feat(vercel/sandbox): fix interactive shell#236
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LukeSheard
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Jun 30, 2026
AndyW22
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Jun 30, 2026
Co-authored-by: Andy <76787794+AndyW22@users.noreply.github.com>
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AndyW22
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Jun 30, 2026
…t readline non-printing markers, so bash overcounts the prompt width and miscalculates cursor position on long/wrapping lines and during line editing. This commit fixes the issue reported at packages/sandbox/src/interactive-shell/interactive-shell.ts:25 ## Bug In `packages/sandbox/src/interactive-shell/interactive-shell.ts` the prompt was changed to: ```ts const PS1 = `▲ \x1b[2m$PWD/\x1b[0m `; ``` This is sent verbatim as the `PS1` env var to the interactive session's shell. The color escape sequences `\x1b[2m` (dim) and `\x1b[0m` (reset) are invisible but occupy ~4 bytes each on the wire. Bash's readline counts **every** character in `PS1` toward the displayed prompt width *unless* it is wrapped in the non-printing markers `[ ... ]` (which bash decodes into the raw readline bytes `\001` = `RL_PROMPT_START_IGNORE` and `\002` = `RL_PROMPT_END_IGNORE`). The previous prompt correctly used those markers: `▲ [\e[2m]\w/[\e[0m]` . The new one dropped them. ### Failure mode / trigger When the customer image's `/bin/sh` is **bash** (very common), readline now believes the prompt is ~8 columns wider than it actually is. Concrete symptoms: * Typing a command line long enough to wrap past `$COLUMNS` causes the cursor to land on the wrong column / row. * Pressing Up/Down through history, or editing (Ctrl-A, arrow keys) on a wrapped line, redraws at the wrong position, leaving visual garbage. It is reproducible whenever the typed line length approaches the terminal width. Severity is cosmetic (no data loss), but it is a real, deterministic regression for bash sessions. ### Why the PR removed the markers The intent was portability: `[`, `]`, `\e`, `\w` are bash-specific and are printed literally by dash/busybox-ash, so the old prompt rendered raw escape text under those shells. Using literal ESC bytes + `$PWD` fixes that for non-bash shells. ## Fix Wrap the escape sequences in the **raw** readline ignore bytes `\x01`/`\x02` rather than the bash-only `[`/`]` text macros: ```ts const PS1 = `▲ \x01\x1b[2m\x02$PWD/\x01\x1b[0m\x02 `; ``` * **bash**: `\x01`/`\x02` *are* `RL_PROMPT_START_IGNORE`/`RL_PROMPT_END_IGNORE` — exactly the bytes that `[`/`]` decode to — so readline correctly excludes the escapes from prompt-width tracking. Width math is restored. * **dash / busybox-ash / zsh**: these are C0 control characters (SOH/STX) that terminal emulators render as non-printing, so the visible prompt is unchanged and `$PWD` + color still render. This keeps the cross-shell portability the PR was aiming for. This achieves both goals with a single PS1 string, so the limitation noted in the issue (no string works across bash and dash) turns out to be avoidable using the raw readline markers instead of the bash-specific text form. Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com> Co-authored-by: marc-vercel <marc.codina@vercel.com>
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This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## sandbox@3.3.1 ### Patch Changes - Fix the interactive shell prompt so that it is built from POSIX-portable primitives — it renders correctly regardless of which POSIX compatible shell (`bash`, `dash`, busybox `ash`) a custom image ships as `/bin/sh`. ([#236](#236)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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Fix interactive shell, so that we render the Vercel icon correctly between different shells.
Before, with a custom image:
Now: