diff --git a/.paul/ISSUES.md b/.paul/ISSUES.md
index 59ef6ec..990ab04 100644
--- a/.paul/ISSUES.md
+++ b/.paul/ISSUES.md
@@ -208,6 +208,26 @@ Enhancements and known issues discovered during execution and codebase analysis.
 
 ---
 
+### ISS-020: Write/Read FTP path asymmetry — `ResolvePath` (Mitsubishi fixed; Siemens/Fagor open)
+
+- **Discovered:** Field test docker FTP, post ISS-018/019 fix (2026-06-02)
+- **Mitsubishi fix applied:** 2026-06-02 — `WriteProgramAsync` now resolves the path identically to `ReadProgramAsync`; `ResolvePath` simplified to single-arg (`path` = identifier or full path, combined with `ProgramDirectory`). Verified against Mitsubishi NC Explorer manual IB-1500904 (`PRG/USER/<Program name>`, no extension, addressed by program name/number). Unit tests updated + roundtrip regression test added. `program.Name` now used for validation only.
+- **Still open (Siemens/Fagor):** same asymmetric pattern, but their `ResolvePath` ties extension handling (`.MPF` / `.nc`) to `name` — needs separate fix + entangled with ISS-013 (Fanuc-parsing coupling in `Program.Invia`). Untested (no field rig yet).
+- **Default ProgramDirectory note:** real Mitsubishi path is `/PRG/USER/`; current config default is `/PRG/`. Adjust per controller (config-level, not code).
+- **Type:** Bug (design) — criticità C2/C3
+- **Description:** `-path` integer is resolved differently for read vs write.
+  - **Read** `ResolvePath("1", null)` → `"1"` has no `/` → `ProgramDirectory + "1"` = `/PRG/1` (correct, file exists).
+  - **Write** `ResolvePath("1", program.Name="O0001")` → `folder="1"` treated as directory → `"1/" + "O0001"` = `1/O0001` (relative dir `1` does not exist → STOR fails with `WebException` surfaced as "Impossibile effettuare la connessione al server remoto").
+  Confirmed against docker FTP: `STOR 1/O0001` → curl exit 9; `STOR /PRG/1` → exit 0; no `1/` dir created (app does not create dirs).
+- **Effect:** INVIO of any valid program fails (`-204`); roundtrip impossible — write target ≠ read target. Was previously masked by ISS-018 (validator blocked all uploads) and ISS-019 (truncated path).
+- **Files:** `Cnc/Mitsubishi/MitsubishiMachine.cs` `ResolvePath`, same pattern in `Cnc/Siemens/SiemensMachine.cs`, `Cnc/Fagor/FagorMachine.cs`
+- **Open design question:** canonical Mitsubishi FTP filename — bare integer (`/PRG/1`, symmetric with read) vs ISO title (`/PRG/O0001`)? Needs real-CNC convention. ResolvePath write branch was designed assuming `path` is a *directory*; CLI passes it as a program *identifier*.
+- **Impact:** High — CLI `Invia` broken for all FTP makers
+- **Effort:** Medium — fix ResolvePath + decide naming convention; verify all 3 makers
+- **Related:** ISS-013 (Fanuc parsing coupling)
+
+---
+
 ## Closed Issues
 
 | ID | Summary | Phase | Commit |
diff --git a/Cnc/Mitsubishi/MitsubishiMachine.cs b/Cnc/Mitsubishi/MitsubishiMachine.cs
index 6c2ab66..ba1fa61 100644
--- a/Cnc/Mitsubishi/MitsubishiMachine.cs
+++ b/Cnc/Mitsubishi/MitsubishiMachine.cs
@@ -70,7 +70,7 @@ namespace NcProgramManager.Cnc.Mitsubishi
             return RunGuardedAsync(() =>
             {
                 EnsureConnected();
-                string ncPath = ResolvePath(path, null);
+                string ncPath = ResolvePath(path);
                 try { return _ftp.DownloadFile(ncPath); }
                 catch (Exception ex)
                 {
@@ -99,7 +99,12 @@ namespace NcProgramManager.Cnc.Mitsubishi
                     _errors.Add(new CncError(0, "Validator", msg));
                     return false;
                 }
-                string ncPath = ResolvePath(path, program.Name);
+                // ISS-020: resolve the write path the same way ReadProgramAsync does.
+                // `path` is the program identifier (e.g. "1" -> /PRG/1) or a full FTP
+                // path, NOT a directory to combine with program.Name. On Mitsubishi the
+                // file in PRG/USER is addressed by its program name/number; program.Name
+                // (the ISO O-number) is used for validation only, not the filename.
+                string ncPath = ResolvePath(path);
                 try { _ftp.UploadFile(ncPath, program.Content); return true; }
                 catch (Exception ex)
                 {
@@ -199,15 +204,16 @@ namespace NcProgramManager.Cnc.Mitsubishi
             }
         }
 
-        /// <summary>Build full FTP path. Mitsubishi programs have no extension.</summary>
-        private string ResolvePath(string folder, string name)
+        /// <summary>
+        /// Build full FTP path. Mitsubishi programs have no extension and are addressed
+        /// by their program name/number under <see cref="MitsubishiConnectionConfig.ProgramDirectory"/>.
+        /// A bare identifier ("1") is combined with the program directory ("/PRG/1");
+        /// an explicit path containing '/' is used as-is. Read and write resolve identically.
+        /// </summary>
+        private string ResolvePath(string path)
         {
-            if (string.IsNullOrEmpty(name))
-                return folder.Contains("/") ? folder : _config.ProgramDirectory + folder;
-
-            string dir = folder ?? _config.ProgramDirectory;
-            if (!dir.EndsWith("/")) dir += "/";
-            return dir + name;
+            if (string.IsNullOrEmpty(path)) return _config.ProgramDirectory;
+            return path.Contains("/") ? path : _config.ProgramDirectory + path;
         }
     }
 }
diff --git a/NcProgramManager.Tests/Unit/MitsubishiMachineTests.cs b/NcProgramManager.Tests/Unit/MitsubishiMachineTests.cs
index 93c1706..839dc3f 100644
--- a/NcProgramManager.Tests/Unit/MitsubishiMachineTests.cs
+++ b/NcProgramManager.Tests/Unit/MitsubishiMachineTests.cs
@@ -96,20 +96,38 @@ namespace NcProgramManager.Tests.Unit
         // WriteProgramAsync
 
         [Test]
-        public void WriteProgramAsync_ValidContent_CallsUploadFileNoExtension()
+        public void WriteProgramAsync_FullPath_CallsUploadFileNoExtension()
         {
+            // ISS-020: write resolves the path identically to read (path = program
+            // identifier / full path, not a directory combined with program.Name).
             _ftpMock.Setup(f => f.Ping()).Returns(true);
             _ftpMock.Setup(f => f.UploadFile("/PRG/O1234", "CONTENT"));
             _machine.ConnectAsync().GetAwaiter().GetResult();
 
             var prog = new CncProgram { Name = "O1234", Content = "CONTENT" };
-            var result = _machine.WriteProgramAsync("/PRG/", prog).GetAwaiter().GetResult();
+            var result = _machine.WriteProgramAsync("/PRG/O1234", prog).GetAwaiter().GetResult();
 
             Assert.That(result.Success, Is.True);
             _ftpMock.Verify(f => f.UploadFile("/PRG/O1234", "CONTENT"), Times.Once);
             _ftpMock.Verify(f => f.UploadFile(It.Is<string>(s => s.EndsWith(".MPF")), It.IsAny<string>()), Times.Never);
         }
 
+        [Test]
+        public void WriteProgramAsync_ShortName_ResolvesWithDirectory_SymmetricWithRead()
+        {
+            // ISS-020 regression: -path "1" must write to ProgramDirectory + "1"
+            // (the same location ReadProgramAsync("1") reads), so roundtrip works.
+            _ftpMock.Setup(f => f.Ping()).Returns(true);
+            _ftpMock.Setup(f => f.UploadFile("/PRG/1", "CONTENT"));
+            _machine.ConnectAsync().GetAwaiter().GetResult();
+
+            var prog = new CncProgram { Name = "O0001", Content = "CONTENT" };
+            var result = _machine.WriteProgramAsync("1", prog).GetAwaiter().GetResult();
+
+            Assert.That(result.Success, Is.True);
+            _ftpMock.Verify(f => f.UploadFile("/PRG/1", "CONTENT"), Times.Once);
+        }
+
         [Test]
         public void WriteProgramAsync_EmptyContent_FailsWithoutCallingUploadFile()
         {