feat(compliance): GET /sdk/v1/compliance/obligation-status (file-backed graph)

Vertical slice over the Compliance Execution Graph: obligation_id -> accepted
controls -> required evidence -> status. NEVER auto-asserts fulfillment - with
no evidence collection wired (MVP), a mapped obligation is "not_assessed" and
every required evidence is "missing". Fail-closed: no id -> 400; unknown id ->
unknown_obligation; mapped-but-no-control -> unmapped; graph not loaded -> 503.

- ComplianceGraphHandlers (separate from the DB-backed ObligationsHandlers):
  loads Registry join keys + accepted control mappings + evidence once at start.
- LoadComplianceGraph: candidate-path resolution across dev/container/test.
- Data plumbing: Dockerfile now COPYs data/{control_mappings,evidence_requirements,
  obligations}; data/obligations/obligation_join_keys.json is a SYNCED COPY of the
  repo-root Registry contract (re-sync on Registry growth).
- Table-driven handler test (mapped/unmapped/unknown/400 + no-fulfillment-claim).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ai-compliance-sdk/internal/ucca/compliance_graph_loader.go

@@ -0,0 +1,89 @@
+package ucca
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+// graphCallerRel resolves a path relative to THIS source file (build-time location), so the
+// graph data is findable under `go test` (cwd = package dir) regardless of working directory.
+// In a built container the source is gone, so cwd-relative candidates carry the load instead.
+func graphCallerRel(rel string) string {
+	_, file, _, ok := runtime.Caller(0)
+	if !ok {
+		return ""
+	}
+	return filepath.Join(filepath.Dir(file), rel)
+}
+
+// firstExisting returns the first candidate path that exists with the requested kind (dir vs
+// file). Empty candidates (e.g. unset env overrides) are skipped.
+func firstExisting(candidates []string, wantDir bool) string {
+	for _, p := range candidates {
+		if p == "" {
+			continue
+		}
+		info, err := os.Stat(p)
+		if err != nil || info.IsDir() != wantDir {
+			continue
+		}
+		return p
+	}
+	return ""
+}
+
+// LoadComplianceGraph loads the file-backed Compliance Execution Graph: the Registry join-key
+// contract (obligations/obligation_join_keys.json — owned by the Obligation session) + our
+// curated, accepted control mappings + evidence requirements. Locations are resolved across
+// three layouts: dev (cwd = ai-compliance-sdk/, canonical contract at ../obligations), container
+// (WORKDIR /app, data/ copied in incl. a synced data/obligations/ copy) and `go test`
+// (cwd = package dir, via graphCallerRel). Fail-closed: a missing/invalid source returns an
+// error so the handler serves 503 — never a half-built graph.
+//
+// NOTE: data/obligations/obligation_join_keys.json is a SYNCED COPY of the repo-root contract
+// (the canonical owner is the Obligation session). Re-sync it when the Registry grows; dev/test
+// prefer the canonical repo-root path, only the container falls back to the copy.
+func LoadComplianceGraph() (*ObligationJoinKeys, *ControlMappingSet, *EvidenceRequirementSet, error) {
+	joinPath := firstExisting([]string{
+		os.Getenv("BP_OBLIGATION_JOIN_KEYS"),
+		"../obligations/obligation_join_keys.json",
+		graphCallerRel("../../../obligations/obligation_join_keys.json"),
+		"data/obligations/obligation_join_keys.json",
+		graphCallerRel("../../data/obligations/obligation_join_keys.json"),
+	}, false)
+	if joinPath == "" {
+		return nil, nil, nil, fmt.Errorf("obligation_join_keys.json not found in any candidate path")
+	}
+	mapDir := firstExisting([]string{
+		os.Getenv("BP_CONTROL_MAPPINGS_DIR"),
+		"data/control_mappings",
+		graphCallerRel("../../data/control_mappings"),
+	}, true)
+	if mapDir == "" {
+		return nil, nil, nil, fmt.Errorf("control_mappings dir not found in any candidate path")
+	}
+	evDir := firstExisting([]string{
+		os.Getenv("BP_EVIDENCE_DIR"),
+		"data/evidence_requirements",
+		graphCallerRel("../../data/evidence_requirements"),
+	}, true)
+	if evDir == "" {
+		return nil, nil, nil, fmt.Errorf("evidence_requirements dir not found in any candidate path")
+	}
+
+	joins, err := LoadObligationJoinKeys(joinPath)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("load join keys (%s): %w", joinPath, err)
+	}
+	mappings, err := LoadControlMappings(mapDir)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("load control mappings (%s): %w", mapDir, err)
+	}
+	evidence, err := LoadEvidenceRequirements(evDir)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("load evidence (%s): %w", evDir, err)
+	}
+	return joins, mappings, evidence, nil
+}