workbench-preview :daily floating tag no longer updated (daily channel disabled) #196

Summary

ghcr.io/posit-dev/workbench-preview:daily is no longer being updated with the
latest daily development build. Consumers pinned to :daily are effectively stuck.

Root cause

The floating channel tag is derived directly from the dev version's channel
name (bakery emits a plain {{ Channel }} tag for the primary-OS / primary-variant /
channel-head target — see posit_bakery/config/tag.py and
ImageTarget.tag_patterns). So channel: daily → :daily, channel: preview → :preview.

In commit 2fe311c ("Temporarily disable daily builds") the daily devVersion
for both workbench and workbench-session was commented out in bakery.yaml,
leaving only the preview devVersion:

    devVersions:
      # Dailies temporarily disabled. See https://github.com/posit-dev/images-shared/issues/632
      # - sourceType: stream
      #   product: workbench
      #   channel: daily
      #   ...
      - sourceType: stream
        product: workbench
        channel: preview
        ...

With the daily channel gone, bakery no longer produces a :daily tag — the same
content is now published under :preview on the same workbench-preview repo.
Nothing is broken in the build itself; the tag simply changed name.

This was a deliberate workaround for shared-tooling issue
posit-dev/images-shared#632 (daily + preview both default release_branch: latest,
resolve to the same version, and produced duplicate builds / duplicate floating
tags pointing at the same digest).

Impact

• Anything pulling ghcr.io/posit-dev/workbench-preview:daily (and the equivalent
  workbench-session-init-preview:daily) stopped receiving updates on 2026-06-22.
• Current dailies are available under :preview instead.

Options

1. Re-enable daily once images-shared#632 lands (the duplicate-build
   problem is what forced disabling it in the first place).
2. Add daily as a tag alias on the preview build so :daily and :preview
   both track the current daily while daily and preview remain identical
   content. Needs a bakery mechanism for extra/alias channel tags (does not exist
   today — tags are 1:1 with the channel name), so this likely rolls into #632.
3. Document the rename and tell consumers to switch :daily → :preview if
   the :daily tag is not coming back.

Blocked by / related to: posit-dev/images-shared#632