feat(gtpv2c): add finite S2b F-TEID receive policy

CHANGELOG.md

@@ -8,6 +8,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Finite S2b Create Session Response F-TEID receive policy —
+  `opc-proto-gtpv2c`:**
+  `S2bCreateSessionResponseReceivePolicy` and the one-shot
+  `decode_create_session_response_summary_with_receive_policy` let callers
+  independently add standardized S5/S8 PGW control type 7 and user-plane type
+  5 to the strict default S2b role sets `{32}` and `{33}`. The copied finite
+  policy binds ProcedureAware first-occurrence validation to typed projection;
+  existing decode/projection APIs and canonical builders remain strict, and
+  errors and Debug output remain value-free.
 - **Durable grouped XFRM object roster transaction — `opc-ipsec-xfrm`:**
   `LinuxXfrmBackend::bind_current_network_namespace_with_object_roster_recovery`
   and the opt-in migration constructor

crates/opc-proto-gtpv2c/CONFORMANCE.md

@@ -168,7 +168,13 @@ failures and must cover at least these rules:
   1/interface type 32, and Bearer Context for accepted responses (Cause 16/17).
   The control endpoint requires a non-zero TEID and at least one address;
   instance-0 Sender F-TEID is unexpected on this S2b response profile and is
-  discarded. Rejected responses may expose Cause-only summaries.
+  discarded. Rejected responses may expose Cause-only summaries. The explicit
+  one-shot receive policy may independently add only S5/S8 PGW control type 7
+  and PGW user-plane type 5 to the strict role sets `{32}` and `{33}`. The
+  policy is copied for one decode and binds validation and typed projection to
+  the same first retained role occurrence. It cannot admit arbitrary interface
+  values or affect another profile; no-policy APIs and canonical builders stay
+  strict S2b and emit only control type 32 and user-plane type 33.
 - S2b Modify Bearer Request is the UE-initiated IPsec tunnel-update profile.
   It requires a non-zero header TEID but no mandatory IE. WLAN Location
   Information (TWAN Identifier instance 0) and WLAN Location Timestamp (TWAN
@@ -245,7 +251,11 @@ failures and must cover at least these rules:
   grouped scope is retained, later occurrences are ignored, and bounded
   `S2bReceiveDiagnostics` records only type, instance, scope/depth, first
   offset, and a saturated duplicate count. A malformed or semantically invalid
-  first value remains an error and cannot be repaired by a later value.
+  first value remains an error and cannot be repaired by a later value. For
+  Create Session Response nested F-TEIDs, this rule applies per `(type,
+  instance)` singleton key: distinct table-defined instances remain eligible
+  for their distinct roles, while a later duplicate at the same instance can
+  never repair the retained first occurrence.
 - ProcedureAware receive classifies every crate-known typed/control IE key
   against one message grammar keyed by procedure, direction, and exact
   enclosing Bearer Context instance before decoding its value. Unexpected

crates/opc-proto-gtpv2c/README.md

@@ -601,6 +601,40 @@ let response = S2bCreateSessionAcceptedResponse {
 };
 ```
 
+Create Session Response receive decoding remains strict by default: the PGW
+control role accepts only interface type 32 and the PGW user-plane role only
+type 33. A caller that has already made its own interworking decision can use
+the one-shot `decode_create_session_response_summary_with_receive_policy`
+helper with `S2bCreateSessionResponseReceivePolicy` to independently add the
+standardized S5/S8 control type 7, user-plane type 5, or both. The policy has no
+arbitrary interface-type constructor, is copied for one decode, and is applied
+to the same first retained singleton used by the returned typed summary. It
+does not affect `S2bMessage::decode`, the no-policy summary helpers, any other
+GTPv2-C procedure, or canonical builders; those remain strict S2b.
+
+```rust
+use opc_proto_gtpv2c::{
+    decode_create_session_response_summary_with_receive_policy,
+    S2bCreateSessionResponseReceivePolicy,
+};
+use opc_protocol::{DecodeContext, ValidationLevel};
+
+# let response_bytes: &[u8] = &[];
+let receive_policy = S2bCreateSessionResponseReceivePolicy::STRICT
+    .allow_s5_s8_pgw_control()
+    .allow_s5_s8_pgw_user_plane();
+let receive_context = DecodeContext {
+    validation_level: ValidationLevel::ProcedureAware,
+    ..DecodeContext::default()
+};
+let summary = decode_create_session_response_summary_with_receive_policy(
+    response_bytes,
+    receive_context,
+    receive_policy,
+);
+# let _ = summary;
+```
+
 The former loose Update Bearer shell with a single `bearer_context` has been
 replaced by the strict dedicated-bearer API. Construct
 `S2bUpdateBearerRequest` with mandatory `apn_ambr` and one to fifteen

crates/opc-proto-gtpv2c/src/lib.rs

@@ -163,32 +163,34 @@ pub use pco::{
 };
 #[allow(deprecated)]
 pub use s2b::{
-    decode_create_session_response_summary, decode_echo_message_evidence, is_s2b_message_type,
-    s2b_create_session_accepted_response, s2b_create_session_rejected_response,
-    s2b_create_session_request, s2b_delete_session_request, s2b_delete_session_response,
-    s2b_echo_request, s2b_echo_response, s2b_modify_bearer_request, s2b_modify_bearer_response,
-    s2b_ue_ipsec_tunnel_update_request, CreateSessionAcceptedResponseSummary,
-    CreateSessionRejectedResponseSummary, CreateSessionResponseSummary,
-    CreateSessionResponseSummaryError, EchoMessageEvidence, EchoMessageEvidenceError,
-    Gtpv2cClientResponseEvidence, Gtpv2cClientTransaction, Gtpv2cClientTransactionDecision,
-    Gtpv2cClientTransactionKey, Gtpv2cClientTransactionMismatch, Gtpv2cClientTransactionPlan,
-    Gtpv2cClientTransactionPlanError, Gtpv2cClientTransactionPolicy,
+    decode_create_session_response_summary,
+    decode_create_session_response_summary_with_receive_policy, decode_echo_message_evidence,
+    is_s2b_message_type, s2b_create_session_accepted_response,
+    s2b_create_session_rejected_response, s2b_create_session_request, s2b_delete_session_request,
+    s2b_delete_session_response, s2b_echo_request, s2b_echo_response, s2b_modify_bearer_request,
+    s2b_modify_bearer_response, s2b_ue_ipsec_tunnel_update_request,
+    CreateSessionAcceptedResponseSummary, CreateSessionRejectedResponseSummary,
+    CreateSessionResponseSummary, CreateSessionResponseSummaryError, EchoMessageEvidence,
+    EchoMessageEvidenceError, Gtpv2cClientResponseEvidence, Gtpv2cClientTransaction,
+    Gtpv2cClientTransactionDecision, Gtpv2cClientTransactionKey, Gtpv2cClientTransactionMismatch,
+    Gtpv2cClientTransactionPlan, Gtpv2cClientTransactionPlanError, Gtpv2cClientTransactionPolicy,
     Gtpv2cClientTransactionProjection, Gtpv2cClientTransactionSnapshot,
     Gtpv2cClientTransactionState, Gtpv2cEchoPeer, Gtpv2cEchoPeerBlocker, Gtpv2cEchoPeerError,
     Gtpv2cEchoPeerEvent, Gtpv2cEchoPeerPolicy, Gtpv2cEchoPeerProjection, Gtpv2cEchoPeerReadiness,
     Gtpv2cEchoPeerSnapshot, Gtpv2cEchoPeerState, Gtpv2cEchoPeerTransition, Gtpv2cPeerToken,
     MessageDirection, Procedure, S2bAaaProvidedMsisdn, S2bCreateSessionAcceptedResponse,
     S2bCreateSessionContext, S2bCreateSessionContextSummary, S2bCreateSessionIdentity,
-    S2bCreateSessionRejectedResponse, S2bCreateSessionRequest, S2bDecodedMessage,
-    S2bDeleteSessionContext, S2bDeleteSessionContextSummary, S2bDeleteSessionRequest,
-    S2bDeleteSessionResponse, S2bMessage, S2bModifyBearerRequest, S2bModifyBearerResponse,
-    S2bProcedureMessage, S2bProfileBuildError, S2bProfileBuildResult, S2bReceiveDiagnostics,
-    S2bSessionContextProjectionError, S2bUeEndpoint, S2bUeIpsecTunnelUpdateEndpoint,
-    S2bUeIpsecTunnelUpdateProjectionError, S2bUeIpsecTunnelUpdateRequest,
-    S2bUeIpsecTunnelUpdateRequestSummary, S2bUeIpsecTunnelUpdateResponseSummary, S2bUeNatTraversal,
-    CREATE_BEARER_REQUEST, CREATE_BEARER_RESPONSE, CREATE_SESSION_REQUEST, CREATE_SESSION_RESPONSE,
-    DELETE_BEARER_REQUEST, DELETE_BEARER_RESPONSE, DELETE_SESSION_REQUEST, DELETE_SESSION_RESPONSE,
-    ECHO_REQUEST, ECHO_RESPONSE, INTERFACE_TYPE_S2B_EPDG_GTP_C, INTERFACE_TYPE_S2B_PGW_GTP_C,
+    S2bCreateSessionRejectedResponse, S2bCreateSessionRequest,
+    S2bCreateSessionResponseReceivePolicy, S2bDecodedMessage, S2bDeleteSessionContext,
+    S2bDeleteSessionContextSummary, S2bDeleteSessionRequest, S2bDeleteSessionResponse, S2bMessage,
+    S2bModifyBearerRequest, S2bModifyBearerResponse, S2bProcedureMessage, S2bProfileBuildError,
+    S2bProfileBuildResult, S2bReceiveDiagnostics, S2bSessionContextProjectionError, S2bUeEndpoint,
+    S2bUeIpsecTunnelUpdateEndpoint, S2bUeIpsecTunnelUpdateProjectionError,
+    S2bUeIpsecTunnelUpdateRequest, S2bUeIpsecTunnelUpdateRequestSummary,
+    S2bUeIpsecTunnelUpdateResponseSummary, S2bUeNatTraversal, CREATE_BEARER_REQUEST,
+    CREATE_BEARER_RESPONSE, CREATE_SESSION_REQUEST, CREATE_SESSION_RESPONSE, DELETE_BEARER_REQUEST,
+    DELETE_BEARER_RESPONSE, DELETE_SESSION_REQUEST, DELETE_SESSION_RESPONSE, ECHO_REQUEST,
+    ECHO_RESPONSE, INTERFACE_TYPE_S2B_EPDG_GTP_C, INTERFACE_TYPE_S2B_PGW_GTP_C,
     INTERFACE_TYPE_S2B_U_EPDG_GTP_U, INTERFACE_TYPE_S2B_U_PGW_GTP_U, MODIFY_BEARER_REQUEST,
     MODIFY_BEARER_RESPONSE, UPDATE_BEARER_REQUEST, UPDATE_BEARER_RESPONSE,
 };