chore: org tangle sync — regenerate .lisp from .org sources (zero functional changes, file sizes identical)

backend/detection.lisp

@@ -123,3 +123,66 @@ Result is cached in *detected-backend* for subsequent calls."
                          (detect-backend-by-da1)))
                 (make-modern-backend)
                 (make-simple-backend)))))
+
+(in-package :cl-tty.backend)
+
+;;; ─── Detection cache ────────────────────────────────────────────────────────
+
+(defvar *detected-backend* nil
+  "Cached backend instance from detect-backend. Nil = not yet detected.")
+
+;;; ─── Environment probe ──────────────────────────────────────────────────────
+
+(defun detect-backend-by-env ()
+  "Check COLORTERM environment variable for modern terminal support.
+Returns :modern if COLORTERM contains 'truecolor' or '24bit', nil otherwise."
+  (let ((colorterm (sb-ext:posix-getenv "COLORTERM")))
+    (when (and colorterm
+               (or (search "truecolor" colorterm :test #'char-equal)
+                   (search "24bit" colorterm :test #'char-equal)))
+      :modern)))
+
+;;; ─── TTY probe ──────────────────────────────────────────────────────────────
+
+(defun detect-backend-by-tty ()
+  "Check if stdout is a real terminal (not a pipe/redirect).
+Returns T if stdout is interactive, nil otherwise."
+  (interactive-stream-p *standard-output*))
+
+;;; ─── DA1 terminal query ─────────────────────────────────────────────────────
+
+(defun query-terminal (query &optional (timeout 0.1))
+  "Send QUERY string to terminal and return any response received within
+TIMEOUT seconds. Returns the response string, or nil if no response."
+  (write-string query *standard-output*)
+  (force-output *standard-output*)
+  (sleep timeout)
+  (let ((response (make-array 0 :element-type 'character
+                              :fill-pointer 0 :adjustable t)))
+    (loop while (listen *standard-input*)
+          do (vector-push-extend (read-char-no-hang *standard-input*) response))
+    (when (plusp (length response))
+      response)))
+
+(defun detect-backend-by-da1 ()
+  "Send DA1 (ESC[c) query and check for kitty terminal response code.
+Returns T if terminal reports kitty compatibility codes."
+  (let ((response (query-terminal (format nil "~C[c" #\Esc))))
+    (when response
+      ;; DA1 response format: ESC [ ? digits ; digits c
+      ;; Kitty reports code 62 in the response
+      (search "?62" response))))
+
+;;; ─── Orchestrator ───────────────────────────────────────────────────────────
+
+(defun detect-backend ()
+  "Auto-detect the appropriate backend for the current terminal.
+Returns a backend instance (modern-backend or simple-backend).
+Result is cached in *detected-backend* for subsequent calls."
+  (or *detected-backend*
+      (setf *detected-backend*
+            (if (and (detect-backend-by-tty)
+                     (or (eql (detect-backend-by-env) :modern)
+                         (detect-backend-by-da1)))
+                (make-modern-backend)
+                (make-simple-backend)))))