fix(tui): preserve Code Mode row background after truncation

docs/research/CODEMODE_TUI_PRESENTATION_2026-10-04.md

@@ -34,3 +34,15 @@ Focused tests passed 13/13 in 1.72 seconds, including actual locked SDK 0.99.1 r
 The local repository check passed. One complete local test run passed 2,283 Node tests (9 skipped; 128.75 seconds) and 1,158 UI tests (32.13 seconds). The candidate was under a narrow cancellation-display correction during that run; final focused tests and exact-head CI must separately cover the frozen correction. No timeout increase, disabled assertion, executor replacement or installed-host edit was used.
 
 Real terminal pixels, keyboard expansion in the user's actual Session and package reload remain unverified. Installation was not changed.
+
+## 2026-10-05: background continuity after truncation
+
+- Status: validated at the ANSI renderer and isolated native SDK boundaries; live terminal pixels after reload remain unverified.
+- Source boundary: main `214fac3786f80107e22d5bd2b53b472461ef16b2` plus the repair linked from [#683](https://github.com/openpi-dev/openpi/issues/683).
+- Created / verified: 2026-10-05. This supplements the earlier observations without replacing their evidence.
+
+A new user screenshot showed the card background ending immediately after a truncated Bash preview. Pi's public `truncateToWidth` inserts SGR `ESC[0m`, resetting background as well as foreground. Wrapping the complete padded row once with `theme.bg` does not restore the background after that embedded reset. The regression reproduced an unpainted ellipsis and trailing space before the fix.
+
+The OpenPI frame now applies its owning background independently to each segment separated by the native full-style reset. The original reset is retained between segments, preserving foreground/style termination. Displayed text, width, truncation budgets, execution and result evidence are unchanged. This repair applies to main and child presentations through their shared Code Mode renderer.
+
+The regression checks ANSI background state for every visible character, including padding, at 40/120/240 columns in collapsed and expanded views with a long Chinese-containing Bash preview. It deliberately retains escape sequences; a stripped-text comparison could not detect this defect. Focused renderer/native tests pass 21/21 on locked Pi 0.99.1 and installed Pi 1.0.2, without model calls. Full repository checks and independent review are reported on the repair PR. The installed dirty source checkout was preserved; no assertion here proves that a running Session reloaded the repair.

extensions/codemode-display/render.ts

@@ -115,9 +115,15 @@ function framed(
       if (edges.top) rows.unshift("");
       if (edges.bottom()) rows.push("");
       const bg = tone();
-      return rows.map((row) =>
-        theme.bg(bg, row + " ".repeat(Math.max(0, width - visibleWidth(row)))),
-      );
+      return rows.map((row) => {
+        const padded = row + " ".repeat(Math.max(0, width - visibleWidth(row)));
+        // Pi's truncation/wrapping resets all SGR styles. Reapply the owning
+        // card background after each reset, including ellipsis and padding.
+        return padded
+          .split("\x1b[0m")
+          .map((segment) => theme.bg(bg, segment))
+          .join("\x1b[0m");
+      });
     },
     invalidate() {},
   };

tests/extensions/codemode-display/render.test.ts

@@ -552,3 +552,51 @@ test("a shared row puts the status in the call header and hides output", () => {
   assert.doesNotMatch(body.join("\n"), /completed/u);
   assert.doesNotMatch(body.join("\n"), /first|second|│/u);
 });
+
+test("truncated previews keep the card background through ellipsis and right padding", () => {
+  const colorTheme = {
+    fg: (_color: string, text: string) => `\x1b[38;5;145m${text}\x1b[39m`,
+    bg: (_color: string, text: string) => `\x1b[48;5;237m${text}\x1b[49m`,
+    bold: (text: string) => `\x1b[1m${text}\x1b[22m`,
+  } as Theme;
+  const value = result("done", [
+    {
+      id: "1",
+      name: "bash",
+      status: "running",
+      args: JSON.stringify({
+        command: `bunx biome format --write ${"extensions/中文.ts ".repeat(20)}`,
+      }),
+    },
+  ]);
+  for (const width of [40, 120, 240]) {
+    for (const expanded of [false, true]) {
+      const rows = codemodeRenderers.renderResult!(
+        value,
+        { expanded, isPartial: true },
+        colorTheme,
+        context(expanded),
+      ).render(width);
+      if (!expanded)
+        assert.ok(
+          rows.some((row) => row.includes("\x1b[0m")),
+          "exercise native truncation/wrapping resets",
+        );
+      for (const row of rows) {
+        assert.equal(visibleWidth(row), width);
+        let background = false;
+        for (const token of row.matchAll(/\x1b\[([\d;]*)m|([^\x1b])/gu)) {
+          if (token[1] !== undefined) {
+            if (token[1] === "0" || token[1] === "49") background = false;
+            if (token[1] === "48;5;237") background = true;
+          } else {
+            assert.ok(
+              background,
+              `unpainted cell at width=${width}, expanded=${expanded}: ${JSON.stringify(row)}`,
+            );
+          }
+        }
+      }
+    }
+  }
+});