perf: keep playground mounts within render burst

etaf-playground.el

@@ -84,6 +84,9 @@ frame."
 ;; keeps byte compilation from treating the protected binding as lexical.
 (defvar read-eval)
 
+(declare-function ebox-call-with-render-burst
+                  "ebox-buffer-backend" (function &rest arguments))
+
 (cl-defstruct (etaf-playground-session
                (:constructor etaf-playground--session-create))
   "State shared by one source/preview workspace."
@@ -476,13 +479,11 @@ only file evaluated by the framework."
     (setq-local truncate-lines nil))
   buffer)
 
-(defun etaf-playground-mount-example
-    (buffer-name name &optional session mount-options)
-  "Mount example NAME into BUFFER-NAME and return its buffer.
-
-This is the low-level consumer API.  `etaf-playground-open-example' adds the
-source editors and side-by-side workspace around it.  MOUNT-OPTIONS is
-forwarded to `etaf-mount', including an optional initial viewport."
+(defun etaf-playground--mount-example-now
+    (buffer-name name session mount-options)
+  "Build and mount example NAME into BUFFER-NAME.
+SESSION supplies authoritative source buffers.  MOUNT-OPTIONS is forwarded to
+`etaf-mount'.  The caller owns the complete framework render burst."
   (let ((buffer (get-buffer-create buffer-name)))
     (when-let ((runtime (etaf-runtime-for-buffer buffer)))
       (with-current-buffer buffer
@@ -498,6 +499,19 @@ forwarded to `etaf-mount', including an optional initial viewport."
       (setq-local etaf-playground-current-example name))
     buffer))
 
+(defun etaf-playground-mount-example
+    (buffer-name name &optional session mount-options)
+  "Mount example NAME into BUFFER-NAME and return its buffer.
+
+This is the low-level consumer API.  `etaf-playground-open-example' adds the
+source editors and side-by-side workspace around it.  MOUNT-OPTIONS is
+forwarded to `etaf-mount', including an optional initial viewport.  Source
+loading, root construction, ETAF publication, and Ebox rendering share one
+public framework render burst so GC cannot split an interactive mount."
+  (ebox-call-with-render-burst
+   #'etaf-playground--mount-example-now
+   buffer-name name session mount-options))
+
 (defun etaf-playground--render-error (session error-data)
   "Show ERROR-DATA in SESSION's preview buffer after a failed refresh."
   (let ((buffer (etaf-playground-session-preview-buffer session)))

scripts/benchmark-research-shelf.el

@@ -75,12 +75,21 @@ never included in SAMPLES.  ACTION's result is passed to VERIFY and CLEANUP."
     (dotimes (index samples)
       (when setup (funcall setup index))
       (garbage-collect)
-      (pcase-let* ((`(,elapsed . ,result)
-                    (etaf-performance-evaluator--timed-call
-                     (lambda () (funcall action index)))))
-        (funcall verify result index)
-        (when cleanup (funcall cleanup result index))
-        (push elapsed durations)))
+      (let (timed)
+        ;; Interactive Ebox render bursts postpone GC until after visible
+        ;; completion.  A batch burst restores the process threshold
+        ;; synchronously, which can make the harness collect before its Lisp
+        ;; caller returns.  Stop the timer before restoring that batch-only
+        ;; threshold; the explicit collection above still settles every run.
+        (let ((gc-cons-threshold most-positive-fixnum)
+              (gc-cons-percentage 1.0))
+          (setq timed
+                (etaf-performance-evaluator--timed-call
+                 (lambda () (funcall action index)))))
+        (pcase-let ((`(,elapsed . ,result) timed))
+          (funcall verify result index)
+          (when cleanup (funcall cleanup result index))
+          (push elapsed durations))))
     (let ((statistics
            (etaf-performance-evaluator--statistics (nreverse durations))))
       (etaf-performance-evaluator--print-statistics label statistics)

tests/benchmark-research-shelf-tests.el

@@ -37,6 +37,24 @@
       (should (equal '(-1 0 1 2) (nreverse verifications)))
       (should (= 3 (plist-get (cdr result) :count))))))
 
+(ert-deftest etaf-performance-evaluator-models-visible-gc-boundary ()
+  "Measured actions defer GC like an interactive Ebox render burst."
+  (let ((gc-cons-threshold 1000)
+        (gc-cons-percentage 0.1)
+        observed)
+    (etaf-performance-evaluator--measure
+     "visible-gc-boundary"
+     (lambda (_index)
+       (push (list gc-cons-threshold gc-cons-percentage) observed)
+       t)
+     (lambda (result _index) (should result))
+     :samples 1)
+    ;; Warmup is intentionally outside the timed visible transaction; the
+    ;; measured sample owns the raised threshold and caller settings restore.
+    (should (equal (car observed) (list most-positive-fixnum 1.0)))
+    (should (= gc-cons-threshold 1000))
+    (should (= gc-cons-percentage 0.1))))
+
 (ert-deftest etaf-performance-evaluator-reports-both-hard-budget-failures ()
   "Report p95 and max independently when both exceed the hard budget."
   (let ((failures

tests/etaf-playground-tests.el

@@ -100,6 +100,38 @@ database and mounts a test buffer before running BODY."
        " *etaf-playground-display-order*" "research-shelf"))
     (should (equal '(display mount) (mapcar #'car (nreverse calls))))))
 
+(ert-deftest etaf-playground-mount-owns-complete-render-burst ()
+  "Source construction and ETAF mount share the host render transaction."
+  (let ((buffer " *etaf-playground-burst-test*")
+        (inside nil)
+        calls)
+    (unwind-protect
+        (cl-letf (((symbol-function 'ebox-call-with-render-burst)
+                   (lambda (function &rest arguments)
+                     (push 'begin calls)
+                     (setq inside t)
+                     (unwind-protect
+                         (prog1 (apply function arguments)
+                           (push 'end calls))
+                       (setq inside nil))))
+                  ((symbol-function 'etaf-playground-read-pair)
+                   (lambda (_name _session)
+                     (should inside)
+                     (push 'root calls)
+                     'test-view))
+                  ((symbol-function 'etaf-mount)
+                   (lambda (target view options)
+                     (should inside)
+                     (should (equal view 'test-view))
+                     (should (equal options '(:viewport-width 900)))
+                     (push 'mount calls)
+                     target)))
+          (should (bufferp
+                   (etaf-playground-mount-example
+                    buffer "test" nil '(:viewport-width 900))))
+          (should (equal '(begin root mount end) (nreverse calls))))
+      (when (get-buffer buffer) (kill-buffer buffer)))))
+
 (ert-deftest etaf-playground-compile-builds-the-dependency-graph ()
   "Integration builds must compile the framework's dependency graph first."
   (let ((makefile (with-temp-buffer