ci: pilot informational Python line and branch coverage (#651)

.github/workflows/python-coverage-pilot.yml

@@ -0,0 +1,85 @@
+name: Python coverage pilot
+
+on:
+  pull_request:
+    branches:
+      - master
+    paths:
+      - ".github/workflows/python-coverage-pilot.yml"
+      - "backend/domain/text_identity.py"
+      - "backend/research_markup.py"
+      - "tests/test_text_identity.py"
+      - "tests/fixtures/text_identity_vectors.json"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: python-coverage-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  text-identity-coverage:
+    name: Python line + branch coverage (informational)
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Set up Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.12"
+
+      - name: Install pinned coverage.py
+        run: >-
+          python -m pip install --isolated --disable-pip-version-check
+          "--only-binary=:all:" "coverage==7.16.2"
+
+      # B1 / #651: bounded pilot on existing, pure-Python test vectors.
+      # This is NOT whole-backend coverage and has no fail-under threshold.
+      # Keep the existing full PRKS Test Gate unchanged (#180 guard).
+      - name: Measure text identity line and branch coverage
+        shell: bash
+        run: |
+          set -euo pipefail
+          python -m coverage run --branch --source=backend.domain.text_identity \
+            -m unittest discover -s tests -p test_text_identity.py
+          python -m coverage report --show-missing
+          python -m coverage json -o "$RUNNER_TEMP/prks-coverage.json"
+          python - <<'PY'
+          import json
+          import os
+          from pathlib import Path
+
+          totals = json.loads(
+              (Path(os.environ["RUNNER_TEMP"]) / "prks-coverage.json").read_text(
+                  encoding="utf-8"
+              )
+          )["totals"]
+          lines = totals["num_statements"]
+          branches = totals["num_branches"]
+          line_rate = (
+              f'{100 * totals["covered_lines"] / lines:.1f}%' if lines else "N/A"
+          )
+          branch_rate = (
+              f'{100 * totals["covered_branches"] / branches:.1f}%'
+              if branches
+              else "N/A"
+          )
+          summary = (
+              "## Python coverage pilot (text identity only)\n\n"
+              f'- Lines: {totals["covered_lines"]}/{lines} ({line_rate})\n'
+              f'- Branches: {totals["covered_branches"]}/{branches} ({branch_rate})\n\n'
+              "Informational only; no threshold. This is a focused module, "
+              "not overall Python/backend coverage. Raw coverage data stays "
+              "on the runner and is not uploaded.\n"
+          )
+          print(summary)
+          with Path(os.environ["GITHUB_STEP_SUMMARY"]).open("a", encoding="utf-8") as out:
+              out.write(summary)
+          PY