+  expect(syncAnnotations(target)).toEqual(syncAnnotations(target));
+});
+
+test("fails closed when the destination was tampered", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const target = input({ dataRoot });
+  syncAnnotations(target);
+
+  const dest = join(dataRoot, "sessions", "research", "revisions", "a".repeat(40), "artifacts", "mschema", "annotations.yaml");
+  chmodSync(dest, 0o600);
+  writeFileSync(dest, "tampered\n");
+
+  expect(() => syncAnnotations(target)).toThrow();
+});
+
+test("fails closed when the ownership manifest does not match", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const target = input({ dataRoot });
+  syncAnnotations(target);
+
+  const manifestPath = join(dataRoot, "sessions", "research", "revisions", "a".repeat(40), "artifacts", "mschema", "annotations.ownership.json");
+  writeFileSync(manifestPath, JSON.stringify({ workspace: "other", commit: "c".repeat(40), blobId: "d".repeat(40), contentDigest: "sha256:x", destination: "/other" }));
+
+  expect(() => syncAnnotations(target)).toThrow();
+});
+
+test("writes different revisions to different directories", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+
+  const first = syncAnnotations(input({ dataRoot, commit: "a".repeat(40) }));
+  const second = syncAnnotations(input({ dataRoot, commit: "b".repeat(40) }));
+
+  expect(first.path).not.toBe(second.path);
+  expect(readFileSync(second.path, "utf8")).toBe("tables: {}\n");
+});
+
+test("rejects a symlink destination and malformed inputs before writing", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const root = join(dataRoot, "sessions", "research", "revisions", "a".repeat(40), "artifacts");
+  mkdirSync(root, { recursive: true });
+  symlinkSync(join(root, "mschema-target"), join(root, "mschema"));
+  mkdirSync(join(root, "mschema-target"));
+
+  expect(() => syncAnnotations(input({ dataRoot }))).toThrow();
+  expect(() => syncAnnotations(input({ dataRoot: "relative" }))).toThrow();
+  expect(() => syncAnnotations(input({ workspaceId: "../x" }))).toThrow();
+  expect(() => syncAnnotations(input({ commit: "HEAD" }))).toThrow();
+  expect(() => syncAnnotations(input({ blobId: "not-hex" }))).toThrow();
+  expect(() => syncAnnotations(input({ contents: Buffer.from("tables: [bad]\n") }))).toThrow();
+});
+
+test("does not follow a symlinked destination when verifying", () => {
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-annotations-sync-"));
+  temporaryRoots.push(dataRoot);
+  const target = input({ dataRoot });
+  syncAnnotations(target);
+
+  const dest = join(dataRoot, "sessions", "research", "revisions", "a".repeat(40), "artifacts", "mschema", "annotations.yaml");
+  rmSync(dest, { force: true });
+  symlinkSync("/etc/hosts", dest);
+
+  expect(() => syncAnnotations(target)).toThrow();
+});
diff --git a/backend/test/registry-annotations.test.ts b/backend/test/registry-annotations.test.ts
index 1f612b64..094d3152 100644
--- a/backend/test/registry-annotations.test.ts
+++ b/backend/test/registry-annotations.test.ts
@@ -1,5 +1,5 @@
 import { execFile } from "node:child_process";
-import { mkdtempSync, mkdirSync, rmSync, writeFileSync } from "node:fs";
+import { mkdtempSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { promisify } from "node:util";
@@ -59,7 +59,7 @@ function config(root: string, remoteUrl: string): WorkspaceRegistryConfig {
 
 type AnnotationsLayout = "absent" | "valid" | "malformed" | "dir";
 
-async function fixture(layout: AnnotationsLayout): Promise<{ root: string; remote: string }> {
+async function fixture(layout: AnnotationsLayout): Promise<{ root: string; remote: string; commit: string }> {
   const root = mkdtempSync(join(tmpdir(), "thoth-registry-annotations-"));
   temporaryRoots.push(root);
   const remote = join(root, "remote.git");
@@ -84,7 +84,8 @@ async function fixture(layout: AnnotationsLayout): Promise<{ root: string; remot
   await git(source, ["commit", "-m", "initial"]);
   await git(source, ["remote", "add", "origin", remote]);
   await git(source, ["push", "origin", "main"]);
-  return { root, remote };
+  const commit = await git(source, ["rev-parse", "HEAD"]);
+  return { root, remote, commit };
 }
 
 test("activation accepts a valid curated annotation blob", async () => {
@@ -114,3 +115,21 @@ test("activation rejects a tree at the annotations path", async () => {
 
   await expect(registry.bootstrap()).rejects.toMatchObject({ code: "workspace_invalid" });
 });
+
+test("activation syncs the curated annotations to the revision root when a data root is set", async () => {
+  const fixtureValue = await fixture("valid");
+  const dataRoot = mkdtempSync(join(tmpdir(), "thoth-registry-annotations-data-"));
+  temporaryRoots.push(dataRoot);
+  const registry = new WorkspaceRegistry({
+    ...config(join(fixtureValue.root, "registry"), fixtureValue.remote),
+    dataRoot,
+  });
+
+  await registry.bootstrap();
+
+  const annotationsPath = join(dataRoot, "sessions", "psd-clinical", "revisions", fixtureValue.commit, "artifacts", "mschema", "annotations.yaml");
+  const manifestPath = join(dataRoot, "sessions", "psd-clinical", "revisions", fixtureValue.commit, "artifacts", "mschema", "annotations.ownership.json");
+  expect(readFileSync(annotationsPath, "utf8")).toBe("tables: {}\n");
+  const manifest = JSON.parse(readFileSync(manifestPath, "utf8"));
+  expect(manifest).toMatchObject({ workspace: "psd-clinical", commit: fixtureValue.commit });
+});