From c14513a8b03c26d989c78da68484302be926d7df Mon Sep 17 00:00:00 2001
From: "T.C. Ferguson" <tc.ferguson@forwardthinking.com>
Date: Sun, 12 Jul 2026 09:52:39 -1000
Subject: [PATCH] fix(tui): skip sparse compacted segments in
 isBlockUncommitted

After #5239 compaction, a later render only fills segments from
#compactedChildStart, leaving undefined holes in the prefix. Iterating
those entries crashed when retiring IRC/ephemeral cards
(`segment2.component`). Guard undefined segment slots and cover the
sparse-hole path with a red/green regression.
---
 .../modes/components/transcript-container.ts  |  6 +++++-
 .../components/transcript-container.test.ts   | 20 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/packages/coding-agent/src/modes/components/transcript-container.ts b/packages/coding-agent/src/modes/components/transcript-container.ts
index 428b46831..576dec064 100644
--- a/packages/coding-agent/src/modes/components/transcript-container.ts
+++ b/packages/coding-agent/src/modes/components/transcript-container.ts
@@ -242,9 +242,13 @@ export class TranscriptContainer
 	 */
 	isBlockUncommitted(component: Component): boolean {
 		const index = this.children.indexOf(component);
+		// Compacted prefix is already committed native history and must not be
+		// retracted. Compacted slots may be sparse holes after a later re-render
+		// (render only fills from #compactedChildStart), so the loop below must
+		// skip undefined entries.
 		if (index >= 0 && index < this.#compactedChildStart) return false;
 		for (const segment of this.#segments) {
-			if (segment.component !== component) continue;
+			if (segment === undefined || segment.component !== component) continue;
 			return segment.rowCount === 0 || segment.startRow >= this.#committedRows;
 		}
 		return true;
diff --git a/packages/coding-agent/test/modes/components/transcript-container.test.ts b/packages/coding-agent/test/modes/components/transcript-container.test.ts
index 56b24164c..6a812f0ba 100644
--- a/packages/coding-agent/test/modes/components/transcript-container.test.ts
+++ b/packages/coding-agent/test/modes/components/transcript-container.test.ts
@@ -700,6 +700,26 @@ describe("TranscriptContainer isBlockUncommitted", () => {
 		container.setNativeScrollbackCommittedRows(100);
 		expect(container.isBlockUncommitted(empty)).toBe(true);
 	});
+
+	it("survives sparse compacted segment holes when checking uncommitted status", () => {
+		const container = new TranscriptContainer();
+		const committed = new StreamingBlock(["committed"], true);
+		const live = new StreamingBlock(["live"], true);
+		container.addChild(committed);
+		container.addChild(live);
+
+		expect(container.render(40)).toEqual(["committed", "", "live"]);
+		container.setNativeScrollbackCommittedRows(2);
+		// Compaction first rewrites the compacted prefix into zero-row placeholders.
+		expect(container.render(40)).toEqual(["live"]);
+		// The next render only repopulates from #compactedChildStart, leaving a
+		// sparse hole at the compacted index. Retiring IRC/ephemeral cards walks
+		// every segment and must not crash on those undefined entries.
+		expect(container.render(40)).toEqual(["live"]);
+		expect(() => container.isBlockUncommitted(live)).not.toThrow();
+		expect(() => container.isBlockUncommitted(committed)).not.toThrow();
+		expect(container.isBlockUncommitted(committed)).toBe(false);
+	});
 });
 
 describe("TranscriptContainer renderViewportTail", () => {
-- 
2.50.1 (Apple Git-155)