feat(syncguard): protect workspace during substantial CouchDB catch-up

src/common/messages/LiveSyncProvisionalMessages.ts

@@ -7,6 +7,14 @@
  * remove it from this map in the same change.
  */
 export const liveSyncProvisionalEnglishMessages = {
+    "Synchronisation protection": "Synchronisation protection",
+    "Synchronising your Vault": "Synchronising your Vault",
+    "Receiving changes from the server…": "Receiving changes from the server…",
+    "Applying received changes to local notes…": "Applying received changes to local notes…",
+    "Synchronisation was interrupted. You can continue locally, but some notes may be out of date.":
+        "Synchronisation was interrupted. You can continue locally, but some notes may be out of date.",
+    "At least ${COUNT} changed files received": "At least ${COUNT} changed files received",
+    "Continue without waiting": "Continue without waiting",
     "Preparing follow-up report…": "Preparing follow-up report…",
     "Cancelling local search. Checked ${COUNT} entries.": "Cancelling local search. Checked ${COUNT} entries.",
     "Search current Vault paths and current local Metadata only. Older history and remote-only files are not searched.":

src/main.ts

@@ -50,6 +50,8 @@ import { createFileReflectionProvenance } from "./serviceModules/FileReflectionP
 import { useInteractiveConflictResolutionFeature } from "./serviceFeatures/interactiveConflictResolution";
 import { ConflictResolveModal } from "./modules/features/InteractiveConflictResolving/ConflictResolveModal.ts";
 import { useObsidianReplicationRibbonFeature } from "./serviceFeatures/obsidianReplicationRibbon.ts";
+import { useSyncGuardFeature } from "./serviceFeatures/syncGuard";
+import { SyncGuardOverlay } from "./serviceFeatures/syncGuard/SyncGuardOverlay";
 import { useStartupLifecycleFeature } from "./serviceFeatures/startupLifecycle";
 import { useDatabaseDiagnosticsFeature } from "./serviceFeatures/useDatabaseDiagnostics";
 export type LiveSyncCore = LiveSyncBaseCore<ObsidianServiceContext, LiveSyncCommands>;
@@ -196,6 +198,7 @@ export default class ObsidianLiveSyncPlugin extends Plugin {
                 useP2PReplicatorCommands(core, replicator);
                 useP2PReplicatorUI(core, core, replicator, createInteractiveP2PReplication(replicator));
                 useObsidianReplicationRibbonFeature(core);
+                useSyncGuardFeature(core, (onBypass) => new SyncGuardOverlay(this.app.workspace.containerEl, onBypass));
                 useDatabaseDiagnosticsFeature(core);
                 useRemoteConfiguration(core);
 

src/serviceFeatures/syncGuard/SyncGuardOverlay.ts

@@ -0,0 +1,105 @@
+import type { SyncGuardPresentation } from "./SyncGuardState";
+import { $msg } from "@/common/translation";
+
+/** Obsidian-owned presentation: blocks workspace input but does not pause replication or other dialogues. */
+export class SyncGuardOverlay {
+    private root?: HTMLDivElement;
+    private stage?: HTMLParagraphElement;
+    private count?: HTMLParagraphElement;
+    private bypassButton?: HTMLButtonElement;
+    private previousFocus?: HTMLElement;
+
+    constructor(
+        private readonly workspace: HTMLElement,
+        private readonly onBypass: () => void
+    ) {}
+
+    update({ phase, receivedFiles }: SyncGuardPresentation): void {
+        if (phase === "idle" || phase === "observing") {
+            this.close();
+            return;
+        }
+        this.open();
+        if (this.stage) {
+            this.stage.textContent =
+                phase === "interrupted"
+                    ? $msg("Synchronisation was interrupted. You can continue locally, but some notes may be out of date.")
+                    : phase === "transferring"
+                      ? $msg("Receiving changes from the server…")
+                      : $msg("Applying received changes to local notes…");
+        }
+        if (this.count) {
+            this.count.textContent = $msg("At least ${COUNT} changed files received", { COUNT: `${receivedFiles}` });
+        }
+    }
+
+    private open(): void {
+        if (this.root) return;
+        const doc = this.workspace.ownerDocument;
+        const root = this.workspace.createDiv({ cls: "sls-sync-guard" });
+        root.setAttribute("role", "region");
+        root.setAttribute("aria-label", $msg("Synchronisation protection"));
+        const panel = root.createEl("section", { cls: "sls-sync-guard-panel" });
+        const title = panel.createEl("h2");
+        title.textContent = $msg("Synchronising your Vault");
+        const stage = panel.createEl("p", { cls: "sls-sync-guard-stage" });
+        stage.setAttribute("aria-live", "polite");
+        const count = panel.createEl("p", { cls: "sls-sync-guard-count" });
+        const bypass = panel.createEl("button", { cls: "mod-cta sls-sync-guard-bypass" });
+        bypass.type = "button";
+        bypass.textContent = $msg("Continue without waiting");
+        bypass.addEventListener("click", this.onBypass);
+        this.root = root;
+        this.stage = stage;
+        this.count = count;
+        this.bypassButton = bypass;
+        const focused = doc.activeElement;
+        const modalFocused = focused instanceof Element && focused.closest(".modal-container") !== null;
+        this.previousFocus = !modalFocused && focused instanceof HTMLElement ? focused : undefined;
+        doc.addEventListener("keydown", this.blockKeyboard, true);
+        // Do not steal focus from an Obsidian conflict or setup dialogue which was already open.
+        if (!modalFocused) bypass.focus();
+    }
+
+    /** Prevent editor shortcuts while allowing our own controls and Obsidian's conflict/setup dialogues. */
+    private readonly blockKeyboard = (event: KeyboardEvent): void => {
+        if (!this.root) return;
+        const target = event.target;
+        if (target instanceof Element && target.closest(".modal-container")) return;
+        if (
+            target instanceof Node &&
+            this.root.contains(target) &&
+            !event.ctrlKey &&
+            !event.altKey &&
+            !event.metaKey &&
+            (event.key === "Enter" || event.key === " ")
+        ) {
+            return;
+        }
+        // The guard has a single focusable control. Keep Tab/Shift+Tab inside it;
+        // otherwise focus could move behind the overlay with no keyboard route back.
+        event.preventDefault();
+        event.stopImmediatePropagation();
+        if (event.key === "Tab") this.bypassButton?.focus();
+    };
+
+    close(): void {
+        if (!this.root) return;
+        const doc = this.workspace.ownerDocument;
+        const focused = doc.activeElement;
+        const ownsFocus = focused instanceof Node && this.root.contains(focused);
+        doc.removeEventListener("keydown", this.blockKeyboard, true);
+        this.root.remove();
+        this.root = undefined;
+        this.stage = undefined;
+        this.count = undefined;
+        this.bypassButton = undefined;
+        // A newer dialogue may own focus now. Never move it back to an old editor.
+        if (ownsFocus && this.previousFocus?.isConnected) this.previousFocus.focus();
+        this.previousFocus = undefined;
+    }
+
+    dispose(): void {
+        this.close();
+    }
+}

src/serviceFeatures/syncGuard/SyncGuardOverlay.unit.spec.ts

@@ -0,0 +1,191 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { SyncGuardOverlay } from "./SyncGuardOverlay";
+
+class FakeDocument {
+    activeElement: FakeElement | undefined;
+    listeners = new Map<string, (event: KeyboardEvent) => void>();
+
+    addEventListener(type: string, listener: (event: KeyboardEvent) => void): void {
+        this.listeners.set(type, listener);
+    }
+
+    removeEventListener(type: string): void {
+        this.listeners.delete(type);
+    }
+}
+
+class FakeElement {
+    readonly children: FakeElement[] = [];
+    readonly handlers = new Map<string, () => void>();
+    readonly attributes = new Map<string, string>();
+    className = "";
+    textContent = "";
+    type = "";
+    isConnected = true;
+    parent: FakeElement | undefined;
+
+    constructor(
+        readonly ownerDocument: FakeDocument,
+        readonly tagName: string
+    ) {}
+
+    createEl(tagName: string, options?: { cls?: string }): FakeElement {
+        return this.append(new FakeElement(this.ownerDocument, tagName), options);
+    }
+
+    createDiv(options?: { cls?: string }): FakeElement {
+        return this.createEl("div", options);
+    }
+
+    private append(child: FakeElement, options?: { cls?: string }): FakeElement {
+        child.className = options?.cls ?? "";
+        child.parent = this;
+        this.children.push(child);
+        return child;
+    }
+
+    setAttribute(name: string, value: string): void {
+        this.attributes.set(name, value);
+    }
+
+    addEventListener(name: string, callback: () => void): void {
+        this.handlers.set(name, callback);
+    }
+
+    contains(target: FakeElement): boolean {
+        return target === this || this.children.some((child) => child.contains(target));
+    }
+
+    closest(selector: string): FakeElement | null {
+        if (selector !== ".modal-container") return null;
+        return this.className === "modal-container" ? this : (this.parent?.closest(selector) ?? null);
+    }
+
+    focus(): void {
+        this.ownerDocument.activeElement = this;
+    }
+
+    remove(): void {
+        if (!this.parent) return;
+        const index = this.parent.children.indexOf(this);
+        if (index >= 0) this.parent.children.splice(index, 1);
+        this.isConnected = false;
+    }
+}
+
+function setup() {
+    vi.stubGlobal("HTMLElement", FakeElement);
+    vi.stubGlobal("Element", FakeElement);
+    vi.stubGlobal("Node", FakeElement);
+    const doc = new FakeDocument();
+    const workspace = new FakeElement(doc, "workspace");
+    const editor = workspace.createEl("textarea");
+    editor.focus();
+    const bypass = vi.fn();
+    const overlay = new SyncGuardOverlay(workspace as unknown as HTMLElement, bypass);
+    return { overlay, doc, workspace, editor, bypass };
+}
+
+describe("SyncGuardOverlay", () => {
+    afterEach(() => vi.unstubAllGlobals());
+
+    it("covers only the workspace, exposes a keyboard-operable bypass, and restores focus", () => {
+        const { overlay, doc, workspace, editor, bypass } = setup();
+        overlay.update({ phase: "observing", receivedFiles: 0 });
+        expect(workspace.children).toHaveLength(1);
+        overlay.update({ phase: "transferring", receivedFiles: 20 });
+        const root = workspace.children[1];
+        const panel = root.children[0];
+        const button = panel.children[3];
+        expect(root.attributes.get("role")).toBe("region");
+        expect(button.tagName).toBe("button");
+        expect(button.type).toBe("button");
+        expect(doc.activeElement).toBe(button);
+        expect(panel.children[2].textContent).toContain("20 changed files");
+        button.handlers.get("click")?.();
+        expect(bypass).toHaveBeenCalledOnce();
+        overlay.update({ phase: "idle", receivedFiles: 20 });
+        expect(workspace.children).toHaveLength(1);
+        expect(doc.activeElement).toBe(editor);
+        expect(doc.listeners.size).toBe(0);
+    });
+
+    it("prevents editor keyboard shortcuts while allowing navigation inside the guard", () => {
+        const { overlay, doc, editor, workspace } = setup();
+        overlay.update({ phase: "applying", receivedFiles: 25 });
+        const button = workspace.children[1].children[0].children[3];
+        const block = doc.listeners.get("keydown");
+        const preventDefault = vi.fn();
+        const stopImmediatePropagation = vi.fn();
+        block?.({ target: editor, key: "x", preventDefault, stopImmediatePropagation } as unknown as KeyboardEvent);
+        expect(preventDefault).toHaveBeenCalledOnce();
+        expect(stopImmediatePropagation).toHaveBeenCalledOnce();
+        block?.({ target: button, key: "Enter", preventDefault, stopImmediatePropagation } as unknown as KeyboardEvent);
+        expect(preventDefault).toHaveBeenCalledOnce();
+        overlay.dispose();
+        expect(doc.listeners.size).toBe(0);
+    });
+
+    it("presents a safe offline bypass when the catch-up is interrupted", () => {
+        const { overlay, workspace } = setup();
+        overlay.update({ phase: "interrupted", receivedFiles: 30 });
+        const panel = workspace.children[1].children[0];
+        expect(panel.children[1].textContent).toContain("some notes may be out of date");
+        overlay.dispose();
+    });
+
+    it("does not steal focus from an existing Obsidian dialogue", () => {
+        const { overlay, doc, workspace } = setup();
+        const modal = new FakeElement(doc, "div");
+        modal.className = "modal-container";
+        const modalInput = modal.createEl("input");
+        modalInput.focus();
+        overlay.update({ phase: "transferring", receivedFiles: 20 });
+        expect(doc.activeElement).toBe(modalInput);
+        const preventDefault = vi.fn();
+        const stopImmediatePropagation = vi.fn();
+        doc.listeners.get("keydown")?.({
+            target: modalInput, key: "Escape", preventDefault, stopImmediatePropagation,
+        } as unknown as KeyboardEvent);
+        expect(preventDefault).not.toHaveBeenCalled();
+        expect(stopImmediatePropagation).not.toHaveBeenCalled();
+        overlay.dispose();
+        expect(workspace.children).toHaveLength(1);
+        expect(doc.activeElement).toBe(modalInput);
+    });
+
+    it("does not restore editor focus if a dialogue opened while the guard was active", () => {
+        const { overlay, doc } = setup();
+        overlay.update({ phase: "transferring", receivedFiles: 20 });
+        const modal = new FakeElement(doc, "div");
+        modal.className = "modal-container";
+        const input = modal.createEl("input");
+        input.focus();
+        overlay.update({ phase: "idle", receivedFiles: 20 });
+        expect(doc.activeElement).toBe(input);
+    });
+
+    it("keeps Tab and Shift+Tab on the bypass button rather than an editor behind the guard", () => {
+        const { overlay, doc, workspace, editor } = setup();
+        overlay.update({ phase: "transferring", receivedFiles: 20 });
+        const button = workspace.children[1].children[0].children[3];
+        for (const shiftKey of [false, true]) {
+            const preventDefault = vi.fn();
+            const stopImmediatePropagation = vi.fn();
+            doc.listeners.get("keydown")?.({
+                target: button, key: "Tab", shiftKey, preventDefault, stopImmediatePropagation,
+            } as unknown as KeyboardEvent);
+            expect(preventDefault).toHaveBeenCalledOnce();
+            expect(stopImmediatePropagation).toHaveBeenCalledOnce();
+            expect(doc.activeElement).toBe(button);
+        }
+        const preventDefault = vi.fn();
+        const stopImmediatePropagation = vi.fn();
+        doc.listeners.get("keydown")?.({
+            target: editor, key: "Tab", preventDefault, stopImmediatePropagation,
+        } as unknown as KeyboardEvent);
+        expect(preventDefault).toHaveBeenCalledOnce();
+        expect(doc.activeElement).toBe(button);
+        overlay.dispose();
+    });
+});

src/serviceFeatures/syncGuard/SyncGuardState.ts

@@ -14,9 +14,9 @@ export class SyncGuardState {
     private phase: SyncGuardPhase = "idle";
     private receivedIds = new Set<string>();
     private minimumFiles = 20;
-    private started = false;
     private finiteActive = false;
     private observedCompletion = false;
+    private hadReflectionFailure = false;
     private bypassed = false;
     private quiescentSince: number | undefined;
 
@@ -29,31 +29,46 @@ export class SyncGuardState {
         return { phase: this.phase, receivedFiles: this.receivedIds.size };
     }
 
+    get wasBypassed(): boolean {
+        return this.bypassed;
+    }
+
     /** Begins a fresh, initially non-blocking observation window on app resume. */
     resume(enabled: boolean, minimumFiles: number): void {
         this.minimumFiles = Number.isFinite(minimumFiles) ? Math.max(1, Math.floor(minimumFiles)) : 20;
         this.receivedIds.clear();
-        this.started = false;
         this.finiteActive = false;
         this.observedCompletion = false;
+        this.hadReflectionFailure = false;
         this.bypassed = false;
         this.quiescentSince = undefined;
         this.setPhase(enabled ? "observing" : "idle");
     }
 
+    /** A changed setting takes effect during observation, without cancelling an active protection. */
+    updateThreshold(minimumFiles: number): void {
+        this.minimumFiles = Number.isFinite(minimumFiles) ? Math.max(1, Math.floor(minimumFiles)) : 20;
+        if (this.phase === "observing" && this.finiteActive && this.receivedIds.size >= this.minimumFiles) {
+            this.setPhase("transferring");
+        }
+    }
+
     /** A completed finite pull is expected before the long-running live connection begins. */
     finiteActivityChanged(active: boolean, pendingCount: number, now: number): void {
         if (this.phase === "idle" || this.bypassed || this.finiteActive === active) return;
         if (active) {
-            if (this.started) return; // Only the first finite transfer of this resume generation is relevant.
+            // A retry or a second pull can begin while the Vault is still applying an earlier batch.
-            this.started = true;
+            // Do not let the previous successful completion unlock an active newer transfer.
             this.finiteActive = true;
+            this.observedCompletion = false;
+            this.quiescentSince = undefined;
+            if (this.isBlocking()) this.setPhase("transferring");
             return;
         }
         this.finiteActive = false;
         if (!this.isBlocking()) {
             this.setPhase("idle");
-        } else if (!this.observedCompletion) {
+        } else if (!this.observedCompletion || this.hadReflectionFailure) {
             this.setPhase("interrupted");
         } else {
             this.setPhase("applying");
@@ -67,15 +82,23 @@ export class SyncGuardState {
         if (status === "COMPLETED") this.observedCompletion = true;
     }
 
+    /** A network-complete batch is not a safe unlock when reflecting a received note failed. */
+    reflectionFailed(): void {
+        if (this.phase === "idle" || this.bypassed) return;
+        this.hadReflectionFailure = true;
+        if (this.phase === "applying") this.setPhase("interrupted");
+    }
+
     /** Count distinct incoming note Metadata, not Chunks or repeated revisions of a note. */
     receivedDocuments(ids: readonly string[]): void {
         if (!this.finiteActive || this.bypassed || this.phase === "idle") return;
         const wasBlocking = this.isBlocking();
+        const previousCount = this.receivedIds.size;
         for (const id of ids) {
             if (id) this.receivedIds.add(id);
-            if (this.receivedIds.size >= this.minimumFiles) break;
         }
         if (!wasBlocking && this.receivedIds.size >= this.minimumFiles) this.setPhase("transferring");
+        else if (wasBlocking && this.receivedIds.size !== previousCount) this.onChange(this.presentation);
     }
 
     /** Unlock only after successful transfer and a stable empty local application queue. */

src/serviceFeatures/syncGuard/SyncGuardState.unit.spec.ts

@@ -27,6 +27,8 @@ describe("SyncGuardState", () => {
         expect(guard.presentation.phase).toBe("observing");
         guard.receivedDocuments(["f:three"]);
         expect(guard.presentation).toEqual({ phase: "transferring", receivedFiles: 3 });
+        guard.receivedDocuments(["f:four", "f:four"]);
+        expect(guard.presentation.receivedFiles).toBe(4);
         guard.replicationStatusChanged("COMPLETED");
         guard.finiteActivityChanged(false, 2, 10);
         expect(guard.presentation.phase).toBe("applying");
@@ -53,6 +55,51 @@ describe("SyncGuardState", () => {
         expect(guard.presentation.phase).toBe("idle");
     });
 
+    it("does not unlock when a new pull starts while applying an earlier completed transfer", () => {
+        const { guard } = setup();
+        guard.resume(true, 1);
+        guard.finiteActivityChanged(true, 0, 0);
+        guard.receivedDocuments(["f:first"]);
+        guard.replicationStatusChanged("COMPLETED");
+        guard.finiteActivityChanged(false, 0, 1);
+        expect(guard.presentation.phase).toBe("applying");
+        guard.finiteActivityChanged(true, 0, 100);
+        expect(guard.presentation.phase).toBe("transferring");
+        guard.tick(0, 10_000);
+        expect(guard.presentation.phase).toBe("transferring");
+        guard.finiteActivityChanged(false, 0, 10_001);
+        expect(guard.presentation.phase).toBe("interrupted");
+    });
+
+    it("can recover an interrupted catch-up when a new pull succeeds", () => {
+        const { guard } = setup();
+        guard.resume(true, 1);
+        guard.finiteActivityChanged(true, 0, 0);
+        guard.receivedDocuments(["f:first"]);
+        guard.finiteActivityChanged(false, 0, 10);
+        expect(guard.presentation.phase).toBe("interrupted");
+        guard.finiteActivityChanged(true, 0, 20);
+        expect(guard.presentation.phase).toBe("transferring");
+        guard.replicationStatusChanged("COMPLETED");
+        guard.finiteActivityChanged(false, 0, 30);
+        guard.tick(0, 2030);
+        expect(guard.presentation.phase).toBe("idle");
+    });
+
+    it("does not declare the Vault ready after a failed received-file reflection", () => {
+        const { guard } = setup();
+        guard.resume(true, 1);
+        guard.finiteActivityChanged(true, 0, 0);
+        guard.receivedDocuments(["f:first"]);
+        guard.reflectionFailed();
+        guard.replicationStatusChanged("COMPLETED");
+        guard.finiteActivityChanged(false, 0, 10);
+        guard.tick(0, 10_000);
+        expect(guard.presentation.phase).toBe("interrupted");
+        guard.bypass();
+        expect(guard.presentation.phase).toBe("idle");
+    });
+
     it("does not confuse a stale completed status with this catch-up", () => {
         const { guard } = setup();
         guard.resume(true, 1);
@@ -88,4 +135,15 @@ describe("SyncGuardState", () => {
         guard.receivedDocuments(["f:one"]);
         expect(guard.presentation.phase).toBe("transferring");
     });
+
+    it("applies a lowered threshold while observing without unlocking an already protected Vault", () => {
+        const { guard } = setup();
+        guard.resume(true, 20);
+        guard.finiteActivityChanged(true, 0, 0);
+        guard.receivedDocuments(["f:one", "f:two", "f:three"]);
+        guard.updateThreshold(3);
+        expect(guard.presentation.phase).toBe("transferring");
+        guard.updateThreshold(200);
+        expect(guard.presentation.phase).toBe("transferring");
+    });
 });

src/serviceFeatures/syncGuard/index.ts

@@ -0,0 +1,150 @@
+import { collectingChunks, chunkFetchCounts } from "@vrtmrz/livesync-commonlib/compat/mock_and_interop/stores";
+import { REMOTE_COUCHDB } from "@vrtmrz/livesync-commonlib/compat/common/types";
+import { isAnyNote } from "@vrtmrz/livesync-commonlib/compat/common/utils";
+import { compatGlobal } from "@vrtmrz/livesync-commonlib/compat/common/coreEnvFunctions";
+import type { LiveSyncCore } from "@/main.ts";
+import { EVENT_SETTING_SAVED, EVENT_VAULT_REFLECTION_FAILED } from "@/common/events";
+import type { SyncGuardOverlay } from "./SyncGuardOverlay";
+import { SyncGuardState } from "./SyncGuardState";
+
+export type SyncGuardOverlayFactory = (onBypass: () => void) => Pick<SyncGuardOverlay, "update" | "dispose">;
+
+/**
+ * Obsidian-only UI policy. The synchronisation service remains fully writable so remote
+ * result reflection, conflict resolution, and file-system access can make progress.
+ */
+export function useSyncGuardFeature(host: LiveSyncCore, createOverlay: SyncGuardOverlayFactory): void {
+    const { services } = host;
+    let disposed = false;
+    let quietTimer: number | undefined;
+    const readPendingCount = () => {
+        const counts = [
+            services.replication.replicationResultCount.value,
+            services.replication.databaseQueueCount.value,
+            services.replication.storageApplyingCount.value,
+            services.fileProcessing.processing.value,
+            services.fileProcessing.totalQueued.value,
+            services.fileProcessing.batched.value,
+            services.conflict.conflictProcessQueueCount.value,
+            collectingChunks.value,
+            chunkFetchCounts.value.initial,
+            chunkFetchCounts.value.retrying,
+        ];
+        return counts.reduce((total, count) => total + Math.max(0, count), 0);
+    };
+    const stopTimer = () => {
+        if (quietTimer !== undefined) compatGlobal.clearTimeout(quietTimer);
+        quietTimer = undefined;
+    };
+
+    let guard: SyncGuardState;
+    const overlay = createOverlay(() => guard.bypass());
+    const checkForUnlock = () => {
+        if (disposed) return;
+        stopTimer();
+        if (guard.presentation.phase !== "applying") return;
+        const pending = readPendingCount();
+        guard.tick(pending, Date.now());
+        if (guard.presentation.phase === "applying" && pending === 0) {
+            quietTimer = compatGlobal.setTimeout(checkForUnlock, 2_100);
+        }
+    };
+    guard = new SyncGuardState((presentation) => {
+        if (disposed) return;
+        overlay.update(presentation);
+        checkForUnlock();
+    });
+
+    const isEnabled = () => {
+        const settings = services.setting.currentSettings();
+        return settings.isConfigured && settings.liveSync && settings.remoteType === REMOTE_COUCHDB &&
+            settings.syncGuardEnabled;
+    };
+    const beginCatchUp = () => {
+        const settings = services.setting.currentSettings();
+        if (!isEnabled()) {
+            guard.disable();
+            return;
+        }
+        // Duplicate resume notifications or a visibility transition must not discard an
+        // already active guard and expose a partly reflected Vault to the user.
+        if (guard.presentation.phase === "transferring" || guard.presentation.phase === "applying" ||
+            guard.presentation.phase === "interrupted") {
+            return;
+        }
+        if (guard.presentation.phase === "observing" &&
+            services.replicator.finiteReplicationActivityCount.value > 0) {
+            return;
+        }
+        guard.resume(Boolean(isEnabled()), settings.syncGuardMinimumFiles);
+        guard.finiteActivityChanged(services.replicator.finiteReplicationActivityCount.value > 0, readPendingCount(), Date.now());
+    };
+    const onFiniteChanged = () => {
+        const active = services.replicator.finiteReplicationActivityCount.value > 0;
+        // Continuous replication can restart its finite pull following an internal reconnect,
+        // without an Obsidian onResumed notification. A new bounded transfer gets its own window.
+        if (active && guard.presentation.phase === "idle" && !guard.wasBypassed && isEnabled()) beginCatchUp();
+        guard.finiteActivityChanged(active, readPendingCount(), Date.now());
+    };
+    const onReplicationChanged = () => {
+        guard.replicationStatusChanged(services.replicator.replicationStatics.value.syncStatus);
+    };
+    const onSettingsChanged = () => {
+        if (!isEnabled()) guard.disable();
+        else guard.updateThreshold(services.setting.currentSettings().syncGuardMinimumFiles);
+    };
+    const onPendingChanged = () => checkForUnlock();
+    const removeReflectionFailureHandler = services.context.events.onEvent(EVENT_VAULT_REFLECTION_FAILED, () => {
+        guard.reflectionFailed();
+    });
+    const removeSettingSavedHandler = services.context.events.onEvent(EVENT_SETTING_SAVED, () => {
+        onSettingsChanged();
+    });
+
+    const finite = services.replicator.finiteReplicationActivityCount;
+    const replication = services.replicator.replicationStatics;
+    const pendingSources = [
+        services.replication.replicationResultCount,
+        services.replication.databaseQueueCount,
+        services.replication.storageApplyingCount,
+        services.fileProcessing.processing,
+        services.fileProcessing.totalQueued,
+        services.fileProcessing.batched,
+        services.conflict.conflictProcessQueueCount,
+        collectingChunks,
+        chunkFetchCounts,
+    ];
+    finite.onChanged(onFiniteChanged);
+    replication.onChanged(onReplicationChanged);
+    for (const source of pendingSources) source.onChanged(onPendingChanged);
+
+    // Register before the ordinary replication scheduling handler so the first finite pull
+    // belongs to the new resume generation even if it starts synchronously.
+    services.appLifecycle.onResumed.addHandler(() => {
+        beginCatchUp();
+        return Promise.resolve(true);
+    }, -100);
+    services.appLifecycle.onSuspending.addHandler(() => {
+        guard.interrupted();
+        return Promise.resolve(true);
+    });
+    services.setting.onSettingRealised.addHandler(() => {
+        onSettingsChanged();
+        return Promise.resolve(true);
+    });
+    services.replication.parseSynchroniseResult.addHandler((documents) => {
+        if (!disposed) guard.receivedDocuments(documents.filter(isAnyNote).map((doc) => doc._id));
+        return Promise.resolve(true);
+    });
+    services.appLifecycle.onUnload.addHandler(() => {
+        disposed = true;
+        stopTimer();
+        finite.offChanged(onFiniteChanged);
+        replication.offChanged(onReplicationChanged);
+        for (const source of pendingSources) source.offChanged(onPendingChanged);
+        overlay.dispose();
+        removeSettingSavedHandler();
+        removeReflectionFailureHandler();
+        return Promise.resolve(true);
+    });
+}

src/serviceFeatures/syncGuard/syncGuardFeature.unit.spec.ts

@@ -0,0 +1,253 @@
+import { reactiveSource } from "octagonal-wheels/dataobject/reactive";
+import { REMOTE_COUCHDB, type EntryDoc } from "@vrtmrz/livesync-commonlib/compat/common/types";
+import { createServiceContext } from "@vrtmrz/livesync-commonlib/context";
+import { EVENT_SETTING_SAVED, EVENT_VAULT_REFLECTION_FAILED } from "@/common/events";
+import { describe, afterEach, expect, it, vi } from "vitest";
+import { useSyncGuardFeature } from "./index";
+import type { SyncGuardPresentation } from "./SyncGuardState";
+
+function receivedNote(id: string): PouchDB.Core.ExistingDocument<EntryDoc> {
+    return {
+        _id: id,
+        _rev: "1-received",
+        path: `${id}.md`,
+        ctime: 1,
+        mtime: 2,
+        size: 1,
+        children: [],
+        datatype: "plain",
+        type: "plain",
+        eden: {},
+    } as unknown as PouchDB.Core.ExistingDocument<EntryDoc>;
+}
+
+function setup(overrides: { enabled?: boolean; minimumFiles?: number } = {}) {
+    const onResumed: Array<() => Promise<boolean>> = [];
+    const onSuspending: Array<() => Promise<boolean>> = [];
+    const onUnload: Array<() => Promise<boolean>> = [];
+    const onSettingRealised: Array<() => Promise<boolean>> = [];
+    const parseHandlers: Array<(docs: PouchDB.Core.ExistingDocument<EntryDoc>[]) => Promise<boolean>> = [];
+    const priority = vi.fn();
+    const finiteReplicationActivityCount = reactiveSource(0);
+    const replicationStatics = reactiveSource({ syncStatus: "NOT_CONNECTED" });
+    const replicationResultCount = reactiveSource(0);
+    const databaseQueueCount = reactiveSource(0);
+    const storageApplyingCount = reactiveSource(0);
+    const processing = reactiveSource(0);
+    const totalQueued = reactiveSource(0);
+    const batched = reactiveSource(0);
+    const conflictProcessQueueCount = reactiveSource(0);
+    const settings = {
+        isConfigured: true,
+        liveSync: true,
+        remoteType: REMOTE_COUCHDB,
+        syncGuardEnabled: overrides.enabled ?? true,
+        syncGuardMinimumFiles: overrides.minimumFiles ?? 2,
+    };
+    const host = {
+        services: {
+            context: createServiceContext(),
+            setting: {
+                currentSettings: () => settings,
+                onSettingRealised: { addHandler: (fn: () => Promise<boolean>) => onSettingRealised.push(fn) },
+            },
+            replication: {
+                replicationResultCount,
+                databaseQueueCount,
+                storageApplyingCount,
+                parseSynchroniseResult: {
+                    addHandler: (fn: (docs: PouchDB.Core.ExistingDocument<EntryDoc>[]) => Promise<boolean>) => {
+                        parseHandlers.push(fn);
+                    },
+                },
+            },
+            replicator: { finiteReplicationActivityCount, replicationStatics },
+            fileProcessing: { processing, totalQueued, batched },
+            conflict: { conflictProcessQueueCount },
+            appLifecycle: {
+                onResumed: {
+                    addHandler: (fn: () => Promise<boolean>, prio?: number) => {
+                        priority(prio);
+                        onResumed.push(fn);
+                    },
+                },
+                onSuspending: { addHandler: (fn: () => Promise<boolean>) => onSuspending.push(fn) },
+                onUnload: { addHandler: (fn: () => Promise<boolean>) => onUnload.push(fn) },
+            },
+        },
+    };
+    const updates: SyncGuardPresentation[] = [];
+    const dispose = vi.fn();
+    let bypass: () => void = () => { throw new Error("Guard not composed"); };
+    useSyncGuardFeature(host as never, (onBypass) => {
+        bypass = onBypass;
+        return { update: (p) => updates.push(p), dispose };
+    });
+    return {
+        settings,
+        events: host.services.context.events,
+        onResumed,
+        onSuspending,
+        onUnload,
+        onSettingRealised,
+        parseHandlers,
+        priority,
+        finiteReplicationActivityCount,
+        replicationStatics,
+        replicationResultCount,
+        databaseQueueCount,
+        storageApplyingCount,
+        updates,
+        bypass: () => bypass(),
+        dispose,
+    };
+}
+
+describe("useSyncGuardFeature", () => {
+    afterEach(() => {
+        vi.useRealTimers();
+    });
+
+    it("observes the initial CouchDB pull ahead of scheduling and unlocks after local queues settle", async () => {
+        vi.useFakeTimers();
+        const h = setup();
+        expect(h.priority).toHaveBeenCalledWith(-100);
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first"), receivedNote("second")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        h.databaseQueueCount.value = 1;
+        h.replicationStatics.value = { syncStatus: "COMPLETED" };
+        h.finiteReplicationActivityCount.value = 0;
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("applying");
+        vi.advanceTimersByTime(5_000);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("applying");
+        h.databaseQueueCount.value = 0;
+        await vi.advanceTimersByTimeAsync(2_150);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("idle");
+        await h.onUnload[0]();
+        expect(h.dispose).toHaveBeenCalledOnce();
+    });
+
+    it("never blocks normal transfers and ignores chunks and duplicate note revisions", async () => {
+        const h = setup({ minimumFiles: 3 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first"), receivedNote("first"), { _id: "h:chunk", _rev: "1-a", type: "leaf" } as never]);
+        expect(h.updates.some((p) => p.phase === "transferring")).toBe(false);
+        await h.onUnload[0]();
+    });
+
+    it("preserves offline access through manual bypass and never re-locks that catch-up", async () => {
+        const h = setup({ minimumFiles: 1 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first")]);
+        h.finiteReplicationActivityCount.value = 0;
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("interrupted");
+        h.bypass();
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("idle");
+        await h.parseHandlers[0]([receivedNote("second")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("idle");
+        await h.onUnload[0]();
+    });
+
+    it("never shows a guard when disabled and releases an active guard when the setting is disabled", async () => {
+        const h = setup({ enabled: false, minimumFiles: 1 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first")]);
+        expect(h.updates.some((p) => p.phase === "transferring")).toBe(false);
+        await h.onUnload[0]();
+
+        const enabled = setup({ minimumFiles: 1 });
+        await enabled.onResumed[0]();
+        enabled.finiteReplicationActivityCount.value = 1;
+        await enabled.parseHandlers[0]([receivedNote("first")]);
+        expect(enabled.updates[enabled.updates.length - 1]?.phase).toBe("transferring");
+        enabled.settings.syncGuardEnabled = false;
+        await enabled.onSettingRealised[0]();
+        expect(enabled.updates[enabled.updates.length - 1]?.phase).toBe("idle");
+        await enabled.onUnload[0]();
+    });
+
+    it("observes an internal LiveSync reconnect even without an application resume notification", async () => {
+        const h = setup({ minimumFiles: 1 });
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("after-reconnect")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        h.replicationStatics.value = { syncStatus: "COMPLETED" };
+        h.finiteReplicationActivityCount.value = 0;
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("applying");
+        await h.onUnload[0]();
+    });
+
+    it("preserves an active guard across duplicate resume notifications", async () => {
+        const h = setup({ minimumFiles: 2 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first"), receivedNote("second")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        await h.onResumed[0]();
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        h.replicationStatics.value = { syncStatus: "COMPLETED" };
+        h.finiteReplicationActivityCount.value = 0;
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("applying");
+        await h.onUnload[0]();
+    });
+
+    it("preserves accumulated files before the threshold when resume fires twice during one pull", async () => {
+        const h = setup({ minimumFiles: 3 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("one"), receivedNote("two")]);
+        await h.onResumed[0]();
+        await h.parseHandlers[0]([receivedNote("three")]);
+        expect(h.updates[h.updates.length - 1]).toMatchObject({
+            phase: "transferring",
+            receivedFiles: 3,
+        });
+        await h.onUnload[0]();
+    });
+
+    it("keeps the guard after a received note could not be written to the Vault", async () => {
+        const h = setup({ minimumFiles: 1 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("failed")]);
+        h.events.emitEvent(EVENT_VAULT_REFLECTION_FAILED);
+        h.replicationStatics.value = { syncStatus: "COMPLETED" };
+        h.finiteReplicationActivityCount.value = 0;
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("interrupted");
+        await h.onUnload[0]();
+    });
+
+    it("responds immediately to settings saved by the UI without setting-realised", async () => {
+        const h = setup({ minimumFiles: 20 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("one"), receivedNote("two")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("observing");
+        h.settings.syncGuardMinimumFiles = 2;
+        h.events.emitEvent(EVENT_SETTING_SAVED, h.settings as never);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        h.settings.syncGuardEnabled = false;
+        h.events.emitEvent(EVENT_SETTING_SAVED, h.settings as never);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("idle");
+        await h.onUnload[0]();
+    });
+
+    it("does not re-lock after manual bypass when an internal reconnect starts", async () => {
+        const h = setup({ minimumFiles: 1 });
+        await h.onResumed[0]();
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("first")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("transferring");
+        h.bypass();
+        h.finiteReplicationActivityCount.value = 0;
+        h.finiteReplicationActivityCount.value = 1;
+        await h.parseHandlers[0]([receivedNote("second")]);
+        expect(h.updates[h.updates.length - 1]?.phase).toBe("idle");
+        await h.onUnload[0]();
+    });
+});

styles.css

@@ -839,3 +839,38 @@ body.is-mobile .livesync-compatibility-review-notice {
     outline-offset: 1px;
     border-radius: 2px;
 }
+
+/* An optional, workspace-only barrier during a substantial catch-up. Other Obsidian dialogues remain usable. */
+.sls-sync-guard {
+    position: absolute;
+    inset: 0;
+    z-index: var(--layer-cover, 30);
+    display: grid;
+    place-items: center;
+    padding: var(--size-4-4);
+    background: var(--background-primary);
+    color: var(--text-normal);
+    pointer-events: auto;
+}
+
+.sls-sync-guard-panel {
+    width: min(100%, 30rem);
+    padding: var(--size-4-6);
+    border: 1px solid var(--background-modifier-border);
+    border-radius: var(--radius-l);
+    background: var(--background-secondary);
+    text-align: center;
+}
+
+.sls-sync-guard-panel h2 {
+    margin-block-start: 0;
+}
+
+.sls-sync-guard-count {
+    color: var(--text-muted);
+}
+
+.sls-sync-guard-bypass {
+    min-height: 44px;
+    min-width: 44px;
+}