fix(preview): suppress narrow-width editor artifacts

etaf-playground.el

@@ -484,6 +484,23 @@ only file evaluated by the framework."
      (etaf-playground--root-factory spec)
      name static-form ecss-form)))
 
+(defun etaf-playground--apply-preview-display-settings ()
+  "Suppress text-editor redisplay artifacts in the current preview buffer.
+
+An ETAF preview owns its viewport and line layout.  Editor continuation and
+truncation indicators otherwise leak into narrow generated canvases as dark
+blocks at the right edge."
+  (setq-local truncate-lines t
+              auto-hscroll-mode t
+              fringe-indicator-alist
+              (cl-remove-if
+               (lambda (entry)
+                 (memq (car-safe entry) '(truncation continuation)))
+               (copy-tree fringe-indicator-alist))
+              bidi-display-reordering nil
+              bidi-paragraph-direction 'left-to-right
+              bidi-inhibit-bpa t))
+
 (defun etaf-playground--preview-mode-setup (buffer session)
   "Prepare generated preview BUFFER for SESSION."
   (with-current-buffer buffer
@@ -497,7 +514,7 @@ only file evaluated by the framework."
                 (format " ETAF Preview  %s  |  g refresh  q close"
                         (etaf-playground-session-name session)))
     (buffer-disable-undo)
-    (setq-local truncate-lines nil))
+    (etaf-playground--apply-preview-display-settings))
   buffer)
 
 (defun etaf-playground--mount-example-now
@@ -517,7 +534,10 @@ SESSION supplies authoritative source buffers.  MOUNT-OPTIONS is forwarded to
       (etaf-mount buffer (etaf-playground-read-pair name session)
                   mount-options))
     (with-current-buffer buffer
-      (setq-local etaf-playground-current-example name))
+      (setq-local etaf-playground-current-example name)
+      ;; Publication may restore renderer-owned buffer settings.  The generated
+      ;; preview display contract is final and must win after the mount.
+      (etaf-playground--apply-preview-display-settings))
     buffer))
 
 (defun etaf-playground-mount-example
@@ -545,6 +565,7 @@ public framework render burst so GC cannot split an interactive mount."
                           (etaf-playground-session-name session)
                           (error-message-string error-data))))
         (setq-local buffer-read-only t)
+        (etaf-playground--apply-preview-display-settings)
         (setq-local header-line-format
                     (format " ETAF Preview  %s  |  ERROR  |  g retry  q close"
                             (etaf-playground-session-name session)))))))
@@ -653,7 +674,7 @@ the preview instead of destroying the source workspace."
 
 (define-derived-mode etaf-playground-preview-mode special-mode "ETAF-Preview"
   "Read-only major mode for a mounted ETAF Playground preview."
-  (setq-local truncate-lines nil)
+  (etaf-playground--apply-preview-display-settings)
   (setq-local buffer-read-only nil)
   (setq-local mode-line-process nil))
 

scripts/playground-gui-scenarios.el

@@ -104,6 +104,10 @@
   (let* ((buffer (etaf-gui-verifier-context-target-buffer context))
          (mounted (and (buffer-live-p buffer)
                        (ebox-surface-buffer-mounted-p buffer)))
+         (canvas-settings
+          (and mounted
+               (with-current-buffer buffer
+                 (list truncate-lines fringe-indicator-alist))))
          (text (and mounted
                     (with-current-buffer buffer
                       (buffer-substring-no-properties
@@ -116,6 +120,12 @@
        (etaf-gui-verifier-assert
         "visible-output-nonempty"
         (etaf-playground-gui-scenarios--visible-window-content-p context))
+       (etaf-gui-verifier-assert
+        "generated-canvas-truncates-editor-lines" (car canvas-settings))
+       (etaf-gui-verifier-assert
+        "generated-canvas-hides-editor-edge-indicators"
+        (and (not (assq 'truncation (cadr canvas-settings)))
+             (not (assq 'continuation (cadr canvas-settings)))))
        (etaf-gui-verifier-assert
         "no-render-error"
         (and text
@@ -351,6 +361,8 @@ product-specific postcondition in the evidence stream."
       (etaf-playground-gui-scenarios--windowed-action)
       (etaf-playground-gui-scenarios--resize-action
        "resize-narrow" 900 500)
+      (etaf-playground-gui-scenarios--resize-action
+       "resize-compact" 700 500)
       (etaf-playground-gui-scenarios--scroll-action
        "scroll-down" #'ebox-scroll-page-down)
       (etaf-playground-gui-scenarios--reset-scroll-action)
@@ -396,7 +408,7 @@ product-specific postcondition in the evidence stream."
       (etaf-playground-gui-scenarios--maximize-action))
      :completion
      (lambda (context)
-       (= (etaf-gui-verifier-context-action-count context) 12))))
+       (= (etaf-gui-verifier-context-action-count context) 13))))
 
 (defun etaf-playground-gui-scenarios-ebox (scenario fixture)
   "Return one Ebox SCENARIO adapter for FIXTURE."

tests/etaf-playground-tests.el

@@ -118,6 +118,54 @@
                                    :type 'file-missing)
                      injected)))))
 
+(ert-deftest etaf-playground-preview-suppresses-editor-redisplay-artifacts ()
+  "Generated previews hide wrapping indicators that appear as edge blocks."
+  (let ((buffer (generate-new-buffer " *etaf-preview-display-settings*"))
+        (session (etaf-playground--session-create :name "display-settings")))
+    (unwind-protect
+        (progn
+          (with-current-buffer buffer
+            (etaf-playground-preview-mode)
+            ;; Reused preview buffers may have settings changed by a caller;
+            ;; session setup must restore the generated-canvas contract.
+            (setq-local truncate-lines nil
+                        auto-hscroll-mode nil
+                        fringe-indicator-alist
+                        '((truncation left-arrow right-arrow)
+                          (continuation left-curly-arrow right-curly-arrow))
+                        bidi-display-reordering t
+                        bidi-paragraph-direction nil
+                        bidi-inhibit-bpa nil))
+          (etaf-playground--preview-mode-setup buffer session)
+          (cl-letf (((symbol-function 'etaf-runtime-for-buffer)
+                     (lambda (_buffer) nil))
+                    ((symbol-function 'etaf-playground-read-pair)
+                     (lambda (&rest _arguments) 'preview-view))
+                    ((symbol-function 'etaf-mount)
+                     (lambda (&rest _arguments)
+                       ;; Model renderer publication restoring ordinary editor
+                       ;; defaults after the preview mode was initialized.
+                       (setq-local truncate-lines nil
+                                   auto-hscroll-mode nil
+                                   fringe-indicator-alist
+                                   '((truncation left-arrow right-arrow)
+                                     (continuation
+                                      left-curly-arrow right-curly-arrow))
+                                   bidi-display-reordering t
+                                   bidi-paragraph-direction nil
+                                   bidi-inhibit-bpa nil))))
+            (etaf-playground--mount-example-now
+             buffer "display-settings" session nil))
+          (with-current-buffer buffer
+            (should truncate-lines)
+            (should auto-hscroll-mode)
+            (should-not (assq 'truncation fringe-indicator-alist))
+            (should-not (assq 'continuation fringe-indicator-alist))
+            (should-not bidi-display-reordering)
+            (should (eq bidi-paragraph-direction 'left-to-right))
+            (should bidi-inhibit-bpa)))
+      (when (buffer-live-p buffer) (kill-buffer buffer)))))
+
 (defun etaf-playground-test--text (buffer)
   "Return BUFFER's plain rendered text."
   (with-current-buffer buffer

tests/playground-gui-scenarios-tests.el

@@ -29,9 +29,9 @@
     (should
      (equal
       (mapcar #'etaf-gui-verifier-action-id actions)
-      '("mount" "leave-fullscreen" "resize-narrow" "scroll-down"
+      '("mount" "leave-fullscreen" "resize-narrow" "resize-compact"
-        "reset-scroll" "resize-wide" "row-select" "data-mutation"
+        "scroll-down" "reset-scroll" "resize-wide" "row-select"
-        "filter-reading" "theme-toggle" "pagination"
+        "data-mutation" "filter-reading" "theme-toggle" "pagination"
         "maximize-frame")))
     (should
      (funcall