diff --git a/src/serviceModules/FileSystemAdapters/ObsidianStorageAdapter.ts b/src/serviceModules/FileSystemAdapters/ObsidianStorageAdapter.ts
index a9133018..508b64a9 100644
--- a/src/serviceModules/FileSystemAdapters/ObsidianStorageAdapter.ts
+++ b/src/serviceModules/FileSystemAdapters/ObsidianStorageAdapter.ts
@@ -2,6 +2,7 @@ import type { UXDataWriteOptions } from "@lib/common/types";
 import type { IStorageAdapter } from "@lib/serviceModules/adapters";
 import { toArrayBuffer } from "@lib/serviceModules/FileAccessBase";
 import type { Stat, App } from "obsidian";
+import { toIntegerTimestamps } from "./sanitizeWriteOptions";
 
 /**
  * Storage adapter implementation for Obsidian
@@ -40,15 +41,15 @@ export class ObsidianStorageAdapter implements IStorageAdapter<Stat> {
     }
 
     async write(path: string, data: string, options?: UXDataWriteOptions): Promise<void> {
-        return await this.app.vault.adapter.write(path, data, options);
+        return await this.app.vault.adapter.write(path, data, toIntegerTimestamps(options));
     }
 
     async writeBinary(path: string, data: ArrayBuffer, options?: UXDataWriteOptions): Promise<void> {
-        return await this.app.vault.adapter.writeBinary(path, toArrayBuffer(data), options);
+        return await this.app.vault.adapter.writeBinary(path, toArrayBuffer(data), toIntegerTimestamps(options));
     }
 
     async append(path: string, data: string, options?: UXDataWriteOptions): Promise<void> {
-        return await this.app.vault.adapter.append(path, data, options);
+        return await this.app.vault.adapter.append(path, data, toIntegerTimestamps(options));
     }
 
     list(basePath: string): Promise<{ files: string[]; folders: string[] }> {
diff --git a/src/serviceModules/FileSystemAdapters/ObsidianVaultAdapter.ts b/src/serviceModules/FileSystemAdapters/ObsidianVaultAdapter.ts
index 42ab566c..6a5c021b 100644
--- a/src/serviceModules/FileSystemAdapters/ObsidianVaultAdapter.ts
+++ b/src/serviceModules/FileSystemAdapters/ObsidianVaultAdapter.ts
@@ -2,6 +2,7 @@ import type { UXDataWriteOptions } from "@lib/common/types";
 import type { IVaultAdapter } from "@lib/serviceModules/adapters";
 import { toArrayBuffer } from "@lib/serviceModules/FileAccessBase";
 import type { TFile, App, TFolder } from "obsidian";
+import { toIntegerTimestamps } from "./sanitizeWriteOptions";
 
 /**
  * Vault adapter implementation for Obsidian
@@ -22,19 +23,19 @@ export class ObsidianVaultAdapter implements IVaultAdapter<TFile, TFolder> {
     }
 
     async modify(file: TFile, data: string, options?: UXDataWriteOptions): Promise<void> {
-        return await this.app.vault.modify(file, data, options);
+        return await this.app.vault.modify(file, data, toIntegerTimestamps(options));
     }
 
     async modifyBinary(file: TFile, data: ArrayBuffer, options?: UXDataWriteOptions): Promise<void> {
-        return await this.app.vault.modifyBinary(file, toArrayBuffer(data), options);
+        return await this.app.vault.modifyBinary(file, toArrayBuffer(data), toIntegerTimestamps(options));
     }
 
     async create(path: string, data: string, options?: UXDataWriteOptions): Promise<TFile> {
-        return await this.app.vault.create(path, data, options);
+        return await this.app.vault.create(path, data, toIntegerTimestamps(options));
     }
 
     async createBinary(path: string, data: ArrayBuffer, options?: UXDataWriteOptions): Promise<TFile> {
-        return await this.app.vault.createBinary(path, toArrayBuffer(data), options);
+        return await this.app.vault.createBinary(path, toArrayBuffer(data), toIntegerTimestamps(options));
     }
 
     async delete(file: TFile | TFolder, force = false): Promise<void> {
diff --git a/src/serviceModules/FileSystemAdapters/sanitizeWriteOptions.ts b/src/serviceModules/FileSystemAdapters/sanitizeWriteOptions.ts
new file mode 100644
index 00000000..4cb92355
--- /dev/null
+++ b/src/serviceModules/FileSystemAdapters/sanitizeWriteOptions.ts
@@ -0,0 +1,25 @@
+import type { UXDataWriteOptions } from "@lib/common/types";
+
+/**
+ * Coerce the timestamp fields of a write-options object to integer milliseconds.
+ *
+ * On mobile, Obsidian forwards `mtime`/`ctime` to Capacitor's
+ * Filesystem.setTimes, whose native binding casts the value to a Java `Long`.
+ * A non-integer (float) timestamp makes that cast throw
+ * `ClassCastException: Double cannot be cast to Long`, which crashes the app on
+ * launch as soon as such a document is replicated in. Float timestamps can
+ * enter the database from any client that stores `fs.Stats.mtimeMs` without
+ * flooring. Flooring at the storage boundary guarantees every Obsidian write
+ * carries an integer, so a float timestamp already present in the mesh cannot
+ * brick the app.
+ *
+ * Returns a shallow copy so the caller's options object is not mutated; passes
+ * `undefined` through unchanged.
+ */
+export function toIntegerTimestamps(options?: UXDataWriteOptions): UXDataWriteOptions | undefined {
+    if (!options) return options;
+    const sanitized: UXDataWriteOptions = { ...options };
+    if (typeof sanitized.mtime === "number") sanitized.mtime = Math.floor(sanitized.mtime);
+    if (typeof sanitized.ctime === "number") sanitized.ctime = Math.floor(sanitized.ctime);
+    return sanitized;
+}