Does `bun upgrade` provide the source code?

Yes, it provides the commits for a "changelog". Canary builds track main closely, 98f664962 is the tip of main.

~$ bun upgrade [2.42s] Upgraded.

Welcome to Bun's latest canary build!

Report any bugs:

    https://github.com/oven-sh/bun/issues
Changelog:

    https://github.com/oven-sh/bun/compare/f161e0311...98f664962

Isn't the source code in the git repo?

v1.4 hasn't been tagged... No idea what the shipped binary corresponds to.