refresh: land only what the build changed, as a patch on the latest gh-pages, instead of copying a stale checkout over it

A run's source checkout is taken at job start; the gh-pages checkout it commits to is taken minutes later, after
the queue and the build. Copying the whole folder reverted whatever landed in between (it just undid two commits
to Havre). Now the build's own diff is applied to the newest gh-pages, three-way; `from` keeps the whole-folder
landing, which is what it's for.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VAvUH72XsdCitHdh3t7mjr

.github/workflows/refresh.yml

@@ -77,11 +77,25 @@ jobs:
         run: |
           set -eu
           [ -f "pages/ventures/ventures.json" ] || { echo "::error::no ledger on gh-pages"; exit 1; }
-          rm -rf "pages/ventures/$SLUG"
-          cp -R "work/ventures/$SLUG" "pages/ventures/$SLUG"
-          find "pages/ventures/$SLUG" -name __pycache__ -type d -prune -exec rm -rf {} +
-          cd pages
-          git add --all "ventures/$SLUG"
+          find "work/ventures/$SLUG" -name __pycache__ -type d -prune -exec rm -rf {} +
+          if [ -n "$FROM" ]; then
+            # a rework from another branch lands whole, in place of what gh-pages has
+            rm -rf "pages/ventures/$SLUG"
+            cp -R "work/ventures/$SLUG" "pages/ventures/$SLUG"
+            cd pages
+            git add --all "ventures/$SLUG"
+          else
+            # the build's own changes only, applied to the newest gh-pages: the source was checked out minutes ago, and
+            # copying it whole would revert whatever landed since (it did, once)
+            cd work
+            git add --all "ventures/$SLUG"
+            git diff --cached --binary > ../build.patch
+            cd ../pages
+            git pull -q --rebase origin gh-pages
+            if [ -s ../build.patch ]; then
+              git apply --index --3way ../build.patch || { echo "::error::the build's changes don't apply to gh-pages as it stands now: refresh again"; exit 1; }
+            fi
+          fi
           if git diff --cached --quiet; then echo "nothing changed in ventures/$SLUG"; exit 0; fi
           git diff --cached --stat | tail -25
           git -c user.name='github-actions[bot]' -c user.email='github-actions[bot]@users.noreply.teahub.xyz' \