fix: Bugbot findings from promotion PR #397

[shujaatTracebloc]

Resolves Cursor Bugbot findings surfaced on the cli promotion PR (#397, develop → main).

Fixes:

• Upgrade pipes installer, duplicates URL — tracebloc upgrade now reuses the shared download-then-execute installer path (prepareHostInstallerCmd) and derives the URL from installerURL, so the installer's prompts keep the TTY and the URL has a single source. (Release develop → main #397 (comment))
• Upgrade ignores cancel exit path — Ctrl-C during upgrade is now treated as a quiet interrupt (exit 130), matching prepare-host, instead of surfacing as a failed upgrade. (Release develop → main #397 (comment))

Lands on develop; the promotion PR head picks these up on the next sync and Bugbot re-reviews.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes how the CLI invokes the cosign-verified installer on upgrade/prepare-host (stdin, download failure, exit codes); behavior is intentional but affects a privileged, user-facing path.

Overview
Unix tracebloc upgrade now runs the official installer the same way as prepare-host, via a shared installerRunScript helper that downloads i.sh to a temp file and executes it (optional subcommand for prepare-host). This replaces the previous curl … | bash pipeline so installer interactive prompts keep the TTY and failed downloads fail closed instead of exiting 0 on empty stdin.

Upgrade’s manual retry hint now reuses installCmd from doctor bootstrap copy instead of a second hardcoded URL, keeping installerURL as the single source.

Ctrl-C during upgrade is handled like prepare-host: installerRunInterrupted (renamed from prepareHostInterrupted) exits quietly with code 130 instead of a failed-upgrade message. Tests were updated to assert no pipe-into-bash, download-then-execute shape, and shared interrupt behavior.

^{Reviewed by Cursor Bugbot for commit 176f15d. Bugbot is set up for automated code reviews on this repo. Configure here.}