fix(launcher): surface curl diagnostics and restore the terminal CLI install prompt

[ryan-mt]

What changed

Two launcher bugs in launcher/start.sh.template that hid information from terminal users:

1. verify_webview_origin never surfaced the captured curl diagnostic. The error file was read back with detail=$(< "$err" 2>/dev/null). In bash, $(< file) only works as the sole element of a command substitution; with the extra redirection it becomes a null command and produces no output, so detail was always empty and every webview-origin failure logged the generic curl exited non-zero with no diagnostic fallback instead of the real cause (connect refused, timeout, HTTP status, ...) that the comment block above documents as the purpose of this code. Now reads with cat.

   Empirical check (bash 5.3):

   $ echo "connection refused" > f
   $ a=$(< f 2>/dev/null); echo "[$a]"
   []
   $ a=$(cat f 2>/dev/null || true); echo "[$a]"
   [connection refused]
   

2. The interactive Install Codex CLI now? [Y/n] terminal prompt was unreachable. The launcher redirects stdout/stderr into the log early (exec >>"$LOG_FILE" 2>&1), so the later [ -t 1 ] check in is_interactive_terminal was always false. Terminal launches with a missing CLI were routed to the GUI prompt path, or hard-exited when no update manager is installed — the elaborate prompt_install_missing_cli flow could never run (and its printf would have gone into the log file anyway). Interactivity is now captured before the redirect, and the prompt reads/writes via /dev/tty.

Source-of-truth files

• launcher/start.sh.template (runtime launcher behavior)
• tests/scripts_smoke.sh (added template assertions)

Validation

• bash -n on install.sh, scripts/lib/*.sh, launcher/start.sh.template, build scripts — clean
• bash tests/scripts_smoke.sh on this branch in Ubuntu (WSL): All script smoke tests passed
• Same suite passes identically on main (baseline)

Notes / limitations

• Verified on Ubuntu under WSL2; not exercised against a real packaged install.

[ilysenko]

Reviewed. No blocking issues found; CI is green and the launcher changes are scoped to the source template.