FLEX-WP-0008 T03-T04: tenant-engine live-lookup context adapter, close

internal/adapters/tenantengine: HTTPClient.LiveRoles() calls tenant-engine's
GET /tenants/{id}/roles/live. LiveRolesResult.Available is the load-bearing
field -- false on any transport error, non-200, or malformed body, never
inferred as zero roles. AttachToContext() writes both tenant_roles and
tenant_roles_available into a CheckRequest.Context map; a consuming Rego
policy must check tenant_roles_available before trusting tenant_roles.

Architectural finding recorded in the workplan: engine.go's Check() has no
context-adapter hook, and none of the existing topaz/relationship/rule
adapters are wired into cmd/flex-auth either -- they're standalone packages
for downstream composition. This adapter is a request-preparation helper a
protected system's own request-building code calls before POST /v1/check,
not an engine-internal hook, matching that precedent exactly.

9 Go tests; gofmt/vet/build clean; go test ./... green repo-wide.

Verified as a real three-service chain: live flex-auth serve + live
tenant-engine, created a tenant and granted it a CUS role through the real
flex-auth-gated write path, then read it back through this adapter (via a
throwaway harness, not committed) -- known tenant: roles=[CUS]
available=true; unknown tenant: roles=[] available=false err="status 404".

FLEX-WP-0008 closed: T01-T04 all done. tenant-engine's write path is now
real end-to-end; any other protected system can pull live tenant capability
role context, fail-closed. Remaining open item unchanged from TEN-WP-0003:
KEY-WP-0005 (key-cape's IAM Profile core-claims gap).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/adapters/tenantengine/http_client.go

@@ -0,0 +1,65 @@
+package tenantengine
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// HTTPClient calls tenant-engine's live-lookup endpoint
+// (GET /tenants/{id}/roles/live).
+type HTTPClient struct {
+	BaseURL string
+	Client  *http.Client
+}
+
+// NewHTTPClient creates an HTTP-backed tenant-engine client.
+func NewHTTPClient(baseURL string) (*HTTPClient, error) {
+	if baseURL == "" {
+		return nil, fmt.Errorf("tenant-engine base URL is required")
+	}
+	return &HTTPClient{
+		BaseURL: strings.TrimRight(baseURL, "/"),
+		Client:  &http.Client{Timeout: 3 * time.Second},
+	}, nil
+}
+
+// LiveRoles calls GET /tenants/{tenantID}/roles/live.
+//
+// Fail-closed by construction: any transport error, non-200 response, or
+// malformed body returns LiveRolesResult{Available: false} alongside a
+// non-nil error. Nothing is inferred as "zero roles" from a failure --
+// callers must check Available, not just the length of Roles.
+func (c *HTTPClient) LiveRoles(ctx context.Context, tenantID string) (LiveRolesResult, error) {
+	url := fmt.Sprintf("%s/tenants/%s/roles/live", c.BaseURL, tenantID)
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return LiveRolesResult{Available: false}, NewBackendError(FailureUnavailable, "live_roles", err)
+	}
+
+	resp, err := c.Client.Do(req)
+	if err != nil {
+		return LiveRolesResult{Available: false}, NewBackendError(FailureUnavailable, "live_roles", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return LiveRolesResult{Available: false}, NewBackendError(
+			FailureUnavailable, "live_roles", fmt.Errorf("status %d", resp.StatusCode),
+		)
+	}
+
+	var body struct {
+		TenantID string   `json:"tenant_id"`
+		Roles    []string `json:"roles"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
+		return LiveRolesResult{Available: false}, NewBackendError(FailureInvalidResponse, "live_roles", err)
+	}
+
+	return LiveRolesResult{Roles: body.Roles, Available: true}, nil
+}