Publish a report: --base-url for the markdown export and renderdiff publish #104

Status (2026-11-02)

• Done: step 1, report --markdown --base-url (#111); step 3, Cloudflare Pages and reports-repo recipes (#111), which now keep .cache/ out (#116).
• Deferred: step 2, renderdiff publish, to be built with the action's publish-repo input and smaller reports (WebP/tiling, zero-diff dedupe from Feedback from a breakpoint parity run: side labels, publishing zero-diff shots, noisy varies output #113).

What
Make a report easy to publish somewhere others can open it: absolute image links in the markdown export, a publish command that pushes a run to a reports repo, and a documented Cloudflare Pages recipe.

Why
report.html and --markdown link to the shots by relative paths, so they only work if the whole out dir is uploaded next to them. Today that means pushing the out dir to a separate GitHub repo by hand and fixing up links for the PR description. A report has two audiences: before/after images inline in a PR (needs absolute image URLs) and a clickable report.html with the slider (needs a static host, since GitHub doesn't render HTML). evidence.html is already self-contained and can go anywhere as one file.

How

1. renderdiff report <out-dir> --markdown <file> --base-url <url>: image links become <url>/<shot> instead of relative paths. This is the primitive every host builds on: upload the out dir anywhere, pass its URL.
2. renderdiff publish <out-dir> --repo owner/name [--path pr-123]: shallow-clones the repo into a temp dir, copies report.html, evidence.html, results.json and only the PNGs the results reference, commits, pushes with the user's own git/gh credentials, and prints the markdown with github.com/<repo>/raw/... URLs (they render for reviewers with access to a private repo), plus the Pages URL if Pages is on. Later, a publish-repo input on the action.
3. Docs only, no code or dependency: a Cloudflare Pages recipe in docs/output.md: npx wrangler pages deploy renderdiff-out --project-name <p> --branch pr-123, then --base-url with the deploy URL. Gives a per-PR URL for report.html; Cloudflare Access can make it private.

Out of scope: built-in R2/S3/Netlify/Vercel backends (each needs its SDK and credentials; --base-url plus one upload command covers them) and anonymous file hosts (screenshots of staging or signed-in pages would be public). Docs should warn against publishing to the main repo as a branch, since git clone fetches every branch.