Add a `django` policy to the policy registry

[bkd-dotcom]

What this is

signetry-core ships a policy registry: a directory of YAML files, one per repository
shape, that says which paths an AI agent may touch for a given task and which it may not.
Six ship today (signetry_core/policies/):
python-library, node-service, monorepo-service, docs-only, dependency-bump,
ci-workflow-fix. A Django application is missing.

This is the highest-leverage thing you can contribute without touching the kernel: one new
file, no Python, and no test to write — tests/test_policy_registry.py is parametrized
over every file in that directory, so your policy is validated the moment it exists.

The deliverable

One file: signetry_core/policies/django.yaml. Copy
python-library.yaml
as your starting shape — the # @policy header comments are load-bearing metadata, not
decoration.

A starting point, not a spec to type in verbatim — argue with it, the reasoning is the
contribution:

# @policy id: django
# @policy title: Django app (apps/ layout, pytest-django)
# @policy summary: A Django project. The agent may change app code, templates and tests, and must keep
#   pytest green. Migrations, production settings and anything that runs at manage.py
#   startup stay off-limits.
# @policy stack: python, django, pytest-django, drf
# @policy author: your-github-handle
# @policy blocks: apps/billing/migrations/0012_add_plan.py, config/settings/production.py, manage.py, .github/workflows/deploy.yml, .env.production
# @policy allows: apps/billing/models.py, apps/billing/views.py, apps/billing/serializers.py, tests/test_billing.py, requirements/base.txt
version: 2
task_type: feature-work

allowed_paths:
  - "apps/**"
  - "templates/**"
  - "tests/**"
  - "requirements/**"
  - "README.md"
  - "CHANGELOG.md"

forbidden_paths:
  # Inside apps/** which is otherwise allowed. A Django migration is applied once
  # against a real database and reversed by hand; `makemigrations` output also
  # encodes state the diff doesn't show, so review of the file is not review of the
  # schema change.
  - "**/migrations/**"
  # Production settings configure the deployed system: ALLOWED_HOSTS, DEBUG, the
  # datasource, middleware order. None of it is exercised by the test suite that
  # gates this change.
  - "**/settings/production.py"
  - "**/settings/prod.py"
  # manage.py and wsgi/asgi entrypoints execute before any test collection.
  - "manage.py"
  - "**/wsgi.py"
  - "**/asgi.py"
  - "**/conftest.py"
  - ".github/**"
  - "infra/**"
  - "deploy/**"
  - "**/.env*"
  - "**/*secret*"

max_files_changed: 12
required_checks:
  - "pytest -q"
  - "python -m django check --deploy --fail-level WARNING"

policy_owner: your-team
policy_version: "1.0"

The part people get wrong

Your blocks list must include at least one path that sits inside your own
allowed_paths. Carving an exception out of a directory you otherwise own is the whole
skill. For a Django application that exception is:

**/migrations/** — apps/** is allowed because that's the application, but every
Django app carries a migrations/ directory inside it, and a migration is a one-way door.

The Django trap worth a comment in the file

Adding to INSTALLED_APPS or MIDDLEWARE in a settings file you do allow loads
new code at boot — the risk isn't the line, it's the import. Also requirements/**: a
pinned bump is routine, an unpinned add is a new dependency at deploy time. Comment which
you intend.

Acceptance criteria

• signetry_core/policies/django.yaml exists; filename matches @policy id.
• blocks and allows each list 3–4 realistic paths for this stack, and don't overlap.
• At least one blocks entry is inside allowed_paths.
• Every forbidden_paths entry that isn't self-evident carries a comment saying why,
  not just that it is. python-library forbids conftest.py at any depth and the comment
  explains it executes at collection time on every developer machine — that is the bar.
• pytest tests/test_policy_registry.py is green. The suite proves each claimed block is
  actually refused by the real evaluate_contract, so a policy that misleads adopters
  fails CI rather than shipping.
• If the policy permits something risky, it says so in a caution: — signetry init
  prints it at adoption time. A risky policy with no caution gets sent back; a risky
  policy that's honest is fine.

Getting started

The full numbered walkthrough, including what makes a policy worth merging, is in
docs/site/policy-registry.md → "Contributing a policy".

git clone https://github.com/Signetry/core && cd core
uv sync
uv run pytest tests/test_policy_registry.py -q
uv run signetry policies          # your entry should appear here once the file exists

Comment to claim it — one policy per contributor so nobody's work gets duplicated. Happy to
review a half-finished scope list; the reasoning matters more than the YAML.