Detailed Description

Gate render preview (Plan 142 prose-preservation, GATE step 3).

Purpose
-------
Regenerate the runtime store from ``oc_chat/roadmap/source`` and render the four
living views into ``.render-preview/`` (gitignored, review-only) with REAL
source/logical hashes — so the operator can read the rendered
``ROADMAP-EXTENDED.md`` / ``ROADMAP-CHANGELOG.md`` etc. at each gate without
touching any live roadmap file.

Responsibilities
----------------
- ``render_preview(repo, out_dir)`` — regenerate + render + write the four files.

Diagnostics
-----------
Domain: OC_CHAT.MAIN
Levels:
    L2 - render lifecycle
    L3 - per-artifact write
    L4 - hash tracing

Contracts
---------
- Writes only under ``.render-preview/``; never mutates a live roadmap file.

Dependencies
------------
- oc_diagnostics (structured debug logging via _dbg)
- oc_chat.registry.regenerate (imported for the contracts bootstrap it runs)
- oc_chat.registry.regenerate.pipeline (regenerate - rebuilds the runtime store from the source records)
- oc_chat.registry.render.roadmap (render_living_set and ARTIFACTS - renders the four living views and names their files)