Stop painting full-width grey spacer rows on user messages

src/tui/components/event-log-assembly.ts

@@ -611,14 +611,17 @@ function blockToLines(
       ];
     }
     case "user": {
-      // A subtle box with a blank padded row above and below so the text has
-      // breathing room. Text starts at column 1 to line up with the assistant's
-      // "●" marker; a 1-col right margin keeps the fill off the edge.
+      // Subtle box: paint background only on content rows. Blank spacer rows
+      // used to be full-width bg fills and could flash as solid grey blocks
+      // during scroll/repaint when content was empty or mid-frame.
+      // plainLines/wrapRanges always yield ≥1 row (even for ""), so gate on
+      // real emptiness rather than userLines.length.
+      if (!block.content.trim()) return [];
       const bg = color("userMessageBg");
       const LEFT = 1;
       const RIGHT = 1;
       const innerWidth = Math.max(1, width - LEFT - RIGHT);
-      const blankRow = [{ text: " ".repeat(width), backgroundColor: bg }];
+      const blankRow: StyledLine = [{ text: "" }];
       const userLines = plainLines(
         compactUserCodeBlocks(block.content),
         { color: color("text"), backgroundColor: bg },

src/tui/components/event-log.test.ts

@@ -15,6 +15,7 @@ import {
 } from "./event-log.js";
 import { formatElapsed } from "./in-flight-indicator.js";
 import type { ContentBlock, ContentBlockData } from "../use-stream.js";
+import { color } from "../theme.js";
 
 function asBlock(data: ContentBlockData & { id: string }): ContentBlock {
   return data as ContentBlock;
@@ -706,6 +707,25 @@ describe("flat line buffer", () => {
     }
   });
 
+  test("user banner spacer rows have no background while body keeps userMessageBg", () => {
+    const block: ContentBlock = { type: "user", id: "user-bg", content: "hello" };
+    const lines = buildLines([block], COLUMNS, false, isExpanded);
+    // blank spacer, body, blank spacer
+    expect(lines.length).toBe(3);
+    const bg = color("userMessageBg");
+    expect(lines[0]!.every((seg) => seg.backgroundColor === undefined)).toBe(true);
+    expect(lines[2]!.every((seg) => seg.backgroundColor === undefined)).toBe(true);
+    expect(lines[1]!.some((seg) => seg.backgroundColor === bg)).toBe(true);
+    expect(lines[1]!.every((seg) => seg.backgroundColor === bg)).toBe(true);
+  });
+
+  test("empty or whitespace user content yields no grey box", () => {
+    for (const content of ["", "   ", "\n\t"]) {
+      const block: ContentBlock = { type: "user", id: "empty-user", content };
+      expect(buildLines([block], COLUMNS, false, isExpanded)).toEqual([]);
+    }
+  });
+
   test("buildResourceBanner shows brand, workspace path, and optional skills/plugins", () => {
     const workspace = "/home/user/project";
     const banner = buildResourceBanner([{ name: "scribe" }, { name: "tdd" }], ["exa"], 80, workspace);