fix(examples): correct from_jwk call signature + warn on missing WEBHOOK_BEARER_TOKEN

Pre-PR review blockers:
- from_jwk takes a JWK dict; kid/alg/adcp_use live inside the dict, not as
  separate kwargs. Fix the doc table and hello_seller.py comment accordingly.
- hello_seller_with_webhooks.py now warns (instead of silently continuing)
  when WEBHOOK_BEARER_TOKEN is unset, so developers discover the dev-fixture
  default rather than running a production server with it.

https://claude.ai/code/session_01Ay2SJvRpBg8EP9nG9DgQMy

Author: claude

docs/handler-authoring.md

@@ -1053,7 +1053,7 @@ Pick one per `WebhookSender` instance. All three share the same
 
 | Constructor | Auth mode | When to use |
 |---|---|---|
-| `WebhookSender.from_jwk(jwk, key_id, alg)` | RFC 9421 HTTP-signature | AdCP-conformant buyers; spec baseline |
+| `WebhookSender.from_jwk(jwk)` | RFC 9421 HTTP-signature | AdCP-conformant buyers; spec baseline (`kid`/`alg`/`adcp_use` live in the JWK dict) |
 | `WebhookSender.from_bearer_token(token)` | `Authorization: Bearer` | Simplest; no key management; requires TLS |
 | `WebhookSender.from_standard_webhooks_secret(secret)` | Standard Webhooks v1 | Svix / Resend / standardwebhooks.com receivers |
 

examples/hello_seller.py

@@ -344,8 +344,9 @@ def _get_packages(req: Any) -> list[dict[str, Any]]:
     #   from adcp.webhook_sender import WebhookSender
     #   from adcp.webhook_supervisor import InMemoryWebhookDeliverySupervisor
     #
-    #   # RFC 9421 JWK signing — AdCP spec baseline (recommended):
-    #   sender = WebhookSender.from_jwk(signing_jwk, key_id="kid_1", alg="ES256")
+    #   # RFC 9421 JWK signing — AdCP spec baseline (recommended).
+    #   # signing_jwk must be a dict with kid, alg, and adcp_use="webhook-signing":
+    #   sender = WebhookSender.from_jwk(signing_jwk)
     #
     #   # Shared bearer token — no key management, requires TLS:
     #   sender = WebhookSender.from_bearer_token(os.environ["WEBHOOK_BEARER_TOKEN"])

examples/hello_seller_with_webhooks.py

@@ -35,7 +35,16 @@
 from adcp.webhook_supervisor import InMemoryWebhookDeliverySupervisor
 
 if __name__ == "__main__":
-    token = os.environ.get("WEBHOOK_BEARER_TOKEN", "dev-fixture-token")
+    token = os.environ.get("WEBHOOK_BEARER_TOKEN", "")
+    if not token:
+        import warnings
+
+        warnings.warn(
+            "WEBHOOK_BEARER_TOKEN is not set; using 'dev-fixture-token'. "
+            "Set WEBHOOK_BEARER_TOKEN=<real-token> before connecting real buyers.",
+            stacklevel=1,
+        )
+        token = "dev-fixture-token"
     sender = WebhookSender.from_bearer_token(token)
     # InMemoryWebhookDeliverySupervisor wraps the sender with retry
     # (exponential backoff, 3 attempts) and per-endpoint circuit breakers.