[SeanLF]

kamal rollback VERSION printed "The app version 'VERSION' is not available as a container" when no host had that version, then exited 0. Scripts and CI saw a successful rollback while the old version kept running.

It now raises with the same message, so bin/kamal prints the error and exits 1. with_lock releases the deploy lock on the way out and neither hook runs. The rolled_back flag is gone: the post-deploy hook is only reached after a boot now.

Related to #1658, where kamal rollback --help lands in this same branch.

[Copilot]

🟢 Approved

No active review issues are reported for the change to fail explicitly when a requested rollback version is unavailable.

No open issues 🎉

What changed in this PR

This PR makes rollback to an unavailable container version fail with a non-zero exit status, so scripts and CI no longer report success when no rollback occurred.

Changes:

• Raise an error instead of printing a warning when the requested version is unavailable.
• Remove the rollback flag; successful boot now leads directly to the post-deploy hook.
• Update the failure test to assert the exception, lock release, and skipped hooks.

[!TIP]
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File	Description
test/​cli/​main_test.rb	Assert unavailable-version errors, lock release, and no hook execution.
lib/​kamal/​cli/​main.rb	Raise on unavailable rollback versions and simplify post-deploy hook execution.

_{Review effort: Balanced}