Document nightly catch-up; stop rendering version footer

Two related cleanups noticed during the v2026.513.0 release run:

1. Release ceremony was missing the nightly catch-up step. After the
   release PR merges, main is ahead of nightly by the release commits
   and nightly's .sync-state.json still says branch_mode "nightly"
   with the old base_release_tag. The merge-down + branch_mode flip is
   manual the first time and must be done by hand. Added as the 4th
   post-merge follow-up, plus a troubleshooting row for the symptom
   "nightly run reports release mode unexpectedly".

2. paperclip_version frontmatter was being rendered as a visible
   "Documenting Paperclip vX.Y.Z" footer on every release-stamped
   page. Treat the field as internal metadata only: build-release.mjs
   still parses and surfaces it into content.json (queryable for
   tooling), but the SPA no longer prints it on-page. Updated the
   skill's builder note to match.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

maintenance/runbook.md

@@ -125,7 +125,7 @@ When a new parent release tag drops (`v2026.X.Y`):
    - Voice quality of any newly-authored pages — these go live on `docs.paperclip.ing` the moment you merge.
    - Frontmatter `paperclip_version` correctly stamped on changed pages.
 4. Merge to `main` when satisfied.
-5. **After merge — three follow-ups:**
+5. **After merge — four follow-ups:**
    - Tag the merge commit:
      ```sh
      git checkout main && git pull
@@ -133,7 +133,18 @@ When a new parent release tag drops (`v2026.X.Y`):
      git push --tags
      ```
    - Verify `.sync-state.json` on `main` now shows `base_release_tag: v2026.X.Y` and `base_release_sha` matches.
-   - Cloudflare Pages auto-deploys on push to `main`. Confirm `docs.paperclip.ing` renders the new "Documenting Paperclip v2026.X.Y" footer.
+   - Cloudflare Pages auto-deploys on push to `main`. Confirm `docs.paperclip.ing` is rebuilt successfully.
+   - **Catch `nightly` back up.** After the release PR merges, `main` is ahead of `nightly` by the release commits and `nightly`'s `.sync-state.json` still reads `branch_mode: "nightly"` with the old `base_release_tag`. Merge `main` down and flip `branch_mode` back, otherwise the next `/sync-docs` run sees a stale state file:
+     ```sh
+     git checkout nightly && git pull
+     git merge main
+     # Edit .sync-state.json on nightly:
+     #   "branch_mode": "nightly"   (the merge inherited "release" from main)
+     # Leave base_release_tag at v2026.X.Y — that's now the correct cumulative-diff base.
+     git commit -am "nightly: catch up to v2026.X.Y release"
+     git push
+     ```
+     The skill's "merge main → nightly at start of each nightly run" rule (see [Daily operation](#daily-operation)) is what keeps subsequent runs aligned, but the **first** post-release merge-down has to be done by hand because the `branch_mode` flip is manual.
 
 **Large gaps (8+ release tags behind)**
 
@@ -247,4 +258,5 @@ Read it weekly. Items get moved out as they're addressed.
 | Skill won't auto-detect mode | `.sync-state.json` missing or malformed | Seed from `scripts/sync/state.example.json`, set `base_release_tag` to current parent state |
 | Verify-edit reports false-positive `env-var-missing` | Env var defined in CLI / plugin source not in watcher's source list | Add to FOLLOW-UPS, or (preferred) extend `verify-edit.mjs`'s env-var source list |
 | First nightly run after release produces empty manifest | Cumulative diff is empty because nightly's base bumped | Verify `.sync-state.json` `base_release_tag` matches parent's latest release tag |
+| Nightly run reports `release` mode unexpectedly | `branch_mode` wasn't flipped back to `nightly` after the last release merge-down | Edit `.sync-state.json` on `nightly`: set `branch_mode` to `"nightly"`, commit, push. See [Release ceremony](#release-ceremony) step 5 follow-up #4 |
 | `wrangler pages deploy` fails | Cloudflare auth | `wrangler login` |

site/app.js

@@ -798,16 +798,6 @@ function appendPageFeedback(article, page, file) {
     </span>
   `;
   article.appendChild(block);
-
-  // If the build pipeline parsed a `paperclip_version` from the page's YAML
-  // frontmatter, surface it as a small sibling line under the feedback row.
-  const version = page.frontmatter?.paperclip_version;
-  if (version) {
-    const versionBlock = document.createElement('div');
-    versionBlock.className = 'page-version';
-    versionBlock.textContent = `Documenting Paperclip ${version}`;
-    article.appendChild(versionBlock);
-  }
 }
 
 function insertMetaRow(article, page) {

skills/sync-docs/SKILL.md

@@ -217,7 +217,7 @@ If all pass: make the mechanical edit directly. Examples: append a row to `envir
 
 **Batched-release mode is exhaustive.** In `--batched` release mode, every doc-relevant manifest entry in EACH window must be processed — no subsampling. This is the equivalent of how nightly mode handles every entry of its cumulative manifest. Wet-run subsampling (e.g. "pick 2 representative entries") was scope-control for testing, not skill design. Skipping entries in real catchup runs leaves docs incomplete. Per-window tier classification still applies — auto-merge and PR entries both get processed; the only thing that varies is how many entries each window contains (some releases are small).
 
-> **Builder note.** `site/build-release.mjs` strips and surfaces YAML frontmatter into `content.json` (the SPA renders `paperclip_version` as a "Documenting Paperclip <version>" footer). Authored pages SHOULD include `paperclip_version` in release mode — the voice rule below is live, not aspirational.
+> **Builder note.** `site/build-release.mjs` strips YAML frontmatter from the rendered markdown body and surfaces parsed fields into `content.json`. `paperclip_version` is **internal metadata only** — the SPA does NOT render it on-page. Authored pages SHOULD still include `paperclip_version` in release mode so the field is queryable from `content.json` (e.g., to drive future per-page version badges or release-PR diff tooling) and so the source of truth for "which release does this page document" lives next to the prose.
 
 **PR tier** (judgment calls):
 - Spawn a subagent per entry, in parallel where possible. Give each: