Change:

--incompatible_disable_starlark_host_transitions makes this Starlark syntax illegal:

cfg = "host"

Instead use:

cfg = "exec"

Rationale:

Rules can't be configured for the host configuration, which is the machine Bazel rules on. They must be configured for the exec configuration, which is the machine that runs builds actions. Sometimes these are the same (local builds), but not always (remote execution builds). exec correctly captures these differences.

Even with this flag disabled, cfg = "host" is an alias for cfg = "exec". So this is a no-op beyond the syntax cleanup.

Expected error for unmigrated code:

Error in label: 'cfg = "host"' is deprecated and should no longer be used. Please use 'cfg = "exec"' instead.