feat: add authz schema compilation

[rodmgwgu]

Problem

Several distributions can contribute to the same authorization schema, and one can extend a role defined by another. The loaded documents need to be resolved into a single set of definitions with per-contribution provenance, and role extensions merged deterministically (ADR 0018 §1, ADR 0023).

Approach

• openedx_authz/engine/schema/compilation.py — SchemaCompiler
• openedx_authz/tests/schema/test_compilation.py

Merge rules follow ADR 0023: metadata replace, add/remove permissions, tri-state hidden, and priority to resolve conflicts. An unresolvable equal-priority conflict raises SchemaCompileError rather than picking a winner. Compilation is pure — no database, no Casbin.

Manual testing instructions

pytest openedx_authz/tests/schema/

Rollback plan

Revert this PR. Nothing consumes the compiler yet, so the revert is inert.

Retro compatibility

No authorization behavior changes. No models, no migration, no automatic code path.

AI Usage

Kiro was used to assist on feature planning and implementation. Implementation was done step by step with human guidance and validation, based on the ADRs.

---

Stack (3/8) — #446 split into reviewable pieces. Bases chain bottom-up; merge in order.

1. feat: add authz schema discovery #474 — schema discovery
2. feat: add authz schema loading #475 — schema loading
3. This PR — schema compilation (base: rod/authz-schema-loader-only)
4. rod/authz-schema-validator — schema validation
5. rod/authz-schema-models — definition models + migration
6. rod/authz-schema-renderer — policy renderer
7. rod/authz-schema-applier — schema applier
8. feat: add authz schema pipeline and load_authz_schema command #446 — pipeline + load_authz_schema command, version bump and changelog

Compilation lands before validation because the post-compile validation rules — and their tests — operate on a CompiledSchema. The compiler itself does not depend on the validator.

Merge checklist:

• Version bumped — deferred to 8/8 so the stack does not conflict on every restack
• Changelog record added — deferred to 8/8
• Documentation updated (not only docstrings) — covered by the already-merged ADRs
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets — depends on feat: add authz schema loading #475; no migration

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[mariajgrimaldi]

LGTM! Thanks so much for addressing all of my comments :)

[mariajgrimaldi]

Suggested change

	def _resolve_contributions(
	def _resolve_contributions_based_on_priority(

[rodmgwgu]

Applied, thanks!

[mariajgrimaldi]

nit:

Suggested change

	if action == "add":
	extension_sources = [
	RelationshipSource(src, SchemaOriginKind.EXTENSION, max_priority) for src in winning_sources
	]
	self._apply_added_permission(role_id, perm, current, provenance, extension_sources)
	else: # remove
	self._apply_removed_permission(role_id, perm, current, provenance)
	match action:
	case ACTION.ADD
	case ACTION.REMOVE
	...

I'd also change all references to the hardcoded "add" to ACTION.ADD and so on.

[rodmgwgu]

changed, thanks

[mariajgrimaldi]

Took me a while to understand this so thanks for the inline comment!