From 5abc62f90cac33cd67396d78f01bf91b703db45c Mon Sep 17 00:00:00 2001
From: Matthew Costabile <mattcosta7@github.com>
Date: Mon, 22 Jun 2026 13:25:32 +0000
Subject: [PATCH 1/2] perf(SelectPanel): reset intermediate selection during
 render, not in an effect

Replace the useEffect that reset the single-select modal's intermediate selection with the adjust-state-during-render pattern (tracking previous {open, selected, isSingleSelectModal}). Behavior is identical but avoids the extra post-commit render, and removing the eslint-disable lets the lint rule guard against regressions.
---
 ...electpanel-intermediate-selected-derive.md |  5 +++++
 .../react/src/SelectPanel/SelectPanel.tsx     | 19 +++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/selectpanel-intermediate-selected-derive.md

diff --git a/.changeset/selectpanel-intermediate-selected-derive.md b/.changeset/selectpanel-intermediate-selected-derive.md
new file mode 100644
index 00000000000..6ed9a5f6507
--- /dev/null
+++ b/.changeset/selectpanel-intermediate-selected-derive.md
@@ -0,0 +1,5 @@
+---
+'@primer/react': patch
+---
+
+SelectPanel: Reset the single-select modal's intermediate selection during render instead of in an effect, avoiding an extra re-render when the panel opens or the selection changes.
diff --git a/packages/react/src/SelectPanel/SelectPanel.tsx b/packages/react/src/SelectPanel/SelectPanel.tsx
index 9bf81f39d8e..ac43ae820fe 100644
--- a/packages/react/src/SelectPanel/SelectPanel.tsx
+++ b/packages/react/src/SelectPanel/SelectPanel.tsx
@@ -241,11 +241,22 @@ function Panel({
     isSingleSelectModal ? selected : undefined,
   )
 
-  // Reset the intermediate selected item when the panel is open/closed
-  useEffect(() => {
-    // eslint-disable-next-line react-hooks/set-state-in-effect, react-you-might-not-need-an-effect/no-derived-state
+  // Reset the intermediate selected item when the panel is opened/closed or the external
+  // selection changes. Adjusting state during render (tracking the previous inputs) rather
+  // than syncing it from an effect avoids an extra post-commit render.
+  const [intermediateSelectedResetKey, setIntermediateSelectedResetKey] = useState({
+    open,
+    selected,
+    isSingleSelectModal,
+  })
+  if (
+    intermediateSelectedResetKey.open !== open ||
+    intermediateSelectedResetKey.selected !== selected ||
+    intermediateSelectedResetKey.isSingleSelectModal !== isSingleSelectModal
+  ) {
+    setIntermediateSelectedResetKey({open, selected, isSingleSelectModal})
     setIntermediateSelected(isSingleSelectModal ? selected : undefined)
-  }, [isSingleSelectModal, open, selected])
+  }
 
   const onListContainerRefChanged: FilteredActionListProps['onListContainerRefChanged'] = useCallback(
     (node: HTMLElement | null) => {

From c962a6d73767121bd7d7fd12af8aa5c32041accd Mon Sep 17 00:00:00 2001
From: Matthew Costabile <mattcosta7@github.com>
Date: Wed, 24 Jun 2026 01:16:25 +0000
Subject: [PATCH 2/2] Only reset intermediate selection when it actually
 changes

---
 packages/react/src/SelectPanel/SelectPanel.tsx | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/react/src/SelectPanel/SelectPanel.tsx b/packages/react/src/SelectPanel/SelectPanel.tsx
index ac43ae820fe..8efd4f1b936 100644
--- a/packages/react/src/SelectPanel/SelectPanel.tsx
+++ b/packages/react/src/SelectPanel/SelectPanel.tsx
@@ -243,19 +243,23 @@ function Panel({
 
   // Reset the intermediate selected item when the panel is opened/closed or the external
   // selection changes. Adjusting state during render (tracking the previous inputs) rather
-  // than syncing it from an effect avoids an extra post-commit render.
+  // than syncing it from an effect avoids an extra post-commit render. The reset is also
+  // gated on the intermediate selection actually changing, so variants that never use it
+  // (e.g. multi-select / anchored, where it stays `undefined`) don't pay for a render-phase
+  // restart on every open/selection change.
+  const nextIntermediateSelected = isSingleSelectModal ? selected : undefined
   const [intermediateSelectedResetKey, setIntermediateSelectedResetKey] = useState({
     open,
     selected,
     isSingleSelectModal,
   })
-  if (
+  const intermediateSelectedInputsChanged =
     intermediateSelectedResetKey.open !== open ||
     intermediateSelectedResetKey.selected !== selected ||
     intermediateSelectedResetKey.isSingleSelectModal !== isSingleSelectModal
-  ) {
+  if (intermediateSelectedInputsChanged && intermediateSelected !== nextIntermediateSelected) {
     setIntermediateSelectedResetKey({open, selected, isSingleSelectModal})
-    setIntermediateSelected(isSingleSelectModal ? selected : undefined)
+    setIntermediateSelected(nextIntermediateSelected)
   }
 
   const onListContainerRefChanged: FilteredActionListProps['onListContainerRefChanged'] = useCallback(