From 58cb556accc7ff9a05dd94ffcbe653d06fa9adc4 Mon Sep 17 00:00:00 2001
From: Brennan Benson <79079362+brennanb2025@users.noreply.github.com>
Date: Thu, 6 Aug 2026 14:11:47 -0700
Subject: [PATCH] fix(terminal): gate metric writes on the pixel box, not the
 fit floor
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canApplyPaneMetricOptions reused canMeasurePaneForFit, whose >=8 cols /
>=4 rows floor exists to stop a fit pinning the PTY to a sliver. But the
divider clamp is 50px, which clears the 48px pixel floor and proposes
~5 cols — so a pane dragged to the clamp deferred every font change and
never flushed: it never hides, and its box never changes, so no reveal
and no ResizeObserver entry ever arrives. It rendered a stale font until
widened, where pre-PR the write was unconditional.

Gate metric writes on display plus the pixel box only. Hidden panes and
the transient worktree-switch overlay are near-zero, so they still
defer — the deferral's purpose is unchanged. The cols/rows floor stays
on the fit, including the post-flush re-check in performSafeFit.

Apply and flush share the same predicate, so no "applies but never
flushes" state can open up.
---
 .../pane-manager/pane-fit-measurability.ts    | 25 ++++++++++++-----
 .../pane-metric-options-deferral.test.ts      | 27 +++++++++++++++++++
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/src/renderer/src/lib/pane-manager/pane-fit-measurability.ts b/src/renderer/src/lib/pane-manager/pane-fit-measurability.ts
index fcd6a4615d3..57186374409 100644
--- a/src/renderer/src/lib/pane-manager/pane-fit-measurability.ts
+++ b/src/renderer/src/lib/pane-manager/pane-fit-measurability.ts
@@ -20,13 +20,18 @@ export function getProposedPaneDimensions(
   }
 }
 
-export function canMeasurePaneForFit(pane: ManagedPane): boolean {
+function hasPaneFitPixelBox(pane: ManagedPane): boolean {
   const measure = pane.container?.getBoundingClientRect
-  if (typeof measure === 'function') {
-    const rect = measure.call(pane.container)
-    if (rect.width < MIN_PANE_FIT_WIDTH_PX || rect.height < MIN_PANE_FIT_HEIGHT_PX) {
-      return false
-    }
+  if (typeof measure !== 'function') {
+    return true
+  }
+  const rect = measure.call(pane.container)
+  return rect.width >= MIN_PANE_FIT_WIDTH_PX && rect.height >= MIN_PANE_FIT_HEIGHT_PX
+}
+
+export function canMeasurePaneForFit(pane: ManagedPane): boolean {
+  if (!hasPaneFitPixelBox(pane)) {
+    return false
   }
   const dims = getProposedPaneDimensions(pane)
   if (!dims) {
@@ -37,8 +42,14 @@ export function canMeasurePaneForFit(pane: ManagedPane): boolean {
   return dims.cols >= MIN_PANE_FIT_COLS && dims.rows >= MIN_PANE_FIT_ROWS
 }
 
+/** Why only the pixel box, not the fit floor: a pane held at the 50px divider
+ *  clamp proposes ~5 cols, so the fit floor would reject it forever — it never
+ *  hides and its box never changes, so nothing would flush and it would render
+ *  a stale font until widened. A hidden pane or the transient worktree-switch
+ *  overlay is near-zero, so the pixel floor still defers those. The cols/rows
+ *  floor stays where it belongs: on the fit. */
 export function canApplyPaneMetricOptions(pane: ManagedPane): boolean {
-  return !isManagedPaneDisplayNone(pane) && canMeasurePaneForFit(pane)
+  return !isManagedPaneDisplayNone(pane) && hasPaneFitPixelBox(pane)
 }
 
 /** Why the pending check comes first: it is an O(1) WeakMap lookup, while the
diff --git a/src/renderer/src/lib/pane-manager/pane-metric-options-deferral.test.ts b/src/renderer/src/lib/pane-manager/pane-metric-options-deferral.test.ts
index f3ffa1cf4c9..e07ae670d18 100644
--- a/src/renderer/src/lib/pane-manager/pane-metric-options-deferral.test.ts
+++ b/src/renderer/src/lib/pane-manager/pane-metric-options-deferral.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import type { ManagedPane, ManagedPaneInternal } from './pane-manager-types'
 import { toPublicPane } from './pane-public-view'
+import { canApplyPaneMetricOptions, canMeasurePaneForFit } from './pane-fit-measurability'
 import {
   applyOrDeferPaneMetricOptions,
   flushDeferredPaneMetricOptions,
@@ -138,3 +139,29 @@ describe('pane-metric-options-deferral', () => {
     expect(pane.terminal.options.fontSize).toBeUndefined()
   })
 })
+
+describe('canApplyPaneMetricOptions gating', () => {
+  function makeSizedPane(rect: { width: number; height: number }, cols: number): ManagedPane {
+    return {
+      id: 2,
+      terminal: { options: {} },
+      container: { getBoundingClientRect: () => rect },
+      fitAddon: { proposeDimensions: () => ({ cols, rows: 20 }) }
+    } as unknown as ManagedPane
+  }
+
+  it('applies to a pane clamped narrow by a divider drag', () => {
+    // 50px is the divider clamp: over the pixel floor but ~5 cols, under the
+    // fit floor. Gating on the fit floor would strand it on a stale font,
+    // because it never hides and its box never changes.
+    expect(canApplyPaneMetricOptions(makeSizedPane({ width: 50, height: 600 }, 5))).toBe(true)
+  })
+
+  it('still defers on a near-zero box (hidden pane / worktree-switch overlay)', () => {
+    expect(canApplyPaneMetricOptions(makeSizedPane({ width: 0, height: 0 }, 0))).toBe(false)
+  })
+
+  it('leaves the cols/rows floor on the fit itself', () => {
+    expect(canMeasurePaneForFit(makeSizedPane({ width: 50, height: 600 }, 5))).toBe(false)
+  })
+})