Add revision registry and deterministic resolver

The registry is a cached snapshot rather than a control-plane client, so
the data plane keeps serving when the control plane dies (Blueprint
34.6). Routing policy generations are monotonic: a delayed older policy
is refused rather than silently rolling back an in-flight experiment's
allocation.

The resolver implements the Blueprint 5.2 precedence chain and records
why each revision was chosen. Experiment allocation is a deterministic
function of a sticky key namespaced by experiment id, so a consumer
stays in one arm for the experiment's duration and does not land in the
same arm of every concurrent experiment.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KmVxhJ35tCo7rE7UnLwWu

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1116572@bnt-lap001
Assistant-Session: 8ba9bb93-a72a-4883-b189-2499cce5c400

internal/runtime/resolver_test.go

@@ -0,0 +1,275 @@
+package runtime
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/tegwick/fluid-core/internal/contract"
+)
+
+const testInterface contract.InterfaceID = "hall-publishing"
+
+// descriptor builds a minimal routable revision descriptor.
+func descriptor(id contract.RevisionID, state contract.RevisionState, cohorts ...contract.CohortID) contract.Revision {
+	d := contract.Revision{
+		SchemaVersion: "0.1",
+		ID:            id,
+		Interface:     testInterface,
+		State:         state,
+		Contract: contract.RevisionContract{
+			Type:   contract.RevisionContractTypeOpenapi,
+			Digest: contract.Digest("sha256:" + zeros(64)),
+		},
+		Runtime: contract.RevisionRuntime{Upstream: "http://adapter:8080"},
+		Intent:  contract.RevisionIntent{Version: "IEI-1"},
+		Policy: contract.RevisionPolicy{
+			Compatibility: contract.RevisionPolicyCompatibilityAdditive,
+			SecurityCheck: contract.RevisionPolicySecurityCheckPassed,
+		},
+	}
+	if len(cohorts) > 0 {
+		d.Routing = &contract.RevisionRouting{EligibleCohorts: cohorts}
+	}
+	return d
+}
+
+func zeros(n int) string {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = '0'
+	}
+	return string(b)
+}
+
+func policyWith(defaultRev contract.RevisionID, gen int64, rules ...contract.RoutingPolicyRulesItem) contract.RoutingPolicy {
+	return contract.RoutingPolicy{
+		SchemaVersion:   "0.1",
+		Interface:       testInterface,
+		Generation:      gen,
+		DefaultRevision: defaultRev,
+		Rules:           rules,
+	}
+}
+
+func newFixture(t *testing.T, revs ...contract.Revision) *Registry {
+	t.Helper()
+	reg := NewRegistry(testInterface)
+	for _, r := range revs {
+		if err := reg.PutRevision(r); err != nil {
+			t.Fatalf("PutRevision(%s): %v", r.ID, err)
+		}
+	}
+	return reg
+}
+
+func TestResolvePrecedence(t *testing.T) {
+	reg := newFixture(t,
+		descriptor("R-1", contract.RevisionStateStable),
+		descriptor("R-2", contract.RevisionStateExperiment),
+		descriptor("R-3", contract.RevisionStateCandidate),
+	)
+	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
+		t.Fatal(err)
+	}
+
+	res := NewResolver(reg, true)
+
+	t.Run("explicit wins", func(t *testing.T) {
+		got, err := res.Resolve(Request{ExplicitRevision: "R-3", BoundRevision: "R-2"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got.Revision != "R-3" {
+			t.Errorf("got %s, want R-3", got.Revision)
+		}
+		if got.Reason != contract.FluidTelemetryResolutionReasonExplicitRevision {
+			t.Errorf("reason = %s", got.Reason)
+		}
+	})
+
+	t.Run("bound contract beats default", func(t *testing.T) {
+		got, err := res.Resolve(Request{BoundRevision: "R-2"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got.Revision != "R-2" || got.Reason != contract.FluidTelemetryResolutionReasonBoundContract {
+			t.Errorf("got %s via %s, want R-2 via bound_contract", got.Revision, got.Reason)
+		}
+	})
+
+	t.Run("falls through to stable default", func(t *testing.T) {
+		got, err := res.Resolve(Request{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got.Revision != "R-1" || got.Reason != contract.FluidTelemetryResolutionReasonStableDefault {
+			t.Errorf("got %s via %s, want R-1 via stable_default", got.Revision, got.Reason)
+		}
+	})
+
+	t.Run("explicit disabled is ignored", func(t *testing.T) {
+		strict := NewResolver(reg, false)
+		got, err := strict.Resolve(Request{ExplicitRevision: "R-3"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got.Revision != "R-1" {
+			t.Errorf("got %s, want the default R-1 when pinning is disabled", got.Revision)
+		}
+	})
+}
+
+func TestUnroutableRevisionsAreRefused(t *testing.T) {
+	reg := newFixture(t,
+		descriptor("R-1", contract.RevisionStateStable),
+		descriptor("R-created", contract.RevisionStateCreated),
+		descriptor("R-retired", contract.RevisionStateRetired),
+	)
+	failed := descriptor("R-insecure", contract.RevisionStateStable)
+	failed.Policy.SecurityCheck = contract.RevisionPolicySecurityCheckFailed
+	if err := reg.PutRevision(failed); err != nil {
+		t.Fatal(err)
+	}
+	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
+		t.Fatal(err)
+	}
+	res := NewResolver(reg, true)
+
+	for _, id := range []contract.RevisionID{"R-created", "R-retired", "R-insecure"} {
+		if _, err := res.Resolve(Request{ExplicitRevision: id}); err == nil {
+			t.Errorf("resolving %s should have been refused", id)
+		} else if !errors.Is(err, ErrRevisionNotRoutable) {
+			t.Errorf("resolving %s: got %v, want ErrRevisionNotRoutable", id, err)
+		}
+	}
+}
+
+func TestBoundRevisionDegradesToDefault(t *testing.T) {
+	// A consumer pinned to a revision that has since retired should keep being
+	// served rather than start failing.
+	reg := newFixture(t,
+		descriptor("R-1", contract.RevisionStateStable),
+		descriptor("R-old", contract.RevisionStateRetired),
+	)
+	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := NewResolver(reg, false).Resolve(Request{BoundRevision: "R-old"})
+	if err != nil {
+		t.Fatalf("a retired binding should degrade, not fail: %v", err)
+	}
+	if got.Revision != "R-1" {
+		t.Errorf("got %s, want R-1", got.Revision)
+	}
+}
+
+func TestCohortEligibility(t *testing.T) {
+	reg := newFixture(t,
+		descriptor("R-1", contract.RevisionStateStable),
+		descriptor("R-2", contract.RevisionStateExperiment, "coding-agents"),
+	)
+	if err := reg.PutPolicy(policyWith("R-1", 1)); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := reg.CheckRoutable("R-2", "coding-agents"); err != nil {
+		t.Errorf("eligible cohort refused: %v", err)
+	}
+	if err := reg.CheckRoutable("R-2", "partner-integrations"); err == nil {
+		t.Error("ineligible cohort accepted")
+	}
+}
+
+func TestAllocationIsStickyAndProportional(t *testing.T) {
+	reg := newFixture(t,
+		descriptor("R-1", contract.RevisionStateStable),
+		descriptor("R-2", contract.RevisionStateExperiment),
+	)
+	exp := contract.ExperimentID("E-1")
+	rule := contract.RoutingPolicyRulesItem{
+		Experiment: &exp,
+		Allocation: map[string]contract.UnitInterval{"R-1": 0.9, "R-2": 0.1},
+	}
+	if err := reg.PutPolicy(policyWith("R-1", 1, rule)); err != nil {
+		t.Fatal(err)
+	}
+	res := NewResolver(reg, false)
+
+	// Stickiness: the same consumer must resolve identically every time.
+	first, err := res.Resolve(Request{ConsumerRef: "consumer-42"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 50; i++ {
+		again, err := res.Resolve(Request{ConsumerRef: "consumer-42"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if again.Revision != first.Revision {
+			t.Fatalf("assignment drifted: %s then %s", first.Revision, again.Revision)
+		}
+	}
+
+	// Proportionality: roughly a tenth of consumers should see the candidate.
+	const n = 4000
+	candidate := 0
+	for i := 0; i < n; i++ {
+		got, err := res.Resolve(Request{ConsumerRef: consumerName(i)})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got.Revision == "R-2" {
+			candidate++
+		}
+		if got.Experiment == nil || *got.Experiment != exp {
+			t.Fatalf("experiment not recorded on resolution for consumer %d", i)
+		}
+	}
+	share := float64(candidate) / n
+	if share < 0.07 || share > 0.13 {
+		t.Errorf("candidate share %.3f, want approximately 0.10", share)
+	}
+}
+
+func consumerName(i int) string {
+	digits := "0123456789"
+	out := []byte("consumer-")
+	if i == 0 {
+		return string(append(out, '0'))
+	}
+	var rev []byte
+	for i > 0 {
+		rev = append(rev, digits[i%10])
+		i /= 10
+	}
+	for j := len(rev) - 1; j >= 0; j-- {
+		out = append(out, rev[j])
+	}
+	return string(out)
+}
+
+func TestStalePolicyRefused(t *testing.T) {
+	reg := newFixture(t, descriptor("R-1", contract.RevisionStateStable))
+	if err := reg.PutPolicy(policyWith("R-1", 5)); err != nil {
+		t.Fatal(err)
+	}
+	if err := reg.PutPolicy(policyWith("R-1", 4)); !errors.Is(err, ErrStalePolicy) {
+		t.Errorf("older generation accepted: %v", err)
+	}
+	if err := reg.PutPolicy(policyWith("R-1", 5)); !errors.Is(err, ErrStalePolicy) {
+		t.Errorf("equal generation accepted: %v", err)
+	}
+	if err := reg.PutPolicy(policyWith("R-1", 6)); err != nil {
+		t.Errorf("newer generation refused: %v", err)
+	}
+}
+
+func TestWrongInterfaceRefused(t *testing.T) {
+	reg := NewRegistry(testInterface)
+	other := descriptor("R-1", contract.RevisionStateStable)
+	other.Interface = "some-other-api"
+	if err := reg.PutRevision(other); !errors.Is(err, ErrWrongInterface) {
+		t.Errorf("foreign descriptor accepted: %v", err)
+	}
+}