Merge pull request #583 from binaricat/feat/show-transport-error-in-disconnect-dialog

feat: show transport error in disconnect dialog

components/Terminal.tsx

@@ -44,6 +44,8 @@ import { TerminalToolbar } from "./terminal/TerminalToolbar";
 import { TerminalComposeBar } from "./terminal/TerminalComposeBar";
 import { TerminalContextMenu } from "./terminal/TerminalContextMenu";
 import { TerminalSearchBar } from "./terminal/TerminalSearchBar";
+import { ZmodemProgressIndicator } from "./terminal/ZmodemProgressIndicator";
+import { useZmodemTransfer } from "./terminal/hooks/useZmodemTransfer";
 import { createTerminalSessionStarters, type PendingAuth } from "./terminal/runtime/createTerminalSessionStarters";
 import { createXTermRuntime, type XTermRuntime } from "./terminal/runtime/createXTermRuntime";
 import { XTERM_PERFORMANCE_CONFIG } from "../infrastructure/config/xtermPerformance";
@@ -500,6 +502,27 @@ const TerminalComponent: React.FC<TerminalProps> = ({
     isVisible,
   });
 
+  const zmodem = useZmodemTransfer(sessionId);
+
+  const zmodemToastedRef = useRef(false);
+  useEffect(() => {
+    if (zmodem.active) {
+      zmodemToastedRef.current = false;
+      return;
+    }
+    if (zmodemToastedRef.current) return;
+    if (zmodem.error) {
+      zmodemToastedRef.current = true;
+      toast.error(zmodem.error, 'ZMODEM');
+    } else if (zmodem.filename) {
+      zmodemToastedRef.current = true;
+      toast.success(
+        `${zmodem.transferType === 'upload' ? 'Uploaded' : 'Downloaded'}: ${zmodem.filename}`,
+        'ZMODEM',
+      );
+    }
+  }, [zmodem.active, zmodem.error, zmodem.filename, zmodem.transferType]);
+
   useEffect(() => {
     if (!error) {
       lastToastedErrorRef.current = null;
@@ -2048,6 +2071,22 @@ const TerminalComponent: React.FC<TerminalProps> = ({
                 }}
               />
             )}
+
+          {/* ZMODEM transfer progress indicator */}
+          {zmodem.active && (
+            <div className="absolute bottom-4 right-4 z-[25] pointer-events-auto">
+              <ZmodemProgressIndicator
+                transferType={zmodem.transferType}
+                filename={zmodem.filename}
+                transferred={zmodem.transferred}
+                total={zmodem.total}
+                fileIndex={zmodem.fileIndex}
+                fileCount={zmodem.fileCount}
+                finalizing={zmodem.finalizing}
+                onCancel={zmodem.cancel}
+              />
+            </div>
+          )}
         </div>
 
         {/* Compose Bar (solo sessions only; workspace uses TerminalLayer's global bar) */}

components/terminal/ZmodemProgressIndicator.tsx

@@ -0,0 +1,79 @@
+import { ArrowDownToLine, ArrowUpFromLine, X } from 'lucide-react';
+import React from 'react';
+
+interface ZmodemProgressIndicatorProps {
+  transferType: 'upload' | 'download' | null;
+  filename: string | null;
+  transferred: number;
+  total: number;
+  fileIndex: number;
+  fileCount: number;
+  finalizing: boolean;
+  onCancel: () => void;
+}
+
+function formatBytes(bytes: number): string {
+  if (bytes <= 0) return '0 B';
+  const k = 1024;
+  const sizes = ['B', 'KB', 'MB', 'GB', 'TB'];
+  const i = Math.min(Math.floor(Math.log(bytes) / Math.log(k)), sizes.length - 1);
+  return `${(bytes / Math.pow(k, i)).toFixed(1)} ${sizes[i]}`;
+}
+
+export const ZmodemProgressIndicator: React.FC<ZmodemProgressIndicatorProps> = ({
+  transferType,
+  filename,
+  transferred,
+  total,
+  fileIndex,
+  fileCount,
+  finalizing,
+  onCancel,
+}) => {
+  const percent = total > 0 ? Math.min(100, Math.round((transferred / total) * 100)) : 0;
+  const Icon = transferType === 'upload' ? ArrowUpFromLine : ArrowDownToLine;
+  const label = finalizing ? 'Waiting for remote...' : transferType === 'upload' ? 'Uploading' : 'Downloading';
+  const fileInfo = fileCount > 0 ? ` (${fileIndex + 1}/${fileCount})` : '';
+
+  return (
+    <div
+      className="flex items-center gap-2.5 px-3 py-2 rounded-lg shadow-lg backdrop-blur-sm min-w-[240px] max-w-[360px]"
+      style={{
+        backgroundColor: 'color-mix(in srgb, var(--terminal-ui-bg, #000000) 90%, transparent)',
+        border: '1px solid color-mix(in srgb, var(--terminal-ui-fg, #ffffff) 15%, var(--terminal-ui-bg, #000000))',
+        color: 'var(--terminal-ui-fg, #ffffff)',
+      }}
+      onClick={(e) => e.stopPropagation()}
+      onMouseDown={(e) => e.stopPropagation()}
+    >
+      <Icon className="h-4 w-4 flex-shrink-0 opacity-60" />
+      <div className="flex-1 min-w-0">
+        <div className="flex items-center justify-between gap-2 mb-1">
+          <span className="text-xs font-medium truncate">
+            {filename || label}{fileInfo}
+          </span>
+          <span className="text-[10px] opacity-60 flex-shrink-0">{percent}%</span>
+        </div>
+        <div className="w-full h-1 rounded-full overflow-hidden" style={{ backgroundColor: 'color-mix(in srgb, var(--terminal-ui-fg, #ffffff) 10%, transparent)' }}>
+          <div
+            className="h-full rounded-full transition-all duration-150"
+            style={{
+              width: `${percent}%`,
+              backgroundColor: transferType === 'upload' ? '#3b82f6' : '#22c55e',
+            }}
+          />
+        </div>
+        <div className="text-[10px] opacity-50 mt-0.5">
+          {formatBytes(transferred)} / {formatBytes(total)}
+        </div>
+      </div>
+      <button
+        onClick={onCancel}
+        className="flex-shrink-0 p-1 rounded transition-colors hover:bg-white/10"
+        title="Cancel transfer (Ctrl+C)"
+      >
+        <X className="h-3.5 w-3.5 opacity-60" />
+      </button>
+    </div>
+  );
+};

components/terminal/hooks/useZmodemTransfer.ts

@@ -0,0 +1,102 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import { netcattyBridge } from '../../../infrastructure/services/netcattyBridge';
+
+export interface ZmodemTransferState {
+  active: boolean;
+  transferType: 'upload' | 'download' | null;
+  filename: string | null;
+  transferred: number;
+  total: number;
+  fileIndex: number;
+  fileCount: number;
+  finalizing: boolean;
+  error: string | null;
+}
+
+const initialState: ZmodemTransferState = {
+  active: false,
+  transferType: null,
+  filename: null,
+  transferred: 0,
+  total: 0,
+  fileIndex: 0,
+  fileCount: 0,
+  finalizing: false,
+  error: null,
+};
+
+export function useZmodemTransfer(sessionId: string | null) {
+  const [state, setState] = useState<ZmodemTransferState>(initialState);
+  const disposeRef = useRef<(() => void) | null>(null);
+
+  const disposeExitRef = useRef<(() => void) | null>(null);
+
+  useEffect(() => {
+    if (!sessionId) return;
+
+    const bridge = netcattyBridge.get();
+    if (!bridge?.onZmodemEvent) return;
+
+    disposeRef.current = bridge.onZmodemEvent(sessionId, (event) => {
+      switch (event.type) {
+        case 'detect':
+          setState({
+            active: true,
+            transferType: event.transferType ?? null,
+            filename: null,
+            transferred: 0,
+            total: 0,
+            fileIndex: 0,
+            fileCount: 0,
+            error: null,
+          });
+          break;
+        case 'progress':
+          setState((prev) => ({
+            ...prev,
+            active: true,
+            transferType: event.transferType ?? prev.transferType,
+            filename: event.filename ?? prev.filename,
+            transferred: event.transferred ?? prev.transferred,
+            total: event.total ?? prev.total,
+            fileIndex: event.fileIndex ?? prev.fileIndex,
+            fileCount: event.fileCount ?? prev.fileCount,
+            finalizing: !!((event as Record<string, unknown>).finalizing),
+          }));
+          break;
+        case 'complete':
+          setState((prev) => ({ ...prev, active: false }));
+          break;
+        case 'error':
+          setState((prev) => ({
+            ...prev,
+            active: false,
+            error: event.error ?? 'Unknown error',
+          }));
+          break;
+      }
+    });
+
+    // If the session exits mid-transfer (disconnect, shell exit, etc.),
+    // reset state so the progress indicator doesn't stay stuck.
+    disposeExitRef.current = bridge.onSessionExit(sessionId, () => {
+      setState(initialState);
+    });
+
+    return () => {
+      disposeRef.current?.();
+      disposeRef.current = null;
+      disposeExitRef.current?.();
+      disposeExitRef.current = null;
+      setState(initialState);
+    };
+  }, [sessionId]);
+
+  const cancel = useCallback(() => {
+    if (!sessionId) return;
+    const bridge = netcattyBridge.get();
+    bridge?.cancelZmodem?.(sessionId);
+  }, [sessionId]);
+
+  return { ...state, cancel };
+}

components/terminal/runtime/createTerminalSessionStarters.ts

@@ -172,7 +172,7 @@ const attachSessionToTerminal = (
   term: XTerm,
   id: string,
   opts?: {
-    onExitMessage?: (evt: { exitCode?: number; signal?: number }) => string;
+    onExitMessage?: (evt: { exitCode?: number; signal?: number; error?: string; reason?: string }) => string;
     onConnected?: () => void;
     // For serial: convert lone LF to CRLF to avoid "staircase effect"
     convertLfToCrlf?: boolean;
@@ -209,6 +209,9 @@ const attachSessionToTerminal = (
 
   ctx.disposeExitRef.current = ctx.terminalBackend.onSessionExit(id, (evt) => {
     ctx.updateStatus("disconnected");
+    if (evt.error) {
+      ctx.setError(evt.error);
+    }
     term.writeln(opts?.onExitMessage?.(evt) ?? "\r\n[session closed]");
 
     if (ctx.onTerminalDataCapture && ctx.serializeAddonRef.current) {

electron/bridges/ai/shellUtils.cjs

@@ -7,7 +7,7 @@
 "use strict";
 
 const { execFileSync } = require("node:child_process");
-const { existsSync } = require("node:fs");
+const { existsSync, statSync } = require("node:fs");
 const path = require("node:path");
 
 // ── ANSI / URL regexes ──
@@ -93,7 +93,11 @@ function normalizeCliPathForPlatform(filePath) {
   if (!normalized) return null;
 
   if (process.platform !== "win32") {
-    return existsSync(normalized) ? normalized : null;
+    // Reject directories (e.g. /Applications/Codex.app) — must be a file
+    try {
+      if (existsSync(normalized) && statSync(normalized).isFile()) return normalized;
+    } catch { /* stat failed */ }
+    return null;
   }
 
   const ext = path.extname(normalized).toLowerCase();

electron/bridges/aiBridge.cjs

@@ -1453,9 +1453,12 @@ function registerHandlers(ipcMain) {
         const result = await runCommand(probeCmd, probeArgs, { env: shellEnv });
         version = (result.stdout || result.stderr || "").trim().split("\n")[0];
       } catch {
-        version = "";
+        // --version failed: not a valid CLI executable (e.g. .app bundle)
+        continue;
       }
 
+      if (!version) continue;
+
       const { resolveAcp: _unused, ...agentInfo } = agent;
       agents.push({
         ...agentInfo,
@@ -1494,7 +1497,12 @@ function registerHandlers(ipcMain) {
       const result = await runCommand(resolvedPath, ["--version"], { env: shellEnv });
       version = (result.stdout || result.stderr || "").trim().split("\n")[0];
     } catch {
-      version = "";
+      // --version failed: not a valid CLI executable
+      return { path: resolvedPath, version: null, available: false };
+    }
+
+    if (!version) {
+      return { path: resolvedPath, version: null, available: false };
     }
 
     return { path: resolvedPath, version, available: true };

electron/bridges/sshBridge.cjs

@@ -24,6 +24,7 @@ const {
 } = require("./sshAuthHelper.cjs");
 const sessionLogStreamManager = require("./sessionLogStreamManager.cjs");
 const { trackSessionIdlePrompt } = require("./ai/shellUtils.cjs");
+const { createZmodemSentry } = require("./zmodemHelper.cjs");
 
 // Default SSH key names in priority order (preferred keys tried first)
 const PREFERRED_KEY_NAMES = ["id_ed25519", "id_ecdsa", "id_rsa"];
@@ -410,9 +411,9 @@ async function connectThroughChain(event, options, jumpHosts, targetHost, target
         username: jump.username || 'root',
         readyTimeout: 120000, // 2 minutes to allow for keyboard-interactive (2FA/MFA)
         // Use user-configured keepalive interval from options (in seconds -> convert to ms)
-        // If 0 or not provided, use 10000ms as default
-        keepaliveInterval: options.keepaliveInterval && options.keepaliveInterval > 0 ? options.keepaliveInterval * 1000 : 10000,
-        keepaliveCountMax: 3,
+        // 0 = disabled (no keepalive packets sent)
+        keepaliveInterval: options.keepaliveInterval > 0 ? options.keepaliveInterval * 1000 : 0,
+        keepaliveCountMax: options.keepaliveInterval > 0 ? 3 : 0,
         // Enable keyboard-interactive authentication (required for 2FA/MFA)
         tryKeyboard: true,
         algorithms: buildAlgorithms(options.legacyAlgorithms),
@@ -680,9 +681,9 @@ async function startSSHSession(event, options) {
       // `readyTimeout` covers the entire connection + authentication flow in ssh2.
       readyTimeout: 20000, // Fast failure for non-interactive auth
       // Use user-configured keepalive interval (in seconds -> convert to ms)
-      // If 0 or not provided, use 10000ms as default
-      keepaliveInterval: options.keepaliveInterval && options.keepaliveInterval > 0 ? options.keepaliveInterval * 1000 : 10000,
-      keepaliveCountMax: 3,
+      // 0 = disabled (no keepalive packets sent)
+      keepaliveInterval: options.keepaliveInterval > 0 ? options.keepaliveInterval * 1000 : 0,
+      keepaliveCountMax: options.keepaliveInterval > 0 ? 3 : 0,
       // Enable keyboard-interactive authentication (required for 2FA/MFA)
       tryKeyboard: true,
       algorithms: buildAlgorithms(options.legacyAlgorithms),
@@ -1246,15 +1247,36 @@ async function startSSHSession(event, options) {
               }
             };
 
+            const sshZmodemSentry = createZmodemSentry({
+              sessionId,
+              onData(buf) {
+                const decoder = getSessionDecoder(sessionId, "stdout");
+                const decoded = decoder.write(buf);
+                trackSessionIdlePrompt(session, decoded);
+                bufferData(decoded);
+                sessionLogStreamManager.appendData(sessionId, decoded);
+              },
+              writeToRemote(buf) {
+                try { return stream.write(buf); } catch { return true; /* ignore */ }
+              },
+              interruptRemote() {
+                try { stream.signal?.("INT"); } catch { /* ignore */ }
+              },
+              getWebContents() {
+                return event.sender;
+              },
+              label: "SSH",
+            });
+            session.zmodemSentry = sshZmodemSentry;
+
             stream.on("data", (data) => {
-              const decoder = getSessionDecoder(sessionId, "stdout");
-              const decoded = decoder.write(data);
-              trackSessionIdlePrompt(session, decoded);
-              bufferData(decoded);
-              sessionLogStreamManager.appendData(sessionId, decoded);
+              // data is Buffer from ssh2 — feed raw bytes to ZMODEM sentry.
+              // In normal mode, sentry's onData callback handles decoding and buffering.
+              sshZmodemSentry.consume(data);
             });
 
             stream.stderr?.on("data", (data) => {
+              // stderr is not used for ZMODEM — decode normally
               const decoder = getSessionDecoder(sessionId, "stderr");
               const decoded = decoder.write(data);
               bufferData(decoded);
@@ -1294,6 +1316,7 @@ async function startSSHSession(event, options) {
                 } else {
                   safeSend(contents, "netcatty:exit", { sessionId, exitCode: streamExitCode, reason: streamExited ? "exited" : "closed" });
                 }
+                sessions.get(sessionId)?.zmodemSentry?.cancel();
                 sessions.delete(sessionId);
                 sessionEncodings.delete(sessionId);
                 sessionDecoders.delete(sessionId);
@@ -1362,6 +1385,7 @@ async function startSSHSession(event, options) {
         sendProgress(totalHops, totalHops, options.hostname, 'error', err.message);
         safeSend(contents, "netcatty:exit", { sessionId, exitCode: 1, error: err.message, reason: "error" });
         sessionLogStreamManager.stopStream(sessionId);
+        sessions.get(sessionId)?.zmodemSentry?.cancel();
         sessions.delete(sessionId);
         sessionEncodings.delete(sessionId);
         sessionDecoders.delete(sessionId);
@@ -1382,6 +1406,7 @@ async function startSSHSession(event, options) {
         sendProgress(totalHops, totalHops, options.hostname, 'error', err.message);
         safeSend(contents, "netcatty:exit", { sessionId, exitCode: 1, error: err.message, reason: "timeout" });
         sessionLogStreamManager.stopStream(sessionId);
+        sessions.get(sessionId)?.zmodemSentry?.cancel();
         sessions.delete(sessionId);
         sessionEncodings.delete(sessionId);
         sessionDecoders.delete(sessionId);
@@ -1412,6 +1437,7 @@ async function startSSHSession(event, options) {
           }
         }
         sessionLogStreamManager.stopStream(sessionId);
+        sessions.get(sessionId)?.zmodemSentry?.cancel();
         sessions.delete(sessionId);
         sessionEncodings.delete(sessionId);
         sessionDecoders.delete(sessionId);

electron/bridges/terminalBridge.cjs

@@ -14,6 +14,7 @@ const { SerialPort } = require("serialport");
 const sessionLogStreamManager = require("./sessionLogStreamManager.cjs");
 const { detectShellKind } = require("./ai/ptyExec.cjs");
 const { trackSessionIdlePrompt } = require("./ai/shellUtils.cjs");
+const { createZmodemSentry } = require("./zmodemHelper.cjs");
 
 // Shared references
 let sessions = null;
@@ -286,6 +287,7 @@ function startLocalSession(event, payload) {
     rows: payload?.rows || 24,
     env,
     cwd,
+    encoding: null, // Return Buffer for ZMODEM binary support
   });
   
   const session = {
@@ -329,11 +331,40 @@ function startLocalSession(event, payload) {
   });
   session.flushPendingData = flushLocal;
 
-  proc.onData((data) => {
-    trackSessionIdlePrompt(session, data);
-    bufferLocalData(data);
-    sessionLogStreamManager.appendData(sessionId, data);
-  });
+  // On Windows, node-pty ignores encoding: null and still emits UTF-8
+  // strings, making raw-byte ZMODEM impossible for local PTY sessions.
+  // Only wire up the sentry on platforms where encoding: null works.
+  if (process.platform !== "win32") {
+    const localDecoder = new StringDecoder("utf8");
+    const zmodemSentry = createZmodemSentry({
+      sessionId,
+      onData(buf) {
+        const str = localDecoder.write(buf);
+        if (!str) return;
+        trackSessionIdlePrompt(session, str);
+        bufferLocalData(str);
+        sessionLogStreamManager.appendData(sessionId, str);
+      },
+      writeToRemote(buf) {
+        try { return proc.write(buf); } catch { return true; }
+      },
+      getWebContents() {
+        return electronModule.webContents.fromId(session.webContentsId);
+      },
+      label: "Local",
+    });
+    session.zmodemSentry = zmodemSentry;
+
+    proc.onData((data) => {
+      zmodemSentry.consume(data);
+    });
+  } else {
+    proc.onData((data) => {
+      trackSessionIdlePrompt(session, data);
+      bufferLocalData(data);
+      sessionLogStreamManager.appendData(sessionId, data);
+    });
+  }
 
   proc.onExit((evt) => {
     flushLocal();
@@ -535,19 +566,57 @@ async function startTelnetSession(event, options) {
       contents?.send("netcatty:data", { sessionId, data });
     });
 
+    const telnetZmodemSentry = createZmodemSentry({
+      sessionId,
+      onData(buf) {
+        const decoded = telnetDecoder.write(buf);
+        if (!decoded) return;
+        const session = sessions.get(sessionId);
+        if (session) trackSessionIdlePrompt(session, decoded);
+        bufferTelnetData(decoded);
+        sessionLogStreamManager.appendData(sessionId, decoded);
+      },
+      writeToRemote(buf) {
+        // Escape 0xFF bytes as 0xFF 0xFF per Telnet spec so binary
+        // ZMODEM data passes through without being treated as IAC.
+        try {
+          let hasFF = false;
+          for (let i = 0; i < buf.length; i++) {
+            if (buf[i] === 0xff) { hasFF = true; break; }
+          }
+          if (hasFF) {
+            const escaped = [];
+            for (let i = 0; i < buf.length; i++) {
+              escaped.push(buf[i]);
+              if (buf[i] === 0xff) escaped.push(0xff);
+            }
+            return socket.write(Buffer.from(escaped));
+          } else {
+            return socket.write(buf);
+          }
+        } catch { return true; }
+      },
+      getWebContents() {
+        return electronModule.webContents.fromId(telnetWebContentsId);
+      },
+      label: "Telnet",
+    });
+    // Attach sentry to session once created (connect callback runs after this)
+    const attachTelnetSentry = () => {
+      const session = sessions.get(sessionId);
+      if (session) session.zmodemSentry = telnetZmodemSentry;
+    };
+    socket.once('connect', attachTelnetSentry);
+
     socket.on('data', (data) => {
       const session = sessions.get(sessionId);
       if (!session) return;
 
+      // Always run Telnet negotiation — even during ZMODEM, the Telnet
+      // layer still escapes 0xFF as IAC IAC and sends control sequences.
       const cleanData = handleTelnetNegotiation(data);
-
       if (cleanData.length > 0) {
-        const decoded = telnetDecoder.write(cleanData);
-        if (decoded) {
-          trackSessionIdlePrompt(session, decoded);
-          bufferTelnetData(decoded);
-          sessionLogStreamManager.appendData(sessionId, decoded);
-        }
+        telnetZmodemSentry.consume(cleanData);
       }
     });
 
@@ -562,6 +631,7 @@ async function startTelnetSession(event, options) {
         sessionLogStreamManager.stopStream(sessionId);
         const session = sessions.get(sessionId);
         if (session) {
+          session.zmodemSentry?.cancel();
           const contents = electronModule.webContents.fromId(session.webContentsId);
           contents?.send("netcatty:exit", { sessionId, exitCode: 1, error: err.message, reason: "error" });
         }
@@ -577,6 +647,7 @@ async function startTelnetSession(event, options) {
       sessionLogStreamManager.stopStream(sessionId);
       const session = sessions.get(sessionId);
       if (session) {
+        session.zmodemSentry?.cancel();
         const contents = electronModule.webContents.fromId(session.webContentsId);
         contents?.send("netcatty:exit", { sessionId, exitCode: hadError ? 1 : 0, reason: hadError ? "error" : "closed" });
       }
@@ -645,6 +716,7 @@ async function startMoshSession(event, options) {
       rows,
       env,
       cwd: os.homedir(),
+      encoding: null, // Return Buffer for ZMODEM binary support
     });
 
     const session = {
@@ -682,11 +754,37 @@ async function startMoshSession(event, options) {
     });
     session.flushPendingData = flushMosh;
 
-    proc.onData((data) => {
-      trackSessionIdlePrompt(session, data);
-      bufferMoshData(data);
-      sessionLogStreamManager.appendData(sessionId, data);
-    });
+    if (process.platform !== "win32") {
+      const moshDecoder = new StringDecoder("utf8");
+      const moshZmodemSentry = createZmodemSentry({
+        sessionId,
+        onData(buf) {
+          const str = moshDecoder.write(buf);
+          if (!str) return;
+          trackSessionIdlePrompt(session, str);
+          bufferMoshData(str);
+          sessionLogStreamManager.appendData(sessionId, str);
+        },
+        writeToRemote(buf) {
+          try { return proc.write(buf); } catch { return true; }
+        },
+        getWebContents() {
+          return electronModule.webContents.fromId(session.webContentsId);
+        },
+        label: "Mosh",
+      });
+      session.zmodemSentry = moshZmodemSentry;
+
+      proc.onData((data) => {
+        moshZmodemSentry.consume(data);
+      });
+    } else {
+      proc.onData((data) => {
+        trackSessionIdlePrompt(session, data);
+        bufferMoshData(data);
+        sessionLogStreamManager.appendData(sessionId, data);
+      });
+    }
 
     proc.onExit((evt) => {
       flushMosh();
@@ -790,17 +888,33 @@ async function startSerialSession(event, options) {
           });
         }
 
-        serialPort.on('data', (data) => {
-          const decoded = serialDecoder.write(data);
-          if (decoded) {
+        const serialZmodemSentry = createZmodemSentry({
+          sessionId,
+          onData(buf) {
+            const decoded = serialDecoder.write(buf);
+            if (!decoded) return;
             const contents = electronModule.webContents.fromId(session.webContentsId);
             contents?.send("netcatty:data", { sessionId, data: decoded });
             sessionLogStreamManager.appendData(sessionId, decoded);
-          }
+          },
+          writeToRemote(buf) {
+            try { return serialPort.write(buf); } catch { return true; }
+          },
+          getWebContents() {
+            return electronModule.webContents.fromId(session.webContentsId);
+          },
+          label: "Serial",
+        });
+        session.zmodemSentry = serialZmodemSentry;
+
+        serialPort.on('data', (data) => {
+          // data is already Buffer from serialport — feed to sentry
+          serialZmodemSentry.consume(data);
         });
 
         serialPort.on('error', (err) => {
           console.error(`[Serial] Port error: ${err.message}`);
+          session.zmodemSentry?.cancel();
           sessionLogStreamManager.stopStream(sessionId);
           const contents = electronModule.webContents.fromId(session.webContentsId);
           contents?.send("netcatty:exit", { sessionId, exitCode: 1, error: err.message, reason: "error" });
@@ -809,6 +923,7 @@ async function startSerialSession(event, options) {
 
         serialPort.on('close', () => {
           console.log(`[Serial] Port closed`);
+          session.zmodemSentry?.cancel();
           sessionLogStreamManager.stopStream(sessionId);
           const contents = electronModule.webContents.fromId(session.webContentsId);
           contents?.send("netcatty:exit", { sessionId, exitCode: 0, reason: "closed" });
@@ -830,7 +945,15 @@ async function startSerialSession(event, options) {
 function writeToSession(event, payload) {
   const session = sessions.get(payload.sessionId);
   if (!session) return;
-  
+
+  // During ZMODEM transfer, block terminal input (Ctrl+C cancels the transfer)
+  if (session.zmodemSentry?.isActive()) {
+    if (payload.data === '\x03') {
+      session.zmodemSentry.cancel();
+    }
+    return;
+  }
+
   try {
     if (session.stream) {
       session.stream.write(payload.data);
@@ -887,6 +1010,7 @@ function closeSession(event, payload) {
   if (!session) return;
   
   try {
+    session.zmodemSentry?.cancel();
     session.flushPendingData?.();
     if (session.stream) {
       session.stream.close();
@@ -999,6 +1123,7 @@ function cleanupAllSessions() {
   console.log(`[Terminal] Cleaning up ${sessions.size} sessions before quit`);
   for (const [sessionId, session] of sessions) {
     try {
+      session.zmodemSentry?.cancel();
       if (session.stream) {
         session.stream.close();
         session.conn?.end();

electron/bridges/zmodemHelper.cjs

@@ -0,0 +1,794 @@
+/**
+ * ZMODEM Helper - Provides ZMODEM file transfer support for terminal sessions.
+ *
+ * Architecture: ZMODEM detection and transfer runs entirely in the main process.
+ * The Sentry wraps the raw data stream and routes data either to the normal
+ * string-based terminal pipeline (via `to_terminal`) or to the ZMODEM protocol
+ * handler.  This avoids any changes to the IPC / preload / renderer data path.
+ *
+ * The renderer is only notified for progress display via lightweight IPC events.
+ */
+
+const Zmodem = require("zmodem.js");
+const fs = require("node:fs");
+const path = require("node:path");
+
+// Lazy-load electron to avoid issues when requiring from non-electron contexts
+let _electron = null;
+function getElectron() {
+  if (!_electron) _electron = require("electron");
+  return _electron;
+}
+
+/**
+ * Create a ZMODEM sentry that wraps a session's data stream.
+ *
+ * All raw data from the PTY / SSH stream / socket should be fed into
+ * `consume()`.  The sentry transparently calls `onData(str)` for normal
+ * terminal output and handles ZMODEM transfers internally.
+ *
+ * @param {object} opts
+ * @param {string} opts.sessionId
+ * @param {(data: Buffer) => void} opts.onData
+ *   Called with raw bytes during normal (non-ZMODEM) operation.
+ *   The caller is responsible for charset-aware decoding (UTF-8, iconv, etc.).
+ * @param {(buf: Buffer) => void} opts.writeToRemote
+ *   Write raw bytes back to the remote side (PTY / SSH stream / socket).
+ * @param {() => import('electron').WebContents | null} opts.getWebContents
+ *   Returns the Electron WebContents for sending progress IPC events.
+ * @param {string} [opts.label]
+ *   Human-readable label for log messages (e.g. "Local", "SSH").
+ * @returns {ZmodemSentryWrapper}
+ */
+function createZmodemSentry(opts) {
+  const {
+    sessionId,
+    onData,
+    writeToRemote,
+    getWebContents,
+    interruptRemote,
+    label = "Session",
+  } = opts;
+
+  let active = false;
+  let currentZSession = null;
+  let _needsDrain = false;
+  const pendingEchoes = [];
+  let pendingTerminalSuppression = null;
+  let cancelInterruptTimer = null;
+  let ignoreDetectionUntil = 0;
+  // After aborting, suppress incoming data briefly so residual ZMODEM
+  // protocol bytes from the remote don't flood the terminal as garbage.
+  let cooldownUntil = 0;
+  const COOLDOWN_MS = 2000;
+  const ECHO_TTL_MS = 1500;
+  const ECHO_MAX_BYTES = 256;
+
+  function prunePendingEchoes(now = Date.now()) {
+    while (pendingEchoes.length && pendingEchoes[0].expiresAt <= now) {
+      pendingEchoes.shift();
+    }
+  }
+
+  function rememberOutgoingEcho(octets) {
+    const buf = Buffer.from(octets);
+    if (!buf.length || buf.length > ECHO_MAX_BYTES) return;
+    prunePendingEchoes();
+    pendingEchoes.push({
+      buf,
+      expiresAt: Date.now() + ECHO_TTL_MS,
+    });
+  }
+
+  function stripEchoedOutgoingData(data) {
+    if (!pendingEchoes.length) return data;
+
+    prunePendingEchoes();
+
+    let buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    let mutated = false;
+
+    while (pendingEchoes.length && buf.length) {
+      const nextEcho = pendingEchoes[0].buf;
+      if (buf.length < nextEcho.length) break;
+      if (!buf.subarray(0, nextEcho.length).equals(nextEcho)) break;
+
+      mutated = true;
+      buf = buf.subarray(nextEcho.length);
+      pendingEchoes.shift();
+    }
+
+    return mutated ? buf : data;
+  }
+
+  function stripPendingTerminalSuppression(data) {
+    if (!pendingTerminalSuppression?.length) return data;
+
+    let buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    const fullMatchAt = buf.indexOf(pendingTerminalSuppression);
+    if (fullMatchAt !== -1) {
+      buf = Buffer.concat([
+        buf.subarray(0, fullMatchAt),
+        buf.subarray(fullMatchAt + pendingTerminalSuppression.length),
+      ]);
+      pendingTerminalSuppression = null;
+      return buf;
+    }
+
+    const maxMatch = Math.min(pendingTerminalSuppression.length, buf.length);
+    let matchLen = 0;
+    while (matchLen < maxMatch && buf[matchLen] === pendingTerminalSuppression[matchLen]) {
+      matchLen += 1;
+    }
+
+    if (!matchLen) return buf;
+
+    buf = buf.subarray(matchLen);
+    pendingTerminalSuppression = matchLen === pendingTerminalSuppression.length
+      ? null
+      : pendingTerminalSuppression.subarray(matchLen);
+
+    return buf;
+  }
+
+  function stripVisibleZmodemHeaders(data) {
+    let buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    let searchFrom = 0;
+
+    while (searchFrom < buf.length) {
+      const prefixAt = buf.indexOf(Buffer.from([0x2a, 0x2a, 0x18, 0x42]), searchFrom);
+      if (prefixAt === -1) break;
+
+      const minHeaderLength = 20;
+      if (buf.length - prefixAt < minHeaderLength) break;
+
+      let isHexHeader = true;
+      for (let i = 0; i < 14; i += 1) {
+        const byte = buf[prefixAt + 4 + i];
+        const isHexDigit =
+          (byte >= 0x30 && byte <= 0x39) ||
+          (byte >= 0x41 && byte <= 0x46) ||
+          (byte >= 0x61 && byte <= 0x66);
+        if (!isHexDigit) {
+          isHexHeader = false;
+          break;
+        }
+      }
+
+      if (!isHexHeader) {
+        searchFrom = prefixAt + 1;
+        continue;
+      }
+
+      let headerLength = 18;
+      if (buf[prefixAt + 18] === 0x0d && buf[prefixAt + 19] === 0x0a) {
+        headerLength = 20;
+        if (buf[prefixAt + 20] === 0x11) {
+          headerLength = 21;
+        }
+      }
+
+      buf = Buffer.concat([
+        buf.subarray(0, prefixAt),
+        buf.subarray(prefixAt + headerLength),
+      ]);
+      searchFrom = prefixAt;
+    }
+
+    return buf;
+  }
+
+  function looksLikeResidualZmodemData(data) {
+    const buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
+    if (!buf.length) return true;
+
+    for (const byte of buf) {
+      const isResidualControl =
+        byte === 0x18 || // CAN / ZDLE
+        byte === 0x08 || // backspace from abort sequence
+        byte === 0x11 || // XON
+        byte === 0x13 || // XOFF
+        byte === 0x0d ||
+        byte === 0x0a;
+      if (isResidualControl) continue;
+      return false;
+    }
+
+    return true;
+  }
+
+  function sendExtraAbortBytes() {
+    try {
+      writeToRemote(Buffer.from([0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18]));
+    } catch {
+      /* ignore */
+    }
+  }
+
+  function scheduleRemoteInterruptAfterCancel(transferRole) {
+    if (cancelInterruptTimer) {
+      clearTimeout(cancelInterruptTimer);
+      cancelInterruptTimer = null;
+    }
+
+    if (transferRole !== "send") return;
+    ignoreDetectionUntil = Date.now() + 300;
+
+    try { interruptRemote?.(); } catch { /* ignore */ }
+
+    // Some rz builds (notably Debian's lrzsz) can stay attached to the tty
+    // after a protocol cancel. Follow up with Ctrl+C so the remote shell
+    // reliably regains control. If rz is already gone, this just refreshes
+    // the prompt like a normal interactive interrupt.
+    cancelInterruptTimer = setTimeout(() => {
+      cancelInterruptTimer = null;
+      try { interruptRemote?.(); } catch { /* ignore */ }
+      try { writeToRemote(Buffer.from("\x03")); } catch { /* ignore */ }
+    }, 120);
+  }
+
+  function isIgnorableSendKeepaliveError(errMsg) {
+    return Boolean(
+      active &&
+      currentZSession?.type === "send" &&
+      !currentZSession?._sending_file &&
+      errMsg.includes("Unhandled header: ZRINIT")
+    );
+  }
+
+  function isIgnorableSendResumePingError(errMsg) {
+    return Boolean(
+      active &&
+      currentZSession?.type === "send" &&
+      !currentZSession?._sending_file &&
+      currentZSession?._next_header_handler?.ZRINIT &&
+      errMsg.includes("Unhandled header: ZRPOS")
+    );
+  }
+
+
+  const sentry = new Zmodem.Sentry({
+    to_terminal(octets) {
+      // Normal data – pass raw bytes to the caller for charset-aware decoding.
+      let sanitizedOctets = stripPendingTerminalSuppression(Buffer.from(octets));
+      sanitizedOctets = stripVisibleZmodemHeaders(sanitizedOctets);
+      if (!sanitizedOctets.length) return;
+      onData(sanitizedOctets);
+    },
+
+    sender(octets) {
+      // ZMODEM protocol bytes – send raw to remote.
+      rememberOutgoingEcho(octets);
+      const ok = writeToRemote(Buffer.from(octets));
+      // Track backpressure: if stream.write() returned false, the
+      // kernel TCP buffer is full.  The upload loop should pause.
+      if (ok === false) _needsDrain = true;
+    },
+
+    on_detect(detection) {
+      if (active) {
+        console.warn(`[ZMODEM][${label}] Detection while transfer active; denying`);
+        detection.deny();
+        return;
+      }
+      if (Date.now() < ignoreDetectionUntil) {
+        console.log(`[ZMODEM][${label}] Ignoring stray detection during cancel grace window`);
+        detection.deny();
+        return;
+      }
+      active = true;
+      const zsession = detection.confirm();
+      currentZSession = zsession;
+      pendingTerminalSuppression = zsession.type === "receive"
+        ? Buffer.from(Zmodem.Header.build("ZRQINIT").to_hex())
+        : zsession._last_ZRINIT?.to_hex
+          ? Buffer.from(zsession._last_ZRINIT.to_hex())
+          : null;
+
+      const contents = getWebContents();
+      const transferType = zsession.type === "send" ? "upload" : "download";
+
+      console.log(`[ZMODEM][${label}] Detected ${transferType} for session ${sessionId}`);
+
+      safeSend(contents, "netcatty:zmodem:detect", {
+        sessionId,
+        transferType,
+      });
+
+      // Provide a drain helper so the upload loop can pause when the
+      // underlying transport's write buffer is full.
+      const transferOpts = {
+        ...opts,
+        waitForDrain: () => {
+          if (!_needsDrain) return Promise.resolve();
+          _needsDrain = false;
+          // Yield to the event loop so Node can flush buffered writes to
+          // the kernel.  Using setImmediate (not setTimeout) avoids any
+          // fixed delay — we resume as soon as the I/O phase completes.
+          return new Promise((resolve) => setImmediate(resolve));
+        },
+      };
+      handleTransfer(zsession, transferType, transferOpts)
+        .then(() => {
+          // Only act if this is still the active session (not replaced by a new one)
+          if (currentZSession !== zsession) return;
+          console.log(`[ZMODEM][${label}] Transfer completed for session ${sessionId}`);
+          safeSend(contents, "netcatty:zmodem:complete", { sessionId });
+        })
+        .catch((err) => {
+          if (currentZSession !== zsession) return;
+          console.error(`[ZMODEM][${label}] Transfer error:`, err.message || err);
+          try { zsession.abort(); } catch { /* ignore */ }
+          safeSend(contents, "netcatty:zmodem:error", {
+            sessionId,
+            error: String(err.message || err),
+          });
+        })
+        .finally(() => {
+          // Only clear state if this is still the active session
+          if (currentZSession === zsession) {
+            active = false;
+            currentZSession = null;
+          }
+        });
+    },
+
+    on_retract() {
+      // False positive – sentry automatically resumes passthrough.
+    },
+  });
+
+  return {
+    /**
+     * Feed raw bytes from the session into the sentry.
+     * @param {Buffer|Uint8Array} data
+     */
+    consume(data) {
+      // During cooldown after abort, unconditionally suppress all incoming
+      // data.  sz can stream large amounts of file data that's still in
+      // SSH/TCP buffers after we send CAN; checking content doesn't help
+      // because the residual data contains arbitrary printable bytes.
+      if (cooldownUntil) {
+        const now = Date.now();
+        if (now < cooldownUntil) {
+          // Keep sending CAN in case earlier ones were lost in the flood
+          if (now - (cooldownUntil - COOLDOWN_MS) > 200) {
+            sendExtraAbortBytes();
+          }
+          return; // drop everything during cooldown
+        }
+        cooldownUntil = 0;
+        // After cooldown, let this chunk through — it's likely the shell prompt
+      }
+
+      try {
+        const sanitizedData = stripEchoedOutgoingData(data);
+        if (!sanitizedData.length) return;
+        sentry.consume(sanitizedData);
+      } catch (err) {
+        const errMsg = String(err.message || err);
+        console.error(`[ZMODEM][${label}] Sentry consume error:`, errMsg);
+
+        const wasActive = active;
+
+        // lrzsz's `rz` may resend ZRINIT while we're waiting for the user
+        // to choose files. zmodem.js doesn't model that pre-offer keepalive,
+        // but the repeated header is harmless, so ignore it and keep waiting.
+        if (isIgnorableSendKeepaliveError(errMsg)) {
+          console.log(`[ZMODEM][${label}] Ignoring repeated pre-offer ZRINIT`);
+          return;
+        }
+
+        // Some receivers emit a final ZRPOS ping right before they send the
+        // post-file ZRINIT. If that ping is processed a beat late, zmodem.js
+        // complains even though the transfer can continue normally.
+        if (isIgnorableSendResumePingError(errMsg)) {
+          console.log(`[ZMODEM][${label}] Ignoring late post-file ZRPOS`);
+          return;
+        }
+
+        // ZFIN/OO mismatch: the file transfer completed (ZFIN exchanged)
+        // but the shell prompt arrived before the "OO" end marker.  This
+        // is common over SSH because sz exits and the shell resumes before
+        // the "OO" acknowledgement is sent.  Treat as successful transfer.
+        // Do NOT abort() here — that sends CAN bytes to the remote shell.
+        // Instead, manually clean up the sentry's internal session state.
+        if (wasActive && errMsg.includes("ZFIN") && errMsg.includes("OO")) {
+          console.log(`[ZMODEM][${label}] ZFIN/OO mismatch — treating as success`);
+          if (currentZSession) {
+            try { currentZSession._on_session_end(); } catch { /* ignore */ }
+          }
+          active = false;
+          currentZSession = null;
+          safeSend(getWebContents(), "netcatty:zmodem:complete", { sessionId });
+          try { sentry.consume(data); } catch { /* ignore */ }
+          return;
+        }
+
+        // For all other errors, abort and send extra CAN sequences to
+        // ensure the remote rz/sz process stops transmitting.
+        if (currentZSession) {
+          try { currentZSession.abort(); } catch { /* ignore */ }
+        }
+        sendExtraAbortBytes();
+        // Follow up with Ctrl+C after a short delay to kill rz/sz on
+        // Debian and other systems where it stays attached after CAN.
+        setTimeout(() => {
+          try { writeToRemote(Buffer.from("\x03")); } catch { /* ignore */ }
+        }, 150);
+
+        active = false;
+        currentZSession = null;
+        // Enter cooldown: discard incoming data briefly while the remote
+        // processes our CAN sequence and stops sending ZMODEM frames.
+        cooldownUntil = Date.now() + COOLDOWN_MS;
+
+        if (wasActive) {
+          safeSend(getWebContents(), "netcatty:zmodem:error", {
+            sessionId,
+            error: errMsg,
+          });
+        }
+      }
+    },
+
+    /** Whether a ZMODEM transfer is currently in progress. */
+    isActive() {
+      return active;
+    },
+
+    /** Cancel the current ZMODEM transfer. */
+    cancel() {
+      if (currentZSession) {
+        const transferRole = currentZSession.type;
+        console.log(`[ZMODEM][${label}] Cancelling transfer for session ${sessionId}`);
+        try { currentZSession.abort(); } catch { /* ignore */ }
+        sendExtraAbortBytes();
+        active = false;
+        currentZSession = null;
+        cooldownUntil = Date.now() + COOLDOWN_MS;
+        scheduleRemoteInterruptAfterCancel(transferRole);
+        safeSend(getWebContents(), "netcatty:zmodem:error", {
+          sessionId,
+          error: "Transfer cancelled",
+        });
+      }
+    },
+  };
+}
+
+// ---------------------------------------------------------------------------
+// Shared helpers (module-level, usable from handleUpload / handleDownload)
+// ---------------------------------------------------------------------------
+
+/**
+ * Race a promise against a timeout.  If the promise doesn't settle within
+ * `ms`, resolve with undefined instead of hanging forever.  This prevents
+ * zmodem.js internal promises (xfer.end, zsession.close) from blocking
+ * indefinitely after cancel/abort.
+ */
+function withTimeout(promise, ms) {
+  let timer;
+  return Promise.race([
+    promise,
+    new Promise((_, reject) => {
+      timer = setTimeout(() => reject(new Error("ZMODEM handshake timeout")), ms);
+    }),
+  ]).finally(() => clearTimeout(timer));
+}
+
+/**
+ * Send CAN bytes + delayed Ctrl-C to kill the remote rz/sz process.
+ * Used from dialog-cancel paths that run outside the sentry closure.
+ */
+function abortRemoteProcess(writeToRemote) {
+  try { writeToRemote(Buffer.from([0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18])); } catch { /* ignore */ }
+  setTimeout(() => {
+    try { writeToRemote(Buffer.from("\x03")); } catch { /* ignore */ }
+  }, 150);
+}
+
+// ---------------------------------------------------------------------------
+// Transfer handlers
+// ---------------------------------------------------------------------------
+
+async function handleTransfer(zsession, transferType, opts) {
+  if (transferType === "upload") {
+    await handleUpload(zsession, opts);
+  } else {
+    await handleDownload(zsession, opts);
+  }
+}
+
+/**
+ * Upload files to the remote (remote executed `rz`).
+ */
+async function handleUpload(zsession, opts) {
+  const { sessionId, getWebContents } = opts;
+  const contents = getWebContents();
+  const { BrowserWindow, dialog } = getElectron();
+  const yieldToIO = () => new Promise((resolve) => setImmediate(resolve));
+
+  const win = contents ? BrowserWindow.fromWebContents(contents) : null;
+  const result = await dialog.showOpenDialog(win || undefined, {
+    properties: ["openFile", "multiSelections"],
+    title: "Select files to upload (ZMODEM)",
+  });
+
+  if (result.canceled || !result.filePaths.length) {
+    try { zsession.abort(); } catch { /* ignore */ }
+    abortRemoteProcess(opts.writeToRemote);
+    throw new Error("Transfer cancelled");
+  }
+
+  const filePaths = result.filePaths;
+  const fileStats = filePaths.map((fp) => fs.statSync(fp));
+
+  for (let i = 0; i < filePaths.length; i++) {
+    const filePath = filePaths[i];
+    const stat = fileStats[i];
+    const name = path.basename(filePath);
+
+    safeSend(contents, "netcatty:zmodem:progress", {
+      sessionId,
+      filename: name,
+      transferred: 0,
+      total: stat.size,
+      fileIndex: i,
+      fileCount: filePaths.length,
+      transferType: "upload",
+    });
+
+    let bytesRemaining = 0;
+    for (let j = i; j < fileStats.length; j++) bytesRemaining += fileStats[j].size;
+
+    const xfer = await zsession.send_offer({
+      name,
+      size: stat.size,
+      mtime: new Date(stat.mtimeMs),
+      files_remaining: filePaths.length - i,
+      bytes_remaining: bytesRemaining,
+    });
+
+    if (!xfer) {
+      // Receiver skipped this file
+      continue;
+    }
+
+    // Read and send in chunks
+    const CHUNK_SIZE = 64 * 1024; // Leave room for inbound ZMODEM control frames
+    const fd = fs.openSync(filePath, "r");
+    const buf = Buffer.alloc(CHUNK_SIZE);
+    let sent = 0;
+
+    try {
+      while (true) {
+        const bytesRead = fs.readSync(fd, buf, 0, CHUNK_SIZE);
+        if (bytesRead === 0) break;
+
+        // zmodem.js send() is synchronous and triggers writeToRemote via
+        // the sentry's sender callback.  Yield after each chunk so the
+        // event loop can flush buffered writes and process inbound control
+        // frames, preventing unbounded memory growth on slow links.
+        xfer.send(new Uint8Array(buf.buffer, buf.byteOffset, bytesRead));
+        sent += bytesRead;
+
+        safeSend(contents, "netcatty:zmodem:progress", {
+          sessionId,
+          filename: name,
+          transferred: sent,
+          total: stat.size,
+          fileIndex: i,
+          fileCount: filePaths.length,
+          transferType: "upload",
+        });
+
+        // Wait for transport to drain if its buffer is full, then yield
+        // so inbound ZMODEM control frames can be processed.
+        if (opts.waitForDrain) await opts.waitForDrain();
+        await yieldToIO();
+      }
+      // All data written to Node.js buffer — but TCP may still be
+      // flushing to the remote.  Show "finalizing" state while we
+      // wait for the remote to acknowledge.
+      safeSend(contents, "netcatty:zmodem:progress", {
+        sessionId,
+        filename: name,
+        transferred: stat.size,
+        total: stat.size,
+        fileIndex: i,
+        fileCount: filePaths.length,
+        transferType: "upload",
+        finalizing: true,
+      });
+      await withTimeout(xfer.end(), 120000);
+    } finally {
+      fs.closeSync(fd);
+    }
+  }
+
+  await withTimeout(zsession.close(), 120000);
+}
+
+/**
+ * Download files from the remote (remote executed `sz <file>`).
+ */
+async function handleDownload(zsession, opts) {
+  const { sessionId, getWebContents } = opts;
+  const contents = getWebContents();
+  const { BrowserWindow, dialog } = getElectron();
+
+  const win = contents ? BrowserWindow.fromWebContents(contents) : null;
+  let fileIndex = 0;
+  const pendingStreams = [];
+  const pendingOffers = [];
+  let lastProgressTime = 0;
+  let downloadDir = null;
+  let rejectSession = () => {};
+
+  const processOffer = (xfer, reject) => {
+    if (!downloadDir) {
+      pendingOffers.push(xfer);
+      return;
+    }
+
+    const detail = xfer.get_details();
+    // Sanitize filename to prevent path traversal attacks
+    const rawName = detail.name || `untitled_${Date.now()}`;
+    const name = path.basename(rawName);
+    const size = detail.size || 0;
+    const savePath = path.join(downloadDir, name);
+    const currentIndex = fileIndex++;
+
+    safeSend(contents, "netcatty:zmodem:progress", {
+      sessionId,
+      filename: name,
+      transferred: 0,
+      total: size,
+      fileIndex: currentIndex,
+      fileCount: -1, // unknown total until session ends
+      transferType: "download",
+    });
+
+    // Avoid overwriting existing files — append (1), (2), etc.
+    let finalPath = savePath;
+    if (fs.existsSync(savePath)) {
+      const ext = path.extname(name);
+      const base = path.basename(name, ext);
+      let n = 1;
+      do {
+        finalPath = path.join(downloadDir, `${base} (${n})${ext}`);
+        n++;
+      } while (fs.existsSync(finalPath));
+    }
+
+    const ws = fs.createWriteStream(finalPath);
+    let received = 0;
+    let writeAborted = false;
+
+    // Track pending write streams (and paths) for cleanup at session end
+    pendingStreams.push({ stream: ws, path: finalPath, completed: false });
+
+    ws.on("error", (err) => {
+      writeAborted = true;
+      console.error(`[ZMODEM] Write stream error for ${name}:`, err.message);
+      ws.destroy();
+      reject(err);
+    });
+
+    xfer.accept({
+      on_input(payload) {
+        if (writeAborted) return;
+        const chunk = Buffer.from(payload);
+        ws.write(chunk);
+        received += chunk.length;
+
+        // Throttle progress IPC to ~10 updates/sec to avoid
+        // overwhelming the renderer on fast links.
+        const now = Date.now();
+        if (now - lastProgressTime >= 100) {
+          lastProgressTime = now;
+          safeSend(contents, "netcatty:zmodem:progress", {
+            sessionId,
+            filename: name,
+            transferred: received,
+            total: size,
+            fileIndex: currentIndex,
+            fileCount: -1,
+            transferType: "download",
+          });
+        }
+      },
+    }).catch((err) => {
+      ws.destroy();
+      reject(err);
+    });
+
+    xfer.on("complete", () => {
+      const entry = pendingStreams.find((e) => e.stream === ws);
+      if (entry) entry.completed = true;
+      ws.end();
+    });
+  };
+
+  const sessionPromise = new Promise((resolve, reject) => {
+    rejectSession = reject;
+    zsession.on("offer", (xfer) => {
+      try {
+        processOffer(xfer, reject);
+      } catch (err) {
+        reject(err);
+      }
+    });
+
+    // Wait for all write streams to finish flushing before resolving.
+    // If a stream never received end() (e.g. transfer was cancelled),
+    // destroy it so the fd is released and finish/close can fire.
+    zsession.on("session_end", async () => {
+      try {
+        await Promise.all(
+          pendingStreams.map((entry) => {
+            const { stream: s, path: filePath, completed } = entry;
+            if (s.writableFinished) {
+              // Delete partial files that never completed
+              if (!completed) {
+                try { fs.unlinkSync(filePath); } catch { /* ignore */ }
+              }
+              return Promise.resolve();
+            }
+            if (!s.writableEnded) s.destroy();
+            return new Promise((r) => {
+              s.on("close", () => {
+                // Clean up partial downloads
+                if (!completed) {
+                  try { fs.unlinkSync(filePath); } catch { /* ignore */ }
+                }
+                r();
+              });
+            });
+          })
+        );
+      } catch { /* ignore — error handler already called reject */ }
+      resolve();
+    });
+  });
+
+  // Start the session BEFORE showing the dialog so lrzsz doesn't
+  // time out waiting for ZRINIT while the user browses for a folder.
+  zsession.start();
+
+  const result = await dialog.showOpenDialog(win || undefined, {
+    properties: ["openDirectory", "createDirectory"],
+    title: "Select download directory (ZMODEM)",
+  });
+
+  if (result.canceled || !result.filePaths.length) {
+    try { zsession.abort(); } catch { /* ignore */ }
+    abortRemoteProcess(opts.writeToRemote);
+    void sessionPromise.catch(() => {});
+    throw new Error("Transfer cancelled");
+  }
+
+  downloadDir = result.filePaths[0];
+  while (pendingOffers.length) {
+    processOffer(pendingOffers.shift(), rejectSession);
+  }
+
+  await sessionPromise;
+}
+
+// ---------------------------------------------------------------------------
+// Utilities
+// ---------------------------------------------------------------------------
+
+function safeSend(contents, channel, data) {
+  try {
+    if (contents && !contents.isDestroyed()) {
+      contents.send(channel, data);
+    }
+  } catch {
+    // WebContents may have been destroyed between the check and the send
+  }
+}
+
+module.exports = { createZmodemSentry };

electron/main.cjs

@@ -505,6 +505,14 @@ const registerBridges = (win) => {
   aiBridge.registerHandlers(ipcMain);
   crashLogBridge.registerHandlers(ipcMain);
 
+  // ZMODEM cancel handler
+  ipcMain.on("netcatty:zmodem:cancel", (_event, payload) => {
+    const session = sessions.get(payload.sessionId);
+    if (session?.zmodemSentry) {
+      session.zmodemSentry.cancel();
+    }
+  });
+
   // Fig autocomplete spec loader — uses dynamic import() since @withfig/autocomplete is ESM
   ipcMain.handle("netcatty:figspec:list", async () => {
     try {

electron/preload.cjs

@@ -8,6 +8,7 @@ const transferCompleteListeners = new Map();
 const transferErrorListeners = new Map();
 const transferCancelledListeners = new Map();
 const chainProgressListeners = new Map();
+const zmodemListeners = new Map();
 const sftpConnectionProgressListeners = new Set();
 const authFailedListeners = new Map();
 const languageChangeListeners = new Set();
@@ -109,6 +110,28 @@ function _deliverToListeners(sessionId, data) {
   });
 }
 
+// ZMODEM file transfer events
+ipcRenderer.on("netcatty:zmodem:detect", (_event, payload) => {
+  const set = zmodemListeners.get(payload.sessionId);
+  if (!set) return;
+  set.forEach((cb) => { try { cb({ type: "detect", ...payload }); } catch {} });
+});
+ipcRenderer.on("netcatty:zmodem:progress", (_event, payload) => {
+  const set = zmodemListeners.get(payload.sessionId);
+  if (!set) return;
+  set.forEach((cb) => { try { cb({ type: "progress", ...payload }); } catch {} });
+});
+ipcRenderer.on("netcatty:zmodem:complete", (_event, payload) => {
+  const set = zmodemListeners.get(payload.sessionId);
+  if (!set) return;
+  set.forEach((cb) => { try { cb({ type: "complete", ...payload }); } catch {} });
+});
+ipcRenderer.on("netcatty:zmodem:error", (_event, payload) => {
+  const set = zmodemListeners.get(payload.sessionId);
+  if (!set) return;
+  set.forEach((cb) => { try { cb({ type: "error", ...payload }); } catch {} });
+});
+
 ipcRenderer.on("netcatty:data", (_event, payload) => {
   const set = dataListeners.get(payload.sessionId);
   if (!set) return;
@@ -153,6 +176,7 @@ ipcRenderer.on("netcatty:exit", (_event, payload) => {
   }
   dataListeners.delete(payload.sessionId);
   exitListeners.delete(payload.sessionId);
+  zmodemListeners.delete(payload.sessionId);
   const pendingTimer = _mcpFlushTimers.get(payload.sessionId);
   if (pendingTimer) {
     clearTimeout(pendingTimer);
@@ -569,6 +593,14 @@ const api = {
   },
   setSessionEncoding: (sessionId, encoding) =>
     ipcRenderer.invoke("netcatty:ssh:setEncoding", { sessionId, encoding }),
+  onZmodemEvent: (sessionId, cb) => {
+    if (!zmodemListeners.has(sessionId)) zmodemListeners.set(sessionId, new Set());
+    zmodemListeners.get(sessionId).add(cb);
+    return () => zmodemListeners.get(sessionId)?.delete(cb);
+  },
+  cancelZmodem: (sessionId) => {
+    ipcRenderer.send("netcatty:zmodem:cancel", { sessionId });
+  },
   onSessionData: (sessionId, cb) => {
     if (!dataListeners.has(sessionId)) dataListeners.set(sessionId, new Set());
     dataListeners.get(sessionId).add(cb);

global.d.ts

@@ -263,6 +263,23 @@ declare global {
     writeToSession(sessionId: string, data: string): void;
     resizeSession(sessionId: string, cols: number, rows: number): void;
     closeSession(sessionId: string): void;
+    // ZMODEM file transfer
+    onZmodemEvent?(
+      sessionId: string,
+      cb: (event: {
+        type: 'detect' | 'progress' | 'complete' | 'error';
+        sessionId: string;
+        transferType?: 'upload' | 'download';
+        filename?: string;
+        transferred?: number;
+        total?: number;
+        fileIndex?: number;
+        fileCount?: number;
+        finalizing?: boolean;
+        error?: string;
+      }) => void
+    ): () => void;
+    cancelZmodem?(sessionId: string): void;
     onSessionData(sessionId: string, cb: (data: string) => void): () => void;
     onSessionExit(
       sessionId: string,

package-lock.json

@@ -57,6 +57,7 @@
         "use-stick-to-bottom": "^1.1.3",
         "uuid": "^13.0.0",
         "webdav": "^5.8.0",
+        "zmodem.js": "^0.1.10",
         "zod": "^4.3.6"
       },
       "devDependencies": {
@@ -8282,6 +8283,18 @@
         "buffer": "^5.1.0"
       }
     },
+    "node_modules/crc-32": {
+      "version": "1.2.2",
+      "resolved": "https://registry.npmjs.org/crc-32/-/crc-32-1.2.2.tgz",
+      "integrity": "sha512-ROmzCKrTnOwybPcJApAA6WBWij23HVfGVNKqqrZpuyZOHqK2CwHSvpGuyt/UNNvaIjEd8X5IFGp4Mh+Ie1IHJQ==",
+      "license": "Apache-2.0",
+      "bin": {
+        "crc32": "bin/crc32.njs"
+      },
+      "engines": {
+        "node": ">=0.8"
+      }
+    },
     "node_modules/cross-dirname": {
       "version": "0.1.0",
       "resolved": "https://registry.npmjs.org/cross-dirname/-/cross-dirname-0.1.0.tgz",
@@ -16276,6 +16289,15 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/zmodem.js": {
+      "version": "0.1.10",
+      "resolved": "https://registry.npmjs.org/zmodem.js/-/zmodem.js-0.1.10.tgz",
+      "integrity": "sha512-Z1DWngunZ/j3BmIzSJpFZVNV73iHkj89rxXX4IciJdU9ga3nZ7rJ5LkfjV/QDsKhc7bazDWTTJCLJ+iRXD82dw==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "crc-32": "^1.1.1"
+      }
+    },
     "node_modules/zod": {
       "version": "4.3.6",
       "resolved": "https://registry.npmjs.org/zod/-/zod-4.3.6.tgz",

package.json

@@ -75,6 +75,7 @@
     "use-stick-to-bottom": "^1.1.3",
     "uuid": "^13.0.0",
     "webdav": "^5.8.0",
+    "zmodem.js": "^0.1.10",
     "zod": "^4.3.6"
   },
   "devDependencies": {