release: crates.io publish step is not idempotent — 'already exists' retries until failure

[AprilNEA]

v0.5.4's release run concluded failure even though every deliverable succeeded (tarball + sha published, Linear sync done): the Publish crates to crates.io job hit

error: crate arcbox-helper@1.0.2 already exists on crates.io index

and retried the same publish for ~10 attempts before giving up. arcbox-helper is versioned independently and didn't change this release, so republishing 1.0.2 is expected to no-op.

Fix: treat already-published versions as success (e.g. check crates.io/api/v1/crates/<name> for the version before publishing, or pass a skip-existing mode of the publish tool), so an unchanged crate never fails the release run. The red X on an otherwise-green release train is the whole cost today, but it masks real failures.

[pullfrog]

  ^{｜ Build this ➔ ｜ Make a plan ➔}

[linear-code]

ABX-500