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/shell.scm

@@ -0,0 +1,36 @@
+;; io/shell.scm - Impure shell execution functions
+
+(define-module (io shell)
+  #:use-module (ice-9 popen)
+  #:use-module (ice-9 textual-ports)
+  #:use-module (utils logging)
+  #:export (execute-command
+            execute-with-output
+            test-command))
+
+;; Impure function: Execute command and return success/failure
+(define (execute-command command)
+  "Execute shell command, return true if successful"
+  (log-debug "Executing: ~a" command)
+  (let ((status (system command)))
+    (zero? status)))
+
+;; Impure function: Execute command and capture output
+(define (execute-with-output command)
+  "Execute command and return (success . output) pair"
+  (log-debug "Executing with output: ~a" command)
+  (let* ((port (open-pipe* OPEN_READ "/bin/sh" "-c" command))
+         (output (get-string-all port))
+         (status (close-pipe port))
+         (success (zero? status)))
+    (log-debug "Command ~a: exit=~a" (if success "succeeded" "failed") status)
+    (cons success output)))
+
+;; Impure function: Test if command succeeds (no output)
+(define (test-command command)
+  "Test if command succeeds, return boolean"
+  (log-debug "Testing command: ~a" command)
+  (let* ((port (open-pipe* OPEN_READ "/bin/sh" "-c" command))
+         (output (get-string-all port))
+         (status (close-pipe port)))
+    (zero? status)))

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))