fix(shellenv): preserve newlines in exported env var values (#2814)

[mikeland73]

Summary

Fixes #2814.

eval "$(devbox global shellenv)" produced bash: 1__bp_interactive_mode: ambiguous redirect on every prompt for users whose PROMPT_COMMAND is set up by bash-preexec (newline-separated commands).

Root cause is in exportify (internal/devbox/envvars.go). It escaped every newline inside a double-quoted value as a backslash-newline:

case '$', '`', '"', '\\', '\n':
    strb.WriteRune('\\')

In the shell, a backslash-newline inside double quotes is a line continuation — the shell deletes it. So any env var whose value spans multiple lines had its newlines silently stripped and its lines glued together when re-imported. For the reporter's PROMPT_COMMAND, ... 2>&1 was joined onto the following __bp_interactive_mode, yielding ... 2>&1__bp_interactive_mode, which bash parses as a redirect to fd 1__bp_interactive_mode → "ambiguous redirect".

A bare newline inside double quotes is already preserved literally, so the fix is simply to stop escaping it (drop '\n' from the escape set). The nushell exporter already writes newlines literally, so this makes the two consistent.

How was it tested?

• Added TestExportifyPreservesNewlines, a regression test that asserts a multi-line value round-trips with literal newlines and contains no backslash-newline continuation. It fails on the old code and passes with the fix.
• go test ./internal/devbox/ -run 'TestExportify|TestIsValidEnvName' — all pass.
• Confirmed the exact symptom in a shell. Before (escaped):

  $ eval 'export PC="cmd >/dev/null 2>&1\
  __bp_interactive_mode";'
  # PC == "cmd >/dev/null 2>&1__bp_interactive_mode"  -> ambiguous redirect
  

  After (literal newline): the value keeps its newline and the two commands stay separate.

cc @proedie (issue reporter) — thanks for the precise diagnosis and workaround in the report, which pinpointed the exact line.

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[Copilot]

Pull request overview

This PR fixes devbox global shellenv exports for multi-line environment variable values (notably PROMPT_COMMAND as configured by bash-preexec), ensuring newlines are preserved instead of being deleted by shell line-continuation semantics.

Changes:

• Stop escaping \n inside double-quoted export values in exportify, preserving literal newlines.
• Add a regression test to ensure multi-line values round-trip with literal newlines and do not include backslash-newline continuations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/devbox/envvars.go	Removes newline from the escape set so multi-line env var values remain intact when exported/imported via shell.
internal/devbox/envvars_test.go	Adds a regression test covering multi-line export behavior and guarding against reintroducing backslash-newline continuations.

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