refactor: apply functional programming to SSH module

- Split complex nested functions into focused, single-responsibility helpers
- Created io/ directory with pure command builders and impure executors
- Eliminated parentheses complexity that was causing compilation errors
- SSH module now compiles and runs successfully with cleaner architecture

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/lab-tool/io/ssh.scm

@@ -0,0 +1,37 @@
+;; io/ssh.scm - Pure SSH command building functions
+
+(define-module (io ssh)
+  #:use-module (ice-9 format)
+  #:export (make-ssh-target
+            build-ssh-command
+            build-rsync-command
+            make-ssh-options))
+
+;; Pure function: Build SSH target string
+(define (make-ssh-target user hostname)
+  "Build SSH target string from user and hostname"
+  (if user
+      (format #f "~a@~a" user hostname)
+      hostname))
+
+;; Pure function: Build SSH options string
+(define (make-ssh-options identity-file timeout)
+  "Build SSH options string"
+  (let ((opts '()))
+    (when identity-file
+      (set! opts (cons (format #f "-i ~a" identity-file) opts)))
+    (when timeout
+      (set! opts (cons (format #f "-o ConnectTimeout=~a" timeout) opts)))
+    (set! opts (cons "-o BatchMode=yes" opts))
+    (string-join (reverse opts) " ")))
+
+;; Pure function: Build SSH command
+(define (build-ssh-command target options command)
+  "Build complete SSH command string"
+  (format #f "ssh ~a ~a '~a'" options target command))
+
+;; Pure function: Build rsync command
+(define (build-rsync-command source-path target dest-path ssh-options)
+  "Build rsync command with SSH transport"
+  (format #f "rsync -avz --delete -e 'ssh ~a' ~a/ ~a:~a/"
+          ssh-options source-path target dest-path))