Fix stale paint when switching Settings tabs (#21) (#23)

JBCefBrowser was built with setOffScreenRendering true. Under OSR, CEF
intermittently fails to invalidate the freed region when a large React
subtree is replaced in one commit (e.g. switching out of LogsTab with
thousands of buffered entries), leaving the previous tab's pixels
visible behind the new one until any other event triggers a repaint.

OSR was set in the initial webview scaffolding (7c0511b) with a "TODO
move to config" note and no specific need for transparency or custom
compositing. Switched to heavyweight rendering.

Author: ericdallo

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## [Unreleased]
 
+- Fix intermittent stale paint when switching Settings tabs (#21) where the previous tab body stayed visible behind the new one. The `JBCefBrowser` was built with `setOffScreenRendering true`; CEF's OSR pipeline occasionally failed to invalidate the freed region when a large React subtree (e.g. `LogsTab`'s up-to-5000-entry buffer) was unmounted and a sibling mounted in the same commit, leaving prior pixels onscreen until the next paint event. Switched to heavyweight rendering.
+
 ## 0.26.14
 
 - Fix empty Settings → MCPs tab on tool-window reopen (#22). `webview/ready` now replays the cached MCP roster as `tool/serversUpdated`, and `on-initialized` merges into `:session` instead of clobbering it (notifications that race ahead of `initialized` no longer get wiped).

src/main/clojure/dev/eca/eca_intellij/extension/tool_window.clj

@@ -183,7 +183,12 @@
 
 (defn ^:private create-webview ^JBCefBrowser [^Project project url]
   (let [browser (-> (JBCefBrowser/createBuilder)
-                    (.setOffScreenRendering true) ;; TODO move to config
+                    ;; Heavyweight (native) rendering. OSR (true) intermittently fails to
+                    ;; invalidate freed regions when a large React subtree is replaced in
+                    ;; one commit (e.g. switching Settings tabs while LogsTab holds
+                    ;; thousands of entries), leaving the prior tab's pixels visible
+                    ;; behind the new one until another event triggers a repaint (#21).
+                    (.setOffScreenRendering false)
                     (.build))
         ;; Per-client JS query pool size. We previously bumped this via a
         ;; global `System.setProperty "ide.browser.jcef.jsQueryPoolSize"` inside