From 95a884bf1e7ed459dfaf628777700a6326cad3e5 Mon Sep 17 00:00:00 2001
From: Karstein Phobic Nyvold Kvistad <karstein.kvistad@maritimerobotics.com>
Date: Sat, 25 Apr 2026 21:04:31 +0200
Subject: [PATCH] fix(launcher): refuse to spawn when a CODESYS.exe is already
 running

The launcher only knew about its own state machine -- so any time a
prior CODESYS.exe was still alive (orphan from a crashed MCP session,
the user's own interactive IDE, or a CODESYS still mid-shutdown),
calling launch() happily spawned a SECOND CODESYS. The two instances
then raced on the project file lock and the loser surfaced the
"project is currently in use by <user> on <host>" modal, which blocks
the IDE thread and freezes every subsequent script call -- the agent
keeps timing out at 60s with no useful diagnostic.

Hit twice in a single session on 2026-04-25 during git_* smoke tests:
the user pointed at the running taskbar twice ("you are opening
shitloads of codesys sessions" / "you keep opening TWO codesyses --
then this message comes up and halts all your progress").

Adds findRunningCodesysPids() -- a tasklist-based scan -- and a
pre-spawn guard at the top of launch() that returns a clear,
action-oriented error listing the offending PIDs and the two
remediations (close the IDE manually, or call shutdown_codesys if the
launcher owns the existing process). No-op on non-Windows.

Doesn't try to adopt the existing process: that would require sharing
its IPC dir + watcher state, which the launcher cannot recover after
the fact. Refusing the spawn is the only safe response.
---
 src/launcher.ts | 59 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

diff --git a/src/launcher.ts b/src/launcher.ts
index 714d1fd..52f7730 100644
--- a/src/launcher.ts
+++ b/src/launcher.ts
@@ -6,7 +6,7 @@
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
-import { spawn, ChildProcess } from 'child_process';
+import { spawn, execSync, ChildProcess } from 'child_process';
 import { v4 as uuidv4 } from 'uuid';
 import { LauncherConfig, LauncherStatus, CodesysState, IpcResult, ScriptExecutor } from './types';
 import { IpcClient, DEFAULT_IPC_CONFIG } from './ipc';
@@ -14,6 +14,40 @@ import { ScriptManager } from './script-manager';
 import { launcherLog } from './logger';
 
 const SESSION_DIR_PREFIX = 'codesys-mcp-persistent';
+
+/**
+ * Returns the PIDs of every CODESYS.exe currently running on this Windows
+ * machine -- whether spawned by this launcher, by a previous MCP session that
+ * crashed without cleanup, or by the user opening CODESYS interactively.
+ *
+ * Used as a pre-launch guard so the launcher never spawns a second CODESYS
+ * alongside an existing one. Two CODESYS instances against the same project
+ * file race on the lock and the loser pops a "project is currently in use"
+ * modal that freezes the IDE thread, breaking every subsequent script call
+ * with 60s timeouts. The cheapest fix is to refuse the duplicate spawn.
+ *
+ * Returns an empty list on non-Windows or if tasklist fails (we treat that
+ * as "can't tell" rather than blocking; the user always retains the option
+ * to close manually).
+ */
+function findRunningCodesysPids(): number[] {
+  if (process.platform !== 'win32') return [];
+  try {
+    const out = execSync(
+      'tasklist /FI "IMAGENAME eq CODESYS.exe" /FO CSV /NH',
+      { encoding: 'utf-8', stdio: ['ignore', 'pipe', 'ignore'] }
+    );
+    const pids: number[] = [];
+    for (const line of out.split(/\r?\n/)) {
+      // CSV with quotes: "CODESYS.exe","12345","Console","1","456,789 K"
+      const m = line.match(/^"CODESYS\.exe","(\d+)"/);
+      if (m) pids.push(Number(m[1]));
+    }
+    return pids;
+  } catch {
+    return [];
+  }
+}
 const READY_TIMEOUT_MS = 60_000;
 const READY_POLL_MS = 500;
 const SHUTDOWN_WAIT_MS = 5_000;
@@ -51,6 +85,29 @@ export class CodesysLauncher implements ScriptExecutor {
       throw new Error(err);
     }
 
+    // Refuse to spawn alongside an existing CODESYS.exe. Two instances against
+    // the same project file race on the lock and the loser pops a modal that
+    // freezes script execution. This catches:
+    //   - orphans from a prior MCP session that crashed (exit code 0) without
+    //     taking the IDE down with it
+    //   - the user's own interactive CODESYS instance
+    //   - a CODESYS still mid-shutdown after a previous shutdown_codesys call
+    const existingPids = findRunningCodesysPids();
+    if (existingPids.length > 0) {
+      const msg =
+        `Refusing to launch: ${existingPids.length} CODESYS.exe process(es) ` +
+        `already running (PID(s): ${existingPids.join(', ')}). The MCP launcher ` +
+        `cannot share IPC with an instance it did not spawn, and a second ` +
+        `CODESYS racing on the same project triggers a "project is currently ` +
+        `in use" modal that blocks all script execution. Close the existing ` +
+        `CODESYS window(s) first, or call shutdown_codesys if this server owns ` +
+        `the running instance, then retry.`;
+      launcherLog.warn(msg);
+      this.lastError = msg;
+      this.setState('error');
+      throw new Error(msg);
+    }
+
     this.setState('launching');
     this.sessionId = uuidv4();
     this.ipcDir = path.join(os.tmpdir(), SESSION_DIR_PREFIX, this.sessionId);