[Bug]: Cmd+A in the rendered Markdown file preview selects the whole app instead of the open file #30727

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open a thread that has some messages, so the chat transcript has text in it.
2. In the Files panel, open a .md file so it shows the rendered preview (not the source view).
3. Click on text inside the rendered Markdown.
4. Press Cmd+A (Ctrl+A on Windows/Linux), then Cmd+C, and paste somewhere.

Expected behavior

Only the rendered content of the open file is selected, and Cmd+C copies just that text.

Actual behavior

The selection covers the whole window: chat transcript, message metadata, composer hint text, file tree, breadcrumbs, and the Markdown body. Cmd+C copies all of it.

This only happens in the rendered Markdown view. With a .txt file open in the same Files panel, clicking or double-clicking inside the text and then pressing Cmd+A selects only the file's content. In the rendered Markdown view, clicking or double-clicking inside the text first makes no difference: Cmd+A still selects the whole app.

Cause, from reading the source on main (8b44f42):

• apps/web/src/components/files/FileMarkdownPreview.tsx renders ChatMarkdown with only a className: no tabIndex, no key handler, and no selection handling. Its parent in FilePreviewPanel.tsx (around line 944) is a plain ScrollArea, which doesn't handle these either.
• packages/shared/src/keybindings.ts has no mod+a binding. (mod+alt+a is theme.select, which is a different shortcut.)
• A project .txt file opens in the editable text editor (EditableFileSurface in FilePreviewPanel.tsx), which handles select-all once it has focus. The rendered Markdown view goes through RenderedMarkdownSurface → FileMarkdownPreview instead, so it has neither.
• Nothing in the pane handles the key, so select-all runs on the whole document. On desktop that's the Edit menu's selectAll role in apps/desktop/src/window/DesktopApplicationMenu.ts.

The draft PR #23248 (for #15927) adds a scoped Cmd/Ctrl+A handler in useSourceTextSelection.ts, but only for the read-only source preview. The rendered Markdown preview has no equivalent, so this bug stays after that PR lands. Using the same approach here, or a shared one, would likely fix both.

Related:

• [Bug]: Copying text from the Files panel returns only part of the file #15927: copying from the Files panel returns only part of the file. It's a different component (the virtualized source preview, where the copy is cut short). One comment there (fionn77, 2026-10-19) also saw Ctrl+A select the whole app on Windows from the source preview, which looks like the same missing select-all scope. fix(web): file previews copy text beyond visible rows #23248 fixes that for the source preview only.
• [Bug]: Cmd+A in the rendered Markdown file viewer selects the entire app instead of the open document #30710: my earlier copy of this report, filed from the wrong account and closed by me. It is not a maintainer decision.

Impact

Minor bug or occasional failure

Version or commit

0.1.8-nightly.20261104.4165 (tag commit 8b44f42)

Environment

macOS 26, Apple Silicon, T3 Code desktop app (Electron). Not tested on Windows or Linux.

Logs or stack traces

None. Nothing crashes or errors; only the selection area is wrong.

Screenshots, recordings, or supporting files

Markdown, rendered view (broken): the whole app is selected.

.txt file (works): only the file's text is selected.

Workaround

Drag to select the text, or triple-click a paragraph.

Filed by: Claude Opus 5.5 (Claude Code, in a T3 Code session). The bug was observed by the reporter. The agent checked the source and wrote this report.