Thumbnail Placement

Read in Step 6. The site's templates compute the image path from the talk-page filename, including for social previews:

assets/images/thumbnails/{talk_page_stem}-thumbnail.png

For geecon-2026-absolutely-right.md, use assets/images/thumbnails/geecon-2026-absolutely-right-thumbnail.png. Do not set thumbnail_url: in frontmatter; see common mistakes, entry 1c for its featured-talk flag semantics.

Decide explicitly:

• If the convention-path image exists, select it as {thumbnail_source} for validation below. A valid PNG needs no rewrite; retain legacy dimensions, including 4:3 thumbnails, so recording updates do not require regeneration. A failed decoding or format validation stops the publish until a valid source is available.
• If it is absent and the talk has slides, a YouTube thumbnail, or a video frame, invoke Skill(skill: "illustrations") with thumbnail_scope: source_only. Follow its source-generation scope: it returns an approved image without calling shownotes or placing/publishing it. Set {thumbnail_source} to the returned file's actual path; the generator may emit PNG or JPEG. Keep that original for its other destinations.
• If it is absent and no source exists yet, explicitly record the deferral. The site's placeholder SVG is the interim. When a source becomes available, invoke the same source-only illustrations handoff and place its result through the command below.

For an available image, run the placement owner; never rename JPEG bytes to PNG:

"{python_path}" "{speaker_toolkit_root}/skills/shownotes-publisher/scripts/place-thumbnail.py" \
  --source "{thumbnail_source}" \
  --destination "{shownotes_repo}/assets/images/thumbnails/{talk_page_stem}-thumbnail.png"

The script's module docstring owns accepted inputs, output validation, atomic placement, source preservation, dependencies, and exit codes. On exit 0, require ok: true and use its emitted PNG path. On failure, stop publishing, repair the reported input/runtime/filesystem problem, and rerun. Never substitute a raw copy.

The site's thumbnail display geometry accepts the illustrations owner's source dimensions. Check title and face visibility in the destination preview. Finish Step 6 only after validated placement or the explicit no-source deferral, then proceed to Step 7. Retain the approved thumbnail_source and placement receipt with the publication result. Return them to an invoking illustrations workflow so it can resume its remaining tracking work without generating the image again.