diff --git a/plugins/file-manager/src/backend/content-routes.ts b/plugins/file-manager/src/backend/content-routes.ts
index 52627730f..f8a285bf2 100644
--- a/plugins/file-manager/src/backend/content-routes.ts
+++ b/plugins/file-manager/src/backend/content-routes.ts
@@ -31,6 +31,21 @@ const parseByteOffset = (value: string | undefined): number | null => {
   return parsed;
 };
 
+/**
+ * The editor sends text. Binary callers say so with encoding "base64";
+ * guessing breaks text that happens to be valid base64.
+ */
+export function decodeWriteContent(
+  content: unknown,
+  encoding?: unknown,
+): Buffer {
+  if (Buffer.isBuffer(content)) return content;
+  if (typeof content === "string") {
+    return Buffer.from(content, encoding === "base64" ? "base64" : "utf8");
+  }
+  return Buffer.from(content as ArrayLike<number>);
+}
+
 export function registerFileContentRoutes(
   app: Express,
   { ctx, sshSessions, verifySessionOwnership }: FileContentRoutesDeps,
@@ -435,16 +450,22 @@ export function registerFileContentRoutes(
    *                 type: string
    *               content:
    *                 type: string
+   *               encoding:
+   *                 type: string
+   *                 enum: [utf8, base64]
+   *                 description: How content is encoded. Defaults to utf8.
    *     responses:
    *       200:
    *         description: File written successfully.
+   *       403:
+   *         description: Permission denied; needsSudo is set when a sudo password would help.
    *       400:
    *         description: Missing required parameters or SSH connection not established.
    *       500:
    *         description: Failed to write file.
    */
   app.post("/writeFile", async (req, res) => {
-    const { sessionId, path: filePath, content } = req.body;
+    const { sessionId, path: filePath, content, encoding } = req.body;
     const sshConn = sshSessions[sessionId];
     const userId = ctx.currentActor()!;
 
@@ -558,24 +579,9 @@ export function registerFileContentRoutes(
         );
         getSessionSftp(sshConn)
           .then((sftp) => {
-            let fileBuffer;
+            let fileBuffer: Buffer;
             try {
-              if (typeof content === "string") {
-                try {
-                  const testBuffer = Buffer.from(content, "base64");
-                  if (testBuffer.toString("base64") === content) {
-                    fileBuffer = testBuffer;
-                  } else {
-                    fileBuffer = Buffer.from(content, "utf8");
-                  }
-                } catch {
-                  fileBuffer = Buffer.from(content, "utf8");
-                }
-              } else if (Buffer.isBuffer(content)) {
-                fileBuffer = content;
-              } else {
-                fileBuffer = Buffer.from(content);
-              }
+              fileBuffer = decodeWriteContent(content, encoding);
             } catch (bufferErr) {
               ctx.log.error("Buffer conversion error:", bufferErr as Error);
               if (!res.headersSent) {
@@ -685,25 +691,12 @@ export function registerFileContentRoutes(
         return;
       }
       try {
-        let contentBuffer: Buffer;
-        if (typeof content === "string") {
-          try {
-            contentBuffer = Buffer.from(content, "base64");
-            if (contentBuffer.toString("base64") !== content) {
-              contentBuffer = Buffer.from(content, "utf8");
-            }
-          } catch {
-            contentBuffer = Buffer.from(content, "utf8");
-          }
-        } else if (Buffer.isBuffer(content)) {
-          contentBuffer = content;
-        } else {
-          contentBuffer = Buffer.from(content);
-        }
+        const contentBuffer = decodeWriteContent(content, encoding);
         const base64Content = contentBuffer.toString("base64");
         const escapedPath = filePath.replace(/'/g, "'\"'\"'");
 
-        const writeCommand = `echo '${base64Content}' | base64 -d > '${escapedPath}' && echo "SUCCESS"`;
+        // Content goes through stdin; a command line argument caps it at 128 KB.
+        const writeCommand = `cat > '${escapedPath}' && echo "SUCCESS"`;
 
         execChannel(sshConn, writeCommand, (err, stream) => {
           if (err) {
@@ -735,6 +728,8 @@ export function registerFileContentRoutes(
             ctx.log.error("Fallback write stderr error:", stderrErr);
           });
 
+          stream.end(contentBuffer);
+
           stream.on("close", (code) => {
             if (outputData.includes("SUCCESS")) {
               restoreOriginalMode(null, () => {
@@ -788,7 +783,7 @@ export function registerFileContentRoutes(
                 `Fallback write failed with code ${code}: ${errorData}`,
               );
               if (!res.headersSent) {
-                res.status(500).json({
+                res.status(isPermDenied ? 403 : 500).json({
                   error: `Write failed: ${errorData}`,
                   needsSudo: isPermDenied,
                   toast: {
diff --git a/plugins/file-manager/src/frontend/components/FileWindow.tsx b/plugins/file-manager/src/frontend/components/FileWindow.tsx
index 4946a276c..2761e509b 100644
--- a/plugins/file-manager/src/frontend/components/FileWindow.tsx
+++ b/plugins/file-manager/src/frontend/components/FileWindow.tsx
@@ -9,7 +9,9 @@ import {
   writeSSHFile,
   getSSHStatus,
   connectSSH,
+  setSudoPassword,
 } from "../api/ssh-file-operations-api";
+import { SudoPasswordDialog } from "../SudoPasswordDialog.tsx";
 import { toast } from "sonner";
 import { DownloadProgressToast } from "./DownloadProgressToast";
 import type { SSHHost } from "../host-types";
@@ -298,6 +300,21 @@ export function FileWindow({
     loadFileContent();
   };
 
+  const [sudoSaveContent, setSudoSaveContent] = useState<string | null>(null);
+
+  const handleSudoSave = async (password: string) => {
+    const pending = sudoSaveContent;
+    setSudoSaveContent(null);
+    if (pending === null) return;
+    try {
+      await setSudoPassword(sshSessionId, password);
+    } catch {
+      toast.error(t("fileManager.sudoAuthFailed"));
+      return;
+    }
+    await handleSave(pending);
+  };
+
   const handleSave = async (newContent: string) => {
     try {
       setIsSaving(true);
@@ -317,13 +334,22 @@ export function FileWindow({
     } catch (error: unknown) {
       console.error("Failed to save file:", error);
 
-      const err = error as { message?: string };
-      if (
+      const err = error as {
+        message?: string;
+        response?: { data?: { needsSudo?: boolean } };
+      };
+      if (err.response?.data?.needsSudo) {
+        setSudoSaveContent(newContent);
+      } else if (
         err.message?.includes("connection") ||
         err.message?.includes("established")
       ) {
         toast.error(
-          `SSH connection failed. Please check your connection to ${sshHost.name} (${sshHost.ip}:${sshHost.port})`,
+          t("fileManager.sshConnectionFailed", {
+            name: sshHost.name,
+            ip: sshHost.ip,
+            port: sshHost.port,
+          }),
         );
       } else {
         toast.error(
@@ -563,6 +589,13 @@ export function FileWindow({
         }
         onMediaDimensionsChange={handleMediaDimensionsChange}
       />
+      <SudoPasswordDialog
+        open={sudoSaveContent !== null}
+        onOpenChange={(open) => {
+          if (!open) setSudoSaveContent(null);
+        }}
+        onSubmit={(password) => void handleSudoSave(password)}
+      />
     </DraggableWindow>
   );
 }
diff --git a/plugins/file-manager/tests/backend/write-content.test.ts b/plugins/file-manager/tests/backend/write-content.test.ts
new file mode 100644
index 000000000..bfa03ac31
--- /dev/null
+++ b/plugins/file-manager/tests/backend/write-content.test.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from "vitest";
+import { decodeWriteContent } from "../../src/backend/content-routes.js";
+
+describe("decodeWriteContent", () => {
+  it("keeps text that happens to be valid base64", () => {
+    expect(decodeWriteContent("test").toString("utf8")).toBe("test");
+    expect(decodeWriteContent("abcd1234").toString("utf8")).toBe("abcd1234");
+  });
+
+  it("decodes base64 only when asked", () => {
+    const encoded = Buffer.from("local x = 1\n").toString("base64");
+    expect(decodeWriteContent(encoded, "base64").toString("utf8")).toBe(
+      "local x = 1\n",
+    );
+  });
+
+  it("passes buffers through", () => {
+    const buffer = Buffer.from([0, 1, 2]);
+    expect(decodeWriteContent(buffer)).toBe(buffer);
+  });
+});