#3016 extension push --dry-run skips auth, collective and version-exists checks, and prints 'No API calls were made' while calling the registry

Problem

A green swamp extension push --dry-run is not a green push. Dry-run skips authentication, the collective-membership check, the reserved-collective check and the version-exists check (src/libswamp/extensions/push.ts:551-595, :872), so an author can get a clean dry-run and then fail on push for any of those. #1393 was the same class for the label cap and shipped a local check; this issue covers the remaining registry-side checks.

Two further mismatches:

• With credentials present, dry-run still calls GET /extensions/{name}/latest for the version-drift check (extension_push.ts:572-590), and still calls OSV and npm, yet the summary prints "No API calls were made." (renderer :283).
• CI runs the real push with --yes from swamp repo init --tool none inside the extension directory (swamp-extensions publish.yml:113-118), a layout no local dry-run reproduces unless the author does the same by hand.

Expected

• With credentials present, dry-run runs auth, collective membership, reserved-collective and version-exists as read-only checks and reports each result the way the real push would. Without credentials it says which checks it could not run.
• The summary lists the API calls actually made (registry, OSV, npm), or says none were made only when that is true.
• The CI layout is reproducible locally: a documented recipe in the swamp skill, or a flag, so the author can run exactly what publish.yml runs.

Acceptance

• Dry-run against a version that already exists on the target channel reports it, exit non-zero, same wording as the real push.
• Dry-run against a collective the caller is not a member of reports it.
• Dry-run summary for a run that hit the registry lists that call; a run with no credentials and --skip-upgrade-check says no calls were made and makes none (verify with a network trace or a fake fetcher).

Out of scope

Explaining entitlement refusals by plan is #1545, which follows this issue in the same lane.

Source: the extension push assessment (2026-10-02, swamp 20261002.194016) and the Extension Push UX Plan, which groups this with its lane and order.