Phase 4: policy engine with deny-wins, default-deny evaluation

internal/policy/:
Priority-based policy engine per ARCHITECTURE.md §4. Stateless
Evaluate() sorts rules by priority, collects all matches, deny-wins
over allow, default-deny if no match. Rule matching: all populated
fields ANDed, empty fields are wildcards, repository glob via
path.Match. Built-in defaults: admin wildcard (all actions), human
user content access (pull/push/delete/catalog), version check
(always accessible). Engine wrapper with sync.RWMutex-protected
cache, SetRules merges with defaults, Reload loads from RuleStore.

internal/db/:
LoadEnabledPolicyRules() parses rule_json column from policy_rules
table into []policy.Rule, filtered by enabled=1, ordered by priority.

internal/server/:
RequirePolicy middleware extracts claims from context, repo from chi
URL param, evaluates policy, returns OCI DENIED (403) on deny with
optional audit callback.

69 tests passing across all packages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/db/policy_test.go

@@ -0,0 +1,79 @@
+package db
+
+import (
+	"testing"
+
+	"git.wntrmute.dev/kyle/mcr/internal/policy"
+)
+
+func TestLoadEnabledPolicyRules(t *testing.T) {
+	d := openTestDB(t)
+	if err := d.Migrate(); err != nil {
+		t.Fatalf("Migrate: %v", err)
+	}
+
+	// Insert two enabled rules and one disabled rule.
+	_, err := d.Exec(`INSERT INTO policy_rules (priority, description, rule_json, enabled)
+		VALUES (50, 'CI push/pull', '{"effect":"allow","subject_uuid":"ci-uuid","actions":["registry:push","registry:pull"],"repositories":["production/*"]}', 1)`)
+	if err != nil {
+		t.Fatalf("insert rule 1: %v", err)
+	}
+
+	_, err = d.Exec(`INSERT INTO policy_rules (priority, description, rule_json, enabled)
+		VALUES (10, 'deny delete', '{"effect":"deny","subject_uuid":"ci-uuid","actions":["registry:delete"]}', 1)`)
+	if err != nil {
+		t.Fatalf("insert rule 2: %v", err)
+	}
+
+	_, err = d.Exec(`INSERT INTO policy_rules (priority, description, rule_json, enabled)
+		VALUES (50, 'disabled rule', '{"effect":"allow","actions":["registry:catalog"]}', 0)`)
+	if err != nil {
+		t.Fatalf("insert rule 3 (disabled): %v", err)
+	}
+
+	rules, err := d.LoadEnabledPolicyRules()
+	if err != nil {
+		t.Fatalf("LoadEnabledPolicyRules: %v", err)
+	}
+
+	// Only 2 enabled rules should be returned.
+	if len(rules) != 2 {
+		t.Fatalf("rule count: got %d, want 2", len(rules))
+	}
+
+	// Rules should be ordered by priority ascending.
+	if rules[0].Priority != 10 {
+		t.Fatalf("first rule priority: got %d, want 10", rules[0].Priority)
+	}
+	if rules[0].Effect != policy.Deny {
+		t.Fatalf("first rule effect: got %s, want deny", rules[0].Effect)
+	}
+
+	if rules[1].Priority != 50 {
+		t.Fatalf("second rule priority: got %d, want 50", rules[1].Priority)
+	}
+	if rules[1].SubjectUUID != "ci-uuid" {
+		t.Fatalf("second rule subject: got %q, want %q", rules[1].SubjectUUID, "ci-uuid")
+	}
+	if len(rules[1].Actions) != 2 {
+		t.Fatalf("second rule actions: got %d, want 2", len(rules[1].Actions))
+	}
+	if len(rules[1].Repositories) != 1 || rules[1].Repositories[0] != "production/*" {
+		t.Fatalf("second rule repositories: got %v, want [production/*]", rules[1].Repositories)
+	}
+}
+
+func TestLoadEnabledPolicyRulesEmpty(t *testing.T) {
+	d := openTestDB(t)
+	if err := d.Migrate(); err != nil {
+		t.Fatalf("Migrate: %v", err)
+	}
+
+	rules, err := d.LoadEnabledPolicyRules()
+	if err != nil {
+		t.Fatalf("LoadEnabledPolicyRules: %v", err)
+	}
+	if rules != nil {
+		t.Fatalf("rules: got %v, want nil", rules)
+	}
+}