fix: fixed tab character display holes in UI by sanitizing output

- Fixed tab character display in error messages and bash tool output by applying replaceTabs() sanitization.
- Added TUI rendering sanitization documentation to AGENTS.md with guidelines for sanitizing text in tool renderers.
- Applied replaceTabs() function to error text in patch shared module to ensure proper tab-to-space conversion.
- Applied replaceTabs() function to bash tool output lines in both expanded and collapsed display modes.

AGENTS.md

@@ -406,6 +406,27 @@ logger.debug("LSP fallback triggered", { reason });
 
 Logs go to `~/.omp/logs/omp.YYYY-MM-DD.log` with automatic rotation.
 
+## TUI Rendering Sanitization
+
+All text displayed in tool renderers must be sanitized before output. Raw content (file contents, error messages, tool output) can contain characters that break terminal rendering — tabs cause visual holes, long lines overflow, and unsanitized paths leak home directories.
+
+### Rules
+
+- **Tabs → spaces**: Always pass displayed text through `replaceTabs()` before rendering. Tabs produce variable-width gaps in terminals and cause visual holes in the TUI. Import from `@oh-my-pi/pi-tui` or `../tools/render-utils`.
+- **Line truncation**: Truncate displayed lines with `truncateToWidth()` or `ui.truncate()` to prevent horizontal overflow. Use constants from `TRUNCATE_LENGTHS` for consistency.
+- **Path shortening**: Use `shortenPath()` for file paths shown to users — replaces home directory prefix with `~`.
+- **Content preview limits**: Use `PREVIEW_LIMITS` constants for collapsed/expanded line counts. Don't invent ad-hoc limits.
+
+### Where to apply
+
+Sanitization applies to **every** code path that renders text to the TUI, including:
+- Success output (file previews, command output, search results)
+- **Error messages** — these often embed file content (e.g., patch failure messages include the lines that failed to match)
+- Diff content (both added/removed lines)
+- Streaming previews
+
+A common mistake is sanitizing the happy path but forgetting error paths. If a message includes file content, it needs `replaceTabs()`.
+
 ## Commands
 
 | Command        | Description                      |

packages/coding-agent/CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## [Unreleased]
+### Fixed
+
+- Fixed tab character display in error messages and bash tool output by properly replacing tabs with spaces
 
 ## [11.4.0] - 2026-02-06
 

packages/coding-agent/src/patch/shared.ts

@@ -265,13 +265,13 @@ export const editToolRenderer = {
 
 				if (result.isError) {
 					if (errorText) {
-						text += `\n\n${uiTheme.fg("error", errorText)}`;
+						text += `\n\n${uiTheme.fg("error", replaceTabs(errorText))}`;
 					}
 				} else if (result.details?.diff) {
 					text += renderDiffSection(result.details.diff, rawPath, expanded, uiTheme, ui, renderDiffFn);
 				} else if (editDiffPreview) {
 					if ("error" in editDiffPreview) {
-						text += `\n\n${uiTheme.fg("error", editDiffPreview.error)}`;
+						text += `\n\n${uiTheme.fg("error", replaceTabs(editDiffPreview.error))}`;
 					} else if (editDiffPreview.diff) {
 						text += renderDiffSection(editDiffPreview.diff, rawPath, expanded, uiTheme, ui, renderDiffFn);
 					}

packages/coding-agent/src/tools/bash.ts

@@ -17,7 +17,7 @@ import { applyHeadTail, normalizeBashCommand } from "./bash-normalize";
 import type { OutputMeta } from "./output-meta";
 import { allocateOutputArtifact, createTailBuffer } from "./output-utils";
 import { resolveToCwd } from "./path-utils";
-import { formatBytes, wrapBrackets } from "./render-utils";
+import { formatBytes, replaceTabs, wrapBrackets } from "./render-utils";
 import { ToolError } from "./tool-errors";
 import { toolResult } from "./tool-result";
 import { DEFAULT_MAX_BYTES } from "./truncate";
@@ -271,11 +271,13 @@ export const bashToolRenderer = {
 				const hasOutput = displayOutput.trim().length > 0;
 				if (hasOutput) {
 					if (expanded) {
-						outputLines.push(...displayOutput.split("\n").map(line => uiTheme.fg("toolOutput", line)));
+						outputLines.push(
+							...displayOutput.split("\n").map(line => uiTheme.fg("toolOutput", replaceTabs(line))),
+						);
 					} else {
 						const styledOutput = displayOutput
 							.split("\n")
-							.map(line => uiTheme.fg("toolOutput", line))
+							.map(line => uiTheme.fg("toolOutput", replaceTabs(line)))
 							.join("\n");
 						const textContent = styledOutput;
 						const result = truncateToVisualLines(textContent, previewLines, width);