From 2be1c125de10f12caa31fbff0ecfefdaba706a64 Mon Sep 17 00:00:00 2001
From: Brennan Benson <79079362+brennanb2025@users.noreply.github.com>
Date: Thu, 6 Aug 2026 14:03:41 -0700
Subject: [PATCH] fix(terminal): route a reveal metric flush through the stable
 fit
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fitRevealedPane's new flush branch called safeFit directly, which is
exactly what the function's contract forbids on reveal: resumeRendering
has just re-attached WebGL, whose cell metrics transiently differ from
the DOM renderer's, so a raw fit can propose a one-column-off grid and
reflow — and xterm's wrap/unwrap is not a perfect inverse, leaving a
diff-painting inline TUI corrupted.

A landed flush leaves pixels unchanged with a diverged grid, the same
shape as a snapshot resize, so it takes the same steady-grid repair.
A real resize still fits synchronously, after the flush.

Reachable via window wake, which calls fitAllRevealedPanes with no
pre-flush loop.
---
 .../lib/pane-manager/pane-reveal-fit.test.ts  | 29 +++++++++++++++----
 .../src/lib/pane-manager/pane-reveal-fit.ts   | 15 +++++-----
 2 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/src/renderer/src/lib/pane-manager/pane-reveal-fit.test.ts b/src/renderer/src/lib/pane-manager/pane-reveal-fit.test.ts
index 439b5f44313..c3ac10f44b4 100644
--- a/src/renderer/src/lib/pane-manager/pane-reveal-fit.test.ts
+++ b/src/renderer/src/lib/pane-manager/pane-reveal-fit.test.ts
@@ -55,10 +55,12 @@ describe('fitRevealedPane routing', () => {
     mocks.flushDeferredPaneMetricOptionsIfMeasurable.mockReturnValue(false)
   })
 
-  it('fits when a deferred metric flush lands on a pane the size checks would skip', () => {
-    // Without this the no-op branch below returns early and the parked font
-    // change never reaches the grid — the stuck-metrics shape the deferral
-    // is supposed to prevent.
+  it('repairs on a steady grid when a deferred metric flush lands on a pane the size checks would skip', () => {
+    // Without the flush branch the checks below both say "nothing to do" and the
+    // parked font change never reaches the grid. It must route through the stable
+    // path, not a raw fit: pixels are unchanged and the grid diverged, so a
+    // synchronous fit would reflow on the WebGL/DOM metric wobble and corrupt a
+    // diff-painting inline TUI.
     mocks.flushDeferredPaneMetricOptionsIfMeasurable.mockReturnValue(true)
     const pane = createPane({
       lastFitClientSize: { width: 800, height: 600 },
@@ -69,8 +71,25 @@ describe('fitRevealedPane routing', () => {
 
     fitRevealedPane(pane)
 
+    expect(mocks.flushDeferredPaneMetricOptionsIfMeasurable).toHaveBeenCalledWith(pane)
+    expect(mocks.requestStablePaneFit).toHaveBeenCalledWith(pane)
+    expect(mocks.safeFit).not.toHaveBeenCalled()
+  })
+
+  it('still flushes parked metric options when the pane also resized while hidden', () => {
+    mocks.flushDeferredPaneMetricOptionsIfMeasurable.mockReturnValue(true)
+    const pane = createPane({
+      lastFitClientSize: { width: 800, height: 600 },
+      currentSize: { width: 640, height: 480 },
+      terminal: { cols: 80, rows: 24 },
+      proposed: { cols: 64, rows: 20 }
+    })
+
+    fitRevealedPane(pane)
+
+    expect(mocks.flushDeferredPaneMetricOptionsIfMeasurable).toHaveBeenCalledWith(pane)
+    // A real resize still takes the synchronous path, and the flush already landed.
     expect(mocks.safeFit).toHaveBeenCalledWith(pane)
-    expect(mocks.requestStablePaneFit).not.toHaveBeenCalled()
   })
 
   it('fits synchronously when the fit element resized while hidden', () => {
diff --git a/src/renderer/src/lib/pane-manager/pane-reveal-fit.ts b/src/renderer/src/lib/pane-manager/pane-reveal-fit.ts
index 1a6dee695ca..f0125433764 100644
--- a/src/renderer/src/lib/pane-manager/pane-reveal-fit.ts
+++ b/src/renderer/src/lib/pane-manager/pane-reveal-fit.ts
@@ -62,18 +62,17 @@ function releaseMeasurableFitContinuations(pane: ManagedPane): void {
 //    mismatch refits but a transient metric wobble does not reflow;
 //  - grid already correct → leave it alone.
 export function fitRevealedPane(pane: ManagedPane): void {
-  // Why first: the pixel/grid checks below can both say "nothing to do" and
-  // return without fitting, which would strand metric options parked while the
-  // pane was unmeasurable. A landed flush changes cell size, so it must fit.
-  if (flushDeferredPaneMetricOptionsIfMeasurable(pane)) {
-    safeFit(pane)
-    return
-  }
+  // Why first: the checks below can both say "nothing to do" and return without
+  // fitting, stranding metric options parked while the pane was unmeasurable.
+  const flushed = flushDeferredPaneMetricOptionsIfMeasurable(pane)
   if (paneFitClientSizeChanged(pane)) {
     safeFit(pane)
     return
   }
-  if (!proposedGridMatchesTerminal(pane)) {
+  // Why the stable path for a flush: it leaves pixels unchanged but the grid
+  // diverged — the same shape as a snapshot resize, and a raw fit here would
+  // reflow on the transient WebGL/DOM metric wobble this function exists to avoid.
+  if (flushed || !proposedGridMatchesTerminal(pane)) {
     requestStablePaneFit(pane)
     return
   }