diff --git a/src/git.ts b/src/git.ts
index 4dbed1e..8a9a594 100644
--- a/src/git.ts
+++ b/src/git.ts
@@ -535,6 +535,65 @@ export class VaultGit {
     await this.run(["update-ref", ref, target]);
   }
 
+  /**
+   * Fast-forward `branch` to `toCommit` — but ONLY if it is a TRUE fast-forward,
+   * i.e. the current `branch` tip is an ancestor of `toCommit` (verified via
+   * `git merge-base --is-ancestor <branch> <toCommit>`). Used to advance the
+   * `docmost` mirror branch after a clean push (SPEC §6 step 3 / §10): once a
+   * push succeeds, Docmost already contains the pushed `main` content, so the
+   * mirror must reflect it — otherwise the NEXT pull would diff our own write
+   * back and re-pull it (loop-guard).
+   *
+   * SAFETY — never force, never clobber divergent history:
+   *   - If `branch` IS an ancestor of `toCommit`, advance it with
+   *     `git update-ref refs/heads/<branch> <toCommit>`. The `docmost` branch is
+   *     NOT checked out during a push (push works on `main`), so updating the ref
+   *     directly is safe and avoids any working-tree touch.
+   *   - If `branch` is NOT an ancestor (divergent / would-be non-fast-forward),
+   *     do NOT move it — return `{ ok: false, reason: 'not-fast-forward' }` and
+   *     let the caller log it. We must never overwrite a `docmost` history that
+   *     has commits the push base does not contain.
+   *
+   * Returns `{ ok: true }` when the branch was advanced (or already at
+   * `toCommit`, a degenerate fast-forward), `{ ok: false, reason }` otherwise.
+   * A missing `branch` or `toCommit` also yields `{ ok: false }` with a reason.
+   */
+  async fastForwardBranch(
+    branch: string,
+    toCommit: string,
+  ): Promise<{ ok: boolean; reason?: string }> {
+    const branchRef = `refs/heads/${branch}`;
+    // Resolve both endpoints first so a missing ref is a clean refusal, not a
+    // confusing `merge-base` failure.
+    const branchSha = await this.revParse(branchRef);
+    if (branchSha === null) {
+      return { ok: false, reason: `branch ${branch} does not exist` };
+    }
+    const targetSha = await this.revParse(toCommit);
+    if (targetSha === null) {
+      return { ok: false, reason: `target ${toCommit} does not resolve` };
+    }
+    // Already at the target -> a no-op fast-forward (still ok).
+    if (branchSha === targetSha) return { ok: true };
+
+    // `merge-base --is-ancestor A B` exits 0 iff A is an ancestor of B. Only a
+    // true ancestor is a fast-forward; anything else is divergent and refused.
+    const ancestor = await this.runRaw([
+      "merge-base",
+      "--is-ancestor",
+      branchSha,
+      targetSha,
+    ]);
+    if (ancestor.code !== 0) {
+      return { ok: false, reason: "not-fast-forward" };
+    }
+
+    // Safe to advance: the branch is not checked out during push, so a direct
+    // ref update avoids a checkout/working-tree touch.
+    await this.updateRef(branchRef, targetSha);
+    return { ok: true };
+  }
+
   /**
    * Read a file's content at a specific ref (`git show <ref>:<path>`), or `null`
    * if the path does not exist there. Used by the push direction to read the
diff --git a/src/loop-guard.ts b/src/loop-guard.ts
new file mode 100644
index 0000000..fb66534
--- /dev/null
+++ b/src/loop-guard.ts
@@ -0,0 +1,29 @@
+/**
+ * Loop-guard primitives (SPEC §10). The sync engine must never re-pull its OWN
+ * write as if it were a remote edit: after a push, the next poll will see the
+ * page it just wrote with a fresh `updatedAt`. To suppress that, we key on two
+ * signals — the body HASH of what we pushed (this module) and the `updatedAt`
+ * returned by the write — recorded per page at push time.
+ *
+ * This module owns the PURE, deterministic body-hash. The CONSUMPTION on the
+ * pull side (comparing an incoming page's body hash against the last pushed hash
+ * to decide "this is our own write, ignore it") is a future increment — here we
+ * only PRODUCE the hash and the per-page push record (see `src/push.ts`).
+ */
+import { createHash } from "node:crypto";
+
+/**
+ * Stable hash of a page's markdown BODY (SPEC §10 "хэш тела"). Deterministic:
+ * the same input string always yields the same digest, a different input a
+ * different one. Used to recognize our own write later (loop suppression).
+ *
+ * We hash the body STRING as-is (UTF-8) with SHA-256 and return lowercase hex.
+ * SPEC §10 keys on the body hash rather than file bytes; callers decide WHAT
+ * counts as "the body" (here it is the exact string passed in — typically the
+ * self-contained markdown that was pushed). No normalization is applied: the
+ * caller is responsible for passing a canonical/stable representation if it
+ * wants hash equality across cosmetic-only differences.
+ */
+export function bodyHash(markdownBody: string): string {
+  return createHash("sha256").update(markdownBody, "utf8").digest("hex");
+}
diff --git a/src/push.ts b/src/push.ts
index 618aa96..d4be749 100644
--- a/src/push.ts
+++ b/src/push.ts
@@ -21,15 +21,15 @@
  *     new parentPageId, then calling `move_page` / `rename_page` (SPEC §6/§8).
  *     `computePushActions` already CLASSIFIES R into `renamesMoves`, and
  *     `applyPushActions` returns them as `deferred` without any client call.
- *   - TODO(next-increment): loop-guard (SPEC §10) — record the `updatedAt` from
- *     each write response + provenance trailer so the next pull does not pull our
- *     own write back; suppress self-writes by body hash.
+ *   - loop-guard PRODUCTION (SPEC §10) — DONE here: `applyPushActions` records,
+ *     per applied page, the pushed body hash + the write's `updatedAt` (see
+ *     `ApplyPushResult.pushed`) and fast-forwards the `docmost` mirror after a
+ *     CLEAN push (loop-close, below). The pull-side CONSUMPTION of that record
+ *     (suppressing a re-pull of our own write) is TODO(next-increment).
  *   - TODO(next-increment): FS-watcher + debounce (SPEC §7.1) that commits on
  *     `main` and triggers a push.
  *   - TODO(next-increment): `git push` to the git remote (SPEC §6 step 1/§7.2,
  *     pull-rebase-push with retry).
- *   - TODO(next-increment): fast-forward the `docmost` mirror branch after a push
- *     (SPEC §6 step 3) — only `refs/docmost/last-pushed` is advanced here.
  *   - TODO(next-increment): a runnable live `main()` wired to a real Docmost.
  *     There is deliberately NO CLI entrypoint in this file: nothing here can run
  *     a destructive write against a real Docmost. `applyPushActions` is reached
@@ -42,6 +42,7 @@ import {
   type DocmostMdMeta,
 } from "docmost-client";
 import type { DiffEntry, VaultGit } from "./git.js";
+import { bodyHash } from "./loop-guard.js";
 
 // Re-export so callers/tests can import the diff row shape from either module.
 export type { DiffEntry } from "./git.js";
@@ -115,10 +116,14 @@ export interface PushActionsInput {
  *
  * Classification rules:
  *   - `A` (added):
- *       - current meta has NO pageId -> CREATE (a brand-new local file; the
- *         page does not exist in Docmost yet).
  *       - current meta HAS a pageId  -> UPDATE (a restored/copied file whose
  *         page already exists; we push its content rather than create a dup).
+ *       - current meta has NO pageId but HAS a non-empty spaceId -> CREATE (a
+ *         brand-new local file; the page does not exist in Docmost yet).
+ *       - current meta has NO pageId and NO usable spaceId -> SKIP with reason
+ *         `create-without-spaceId`: Docmost `create_page` REQUIRES a spaceId
+ *         (§16), and a new local file may carry only partial human meta. We
+ *         refuse to create rather than guess a space (SPEC §8 guard spirit).
  *   - `M` (modified): current meta has a pageId -> UPDATE content. (If a modified
  *       file somehow lost its pageId it is skipped — there is nothing to target.)
  *   - `D` (deleted): recover the pageId from the PRE-IMAGE meta (`metaAt(path,
@@ -149,10 +154,20 @@ export function computePushActions(input: PushActionsInput): PushActions {
           // Added but already carries a pageId (restored/copied file): the page
           // exists in Docmost, so push content as an UPDATE — never a duplicate.
           actions.updates.push({ pageId, path: change.path });
-        } else {
-          // Brand-new local file -> create the page, then write the assigned
-          // pageId back into its meta (done in `applyPushActions`).
+        } else if (meta?.spaceId) {
+          // Brand-new local file with a target space -> create the page, then
+          // write the assigned pageId back into its meta (in `applyPushActions`).
+          // `meta.spaceId` is truthy here, so empty-string is also rejected.
           actions.creates.push({ path: change.path });
+        } else {
+          // A create needs a spaceId (Docmost `create_page` requires it, §16). A
+          // new file with partial meta and no usable spaceId is SKIPPED rather
+          // than created into a guessed space (SPEC §8 guard spirit).
+          actions.skipped.push({
+            path: change.path,
+            status: "A",
+            reason: "create-without-spaceId",
+          });
         }
         break;
       }
@@ -231,6 +246,13 @@ export function computePushActions(input: PushActionsInput): PushActions {
 /** The marker the push direction advances after a successful push (SPEC §5/§6). */
 export const LAST_PUSHED_REF = "refs/docmost/last-pushed";
 
+/**
+ * The mirror branch fast-forwarded after a clean push (SPEC §5/§6 step 3). It
+ * reflects "what Docmost currently contains"; advancing it to the pushed `main`
+ * commit closes the loop so the next pull diffs empty for the pushed pages.
+ */
+export const DOCMOST_BRANCH = "docmost";
+
 /**
  * Injectable IO for `applyPushActions`. The real `main` (NEXT increment) wires
  * these to the live client, `node:fs/promises`, and the vault git wrapper; this
@@ -239,7 +261,9 @@ export const LAST_PUSHED_REF = "refs/docmost/last-pushed";
  *   - `readFile`/`writeFile`: read a changed file's body / write a file back
  *     (by vault-relative path; the applier does not resolve absolute paths so
  *     fakes stay trivial).
- *   - `git`: only `updateRef` is used here (advance `refs/docmost/last-pushed`).
+ *   - `git`: `updateRef` (advance `refs/docmost/last-pushed`) and
+ *     `fastForwardBranch` (advance the `docmost` mirror after a clean push, the
+ *     loop-close — SPEC §6 step 3 / §10).
  */
 export interface ApplyPushDeps {
   client: Pick<
@@ -250,7 +274,7 @@ export interface ApplyPushDeps {
   readFile: (path: string) => Promise<string>;
   /** Write a file's full text by its vault-relative path. */
   writeFile: (path: string, text: string) => Promise<void>;
-  git: Pick<VaultGit, "updateRef">;
+  git: Pick<VaultGit, "updateRef" | "fastForwardBranch">;
 }
 
 /** A file whose meta was rewritten with a freshly-assigned pageId (post-create). */
@@ -259,6 +283,38 @@ export interface WrittenBackPage {
   pageId: string;
 }
 
+/**
+ * The per-page push record consulted by a FUTURE poll-suppression (SPEC §10): a
+ * pulled page whose body hash + `updatedAt` match a record here is OUR OWN write
+ * and must not be re-pulled. PRODUCED here; CONSUMED on the pull side later.
+ */
+export interface PushedPageRecord {
+  /** The Docmost pageId that was updated/created. */
+  pageId: string;
+  /**
+   * The `updatedAt` from the create/update client result, when the result
+   * exposed one. Absent when the (fake) client did not return it.
+   */
+  updatedAt?: string;
+  /** Stable hash of the markdown BODY that was pushed (SPEC §10 "хэш тела"). */
+  bodyHash: string;
+}
+
+/**
+ * One page whose operation FAILED during apply (SPEC §12 resumability). The bad
+ * page is isolated — recorded here — and the rest of the batch still runs; the
+ * refs are NOT advanced when there is any failure, so a re-run retries cleanly.
+ */
+export interface PushFailure {
+  kind: "update" | "create" | "delete";
+  /** The pageId for update/delete; absent for a create that never got one. */
+  pageId?: string;
+  /** The vault-relative path for create/update; absent for a delete. */
+  path?: string;
+  /** The error message captured from the thrown error. */
+  error: string;
+}
+
 /** Structured outcome of `applyPushActions` (counts + write-backs + deferred). */
 export interface ApplyPushResult {
   created: number;
@@ -271,12 +327,31 @@ export interface ApplyPushResult {
    * not lost.
    */
   writtenBack: WrittenBackPage[];
+  /**
+   * Per-page push records (pageId + optional `updatedAt` + body hash) for every
+   * page successfully updated/created — the §10 loop-guard data a future
+   * poll-suppression (pull side) will consult so it does not re-pull our own
+   * write. Deletes are not included (no body was pushed).
+   */
+  pushed: PushedPageRecord[];
+  /**
+   * Pages whose operation threw — isolated and recorded, the batch continued
+   * (SPEC §12). Non-empty here means the refs were NOT advanced.
+   */
+  failures: PushFailure[];
   /** Rename/move actions NOT executed this increment (apply is deferred). */
   deferred: RenameMoveAction[];
   /** Diff rows the planner could not classify (carried through for logging). */
   skipped: PushActions["skipped"];
-  /** Whether `refs/docmost/last-pushed` was advanced (only when `pushedCommit`). */
+  /** Whether `refs/docmost/last-pushed` was advanced (only on a CLEAN push). */
   lastPushedAdvanced: boolean;
+  /**
+   * Result of fast-forwarding the `docmost` mirror branch after a CLEAN push
+   * (the loop-close, SPEC §6 step 3 / §10). `null` when no advance was attempted
+   * (no `pushedCommit`, or there were failures). `{ ok:false, reason }` when a
+   * non-fast-forward was REFUSED (divergent `docmost` history is never clobbered).
+   */
+  docmostFastForward: { ok: boolean; reason?: string } | null;
 }
 
 /**
@@ -296,12 +371,32 @@ export interface ApplyPushResult {
  *   - DELETE: `client.deletePage(pageId)` — soft-delete to Trash (SPEC §8).
  *   - RENAME/MOVE: NOT executed — returned as `deferred` (NEXT increment).
  *
- * After applying, if a `pushedCommit` is given, advance
- * `refs/docmost/last-pushed` to it (SPEC §6 step 3). Fast-forwarding the
- * `docmost` branch and the loop-guard are DEFERRED (see the module TODO list).
+ * FAIL-SAFE / per-page isolation (SPEC §12 resumability). Each page's operation
+ * is wrapped in its own try/catch: a single failing page is recorded in
+ * `failures[]` (with its kind + pageId/path + error) and the batch CONTINUES —
+ * one bad page must never block the rest. Crucially, the refs are advanced ONLY
+ * when `failures.length === 0`: a PARTIAL push must NOT advance
+ * `refs/docmost/last-pushed` or the `docmost` mirror, so a re-run retries the
+ * whole batch cleanly (the already-applied pages are idempotent re-applies).
+ *
+ * LOOP-CLOSE (SPEC §6 step 3 / §10). After a fully-successful push, when a
+ * `pushedCommit` is supplied:
+ *   - advance `refs/docmost/last-pushed` to it (what of `main` is in Docmost), AND
+ *   - fast-forward the `docmost` mirror branch to it via
+ *     `git.fastForwardBranch('docmost', pushedCommit)` — so the mirror reflects
+ *     what Docmost now contains and the NEXT pull diffs EMPTY for these pages
+ *     (it does not re-pull our own write). The ff is REFUSED (not forced) if
+ *     `docmost` is not an ancestor of the pushed commit; the result is surfaced
+ *     in `docmostFastForward`. On ANY failure, NEITHER ref is advanced.
+ *
+ * LOOP-GUARD DATA (SPEC §10). For every page successfully updated/created the
+ * result carries a `pushed` record `{ pageId, updatedAt?, bodyHash }` — the body
+ * hash of what was pushed plus the write's `updatedAt` (when the client returned
+ * one). A future pull-side poll-suppression consults this so it does not re-pull
+ * our own write; producing it is in scope here, consuming it is deferred.
  *
  * @param pushedCommit The `main` commit just reflected into Docmost (SHA or
- *   commit-ish). When omitted, the ref is NOT advanced (e.g. a dry plan).
+ *   commit-ish). When omitted, NEITHER ref is advanced (e.g. a dry plan).
  */
 export async function applyPushActions(
   deps: ApplyPushDeps,
@@ -314,59 +409,105 @@ export async function applyPushActions(
   let updated = 0;
   let deleted = 0;
   const writtenBack: WrittenBackPage[] = [];
+  const pushed: PushedPageRecord[] = [];
+  const failures: PushFailure[] = [];
 
   // 1. UPDATES — collab/Yjs write path (SPEC §2/§15.6), never a raw overwrite.
+  //    Each update is isolated: a thrown page is recorded and the batch goes on.
   for (const u of actions.updates) {
-    const fullMarkdown = await deps.readFile(u.path);
-    await client.importPageMarkdown(u.pageId, fullMarkdown);
-    updated++;
+    try {
+      const fullMarkdown = await deps.readFile(u.path);
+      const result = await client.importPageMarkdown(u.pageId, fullMarkdown);
+      updated++;
+      // §10 loop-guard data: hash the body we pushed + capture `updatedAt`.
+      pushed.push({
+        pageId: u.pageId,
+        ...extractUpdatedAt(result),
+        bodyHash: bodyHash(fullMarkdown),
+      });
+    } catch (err: unknown) {
+      failures.push({
+        kind: "update",
+        pageId: u.pageId,
+        path: u.path,
+        error: errMessage(err),
+      });
+    }
   }
 
   // 2. CREATES — create the page, then write the assigned pageId back to meta so
   //    the file becomes tracked (SPEC §4 "записать присвоенный pageId обратно").
+  //    Isolated per page like updates.
   for (const c of actions.creates) {
-    const text = await deps.readFile(c.path);
-    const { meta, body } = parseDocmostMarkdown(text);
-    // Derive create args from the file's current meta. A new local file may have
-    // a partial meta (e.g. title/spaceId only); spaceId is required by Docmost.
-    const title = meta?.title ?? "";
-    const spaceId = meta?.spaceId ?? "";
-    const parentPageId = meta?.parentPageId ?? undefined;
-    const result = await client.createPage(title, body, spaceId, parentPageId);
-    // `createPage` returns `{ data: { id, ... }, success }`; the assigned pageId
-    // is at `result.data.id`.
-    const assignedPageId: string | undefined = result?.data?.id;
-    if (assignedPageId) {
-      // Re-serialize the file with the pageId written into meta, body preserved.
-      const newMeta: DocmostMdMeta = {
-        version: meta?.version ?? 1,
-        ...meta,
-        pageId: assignedPageId,
-      };
-      const rewritten = serializeDocmostMarkdownBody(newMeta, body);
-      await deps.writeFile(c.path, rewritten);
-      writtenBack.push({ path: c.path, pageId: assignedPageId });
+    try {
+      const text = await deps.readFile(c.path);
+      const { meta, body } = parseDocmostMarkdown(text);
+      // Derive create args from the file's current meta. A new local file may
+      // have partial meta (e.g. title/spaceId only); spaceId is required by
+      // Docmost (the planner already guards a create against a missing spaceId).
+      const title = meta?.title ?? "";
+      const spaceId = meta?.spaceId ?? "";
+      const parentPageId = meta?.parentPageId ?? undefined;
+      const result = await client.createPage(title, body, spaceId, parentPageId);
+      // `createPage` returns `{ data: { id, ... }, success }`; the assigned
+      // pageId is at `result.data.id`.
+      const assignedPageId: string | undefined = result?.data?.id;
+      if (assignedPageId) {
+        // Re-serialize the file with the pageId in meta, body preserved.
+        const newMeta: DocmostMdMeta = {
+          version: meta?.version ?? 1,
+          ...meta,
+          pageId: assignedPageId,
+        };
+        const rewritten = serializeDocmostMarkdownBody(newMeta, body);
+        await deps.writeFile(c.path, rewritten);
+        writtenBack.push({ path: c.path, pageId: assignedPageId });
+        // §10 loop-guard data for the created page (hash the pushed body).
+        pushed.push({
+          pageId: assignedPageId,
+          ...extractUpdatedAt(result),
+          bodyHash: bodyHash(text),
+        });
+      }
+      created++;
+    } catch (err: unknown) {
+      failures.push({ kind: "create", path: c.path, error: errMessage(err) });
     }
-    created++;
   }
 
-  // 3. DELETES — soft-delete to Trash (SPEC §8), obratimo.
+  // 3. DELETES — soft-delete to Trash (SPEC §8), reversible. Isolated per page.
   for (const d of actions.deletes) {
-    await client.deletePage(d.pageId);
-    deleted++;
+    try {
+      await client.deletePage(d.pageId);
+      deleted++;
+    } catch (err: unknown) {
+      failures.push({
+        kind: "delete",
+        pageId: d.pageId,
+        error: errMessage(err),
+      });
+    }
   }
 
   // 4. RENAME/MOVE — DEFERRED (NEXT increment): no client call. Returned as
   //    `deferred` so the caller can see what still needs the move/rename apply.
 
-  // 5. Advance `refs/docmost/last-pushed` to the pushed `main` commit (SPEC §6
-  //    step 3 / §5). TODO(next-increment): fast-forward the `docmost` mirror
-  //    branch (Docmost already contains these changes) and record the `updatedAt`
-  //    from each write response for the loop-guard (SPEC §10).
+  // 5. Advance the refs ONLY on a CLEAN push (no failures) AND when a pushed
+  //    commit is supplied. A partial push must advance NEITHER ref, so a re-run
+  //    retries the whole batch (SPEC §12). The loop-close (SPEC §6 step 3 / §10):
+  //    advance `refs/docmost/last-pushed` AND fast-forward the `docmost` mirror,
+  //    so Docmost's new content is mirrored and the next pull diffs empty.
   let lastPushedAdvanced = false;
-  if (pushedCommit) {
+  let docmostFastForward: { ok: boolean; reason?: string } | null = null;
+  if (pushedCommit && failures.length === 0) {
     await git.updateRef(LAST_PUSHED_REF, pushedCommit);
     lastPushedAdvanced = true;
+    // Fast-forward the mirror (refused, not forced, on a non-fast-forward — the
+    // caller logs the reason). Surfaced in the result.
+    docmostFastForward = await git.fastForwardBranch(
+      DOCMOST_BRANCH,
+      pushedCommit,
+    );
   }
 
   return {
@@ -374,8 +515,30 @@ export async function applyPushActions(
     updated,
     deleted,
     writtenBack,
+    pushed,
+    failures,
     deferred: actions.renamesMoves,
     skipped: actions.skipped,
     lastPushedAdvanced,
+    docmostFastForward,
   };
 }
+
+/** Stringify a thrown value into a stable error message. */
+function errMessage(err: unknown): string {
+  return err instanceof Error ? err.message : String(err);
+}
+
+/**
+ * Pull an `updatedAt` out of a create/update client result, if present. The
+ * shape is `{ data: { updatedAt? }, ... }` (createPage) or a flatter object;
+ * absent in the simple fakes, so the field is omitted rather than `undefined`.
+ */
+function extractUpdatedAt(result: unknown): { updatedAt?: string } {
+  const r = result as
+    | { updatedAt?: unknown; data?: { updatedAt?: unknown } }
+    | null
+    | undefined;
+  const raw = r?.data?.updatedAt ?? r?.updatedAt;
+  return typeof raw === "string" ? { updatedAt: raw } : {};
+}
diff --git a/test/apply-push-actions.test.ts b/test/apply-push-actions.test.ts
index aa9536e..01e6264 100644
--- a/test/apply-push-actions.test.ts
+++ b/test/apply-push-actions.test.ts
@@ -1,5 +1,6 @@
 import { describe, expect, it, vi, beforeEach, afterEach } from 'vitest';
 import { applyPushActions, LAST_PUSHED_REF } from '../src/push.js';
+import { bodyHash } from '../src/loop-guard.js';
 import type { ApplyPushDeps, PushActions } from '../src/push.js';
 import {
   parseDocmostMarkdown,
@@ -36,15 +37,24 @@ function makeClient(opts?: { createId?: string }) {
   return client;
 }
 
-/** A recording git fake (only updateRef is used by the push applier). */
-function makeGit() {
+/**
+ * A recording git fake: `updateRef` (advance last-pushed) and `fastForwardBranch`
+ * (advance the `docmost` mirror, the loop-close). `ffResult` configures what the
+ * ff returns (default a successful advance).
+ */
+function makeGit(opts?: { ffResult?: { ok: boolean; reason?: string } }) {
   const updateRefCalls: { ref: string; target: string }[] = [];
+  const ffCalls: { branch: string; toCommit: string }[] = [];
   const git = {
     updateRef: vi.fn(async (ref: string, target: string) => {
       updateRefCalls.push({ ref, target });
     }),
+    fastForwardBranch: vi.fn(async (branch: string, toCommit: string) => {
+      ffCalls.push({ branch, toCommit });
+      return opts?.ffResult ?? { ok: true };
+    }),
   };
-  return { git, updateRefCalls };
+  return { git, updateRefCalls, ffCalls };
 }
 
 /** A recording fs fake over a path->text store. */
@@ -199,10 +209,10 @@ describe('applyPushActions — rename/move is DEFERRED (NEXT increment)', () =>
   });
 });
 
-describe('applyPushActions — last-pushed ref advance (SPEC §6 step 3)', () => {
-  it('advances refs/docmost/last-pushed to the pushed commit', async () => {
+describe('applyPushActions — loop-close: ref advance + docmost ff (SPEC §6 step 3 / §10)', () => {
+  it('advances last-pushed AND fast-forwards the docmost mirror on a clean push', async () => {
     const client = makeClient();
-    const { git, updateRefCalls } = makeGit();
+    const { git, updateRefCalls, ffCalls } = makeGit();
     const fs = makeFs();
 
     const res = await applyPushActions(
@@ -215,9 +225,34 @@ describe('applyPushActions — last-pushed ref advance (SPEC §6 step 3)', () =>
     expect(updateRefCalls).toEqual([
       { ref: LAST_PUSHED_REF, target: 'commit-sha-abc' },
     ]);
+    // The loop-close: the docmost mirror is fast-forwarded to the pushed commit.
+    expect(ffCalls).toEqual([{ branch: 'docmost', toCommit: 'commit-sha-abc' }]);
+    expect(res.docmostFastForward).toEqual({ ok: true });
   });
 
-  it('does NOT advance the ref when no pushed commit is given', async () => {
+  it('surfaces a REFUSED non-fast-forward (mirror NOT clobbered)', async () => {
+    const client = makeClient();
+    // The ff is refused because docmost is not an ancestor of the pushed commit.
+    const { git, updateRefCalls, ffCalls } = makeGit({
+      ffResult: { ok: false, reason: 'not-fast-forward' },
+    });
+    const fs = makeFs();
+
+    const res = await applyPushActions(
+      deps(client, git, fs),
+      actions({ deletes: [{ pageId: 'p' }] }),
+      'sha-div',
+    );
+
+    // last-pushed still advances (it is our own marker), but the ff result is
+    // surfaced so the caller can log the refusal.
+    expect(res.lastPushedAdvanced).toBe(true);
+    expect(updateRefCalls).toEqual([{ ref: LAST_PUSHED_REF, target: 'sha-div' }]);
+    expect(ffCalls).toEqual([{ branch: 'docmost', toCommit: 'sha-div' }]);
+    expect(res.docmostFastForward).toEqual({ ok: false, reason: 'not-fast-forward' });
+  });
+
+  it('does NOT advance either ref when no pushed commit is given', async () => {
     const client = makeClient();
     const { git, updateRefCalls } = makeGit();
     const fs = makeFs();
@@ -229,7 +264,117 @@ describe('applyPushActions — last-pushed ref advance (SPEC §6 step 3)', () =>
 
     expect(res.lastPushedAdvanced).toBe(false);
     expect(updateRefCalls).toEqual([]);
+    expect(res.docmostFastForward).toBeNull();
     expect(git.updateRef).not.toHaveBeenCalled();
+    expect(git.fastForwardBranch).not.toHaveBeenCalled();
+  });
+});
+
+describe('applyPushActions — per-page error isolation + refs gated on success (SPEC §12)', () => {
+  it('continues the batch when an update throws; records the failure; refs NOT advanced', async () => {
+    // A client whose 2nd importPageMarkdown call throws — the 1st and 3rd must
+    // still be applied, the 2nd recorded as a failure, and NO ref advanced.
+    let call = 0;
+    const client = {
+      importPageMarkdown: vi.fn(async (_pageId: string, _md: string) => {
+        call++;
+        if (call === 2) throw new Error('boom on page 2');
+        return { success: true };
+      }),
+      createPage: vi.fn(),
+      deletePage: vi.fn(),
+    };
+    const { git, updateRefCalls, ffCalls } = makeGit();
+    const fs = makeFs({
+      'A.md': 'a body',
+      'B.md': 'b body',
+      'C.md': 'c body',
+    });
+
+    const res = await applyPushActions(
+      deps(client, git, fs),
+      actions({
+        updates: [
+          { pageId: 'p-a', path: 'A.md' },
+          { pageId: 'p-b', path: 'B.md' },
+          { pageId: 'p-c', path: 'C.md' },
+        ],
+      }),
+      'sha-partial',
+    );
+
+    // The 1st and 3rd were applied; the 2nd threw.
+    expect(res.updated).toBe(2);
+    expect(client.importPageMarkdown).toHaveBeenCalledTimes(3);
+    expect(client.importPageMarkdown).toHaveBeenNthCalledWith(1, 'p-a', 'a body');
+    expect(client.importPageMarkdown).toHaveBeenNthCalledWith(3, 'p-c', 'c body');
+
+    // The failure is recorded with kind/pageId/path/error.
+    expect(res.failures).toEqual([
+      { kind: 'update', pageId: 'p-b', path: 'B.md', error: 'boom on page 2' },
+    ]);
+
+    // Only the successful pages carry a loop-guard push record.
+    expect(res.pushed.map((p) => p.pageId)).toEqual(['p-a', 'p-c']);
+
+    // A PARTIAL push advances NEITHER ref, so a re-run retries cleanly (§12).
+    expect(res.lastPushedAdvanced).toBe(false);
+    expect(updateRefCalls).toEqual([]);
+    expect(ffCalls).toEqual([]);
+    expect(res.docmostFastForward).toBeNull();
+    expect(git.updateRef).not.toHaveBeenCalled();
+    expect(git.fastForwardBranch).not.toHaveBeenCalled();
+  });
+});
+
+describe('applyPushActions — loop-guard push record (SPEC §10)', () => {
+  it('records pageId + updatedAt + bodyHash per applied update', async () => {
+    const fileBody =
+      '<!-- docmost:meta\n{"version":1,"pageId":"p-1"}\n-->\n\nupdated body\n';
+    const client = {
+      importPageMarkdown: vi.fn(async (_pageId: string, _md: string) => ({
+        // The write returns an updatedAt the loop-guard records.
+        data: { updatedAt: '2026-06-20T10:00:00.000Z' },
+        success: true,
+      })),
+      createPage: vi.fn(),
+      deletePage: vi.fn(),
+    };
+    const { git } = makeGit();
+    const fs = makeFs({ 'Doc.md': fileBody });
+
+    const res = await applyPushActions(
+      deps(client, git, fs),
+      actions({ updates: [{ pageId: 'p-1', path: 'Doc.md' }] }),
+    );
+
+    expect(res.pushed).toHaveLength(1);
+    expect(res.pushed[0].pageId).toBe('p-1');
+    expect(res.pushed[0].updatedAt).toBe('2026-06-20T10:00:00.000Z');
+    // The bodyHash is a stable sha256 hex of the pushed markdown.
+    expect(res.pushed[0].bodyHash).toBe(bodyHash(fileBody));
+    expect(res.pushed[0].bodyHash).toMatch(/^[0-9a-f]{64}$/);
+  });
+
+  it('omits updatedAt when the client result does not expose one', async () => {
+    const newFile = serializeDocmostMarkdownBody(
+      { version: 1, title: 'N', spaceId: 'sp' },
+      'fresh body',
+    );
+    const client = makeClient({ createId: 'created-9' });
+    const { git } = makeGit();
+    const fs = makeFs({ 'N.md': newFile });
+
+    const res = await applyPushActions(
+      deps(client, git, fs),
+      actions({ creates: [{ path: 'N.md' }] }),
+    );
+
+    expect(res.pushed).toHaveLength(1);
+    expect(res.pushed[0].pageId).toBe('created-9');
+    expect(res.pushed[0].updatedAt).toBeUndefined();
+    // bodyHash of the ORIGINAL pushed file text (what createPage received).
+    expect(res.pushed[0].bodyHash).toBe(bodyHash(newFile));
   });
 });
 
diff --git a/test/compute-push-actions.test.ts b/test/compute-push-actions.test.ts
index 9ead7db..84afa55 100644
--- a/test/compute-push-actions.test.ts
+++ b/test/compute-push-actions.test.ts
@@ -36,10 +36,40 @@ describe('computePushActions — A (added)', () => {
     expect(actions.skipped).toEqual([]);
   });
 
-  it('added file with NO meta at all -> create (treated as new)', () => {
+  it('added file with NO meta at all -> skipped (a create needs a spaceId)', () => {
+    // No meta -> no spaceId -> cannot create (Docmost create_page requires it).
     const changes: DiffEntry[] = [{ status: 'A', path: 'Plain.md' }];
     const actions = computePushActions({ changes, metaAt: metaTable({}) });
-    expect(actions.creates).toEqual([{ path: 'Plain.md' }]);
+    expect(actions.creates).toEqual([]);
+    expect(actions.skipped).toEqual([
+      { path: 'Plain.md', status: 'A', reason: 'create-without-spaceId' },
+    ]);
+  });
+
+  it('added file with meta but NO spaceId -> skipped (create-without-spaceId)', () => {
+    // Partial human meta (title only, no spaceId) -> refuse to create.
+    const changes: DiffEntry[] = [{ status: 'A', path: 'Partial.md' }];
+    const metaAt = metaTable({
+      'Partial.md|current': meta({ title: 'Partial' }),
+    });
+    const actions = computePushActions({ changes, metaAt });
+    expect(actions.creates).toEqual([]);
+    expect(actions.skipped).toEqual([
+      { path: 'Partial.md', status: 'A', reason: 'create-without-spaceId' },
+    ]);
+  });
+
+  it('added file with an EMPTY-string spaceId -> skipped (create-without-spaceId)', () => {
+    // An empty spaceId is not a usable target either.
+    const changes: DiffEntry[] = [{ status: 'A', path: 'Empty.md' }];
+    const metaAt = metaTable({
+      'Empty.md|current': meta({ title: 'E', spaceId: '' }),
+    });
+    const actions = computePushActions({ changes, metaAt });
+    expect(actions.creates).toEqual([]);
+    expect(actions.skipped).toEqual([
+      { path: 'Empty.md', status: 'A', reason: 'create-without-spaceId' },
+    ]);
   });
 
   it('added file WITH a pageId (restored/copied) -> update (page exists)', () => {
diff --git a/test/git.test.ts b/test/git.test.ts
index 7450dbe..78e56d1 100644
--- a/test/git.test.ts
+++ b/test/git.test.ts
@@ -622,4 +622,89 @@ describe('VaultGit (integration; temp repo)', () => {
     expect(preImage).toBe(meta);
     expect(preImage).toContain('page-123');
   });
+
+  it('fastForwardBranch advances a true fast-forward (the loop-close, SPEC §6 step 3)', async () => {
+    if (!available) return;
+    const vault = await freshDir();
+    const git = new VaultGit(vault);
+    await git.ensureRepo();
+
+    // docmost branches off main at the initial commit; main then moves ahead.
+    await git.ensureBranch('docmost', 'main');
+    const base = await git.revParse('refs/heads/docmost');
+
+    await writeFile(join(vault, 'page.md'), 'pushed content\n', 'utf8');
+    await git.stageAll();
+    await git.commit('push page', { authorName: BOT_AUTHOR_NAME, authorEmail: BOT_AUTHOR_EMAIL });
+    const mainTip = await git.revParse('HEAD');
+
+    // docmost is BEHIND main and an ancestor -> a true fast-forward advances it.
+    expect(await git.revParse('refs/heads/docmost')).toBe(base);
+    const res = await git.fastForwardBranch('docmost', mainTip!);
+    expect(res).toEqual({ ok: true });
+    // The branch now points at the pushed main commit (mirror reflects Docmost).
+    expect(await git.revParse('refs/heads/docmost')).toBe(mainTip);
+
+    // It does NOT touch the working tree / current branch (still on main).
+    expect(await git.currentBranch()).toBe('main');
+  });
+
+  it('fastForwardBranch is a no-op (ok) when the branch is already at the target', async () => {
+    if (!available) return;
+    const vault = await freshDir();
+    const git = new VaultGit(vault);
+    await git.ensureRepo();
+    await git.ensureBranch('docmost', 'main');
+    const mainTip = await git.revParse('HEAD');
+
+    // Already equal -> a degenerate fast-forward, still ok, branch unchanged.
+    const res = await git.fastForwardBranch('docmost', mainTip!);
+    expect(res).toEqual({ ok: true });
+    expect(await git.revParse('refs/heads/docmost')).toBe(mainTip);
+  });
+
+  it('fastForwardBranch REFUSES a non-fast-forward (never clobbers divergent history)', async () => {
+    if (!available) return;
+    const vault = await freshDir();
+    const git = new VaultGit(vault);
+    await git.ensureRepo();
+
+    // Make docmost diverge: it has a commit that main does NOT contain.
+    await git.checkout('main'); // ensure on main first
+    await git.ensureBranch('docmost', 'main');
+    await git.checkout('docmost');
+    await writeFile(join(vault, 'only-on-docmost.md'), 'mirror-only\n', 'utf8');
+    await git.stageAll();
+    await git.commit('docmost-only commit', { authorName: BOT_AUTHOR_NAME, authorEmail: BOT_AUTHOR_EMAIL });
+    const docmostTip = await git.revParse('refs/heads/docmost');
+
+    // main moves ahead independently (divergent from docmost).
+    await git.checkout('main');
+    await writeFile(join(vault, 'only-on-main.md'), 'main-only\n', 'utf8');
+    await git.stageAll();
+    await git.commit('main-only commit', { authorName: BOT_AUTHOR_NAME, authorEmail: BOT_AUTHOR_EMAIL });
+    const mainTip = await git.revParse('HEAD');
+
+    // docmost is NOT an ancestor of main -> the ff is REFUSED, branch untouched.
+    const res = await git.fastForwardBranch('docmost', mainTip!);
+    expect(res).toEqual({ ok: false, reason: 'not-fast-forward' });
+    expect(await git.revParse('refs/heads/docmost')).toBe(docmostTip);
+  });
+
+  it('fastForwardBranch refuses a missing branch / unresolved target with a reason', async () => {
+    if (!available) return;
+    const vault = await freshDir();
+    const git = new VaultGit(vault);
+    await git.ensureRepo();
+    const mainTip = await git.revParse('HEAD');
+
+    const noBranch = await git.fastForwardBranch('nope', mainTip!);
+    expect(noBranch.ok).toBe(false);
+    expect(noBranch.reason).toContain('nope');
+
+    await git.ensureBranch('docmost', 'main');
+    const noTarget = await git.fastForwardBranch('docmost', 'deadbeefdeadbeef');
+    expect(noTarget.ok).toBe(false);
+    expect(noTarget.reason).toContain('deadbeefdeadbeef');
+  });
 });
diff --git a/test/loop-guard.test.ts b/test/loop-guard.test.ts
new file mode 100644
index 0000000..891d85c
--- /dev/null
+++ b/test/loop-guard.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from 'vitest';
+import { createHash } from 'node:crypto';
+import { bodyHash } from '../src/loop-guard.js';
+
+// Loop-guard body hash (SPEC §10 "хэш тела"). The hash is the signal a future
+// pull-side poll-suppression uses to recognize our OWN write. It MUST be
+// deterministic (same input -> same hash) and discriminating (different input ->
+// different hash).
+
+describe('bodyHash (pure, SPEC §10)', () => {
+  it('is deterministic — same input yields the same hash', () => {
+    const body = '# Title\n\nsome body with <span data-comment-id="x">mark</span>\n';
+    expect(bodyHash(body)).toBe(bodyHash(body));
+  });
+
+  it('differs for different input', () => {
+    expect(bodyHash('alpha')).not.toBe(bodyHash('beta'));
+    // Even a one-character difference produces a different digest.
+    expect(bodyHash('alpha')).not.toBe(bodyHash('alphb'));
+  });
+
+  it('returns lowercase sha256 hex (64 chars)', () => {
+    const h = bodyHash('hello');
+    expect(h).toMatch(/^[0-9a-f]{64}$/);
+    // Matches an independent sha256 of the same UTF-8 bytes.
+    expect(h).toBe(createHash('sha256').update('hello', 'utf8').digest('hex'));
+  });
+
+  it('hashes the empty string to the well-known sha256 empty digest', () => {
+    expect(bodyHash('')).toBe(
+      'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855',
+    );
+  });
+
+  it('is sensitive to UTF-8 content (Cyrillic body)', () => {
+    expect(bodyHash('Колонка')).not.toBe(bodyHash('Колонкa'));
+    expect(bodyHash('Колонка')).toBe(
+      createHash('sha256').update('Колонка', 'utf8').digest('hex'),
+    );
+  });
+});
diff --git a/test/markdown-roundtrip.property.test.ts b/test/markdown-roundtrip.property.test.ts
index a98682a..9f3b579 100644
--- a/test/markdown-roundtrip.property.test.ts
+++ b/test/markdown-roundtrip.property.test.ts
@@ -1,5 +1,12 @@
-import { describe, expect, it } from 'vitest';
+import { describe, expect, it, vi } from 'vitest';
 import fc from 'fast-check';
+
+// These property tests run real ProseMirror<->Markdown conversion × NUM_RUNS, so
+// each takes ~4–5s. Inputs are DETERMINISTIC (fixed SEED below) — the only source
+// of flakiness is wall-clock: under the full suite's parallel worker load they can
+// exceed vitest's default 5000ms per-test timeout. Give them ample headroom so CI
+// (which gates the docker build, AGENTS.md) is deterministic regardless of load.
+vi.setConfig({ testTimeout: 30000 });
 // Import the converter DIRECTLY from src (NOT the docmost-client barrel) so we
 // match the path used by the other converter unit tests.
 import { convertProseMirrorToMarkdown } from '../packages/docmost-client/src/lib/markdown-converter.js';