feat: [PR-1797] add sf migrate command and Rust CLI migration banner

[sigmachirality]

Summary

When no upgrade banner is shown on startup, the legacy CLI now nudges users to migrate to the new Rust-based sf (blueprint/preview docs). Adds a sf migrate subcommand that runs the new install script from https://cli.sfcompute.com.

Motivation

sf-cli (the Rust replacement living in sfcompute/sfcompute) is the path forward. We want every invocation of the legacy CLI to surface that path — but only when we're not already asking the user to upgrade the current binary, to avoid double-stacking banners.

The new install script at cli.sfcompute.com already moves the existing sf binary to sf-old, so users keep access to the legacy CLI during the transition. The banner and sf migrate output both call that out.

Changes

[indent]

PR Summary

Introduces a nudge toward a new Rust-based sf CLI by adding a sf migrate command (which downloads https://cli.sfcompute.com and pipes it into bash) and a recurring cyan banner shown when no upgrade banner is printed. checkVersion() is refactored to return a boolean so the caller can decide whether to print the migrate banner. The follow-up commit hardens both surfaces based on review feedback.

• Refactored checkVersion() to Promise<boolean> (returns true when an upgrade banner or auto-upgrade ran) and updated every early-return path accordingly.
• Added src/lib/migrate.ts with showMigrateBanner, handleMigrate, and registerMigrate; runInstallScript now uses a Promise.race over close/error with a try/catch around stdin.write, so missing/non-executable bash surfaces as a clean failure instead of an unhandled crash.
• Gated the migrate banner in src/index.ts on process.argv[2] (tighter scoping), excluded both migrate and upgrade subcommands, and added an SF_CLI_DISABLE_MIGRATE_BANNER opt-out which is also surfaced inside the banner text.
• Registered the new migrate command on the Commander program.

Issues

All clear! No issues remaining. 🎉

4 issues already resolved

• Migrate banner prints during sf upgrade: checkVersion returns false early when args[0] === "upgrade", and the gate in index.ts only excludes migrate, so users running sf upgrade see the cyan "switch to the Rust CLI" banner above their upgrade output — the opposite of what the inline comment promises. (fixed by commit 8f91f5f)
• spawn("bash", [], ...) in handleMigrate has no error listener — if bash is missing or non-executable (ENOENT/EACCES) the child emits an unhandled error event and crashes the CLI instead of returning a clean failure from runInstallScript. (fixed by commit 8f91f5f)
• process.argv.slice(2).includes("migrate") matches the string migrate anywhere in argv (e.g. as a flag value or positional arg of another command), and diverges from the args[0] === "upgrade" pattern used a few lines away in checkVersion.ts. Use process.argv[2] === "migrate" for consistency and tighter scoping. (fixed by commit 8f91f5f)
• No opt-out for the migrate banner: it prints on essentially every sf invocation forever, with no env var (compare SF_CLI_DISABLE_AUTO_UPGRADE in checkVersion.ts) and no cooldown like the 1h version cache. Power users running sf in scripts/shells will get spammed with no way to silence it. (fixed by commit 8f91f5f)

CI Checks

All CI checks passed on commit 63fd7bd.

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[joshi4]

LGTM.

you can consider the alternative banner copy I suggested or ship as is, I leave that up to you.