Feature request: opt out of auto-update / pin a version for Macs below the new minimum OS

This is a feature request about the update mechanism, not a bug report about macOS 12 support. I accept the decision in #37019 / #37070 to raise the minimum macOS to 13. The problem is the downstream consequence for users on hardware that cannot upgrade past Monterey, and the lack of any opt-out.

Context

• MacBook Pro A1707 (2017, Intel). macOS 12.7.6 Monterey is the hardware ceiling — this machine will never run macOS 13.
• Codex desktop worked fine on build 6119 (26.727.x).
• Sparkle auto-updated to build 6223+ → app no longer launches (NSOSStatusErrorDomain Code=-10825, LC_BUILD_VERSION minos 13.0).
• The workaround from @gpeal (download 26.715.72359) works — but only until Sparkle runs again and re-installs the broken build.

The gap

Once a Mac is on an OS below the new minimum, there is no supported way to stay on the last-working version:

1. Sparkle's appcast still advertises minimumSystemVersion 12.0, so the incompatible update keeps being offered.
2. There is no "disable auto-update" toggle in the app.
3. There is no "check for updates but let me choose" option.
4. There is no documented way to pin a version.

The only way to stay on 26.715 is to block oaistatic.com at the network level — not something most users will figure out, and it also blocks legitimate downloads.

Request

Any one of these would unblock users on unsupported-but-still-functional hardware:

1. Fix the Sparkle appcast minimumSystemVersion to 13.0 so macOS 12 clients stop being offered the incompatible build. (This is also just correct — the manifest should match the binary.)
2. Add a "Check for updates but let me choose to install" option, or a "Disable auto-update" toggle in Settings.
3. Document a supported way to pin a version (a defaults key, a config file, or a "skip this version" action in the update prompt).

I'm not asking to restore macOS 12 support. I'm asking for a graceful way to stay on the last version that works on my hardware, so I'm not one reboot away from a bricked install every time Sparkle runs.

Why this isn't a duplicate of #37019 / #37070

Those are bug reports about the macOS 12 drop and were closed as "won't fix" (Chrome/security rationale). This is a feature request about the update mechanism itself, which applies to any future minimum-OS bump — not just this one. The next time the minimum OS rises, the same users will be in the same loop unless one of the above options exists.