fix(process): harden capture validation and cleanup

src/application/ProcessCaptureCapability.ts

@@ -0,0 +1,38 @@
+import { tmpdir } from "node:os";
+import { spawn } from "node-pty";
+
+export type ProcessCaptureCapability =
+  | { readonly available: true; readonly backend: "node-pty" }
+  | {
+      readonly available: false;
+      readonly backend: "node-pty";
+      readonly reason: string;
+    };
+
+/** Probe the actual native PTY seam instead of inferring support from the OS name. */
+export const probeProcessCaptureCapability =
+  async (): Promise<ProcessCaptureCapability> => {
+    try {
+      const terminal = spawn(
+        process.platform === "win32" ? "cmd.exe" : "/bin/sh",
+        process.platform === "win32" ? ["/c", "exit", "0"] : ["-c", "exit 0"],
+        {
+          cwd: tmpdir(),
+          env: { HOME: tmpdir(), TERM: "xterm-256color" },
+          cols: 80,
+          rows: 24,
+          name: "xterm-256color",
+        },
+      );
+      await new Promise<void>((resolveExit) =>
+        terminal.onExit(() => resolveExit()),
+      );
+      return { available: true, backend: "node-pty" };
+    } catch {
+      return {
+        available: false,
+        backend: "node-pty",
+        reason: "the native PTY backend could not start a probe process",
+      };
+    }
+  };