From a8c9128841eb953a2d3afbe445fc15e130f5cb0d Mon Sep 17 00:00:00 2001
From: Nick Gregory <computerfreak97@gmail.com>
Date: Wed, 7 Jan 2026 16:04:49 -0800
Subject: [PATCH 1/2] improve SearchLineCache performance

---
 addons/addon-search/src/SearchLineCache.ts | 24 +++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/addons/addon-search/src/SearchLineCache.ts b/addons/addon-search/src/SearchLineCache.ts
index 535a3cc5e9..175f3919cd 100644
--- a/addons/addon-search/src/SearchLineCache.ts
+++ b/addons/addon-search/src/SearchLineCache.ts
@@ -38,6 +38,9 @@ export class SearchLineCache extends Disposable {
   private _linesCache: LineCacheEntry[] | undefined;
   private _linesCacheTimeout = this._register(new MutableDisposable());
   private _linesCacheDisposables = this._register(new MutableDisposable());
+  // Track access to avoid recreating a timeout on every init call which occurs once per search
+  // result (findNext/findPrevious -> _highlightAllMatches -> find loop).
+  private _lastAccessTimestamp = 0;
 
   constructor(private readonly _terminal: Terminal) {
     super();
@@ -57,15 +60,34 @@ export class SearchLineCache extends Disposable {
       );
     }
 
-    this._linesCacheTimeout.value = disposableTimeout(() => this._destroyLinesCache(), Constants.LINES_CACHE_TIME_TO_LIVE);
+    this._lastAccessTimestamp = Date.now();
+    if (!this._linesCacheTimeout.value) {
+      this._scheduleLinesCacheTimeout(Constants.LINES_CACHE_TIME_TO_LIVE);
+    }
   }
 
   private _destroyLinesCache(): void {
     this._linesCache = undefined;
+    this._lastAccessTimestamp = 0;
     this._linesCacheDisposables.clear();
     this._linesCacheTimeout.clear();
   }
 
+  private _scheduleLinesCacheTimeout(delay: number): void {
+    this._linesCacheTimeout.value = disposableTimeout(() => {
+      if (!this._linesCache) {
+        return;
+      }
+      const now = Date.now();
+      const elapsed = now - this._lastAccessTimestamp;
+      if (elapsed >= Constants.LINES_CACHE_TIME_TO_LIVE) {
+        this._destroyLinesCache();
+        return;
+      }
+      this._scheduleLinesCacheTimeout(Constants.LINES_CACHE_TIME_TO_LIVE - elapsed);
+    }, delay);
+  }
+
   public getLineFromCache(row: number): LineCacheEntry | undefined {
     return this._linesCache?.[row];
   }

From bf7c95b6ccc4b65c4e55ce2a5eab9cb351567e0a Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Thu, 8 Jan 2026 19:50:51 -0800
Subject: [PATCH 2/2] Flush writes on resize

Fixes #5597
---
 src/common/CoreTerminal.ts           |  4 ++++
 src/common/input/WriteBuffer.test.ts | 19 +++++++++++++++++
 src/common/input/WriteBuffer.ts      | 32 ++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/src/common/CoreTerminal.ts b/src/common/CoreTerminal.ts
index 5a46570ecb..dd312af11a 100644
--- a/src/common/CoreTerminal.ts
+++ b/src/common/CoreTerminal.ts
@@ -176,6 +176,10 @@ export abstract class CoreTerminal extends Disposable implements ICoreTerminal {
     x = Math.max(x, MINIMUM_COLS);
     y = Math.max(y, MINIMUM_ROWS);
 
+    // Flush pending writes before resize to avoid race conditions where async
+    // writes are processed with incorrect dimensions
+    this._writeBuffer.flushSync();
+
     this._bufferService.resize(x, y);
   }
 
diff --git a/src/common/input/WriteBuffer.test.ts b/src/common/input/WriteBuffer.test.ts
index 8910642301..c534bbae48 100644
--- a/src/common/input/WriteBuffer.test.ts
+++ b/src/common/input/WriteBuffer.test.ts
@@ -106,5 +106,24 @@ describe('WriteBuffer', () => {
       wb.writeSync('1', 10);
       assert.equal(last, '11'); // 1 + 10 sub calls = 11
     });
+    it('flushSync processes all pending writes', done => {
+      wb.write('a', () => { cbStack.push('a'); });
+      wb.write('b', () => { cbStack.push('b'); });
+      wb.write('c', () => { cbStack.push('c'); });
+      wb.flushSync();
+      assert.deepEqual(stack, ['a', 'b', 'c']);
+      assert.deepEqual(cbStack, ['a', 'b', 'c']);
+      wb.write('x', () => { cbStack.push('x'); });
+      wb.write('', () => {
+        assert.deepEqual(stack, ['a', 'b', 'c', 'x', '']);
+        assert.deepEqual(cbStack, ['a', 'b', 'c', 'x']);
+        done();
+      });
+    });
+    it('flushSync with no pending writes is a no-op', () => {
+      wb.flushSync();
+      assert.deepEqual(stack, []);
+      assert.deepEqual(cbStack, []);
+    });
   });
 });
diff --git a/src/common/input/WriteBuffer.ts b/src/common/input/WriteBuffer.ts
index 801cf3efba..f6d83ba882 100644
--- a/src/common/input/WriteBuffer.ts
+++ b/src/common/input/WriteBuffer.ts
@@ -54,6 +54,38 @@ export class WriteBuffer extends Disposable {
     this._didUserInput = true;
   }
 
+  /**
+   * Flushes all pending writes synchronously. This is useful when you need to
+   * ensure all queued data is processed before performing an operation that
+   * depends upon everything being parsed like resize.
+   *
+   * Note: This is unreliable with async parser handlers as it does not wait for
+   * promises to resolve.
+   */
+  public flushSync(): void {
+    // exit early if another sync write loop is active
+    if (this._isSyncWriting) {
+      return;
+    }
+    this._isSyncWriting = true;
+
+    // Process all pending chunks synchronously
+    let chunk: string | Uint8Array | undefined;
+    while (chunk = this._writeBuffer.shift()) {
+      this._action(chunk);
+      const cb = this._callbacks.shift();
+      if (cb) cb();
+    }
+
+    // Reset buffer state
+    this._pendingData = 0;
+    this._bufferOffset = 0x7FFFFFFF;
+    this._writeBuffer.length = 0;
+    this._callbacks.length = 0;
+
+    this._isSyncWriting = false;
+  }
+
   /**
    * @deprecated Unreliable, to be removed soon.
    */