Scheduled CI refresh with the output-snapshot gate

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Tesserae's compile writes a machine-readable no-op signal to .tesserae/output-snapshot.json (see tesserae/output_snapshot.py): after every compile, changed is true only when the byte-idempotent artifact set (graph layer + wiki//site//markdown_projection/) actually differs from the previous state. A scheduled workflow can gate its PR step on that flag — mirroring OpenWiki's examples/openwiki-update.yml snapshot gate.

The changed gate is what prevents endless scheduled-PR loops (the OpenWiki lesson): without it, every cron run opens a PR whether or not anything moved. Corollary: a refresh PR appearing when nothing changed in the repo is the live symptom of a byte-idempotence regression — the compile rewrote a projection of identical inputs differently. File it as a bug instead of merging it.

name: Tesserae refresh

on:
  schedule:
    - cron: "0 8 * * *"
  workflow_dispatch: {}

permissions:
  contents: write
  pull-requests: write

jobs:
  refresh:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          persist-credentials: true

      - uses: actions/setup-python@v5
        with:
          python-version: "3.11"

      - name: Install Tesserae
        run: pip install tesserae

      - name: Compile the knowledge base
        run: tesserae compile --project .

      - name: Read the output-snapshot gate
        id: gate
        run: |
          if [ "$(jq -r .changed .tesserae/output-snapshot.json)" != "true" ]; then
            echo "no-op compile — skipping PR"
            echo "changed=false" >> "$GITHUB_OUTPUT"
          else
            echo "changed=true" >> "$GITHUB_OUTPUT"
          fi

      - name: Open refresh PR
        if: steps.gate.outputs.changed == 'true'
        uses: peter-evans/create-pull-request@v7
        with:
          add-paths: .tesserae/wiki
          branch: tesserae/refresh
          commit-message: "docs: refresh tesserae knowledge base"
          title: "docs: refresh tesserae knowledge base"