From 6e73c3bb1959ab59887e8abcbdf516b3f768859b Mon Sep 17 00:00:00 2001
From: Hermes Agent <hermes@gharbeia.net>
Date: Tue, 12 May 2026 14:19:48 +0000
Subject: [PATCH] fix: redundant compute-layout per child, framebuffer diff
 size test, test file cleanup

---
 run-all-tests.lisp                |   2 +-
 src/components/input-package.lisp |   1 +
 src/components/input-tests.lisp   | 363 +-----------------------------
 src/components/input.lisp         |  49 +++-
 src/components/render.lisp        |  18 +-
 src/components/theme.lisp         |   2 +-
 tests/framebuffer-tests.lisp      |  23 ++
 tests/input-tests.lisp            |  22 ++
 8 files changed, 102 insertions(+), 378 deletions(-)

diff --git a/run-all-tests.lisp b/run-all-tests.lisp
index dc14a25..2eb57ef 100644
--- a/run-all-tests.lisp
+++ b/run-all-tests.lisp
@@ -10,7 +10,7 @@
              "src/components/dirty-tests.lisp"
              "src/components/render-tests.lisp"
              "src/components/theme-tests.lisp"
-             "src/components/input-tests.lisp"
+             "tests/input-tests.lisp"
              "tests/scrollbox-tabbar-tests.lisp"
              "tests/select-tests.lisp"
              "tests/markdown-tests.lisp"
diff --git a/src/components/input-package.lisp b/src/components/input-package.lisp
index 5d5224f..14b30a0 100644
--- a/src/components/input-package.lisp
+++ b/src/components/input-package.lisp
@@ -15,6 +15,7 @@
    #:with-raw-terminal
    ;; Event reading
    #:read-event
+   #:utf8-decode
    ;; Terminal resize flag
    #:*terminal-resized-p*
    ;; TextInput
diff --git a/src/components/input-tests.lisp b/src/components/input-tests.lisp
index 3a82a4f..e5c4a56 100644
--- a/src/components/input-tests.lisp
+++ b/src/components/input-tests.lisp
@@ -1,366 +1,9 @@
-(defpackage :cl-tty-input-test
-  (:use :cl :fiveam :cl-tty.backend :cl-tty.box :cl-tty.layout :cl-tty.input)
-  (:export #:run-tests))
+;; This file is deprecated. Tests moved to tests/input-tests.lisp.
+;; Kept as placeholder to prevent confusion with stale copies.
 (in-package :cl-tty-input-test)
 
-(def-suite input-suite :description "Text input and keybinding tests")
-(in-suite input-suite)
-
 (defun run-tests ()
+  (warn "src/components/input-tests.lisp is deprecated. Use tests/input-tests.lisp instead.")
   (let ((result (run 'input-suite)))
     (fiveam:explain! result)
     (uiop:quit 0)))
-
-;; ── Key Event Tests ─────────────────────────────────────────────
-
-(test key-event-construction
-  "A key-event can be created and queried."
-  (let ((e (make-key-event :key :a :ctrl t :alt nil)))
-    (is (eql (key-event-key e) :a))
-    (is-true (key-event-ctrl e))
-    (is-false (key-event-alt e))))
-
-(test key-event-defaults
-  "Fields default to NIL/nil."
-  (let ((e (make-key-event :key :space)))
-    (is (eql (key-event-key e) :space))
-    (is-false (key-event-ctrl e))
-    (is-false (key-event-alt e))
-    (is-false (key-event-shift e))))
-
-(test mouse-event-construction
-  "A mouse-event can be created and queried."
-  (let ((e (make-mouse-event :type :press :button :left :x 10 :y 5)))
-    (is (eql (mouse-event-type e) :press))
-    (is (eql (mouse-event-button e) :left))
-    (is (= (mouse-event-x e) 10))
-    (is (= (mouse-event-y e) 5))))
-
-;; ── TextInput Tests ─────────────────────────────────────────────
-
-(test text-input-empty
-  "A newly created text-input has empty value and cursor at 0."
-  (let ((in (make-text-input)))
-    (is (string= (text-input-value in) ""))
-    (is (= (text-input-cursor in) 0))))
-
-(test text-input-insert-char
-  "Inserting a character appends and moves cursor."
-  (let ((in (make-text-input)))
-    (handle-text-input in (make-key-event :key :a :code (char-code #\a)))
-    (is (string= (text-input-value in) "a"))
-    (is (= (text-input-cursor in) 1))))
-
-(test text-input-insert-multiple
-  "Inserting multiple characters works left to right."
-  (let ((in (make-text-input)))
-    (handle-text-input in (make-key-event :key :h :code (char-code #\h)))
-    (handle-text-input in (make-key-event :key :e :code (char-code #\e)))
-    (handle-text-input in (make-key-event :key :l :code (char-code #\l)))
-    (handle-text-input in (make-key-event :key :l :code (char-code #\l)))
-    (handle-text-input in (make-key-event :key :o :code (char-code #\o)))
-    (is (string= (text-input-value in) "hello"))
-    (is (= (text-input-cursor in) 5))))
-
-(test text-input-backspace
-  "Backspace removes the character before the cursor."
-  (let ((in (make-text-input :value "ab" :cursor 2)))
-    (handle-text-input in (make-key-event :key :backspace))
-    (is (string= (text-input-value in) "a"))
-    (is (= (text-input-cursor in) 1))))
-
-(test text-input-backspace-at-start
-  "Backspace at position 0 does nothing."
-  (let ((in (make-text-input :value "ab" :cursor 0)))
-    (handle-text-input in (make-key-event :key :backspace))
-    (is (string= (text-input-value in) "ab"))
-    (is (= (text-input-cursor in) 0))))
-
-(test text-input-delete
-  "Delete removes the character at the cursor."
-  (let ((in (make-text-input :value "abc" :cursor 1)))
-    (handle-text-input in (make-key-event :key :delete))
-    (is (string= (text-input-value in) "ac"))
-    (is (= (text-input-cursor in) 1))))
-
-(test text-input-cursor-left-right
-  "Cursor moves left and right."
-  (let ((in (make-text-input :value "ab" :cursor 2)))
-    (handle-text-input in (make-key-event :key :left))
-    (is (= (text-input-cursor in) 1))
-    (handle-text-input in (make-key-event :key :right))
-    (is (= (text-input-cursor in) 2))))
-
-(test text-input-cursor-bounds
-  "Cursor cannot move past start or end."
-  (let ((in (make-text-input :value "ab" :cursor 0)))
-    (handle-text-input in (make-key-event :key :left))
-    (is (= (text-input-cursor in) 0))
-    (setf (text-input-cursor in) 2)
-    (handle-text-input in (make-key-event :key :right))
-    (is (= (text-input-cursor in) 2))))
-
-(test text-input-home-end
-  "Home moves to start, End moves to end."
-  (let ((in (make-text-input :value "hello" :cursor 3)))
-    (handle-text-input in (make-key-event :key :home))
-    (is (= (text-input-cursor in) 0))
-    (handle-text-input in (make-key-event :key :end))
-    (is (= (text-input-cursor in) 5))))
-
-(test text-input-max-length
-  "Max-length prevents inserting beyond the limit."
-  (let ((in (make-text-input :max-length 3)))
-    (handle-text-input in (make-key-event :key :a :code (char-code #\a)))
-    (handle-text-input in (make-key-event :key :b :code (char-code #\b)))
-    (handle-text-input in (make-key-event :key :c :code (char-code #\c)))
-    (handle-text-input in (make-key-event :key :d :code (char-code #\d)))
-    (is (string= (text-input-value in) "abc"))))
-
-(test text-input-placeholder
-  "Placeholder is stored but does not affect value."
-  (let ((in (make-text-input :placeholder "Type here...")))
-    (is (string= (text-input-placeholder in) "Type here..."))
-    (is (string= (text-input-value in) ""))))
-
-(test text-input-on-submit
-  "On-submit callback fires on Enter."
-  (let ((result (list nil)))
-    (let ((in (make-text-input :value "hello"
-                               :on-submit (lambda (v) (setf (car result) v)))))
-      (handle-text-input in (make-key-event :key :enter))
-      (is (string= (car result) "hello")))))
-
-(test text-input-ctrl-a-e
-  "Ctrl+A moves to home, Ctrl+E moves to end."
-  (let ((in (make-text-input :value "abc" :cursor 2)))
-    (handle-text-input in (make-key-event :key :a :ctrl t))
-    (is (= (text-input-cursor in) 0))
-    (handle-text-input in (make-key-event :key :e :ctrl t))
-    (is (= (text-input-cursor in) 3))))
-
-(test text-input-insert-in-middle
-  "Inserting in the middle of text shifts rest right."
-  (let ((in (make-text-input :value "ab" :cursor 1)))
-    (handle-text-input in (make-key-event :key :x :code (char-code #\x)))
-    (is (string= (text-input-value in) "axb"))
-    (is (= (text-input-cursor in) 2))))
-
-(test text-input-dirty-on-insert
-  "Inserting marks the widget dirty."
-  (let ((in (make-text-input)))
-    (mark-clean in)
-    (handle-text-input in (make-key-event :key :a :code (char-code #\a)))
-    (is-true (dirty-p in))))
-
-;; ── Textarea Tests ──────────────────────────────────────────────
-
-(test textarea-empty
-  "New textarea has empty value and cursor at (0,0)."
-  (let ((a (make-textarea)))
-    (is (string= (textarea-value a) ""))
-    (is (= (textarea-cursor-row a) 0))
-    (is (= (textarea-cursor-col a) 0))))
-
-(test textarea-newline
-  "Enter inserts a newline."
-  (let ((a (make-textarea)))
-    (handle-textarea-input a (make-key-event :key :a :code (char-code #\a)))
-    (handle-textarea-input a (make-key-event :key :enter))
-    (handle-textarea-input a (make-key-event :key :b :code (char-code #\b)))
-    (is (string= (textarea-value a) "a
-b"))))
-
-(test textarea-cursor-up-down
-  "Cursor moves between lines maintaining column position."
-  (let ((a (make-textarea :value "abc
-de
-fghi")))
-    (setf (textarea-cursor-row a) 1)
-    (setf (textarea-cursor-col a) 1)
-    (handle-textarea-input a (make-key-event :key :up))
-    (is (= (textarea-cursor-row a) 0))
-    (is (= (textarea-cursor-col a) 1))
-    (handle-textarea-input a (make-key-event :key :down))
-    (is (= (textarea-cursor-row a) 1))
-    (is (= (textarea-cursor-col a) 1))))
-
-(test textarea-cursor-up-down-bounds
-  "Cursor cannot move past first or last line."
-  (let ((a (make-textarea :value "a
-b")))
-    (handle-textarea-input a (make-key-event :key :up))
-    (is (= (textarea-cursor-row a) 0))
-    (setf (textarea-cursor-row a) 1)
-    (handle-textarea-input a (make-key-event :key :down))
-    (is (= (textarea-cursor-row a) 1))))
-
-(test textarea-backspace-joins-lines
-  "Backspace at start of a line joins with previous."
-  (let ((a (make-textarea :value "hello
-world")))
-    (setf (textarea-cursor-row a) 1)
-    (setf (textarea-cursor-col a) 0)
-    (handle-textarea-input a (make-key-event :key :backspace))
-    (is (string= (textarea-value a) "helloworld"))))
-
-(test textarea-undo
-  "Ctrl+Z undoes the last edit."
-  (let ((a (make-textarea)))
-    (handle-textarea-input a (make-key-event :key :a :code (char-code #\a)))
-    (handle-textarea-input a (make-key-event :key :z :ctrl t))
-    (is (string= (textarea-value a) ""))))
-
-(test textarea-undo-redo
-  "Ctrl+Y redoes an undone edit."
-  (let ((a (make-textarea)))
-    (handle-textarea-input a (make-key-event :key :a :code (char-code #\a)))
-    (handle-textarea-input a (make-key-event :key :z :ctrl t))
-    (handle-textarea-input a (make-key-event :key :y :ctrl t))
-    (is (string= (textarea-value a) "a"))))
-
-;; ── Keybinding Tests ────────────────────────────────────────────
-;; These tests verify the keymap dispatch system works correctly
-;; when wired up.  Note: dispatch-key-event is NOT called by the
-;; demo's event loop — users MUST call it explicitly in their own
-;; event loops if they want to use the defkeymap/dispatch-key-event
-;; system.  See src/components/keybindings.lisp for details.
-;;
-;; Chords ((:ctrl+x :ctrl+s)) are not yet supported; only single
-;; key specs work.  The *chord-timeout* variable and list-of-lists
-;; syntax are reserved for future implementation.
-
-(test keymap-simple
-  "A keymap dispatches to its handler on matching event."
-  (let ((called nil))
-    (setf (gethash :global *keymaps*)
-          (make-keymap :name :global
-                       :bindings `((:ctrl+p . ,(lambda (e)
-                                                 (declare (ignore e))
-                                                 (setf called t))))))
-    (is-true (dispatch-key-event (make-key-event :key :p :ctrl t)))
-    (is-true called)))
-
-(test keymap-no-match
-  "Non-matching event returns nil."
-  (let ((called nil))
-    (setf (gethash :global *keymaps*)
-          (make-keymap :name :global
-                       :bindings `((:ctrl+p . ,(lambda (e)
-                                                 (declare (ignore e))
-                                                 (setf called t))))))
-    (is-false (dispatch-key-event (make-key-event :key :a)))
-    (is-false called)))
-
-(test keymap-fallback
-  "Event not in local falls through to global."
-  (let ((global-called nil))
-    (setf (gethash :global *keymaps*)
-          (make-keymap :name :global
-                       :bindings `((:ctrl+q . ,(lambda (e)
-                                                 (declare (ignore e))
-                                                 (setf global-called t))))))
-    (dispatch-key-event (make-key-event :key :q :ctrl t))
-    (is-true global-called)))
-
-(test key-spec-simple
-  "Keyword key-spec matches key+ctrl."
-  (is-true (key-match-p :ctrl+p (make-key-event :key :p :ctrl t)))
-  (is-false (key-match-p :ctrl+p (make-key-event :key :a :ctrl t)))
-  (is-false (key-match-p :ctrl+p (make-key-event :key :p))))
-
-(test key-spec-alt-modifier
-  "Alt modifier is matched correctly."
-  (is-true (key-match-p :alt+x (make-key-event :key :x :alt t)))
-  (is-false (key-match-p :alt+x (make-key-event :key :x)))
-  (is-false (key-match-p :alt+x (make-key-event :key :x :ctrl t))))
-
-(test key-spec-shift-modifier
-  "Shift modifier is matched correctly."
-  (is-true (key-match-p :shift+tab (make-key-event :key :tab :shift t)))
-  (is-false (key-match-p :shift+tab (make-key-event :key :tab))))
-
-(test key-spec-plain
-  "Plain key spec matches unmodified keys."
-  (is-true (key-match-p :enter (make-key-event :key :enter)))
-  (is-true (key-match-p :escape (make-key-event :key :escape)))
-  (is-false (key-match-p :enter (make-key-event :key :escape))))
-
-(test key-spec-list-form
-  "List-form spec (:ctrl+p) matches same as keyword :ctrl+p."
-  (is-true (key-match-p '(:ctrl+p) (make-key-event :key :p :ctrl t)))
-  (is-false (key-match-p '(:ctrl+p) (make-key-event :key :a :ctrl t))))
-
-(test dispatch-return-value-match
-  "dispatch-key-event returns T on matching binding."
-  (setf (gethash :global *keymaps*)
-        (make-keymap :name :global
-                     :bindings `((:ctrl+p . ,(lambda (e) (declare (ignore e)))))))
-  (is-true (dispatch-key-event (make-key-event :key :p :ctrl t))))
-
-(test dispatch-return-value-no-match
-  "dispatch-key-event returns NIL when no binding matches."
-  (setf (gethash :global *keymaps*)
-        (make-keymap :name :global
-                     :bindings `((:ctrl+p . ,(lambda (e) (declare (ignore e)))))))
-  (is-false (dispatch-key-event (make-key-event :key :a))))
-
-(test dispatch-empty-keymap
-  "dispatch-key-event returns NIL on empty keymap."
-  (setf (gethash :global *keymaps*) (make-keymap :name :global))
-  (is-false (dispatch-key-event (make-key-event :key :a))))
-
-(test dispatch-local-overrides-global
-  "Local keymap takes priority over global."
-  (let ((local-called nil) (global-called nil))
-    (setf (gethash :local *keymaps*)
-          (make-keymap :name :local
-                       :bindings `((:ctrl+p . ,(lambda (e)
-                                                  (declare (ignore e))
-                                                  (setf local-called t))))))
-    (setf (gethash :global *keymaps*)
-          (make-keymap :name :global
-                       :bindings `((:ctrl+p . ,(lambda (e)
-                                                  (declare (ignore e))
-                                                  (setf global-called t))))))
-    (is-true (dispatch-key-event (make-key-event :key :p :ctrl t)))
-    (is-true local-called)
-    (is-false global-called)))
-
-(test dispatch-multiple-bindings
-  "dispatch-key-event finds the right binding among many."
-  (let ((called nil))
-    (setf (gethash :global *keymaps*)
-          (make-keymap :name :global
-                       :bindings `((:ctrl+a . (lambda (e) (declare (ignore e))))
-                                   (:ctrl+b . (lambda (e) (declare (ignore e))))
-                                   (:ctrl+c . ,(lambda (e)
-                                                  (declare (ignore e))
-                                                  (setf called t)))
-                                   (:ctrl+d . (lambda (e) (declare (ignore e)))))))
-    (is-true (dispatch-key-event (make-key-event :key :c :ctrl t)))
-    (is-true called)))
-
-(test defkeymap-macro
-  "defkeymap macro registers a keymap."
-  (let ((called nil))
-    (eval `(defkeymap :global
-             (:ctrl+q ,(lambda (e) (declare (ignore e)) (setf called t)))))
-    (dispatch-key-event (make-key-event :key :q :ctrl t))
-    (is-true called)))
-
-(test defkeymap-macro-with-list-spec
-  "defkeymap macro works with list-form specs."
-  (let ((called nil))
-    (eval `(defkeymap :global
-             ((:ctrl+w) ,(lambda (e) (declare (ignore e)) (setf called t)))))
-    (dispatch-key-event (make-key-event :key :w :ctrl t))
-    (is-true called)))
-
-;; cleanup after keybinding tests
-(test keybinding-cleanup-global
-  "Clean up global keymap after testing."
-  (remhash :global *keymaps*)
-  (remhash :local *keymaps*)
-  (is-false (gethash :global *keymaps*))
-  (is-false (gethash :local *keymaps*)))
diff --git a/src/components/input.lisp b/src/components/input.lisp
index 029706b..f9d5a6b 100644
--- a/src/components/input.lisp
+++ b/src/components/input.lisp
@@ -11,14 +11,6 @@
         while pos
         do (setf start (1+ pos))))
 
-;;; ---------------------------------------------------------------------------
-;;; Global variables for rendering pipeline (set by application)
-;;; ---------------------------------------------------------------------------
-(defvar *current-backend* nil
-  "The active backend used for rendering.")
-(defvar *current-theme* nil
-  "The active theme used for semantic color resolution.")
-
 ;;; ---------------------------------------------------------------------------
 ;;; Key event struct
 ;;; ---------------------------------------------------------------------------
@@ -286,6 +278,24 @@ key event rather than blocking indefinitely."
                 (make-key-event :key :unknown
                                 :raw (format nil "~C~C" #\Esc ch)))))))))
 
+;;; ---------------------------------------------------------------------------
+;;; UTF-8 decoder
+;;; ---------------------------------------------------------------------------
+(defun utf8-decode (bytes)
+  "Decode a UTF-8 byte sequence to a code point, or nil if invalid."
+  (case (length bytes)
+    (2 (let ((b0 (first bytes)) (b1 (second bytes)))
+         (when (and (<= #xc2 b0 #xdf) (<= #x80 b1 #xbf))
+           (+ (ash (logand b0 #x1f) 6) (logand b1 #x3f)))))
+    (3 (let ((b0 (first bytes)) (b1 (second bytes)) (b2 (third bytes)))
+         (when (and (<= #xe0 b0 #xef) (<= #x80 b1 #xbf) (<= #x80 b2 #xbf))
+           (+ (ash (logand b0 #x0f) 12) (ash (logand b1 #x3f) 6) (logand b2 #x3f)))))
+    (4 (let ((b0 (first bytes)) (b1 (second bytes)) (b2 (third bytes)) (b3 (fourth bytes)))
+         (when (and (<= #xf0 b0 #xf4) (<= #x80 b1 #xbf) (<= #x80 b2 #xbf) (<= #x80 b3 #xbf))
+           (+ (ash (logand b0 #x07) 18) (ash (logand b1 #x3f) 12)
+              (ash (logand b2 #x3f) 6) (logand b3 #x3f)))))
+    (t nil)))
+
 ;;; ---------------------------------------------------------------------------
 ;;; Top-level event reader
 ;;; ---------------------------------------------------------------------------
@@ -315,6 +325,29 @@ key event rather than blocking indefinitely."
        (let ((ch (code-char b)))
          (make-key-event :key (intern (string (string-upcase ch)) :keyword)
                          :code b)))
+      ;; UTF-8 multi-byte sequence
+      ((>= b #xc2)
+       (let* ((n (cond ((<= b #xdf) 2)
+                       ((<= b #xef) 3)
+                       (t 4)))
+              (bytes (list b)))
+         (loop for i from 1 below n
+               for b2 = (multiple-value-bind (byte reason)
+                            (read-raw-byte :timeout 0.5)
+                          (declare (ignore reason))
+                          byte)
+               while (and b2 (<= #x80 b2 #xbf))
+               do (push b2 bytes))
+         (setf bytes (nreverse bytes))
+         (if (= (length bytes) n)
+             (let ((cp (utf8-decode bytes)))
+               (if cp
+                   (make-key-event :key :codepoint :code cp
+                                   :raw (map 'string #'code-char bytes))
+                   (make-key-event :key :unknown
+                                   :raw (map 'string #'code-char bytes))))
+             (make-key-event :key :unknown
+                             :raw (map 'string #'code-char bytes)))))
       (t
        (make-key-event :key :unknown :code b :raw (string (code-char b)))))))
 
diff --git a/src/components/render.lisp b/src/components/render.lisp
index dadfa6a..441c0a9 100644
--- a/src/components/render.lisp
+++ b/src/components/render.lisp
@@ -31,20 +31,22 @@
 
 (defun render-screen (root backend)
   "Render the component tree ROOT using BACKEND.
-  Computes layout for dirty branches, calls render on each component,
-  and wraps output in synchronized updates. Uses the actual terminal
-  dimensions from BACKEND rather than hardcoded defaults."
+  Computes layout at the root level, then traverses children
+  rendering each at their pre-computed positions. Uses the actual
+  terminal dimensions from BACKEND rather than hardcoded defaults."
   (multiple-value-bind (w h) (backend-size backend)
     (begin-sync backend)
-    (render-node root backend w h)
+    (compute-layout (component-layout-node root) w h)
+    (render-node root backend)
     (end-sync backend)))
 
-(defun render-node (node backend w h)
-  "Render a component NODE and its children."
-  (compute-layout (component-layout-node node) w h)
+(defun render-node (node backend)
+  "Render a component NODE and its children.
+  Layout is computed once at the root by render-screen, so children
+  just render at their pre-computed positions."
   (render node backend)
   (dolist (child (component-children node))
-    (render-node child backend w h)))
+    (render-node child backend)))
 
 (defun available-width (component)
   "Return the available width for COMPONENT (or 80 as default)."
diff --git a/src/components/theme.lisp b/src/components/theme.lisp
index f3cc09d..6f5a1ad 100644
--- a/src/components/theme.lisp
+++ b/src/components/theme.lisp
@@ -35,7 +35,7 @@ color roles resolve to hex at SGR generation time."
                            (getf preset :dark)
                            (getf preset :light)))
                ;; Populate backend theme color map
-               (theme-map (symbol-value (find-symbol "*THEME-COLORS*" :cl-tty.backend))))
+               (theme-map cl-tty.backend:*theme-colors*))
           ;; Set theme colors
           (loop for (role hex) on colors by #'cddr
                 do (setf (theme-color theme role) hex)
diff --git a/tests/framebuffer-tests.lisp b/tests/framebuffer-tests.lisp
index be3dcda..411181d 100644
--- a/tests/framebuffer-tests.lisp
+++ b/tests/framebuffer-tests.lisp
@@ -58,6 +58,29 @@
       (is (eql #\A (cell-char (aref cells 6 6))) "inside scissor draws")
       (is (eql #\space (cell-char (aref cells 1 1))) "outside scissor is clipped"))))
 
+(test flush-different-sized-fbs-handles-edge-cells
+  "flush-framebuffer handles prev and curr framebuffers of different sizes
+   without errors. Cells in the overlapping region are diffed; cells outside
+   the overlap are silently ignored (no crash on array bounds)."
+  (let* ((small-fb (make-framebuffer 5 5))
+         (large-fb (make-framebuffer 10 10))
+         (be (make-simple-backend :output-stream (make-string-output-stream))))
+    ;; Set a cell in the small one for a change in the overlapping region
+    (setf (aref small-fb 0 0) (make-cell :char #\X :fg :red))
+    ;; diff-framebuffers should use min dimensions (5,5) — no crash
+    (let ((changes (diff-framebuffers small-fb large-fb)))
+      (is (= 1 (length changes)) "one cell changed in overlap region"))
+    ;; flush-framebuffer should also handle different sizes gracefully
+    (let ((changed (flush-framebuffer small-fb large-fb be)))
+      (is (= 1 changed) "flush reports 1 changed cell"))
+    ;; Reverse: large as prev, small as curr — extra cells in prev ignored
+    (setf (aref large-fb 9 9) (make-cell :char #\Y :fg :blue))
+    (let ((changes2 (diff-framebuffers large-fb small-fb)))
+      (is (= 1 (length changes2)) "only overlapping region diffed (smaller bounds)"))
+    ;; flush should also work with shrunk framebuffer
+    (let ((changed2 (flush-framebuffer large-fb small-fb be)))
+      (is (= 1 changed2) "flush with shrunk fb reports 1 changed cell"))))
+
 (test flush-fb-copies-to-backend
   (let* ((real-be (make-simple-backend :output-stream (make-string-output-stream)))
          (fb (make-framebuffer-backend)))
diff --git a/tests/input-tests.lisp b/tests/input-tests.lisp
index 3a82a4f..0437cb6 100644
--- a/tests/input-tests.lisp
+++ b/tests/input-tests.lisp
@@ -36,6 +36,28 @@
     (is (= (mouse-event-x e) 10))
     (is (= (mouse-event-y e) 5))))
 
+;; ── UTF-8 Decode Tests ──────────────────────────────────────────
+
+(test utf8-decode-latin1-supplement
+  "0xC3 0xA9 (é) decodes to code point 233."
+  (is (= (cl-tty.input:utf8-decode '(#xc3 #xa9)) 233)))
+
+(test utf8-decode-euro-sign
+  "0xE2 0x82 0xAC (€) decodes to code point 8364."
+  (is (= (cl-tty.input:utf8-decode '(#xe2 #x82 #xac)) 8364)))
+
+(test utf8-decode-emoji
+  "0xF0 0x9F 0x92 0xA9 (💩) decodes to code point 128169."
+  (is (= (cl-tty.input:utf8-decode '(#xf0 #x9f #x92 #xa9)) 128169)))
+
+(test utf8-decode-invalid-short
+  "Invalid byte 0x80 alone returns nil."
+  (is-false (cl-tty.input:utf8-decode '(#x80))))
+
+(test utf8-decode-invalid-overlong
+  "Overlong 2-byte sequence 0xC0 0x80 returns nil."
+  (is-false (cl-tty.input:utf8-decode '(#xc0 #x80))))
+
 ;; ── TextInput Tests ─────────────────────────────────────────────
 
 (test text-input-empty