refactor(sync-ui): split runtime into focused modules

- Extract sync-ui-runtime.ts into sync-ui-hosts-state, sync-ui-ipc-handlers, sync-ui-run-lifecycle, sync-ui-snapshots
- Reject sync --ui combined with --remote-cmd or --db in cli-parser-builder

launcher/config/cli-parser-builder.test.ts

@@ -87,7 +87,10 @@ test('parseCliPrograms lowers sync options into app-owned CLI tokens', () => {
   const makeTemp = parseCliPrograms(['sync', '--make-temp'], 'subminer');
   assert.deepEqual(makeTemp.invocations.syncCliTokens, ['--make-temp']);
 
-  const removeTemp = parseCliPrograms(['sync', '--remove-temp', '/tmp/subminer-sync-x'], 'subminer');
+  const removeTemp = parseCliPrograms(
+    ['sync', '--remove-temp', '/tmp/subminer-sync-x'],
+    'subminer',
+  );
   assert.deepEqual(removeTemp.invocations.syncCliTokens, ['--remove-temp', '/tmp/subminer-sync-x']);
 });
 
@@ -112,3 +115,16 @@ test('parseCliPrograms captures sync --ui', () => {
     /--ui cannot be combined/,
   );
 });
+
+test('parseCliPrograms rejects sync --ui with --remote-cmd', () => {
+  assert.throws(
+    () => parseCliPrograms(['sync', '--ui', '--remote-cmd', '/opt/SubMiner.AppImage'], 'subminer'),
+    { message: 'Sync --ui cannot be combined with other sync options.' },
+  );
+});
+
+test('parseCliPrograms rejects sync --ui with --db', () => {
+  assert.throws(() => parseCliPrograms(['sync', '--ui', '--db', '/tmp/db.sqlite'], 'subminer'), {
+    message: 'Sync --ui cannot be combined with other sync options.',
+  });
+});

launcher/config/cli-parser-builder.ts

@@ -340,6 +340,8 @@ export function parseCliPrograms(
           check ||
           makeTemp ||
           removeTemp ||
+          options.remoteCmd !== undefined ||
+          options.db !== undefined ||
           options.json === true ||
           options.force === true
         ) {

src/main/runtime/sync-ui-hosts-state.ts

@@ -0,0 +1,23 @@
+import {
+  readSyncHostsState,
+  writeSyncHostsState,
+  type SyncHostsState,
+} from '../../shared/sync/sync-hosts-store';
+
+interface SyncUiHostsStateDeps {
+  hostsFilePath: string;
+  broadcastStateChanged: () => void;
+}
+
+export function createSyncUiHostsState(deps: SyncUiHostsStateDeps) {
+  function readState(): SyncHostsState {
+    return readSyncHostsState(deps.hostsFilePath);
+  }
+
+  function writeState(state: SyncHostsState): void {
+    writeSyncHostsState(deps.hostsFilePath, state);
+    deps.broadcastStateChanged();
+  }
+
+  return { readState, writeState };
+}

src/main/runtime/sync-ui-ipc-handlers.ts

@@ -0,0 +1,63 @@
+import { IPC_CHANNELS } from '../../shared/ipc/contracts';
+import { removeSyncHost, upsertSyncHost } from '../../shared/sync/sync-hosts-store';
+import type {
+  SyncUiHostUpdateRequest,
+  SyncUiRunRequest,
+  SyncUiSnapshot,
+  SyncUiStartResult,
+} from '../../types/sync-ui';
+
+interface SyncUiIpcHandlersDeps {
+  ipcMain: {
+    handle(channel: string, listener: (event: unknown, ...args: unknown[]) => unknown): unknown;
+  };
+  nowMs: () => number;
+  revealPath: (targetPath: string) => void;
+  pickSnapshotFile: () => Promise<string | null>;
+  getSnapshot: () => SyncUiSnapshot;
+  readState: () => SyncUiSnapshot['hosts'];
+  writeState: (state: SyncUiSnapshot['hosts']) => void;
+  runHostSync: (request: SyncUiRunRequest) => SyncUiStartResult;
+  cancelRun: () => boolean;
+  checkHost: (host: string) => unknown;
+  createSnapshot: () => SyncUiStartResult;
+  mergeSnapshotFile: (filePath: string, force?: boolean) => SyncUiStartResult;
+  deleteSnapshot: (filePath: string) => void;
+}
+
+export function registerSyncUiIpcHandlers(deps: SyncUiIpcHandlersDeps): void {
+  const channels = IPC_CHANNELS.request;
+  deps.ipcMain.handle(channels.syncUiGetSnapshot, () => deps.getSnapshot());
+  deps.ipcMain.handle(channels.syncUiSaveHost, (_event, update) => {
+    deps.writeState(
+      upsertSyncHost(deps.readState(), update as SyncUiHostUpdateRequest, deps.nowMs()),
+    );
+  });
+  deps.ipcMain.handle(channels.syncUiRemoveHost, (_event, host) => {
+    deps.writeState(removeSyncHost(deps.readState(), String(host)));
+  });
+  deps.ipcMain.handle(channels.syncUiSetAutoSyncInterval, (_event, minutes) => {
+    const value = Number(minutes);
+    if (!Number.isFinite(value) || value < 1 || value > 24 * 60) {
+      throw new Error('Auto-sync interval must be between 1 and 1440 minutes.');
+    }
+    deps.writeState({ ...deps.readState(), autoSyncIntervalMinutes: Math.floor(value) });
+  });
+  deps.ipcMain.handle(channels.syncUiRunSync, (_event, request) =>
+    deps.runHostSync(request as SyncUiRunRequest),
+  );
+  deps.ipcMain.handle(channels.syncUiCancelRun, () => deps.cancelRun());
+  deps.ipcMain.handle(channels.syncUiCheckHost, (_event, host) => deps.checkHost(String(host)));
+  deps.ipcMain.handle(channels.syncUiCreateSnapshot, () => deps.createSnapshot());
+  deps.ipcMain.handle(channels.syncUiMergeSnapshotFile, (_event, filePath, force) =>
+    deps.mergeSnapshotFile(String(filePath), force === true),
+  );
+  deps.ipcMain.handle(channels.syncUiDeleteSnapshot, (_event, filePath) => {
+    deps.deleteSnapshot(String(filePath));
+  });
+  deps.ipcMain.handle(channels.syncUiRevealSnapshot, (_event, filePath) => {
+    deps.revealPath(String(filePath));
+    return true;
+  });
+  deps.ipcMain.handle(channels.syncUiPickSnapshotFile, () => deps.pickSnapshotFile());
+}

src/main/runtime/sync-ui-run-lifecycle.ts

@@ -0,0 +1,183 @@
+import { IPC_CHANNELS } from '../../shared/ipc/contracts';
+import { isValidSyncHost } from '../../shared/sync/sync-hosts-store';
+import type { SyncProgressEvent } from '../../shared/sync/sync-events';
+import type {
+  SyncUiCheckResult,
+  SyncUiRunKind,
+  SyncUiRunState,
+  SyncUiStartResult,
+} from '../../types/sync-ui';
+import {
+  runSyncLauncher,
+  type SyncLauncherRunHandle,
+  type SyncLauncherRunResult,
+} from './sync-launcher-client';
+
+interface ActiveRun {
+  id: number;
+  kind: SyncUiRunKind;
+  host: string | null;
+  handle: SyncLauncherRunHandle;
+  resultSeen: boolean;
+  completion?: Promise<void>;
+}
+
+interface SyncUiRunLifecycleDeps {
+  runLauncher: typeof runSyncLauncher;
+  resolveLauncherCommand: () => string[];
+  log?: (message: string) => void;
+  notify?: (payload: { title: string; body: string; variant: 'success' | 'error' }) => void;
+  sendToWindow: (channel: string, payload?: unknown) => void;
+  broadcastStateChanged: () => void;
+}
+
+export function createSyncUiRunLifecycle(deps: SyncUiRunLifecycleDeps) {
+  let runCounter = 0;
+  let currentRun: ActiveRun | null = null;
+
+  function launchRun(
+    kind: SyncUiRunKind,
+    host: string | null,
+    args: string[],
+    options: {
+      notify?: boolean;
+      timeoutMs?: number;
+      emitProgress?: boolean;
+      onEvent?: (event: SyncProgressEvent) => void;
+    } = {},
+  ): { start: SyncUiStartResult; done: Promise<SyncLauncherRunResult> | null } {
+    if (currentRun) {
+      return {
+        start: { started: false, runId: null, reason: 'A sync operation is already running.' },
+        done: null,
+      };
+    }
+    const emitProgress = options.emitProgress ?? true;
+    runCounter += 1;
+    const runId = runCounter;
+    const run: ActiveRun = {
+      id: runId,
+      kind,
+      host,
+      resultSeen: false,
+      handle: deps.runLauncher({
+        command: deps.resolveLauncherCommand(),
+        args,
+        timeoutMs: options.timeoutMs,
+        onEvent: (event: SyncProgressEvent) => {
+          if (event.type === 'result') run.resultSeen = true;
+          options.onEvent?.(event);
+          if (emitProgress) {
+            deps.sendToWindow(IPC_CHANNELS.event.syncUiProgress, { runId, kind, host, event });
+          }
+        },
+        onStderr: (text) => deps.log?.(`[sync-ui] ${text.trimEnd()}`),
+      }),
+    };
+    currentRun = run;
+    run.completion = run.handle.done
+      .then((result: SyncLauncherRunResult) => {
+        if (currentRun?.id === runId) currentRun = null;
+        if (emitProgress && !run.resultSeen) {
+          deps.sendToWindow(IPC_CHANNELS.event.syncUiProgress, {
+            runId,
+            kind,
+            host,
+            event: { type: 'result', ok: result.ok, error: result.error },
+          });
+        }
+        deps.broadcastStateChanged();
+        if (options.notify && deps.notify) {
+          const target = host ?? 'local database';
+          deps.notify(
+            result.ok
+              ? { title: 'Sync complete', body: `Synced with ${target}`, variant: 'success' }
+              : {
+                  title: 'Sync failed',
+                  body: `${target}: ${result.error ?? 'unknown error'}`,
+                  variant: 'error',
+                },
+          );
+        }
+      })
+      .catch((error) => {
+        deps.log?.(
+          `[sync-ui] Post-run cleanup failed: ${error instanceof Error ? error.message : String(error)}`,
+        );
+      });
+    return { start: { started: true, runId, reason: null }, done: run.handle.done };
+  }
+
+  function startRun(
+    kind: SyncUiRunKind,
+    host: string | null,
+    args: string[],
+    options: { notify?: boolean } = {},
+  ): SyncUiStartResult {
+    return launchRun(kind, host, args, options).start;
+  }
+
+  function checkHost(host: string): Promise<SyncUiCheckResult> {
+    const trimmed = host.trim();
+    const failed = (error: string): SyncUiCheckResult => ({
+      host: trimmed,
+      sshOk: false,
+      remoteCommand: null,
+      remoteVersion: null,
+      ok: false,
+      error,
+    });
+    if (!isValidSyncHost(trimmed)) {
+      return Promise.resolve(failed(`Invalid sync host: ${host}`));
+    }
+    let checkResult: SyncUiCheckResult | null = null;
+    const { start, done } = launchRun('check', trimmed, ['sync', trimmed, '--check', '--json'], {
+      timeoutMs: 30_000,
+      emitProgress: false,
+      onEvent: (event) => {
+        if (event.type === 'check-result') {
+          checkResult = {
+            host: event.host,
+            sshOk: event.sshOk,
+            remoteCommand: event.remoteCommand,
+            remoteVersion: event.remoteVersion,
+            ok: event.ok,
+            error: event.error,
+          };
+        }
+      },
+    });
+    if (!start.started || !done) {
+      return Promise.resolve(failed(start.reason ?? 'A sync operation is already running.'));
+    }
+    return done.then((result) => checkResult ?? failed(result.error ?? 'Connection check failed.'));
+  }
+
+  function cancelRun(): boolean {
+    if (!currentRun) return false;
+    currentRun.handle.cancel();
+    return true;
+  }
+
+  async function shutdown(): Promise<void> {
+    const run = currentRun;
+    if (!run) return;
+    run.handle.cancel();
+    await (run.completion ?? run.handle.done.then(() => undefined));
+  }
+
+  function runState(): SyncUiRunState {
+    return currentRun
+      ? { running: true, runId: currentRun.id, kind: currentRun.kind, host: currentRun.host }
+      : { running: false, runId: null, kind: null, host: null };
+  }
+
+  return {
+    startRun,
+    checkHost,
+    cancelRun,
+    shutdown,
+    runState,
+    isRunning: () => currentRun !== null,
+  };
+}

src/main/runtime/sync-ui-runtime.ts

@@ -1,28 +1,15 @@
-import fs from 'node:fs';
-import path from 'node:path';
 import { IPC_CHANNELS } from '../../shared/ipc/contracts';
 import {
   isValidSyncHost,
-  readSyncHostsState,
-  removeSyncHost,
   upsertSyncHost,
-  writeSyncHostsState,
   type SyncDirection,
-  type SyncHostsState,
 } from '../../shared/sync/sync-hosts-store';
-import type { SyncProgressEvent } from '../../shared/sync/sync-events';
-import type {
-  SyncUiCheckResult,
-  SyncUiHostUpdateRequest,
-  SyncUiRunKind,
-  SyncUiRunRequest,
-  SyncUiRunState,
-  SyncUiSnapshot,
-  SyncUiSnapshotFile,
-  SyncUiStartResult,
-} from '../../types/sync-ui';
-import type { SyncLauncherRunHandle, SyncLauncherRunResult } from './sync-launcher-client';
+import type { SyncUiRunRequest, SyncUiSnapshot } from '../../types/sync-ui';
+import { createSyncUiHostsState } from './sync-ui-hosts-state';
+import { registerSyncUiIpcHandlers } from './sync-ui-ipc-handlers';
+import { createSyncUiRunLifecycle } from './sync-ui-run-lifecycle';
 import { runSyncLauncher } from './sync-launcher-client';
+import { createSyncUiSnapshots } from './sync-ui-snapshots';
 
 interface SyncUiWindowLike {
   isDestroyed(): boolean;
@@ -46,27 +33,7 @@ export interface SyncUiRuntimeDeps {
   notify?: (payload: { title: string; body: string; variant: 'success' | 'error' }) => void;
 }
 
-interface ActiveRun {
-  id: number;
-  kind: SyncUiRunKind;
-  host: string | null;
-  handle: SyncLauncherRunHandle;
-  resultSeen: boolean;
-  completion?: Promise<void>;
-}
-
-// Milliseconds are part of the stamp so two snapshots taken in the same second
-// do not land on the same path and silently overwrite each other.
-function formatSnapshotName(nowMs: number): string {
-  const iso = new Date(nowMs).toISOString();
-  const stamp = iso.slice(0, 23).replace(/[-:.]/g, '').replace('T', '-');
-  return `immersion-${stamp}.sqlite`;
-}
-
 export function createSyncUiRuntime(deps: SyncUiRuntimeDeps) {
-  let runCounter = 0;
-  let currentRun: ActiveRun | null = null;
-
   function sendToWindow(channel: string, payload?: unknown): void {
     const window = deps.getWindow();
     if (!window || window.isDestroyed()) return;
@@ -77,146 +44,35 @@ export function createSyncUiRuntime(deps: SyncUiRuntimeDeps) {
     sendToWindow(IPC_CHANNELS.event.syncUiStateChanged);
   }
 
-  function readState(): SyncHostsState {
-    return readSyncHostsState(deps.hostsFilePath);
-  }
-
-  function writeState(state: SyncHostsState): void {
-    writeSyncHostsState(deps.hostsFilePath, state);
-    broadcastStateChanged();
-  }
-
-  function listSnapshots(): SyncUiSnapshotFile[] {
-    let names: string[];
-    try {
-      names = fs.readdirSync(deps.snapshotsDir);
-    } catch {
-      return [];
-    }
-    const files: SyncUiSnapshotFile[] = [];
-    for (const name of names) {
-      if (!name.endsWith('.sqlite')) continue;
-      const filePath = path.join(deps.snapshotsDir, name);
-      try {
-        const stat = fs.statSync(filePath);
-        if (!stat.isFile()) continue;
-        files.push({
-          path: filePath,
-          name,
-          sizeBytes: stat.size,
-          modifiedAtMs: stat.mtimeMs,
-        });
-      } catch {
-        // file disappeared between readdir and stat
-      }
-    }
-    files.sort((a, b) => b.modifiedAtMs - a.modifiedAtMs);
-    return files;
-  }
-
-  function runState(): SyncUiRunState {
-    return currentRun
-      ? { running: true, runId: currentRun.id, kind: currentRun.kind, host: currentRun.host }
-      : { running: false, runId: null, kind: null, host: null };
-  }
+  const hostsState = createSyncUiHostsState({
+    hostsFilePath: deps.hostsFilePath,
+    broadcastStateChanged,
+  });
+  const runLifecycle = createSyncUiRunLifecycle({
+    runLauncher: deps.runLauncher,
+    resolveLauncherCommand: deps.resolveLauncherCommand,
+    log: deps.log,
+    notify: deps.notify,
+    sendToWindow,
+    broadcastStateChanged,
+  });
+  const snapshots = createSyncUiSnapshots({
+    snapshotsDir: deps.snapshotsDir,
+    nowMs: deps.nowMs,
+    startRun: runLifecycle.startRun,
+    broadcastStateChanged,
+  });
 
   function getSnapshot(): SyncUiSnapshot {
     return {
       dbPath: deps.getDbPath(),
-      hosts: readState(),
+      hosts: hostsState.readState(),
       snapshotsDir: deps.snapshotsDir,
-      snapshots: listSnapshots(),
-      run: runState(),
+      snapshots: snapshots.listSnapshots(),
+      run: runLifecycle.runState(),
     };
   }
 
-  // Shared run lifecycle: single-run mutex, launcher spawn, cleanup + state
-  // broadcast on completion. `emitProgress: false` runs silently (no renderer
-  // progress events); `onEvent` taps every NDJSON event either way.
-  function launchRun(
-    kind: SyncUiRunKind,
-    host: string | null,
-    args: string[],
-    options: {
-      notify?: boolean;
-      timeoutMs?: number;
-      emitProgress?: boolean;
-      onEvent?: (event: SyncProgressEvent) => void;
-    } = {},
-  ): { start: SyncUiStartResult; done: Promise<SyncLauncherRunResult> | null } {
-    if (currentRun) {
-      return {
-        start: { started: false, runId: null, reason: 'A sync operation is already running.' },
-        done: null,
-      };
-    }
-    const emitProgress = options.emitProgress ?? true;
-    runCounter += 1;
-    const runId = runCounter;
-    const run: ActiveRun = {
-      id: runId,
-      kind,
-      host,
-      resultSeen: false,
-      handle: deps.runLauncher({
-        command: deps.resolveLauncherCommand(),
-        args,
-        timeoutMs: options.timeoutMs,
-        onEvent: (event: SyncProgressEvent) => {
-          if (event.type === 'result') run.resultSeen = true;
-          options.onEvent?.(event);
-          if (emitProgress) {
-            sendToWindow(IPC_CHANNELS.event.syncUiProgress, { runId, kind, host, event });
-          }
-        },
-        onStderr: (text) => deps.log?.(`[sync-ui] ${text.trimEnd()}`),
-      }),
-    };
-    currentRun = run;
-    run.completion = run.handle.done
-      .then((result: SyncLauncherRunResult) => {
-        if (currentRun?.id === runId) currentRun = null;
-        // If the launcher died without emitting a result event (spawn failure,
-        // kill), synthesize one so the renderer can settle its progress view.
-        if (emitProgress && !run.resultSeen) {
-          sendToWindow(IPC_CHANNELS.event.syncUiProgress, {
-            runId,
-            kind,
-            host,
-            event: { type: 'result', ok: result.ok, error: result.error },
-          });
-        }
-        broadcastStateChanged();
-        if (options.notify && deps.notify) {
-          const target = host ?? 'local database';
-          deps.notify(
-            result.ok
-              ? { title: 'Sync complete', body: `Synced with ${target}`, variant: 'success' }
-              : {
-                  title: 'Sync failed',
-                  body: `${target}: ${result.error ?? 'unknown error'}`,
-                  variant: 'error',
-                },
-          );
-        }
-      })
-      .catch((error) => {
-        deps.log?.(
-          `[sync-ui] Post-run cleanup failed: ${error instanceof Error ? error.message : String(error)}`,
-        );
-      });
-    return { start: { started: true, runId, reason: null }, done: run.handle.done };
-  }
-
-  function startRun(
-    kind: SyncUiRunKind,
-    host: string | null,
-    args: string[],
-    options: { notify?: boolean } = {},
-  ): SyncUiStartResult {
-    return launchRun(kind, host, args, options).start;
-  }
-
   function runHostSync(request: SyncUiRunRequest, options: { notify?: boolean } = {}) {
     const host = request.host.trim();
     if (!isValidSyncHost(host)) {
@@ -228,132 +84,46 @@ export function createSyncUiRuntime(deps: SyncUiRuntimeDeps) {
     if (direction === 'pull') args.push('--pull');
     if (request.force) args.push('--force');
     args.push('--json');
-    const result = startRun('host-sync', host, args, options);
+    const result = runLifecycle.startRun('host-sync', host, args, options);
     if (result.started) {
-      // Remember the host (and the direction used) before the launcher's own
-      // bookkeeping lands, so it shows up in the UI immediately.
-      writeState(upsertSyncHost(readState(), { host, direction: request.direction }, deps.nowMs()));
+      // Persist before launcher bookkeeping lands so the host appears immediately.
+      hostsState.writeState(
+        upsertSyncHost(
+          hostsState.readState(),
+          { host, direction: request.direction },
+          deps.nowMs(),
+        ),
+      );
     }
     return result;
   }
 
-  function checkHost(host: string): Promise<SyncUiCheckResult> {
-    const trimmed = host.trim();
-    const failed = (error: string): SyncUiCheckResult => ({
-      host: trimmed,
-      sshOk: false,
-      remoteCommand: null,
-      remoteVersion: null,
-      ok: false,
-      error,
-    });
-    if (!isValidSyncHost(trimmed)) {
-      return Promise.resolve(failed(`Invalid sync host: ${host}`));
-    }
-    let checkResult: SyncUiCheckResult | null = null;
-    const { start, done } = launchRun('check', trimmed, ['sync', trimmed, '--check', '--json'], {
-      timeoutMs: 30_000,
-      emitProgress: false,
-      onEvent: (event) => {
-        if (event.type === 'check-result') {
-          checkResult = {
-            host: event.host,
-            sshOk: event.sshOk,
-            remoteCommand: event.remoteCommand,
-            remoteVersion: event.remoteVersion,
-            ok: event.ok,
-            error: event.error,
-          };
-        }
-      },
-    });
-    if (!start.started || !done) {
-      return Promise.resolve(failed(start.reason ?? 'A sync operation is already running.'));
-    }
-    return done.then((result) => checkResult ?? failed(result.error ?? 'Connection check failed.'));
-  }
-
-  function createSnapshot(): SyncUiStartResult {
-    const outPath = path.join(deps.snapshotsDir, formatSnapshotName(deps.nowMs()));
-    return startRun('snapshot', null, ['sync', '--snapshot', outPath, '--json']);
-  }
-
-  function mergeSnapshotFile(filePath: string, force = false): SyncUiStartResult {
-    if (!fs.existsSync(filePath)) {
-      return { started: false, runId: null, reason: `Snapshot file not found: ${filePath}` };
-    }
-    const args = ['sync', '--merge', filePath];
-    if (force) args.push('--force');
-    args.push('--json');
-    return startRun('merge', null, args);
-  }
-
-  function deleteSnapshot(filePath: string): void {
-    const resolved = path.resolve(filePath);
-    const dir = path.resolve(deps.snapshotsDir);
-    if (resolved !== path.join(dir, path.basename(resolved)) || !resolved.endsWith('.sqlite')) {
-      throw new Error('Refusing to delete a file outside the snapshots directory.');
-    }
-    fs.rmSync(resolved, { force: true });
-    broadcastStateChanged();
-  }
-
-  function cancelRun(): boolean {
-    if (!currentRun) return false;
-    currentRun.handle.cancel();
-    return true;
-  }
-
-  async function shutdown(): Promise<void> {
-    const run = currentRun;
-    if (!run) return;
-    run.handle.cancel();
-    await (run.completion ?? run.handle.done.then(() => undefined));
-  }
-
   function registerHandlers(): void {
-    const channels = IPC_CHANNELS.request;
-    deps.ipcMain.handle(channels.syncUiGetSnapshot, () => getSnapshot());
-    deps.ipcMain.handle(channels.syncUiSaveHost, (_event, update) => {
-      writeState(upsertSyncHost(readState(), update as SyncUiHostUpdateRequest, deps.nowMs()));
+    registerSyncUiIpcHandlers({
+      ipcMain: deps.ipcMain,
+      nowMs: deps.nowMs,
+      revealPath: deps.revealPath,
+      pickSnapshotFile: deps.pickSnapshotFile,
+      getSnapshot,
+      readState: hostsState.readState,
+      writeState: hostsState.writeState,
+      runHostSync,
+      cancelRun: runLifecycle.cancelRun,
+      checkHost: runLifecycle.checkHost,
+      createSnapshot: snapshots.createSnapshot,
+      mergeSnapshotFile: snapshots.mergeSnapshotFile,
+      deleteSnapshot: snapshots.deleteSnapshot,
     });
-    deps.ipcMain.handle(channels.syncUiRemoveHost, (_event, host) => {
-      writeState(removeSyncHost(readState(), String(host)));
-    });
-    deps.ipcMain.handle(channels.syncUiSetAutoSyncInterval, (_event, minutes) => {
-      const value = Number(minutes);
-      if (!Number.isFinite(value) || value < 1 || value > 24 * 60) {
-        throw new Error('Auto-sync interval must be between 1 and 1440 minutes.');
-      }
-      writeState({ ...readState(), autoSyncIntervalMinutes: Math.floor(value) });
-    });
-    deps.ipcMain.handle(channels.syncUiRunSync, (_event, request) =>
-      runHostSync(request as SyncUiRunRequest),
-    );
-    deps.ipcMain.handle(channels.syncUiCancelRun, () => cancelRun());
-    deps.ipcMain.handle(channels.syncUiCheckHost, (_event, host) => checkHost(String(host)));
-    deps.ipcMain.handle(channels.syncUiCreateSnapshot, () => createSnapshot());
-    deps.ipcMain.handle(channels.syncUiMergeSnapshotFile, (_event, filePath, force) =>
-      mergeSnapshotFile(String(filePath), force === true),
-    );
-    deps.ipcMain.handle(channels.syncUiDeleteSnapshot, (_event, filePath) => {
-      deleteSnapshot(String(filePath));
-    });
-    deps.ipcMain.handle(channels.syncUiRevealSnapshot, (_event, filePath) => {
-      deps.revealPath(String(filePath));
-      return true;
-    });
-    deps.ipcMain.handle(channels.syncUiPickSnapshotFile, () => deps.pickSnapshotFile());
   }
 
   return {
     registerHandlers,
     getSnapshot,
-    readState,
+    readState: hostsState.readState,
     runHostSync,
-    checkHost,
-    cancelRun,
-    shutdown,
-    isRunning: () => currentRun !== null,
+    checkHost: runLifecycle.checkHost,
+    cancelRun: runLifecycle.cancelRun,
+    shutdown: runLifecycle.shutdown,
+    isRunning: runLifecycle.isRunning,
   };
 }

src/main/runtime/sync-ui-snapshots.ts

@@ -0,0 +1,74 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import type { SyncUiSnapshotFile, SyncUiStartResult } from '../../types/sync-ui';
+
+interface SyncUiSnapshotsDeps {
+  snapshotsDir: string;
+  nowMs: () => number;
+  startRun: (kind: 'snapshot' | 'merge', host: null, args: string[]) => SyncUiStartResult;
+  broadcastStateChanged: () => void;
+}
+
+function formatSnapshotName(nowMs: number): string {
+  // Milliseconds prevent snapshots taken in the same second from overwriting each other.
+  const iso = new Date(nowMs).toISOString();
+  const stamp = iso.slice(0, 23).replace(/[-:.]/g, '').replace('T', '-');
+  return `immersion-${stamp}.sqlite`;
+}
+
+export function createSyncUiSnapshots(deps: SyncUiSnapshotsDeps) {
+  function listSnapshots(): SyncUiSnapshotFile[] {
+    let names: string[];
+    try {
+      names = fs.readdirSync(deps.snapshotsDir);
+    } catch {
+      return [];
+    }
+    const files: SyncUiSnapshotFile[] = [];
+    for (const name of names) {
+      if (!name.endsWith('.sqlite')) continue;
+      const filePath = path.join(deps.snapshotsDir, name);
+      try {
+        const stat = fs.statSync(filePath);
+        if (!stat.isFile()) continue;
+        files.push({
+          path: filePath,
+          name,
+          sizeBytes: stat.size,
+          modifiedAtMs: stat.mtimeMs,
+        });
+      } catch {
+        // file disappeared between readdir and stat
+      }
+    }
+    files.sort((a, b) => b.modifiedAtMs - a.modifiedAtMs);
+    return files;
+  }
+
+  function createSnapshot(): SyncUiStartResult {
+    const outPath = path.join(deps.snapshotsDir, formatSnapshotName(deps.nowMs()));
+    return deps.startRun('snapshot', null, ['sync', '--snapshot', outPath, '--json']);
+  }
+
+  function mergeSnapshotFile(filePath: string, force = false): SyncUiStartResult {
+    if (!fs.existsSync(filePath)) {
+      return { started: false, runId: null, reason: `Snapshot file not found: ${filePath}` };
+    }
+    const args = ['sync', '--merge', filePath];
+    if (force) args.push('--force');
+    args.push('--json');
+    return deps.startRun('merge', null, args);
+  }
+
+  function deleteSnapshot(filePath: string): void {
+    const resolved = path.resolve(filePath);
+    const dir = path.resolve(deps.snapshotsDir);
+    if (resolved !== path.join(dir, path.basename(resolved)) || !resolved.endsWith('.sqlite')) {
+      throw new Error('Refusing to delete a file outside the snapshots directory.');
+    }
+    fs.rmSync(resolved, { force: true });
+    deps.broadcastStateChanged();
+  }
+
+  return { listSnapshots, createSnapshot, mergeSnapshotFile, deleteSnapshot };
+}