Returning the hardcoded default from get_caddy_ingress_image() when
the spec key was absent meant every `deployment start` would patch a
running Caddy back to :latest — silently reverting any image set
out-of-band (ansible playbook, prior deployment's spec).
Make get_caddy_ingress_image() return Optional[str]. Install path
still falls back to the default (needs *some* image to install); the
update-on-reuse path treats None as "operator didn't ask, leave the
running Caddy alone".
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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