Options drained out of the pre-0.38.0 `DOCKER_OPTIONS_<PHASE>` files were copied verbatim rather than re-serialized the way `docker-options:add` stores them, so `docker-options:remove` compared the canonical string it builds against a stored value that could never match it and exited successfully without removing anything. Removal now matches stored options by shell word, and stored options are rewritten into the canonical form once on upgrade, which additionally splits an entry that carried several flags on a single line into one entry per flag so a single flag can be removed and so the readers that match on a flag prefix see one value per entry. The leftover `.migrated` sentinel drain is restored to running ahead of the global short-circuit that had made it unreachable, and the plugin's Go tests are added to the test target that had never run them.
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