Multi-interface gateway and per-channel filtering

The gateway-side multiplexer. This cluster :satisfies: CAN (SocketCAN) reference c... (FEAT_0046).

Feature: Multi-interface gateway and per-channel filtering FEAT_0048
status: open
satisfies: FEAT_0046
is satisfied by: REQ_0620, REQ_0621, REQ_0622, REQ_0623, REQ_0624, REQ_0625

The gateway-side multiplexer: one gateway instance can own multiple Linux CAN interfaces (broader than Single MainDevice per gatew... (REQ_0312)’s single-MainDevice EtherCAT posture). Per-channel CAN ID and mask are compiled into one CAN_RAW_FILTER setsockopt per interface, recomputed when channels are added or removed.
Requirement: Multiple interfaces per gateway REQ_0620
status: approved
satisfies: FEAT_0048
is refined by: IMPL_0080, ARCH_0061
is implemented by: BB_0072
is verified by: TEST_0505

A single CanGateway instance shall be capable of owning multiple Linux SocketCAN interfaces (e.g. can0, can1, vcan0) simultaneously. The set of interfaces shall be declared at gateway construction via CanConnectorOptions::ifaces. This requirement is broader than Single MainDevice per gatew... (REQ_0312)’s single-MainDevice EtherCAT posture because SocketCAN bus saturation per interface is far lower than EtherCAT process-image throughput and multi-bus deployments are common in CAN.
Requirement: Routing identifies the interface REQ_0621
status: open
satisfies: FEAT_0048
is refined by: IMPL_0080, ARCH_0060
is implemented by: BB_0071
is verified by: TEST_0505

CanRouting::iface shall identify which gateway-owned SocketCAN interface a channel binds to. The gateway shall reject Connector::create_writer / create_reader calls referencing an interface not listed in CanConnectorOptions::ifaces with ConnectorError::Configuration.
Requirement: Per-interface filter is the union of channel masks REQ_0622
status: approved
satisfies: FEAT_0048
is refined by: IMPL_0080, ARCH_0061
is implemented by: BB_0074
is verified by: TEST_0504

For each owned interface, the gateway shall compute the union of (can_id, mask, extended) tuples drawn from every currently-open inbound channel bound to that interface, and apply the result as a single setsockopt(SOL_CAN_RAW, CAN_RAW_FILTER, …) call. Frames not matching any registered filter shall be discarded by the kernel before reaching the gateway’s read loop.
Requirement: Filter recomputed on channel add/remove REQ_0623
status: approved
satisfies: FEAT_0048
is refined by: IMPL_0080
is implemented by: BB_0074
is verified by: TEST_0504

The per-interface filter (per Per-interface filter is the... (REQ_0622)) shall be recomputed and re-applied whenever a ChannelReader is created or dropped. The recompute shall not require the interface to be re-opened or the bus to leave its current state.
Requirement: Inbound demux to all matching readers REQ_0624
status: approved
satisfies: FEAT_0048
is refined by: IMPL_0080, ARCH_0061
is implemented by: BB_0072, BB_0074
is verified by: TEST_0505

When a CAN frame arrives on an interface, the gateway shall publish the frame’s data bytes (per Inbound gateway is byte-onl... (REQ_0614)) onto the inbound iceoryx2 service of every registered channel whose (iface, can_id, mask, extended) matches the received frame’s identifier under kernel CAN_RAW_FILTER semantics. Overlapping channel filters shall each receive their own envelope copy.
Requirement: Per-iface routing registry has stable iteration order REQ_0625
status: approved
satisfies: FEAT_0048
is refined by: IMPL_0080
is implemented by: BB_0072
is verified by: TEST_0514

The gateway shall maintain a per-interface routing registry mapping each open ChannelDescriptor to its CanRouting and direction (outbound writer / inbound reader). The RX/TX loops shall iterate this registry on every frame and every send drain without per-iteration heap allocation (no Vec resize, no HashMap re-hash) — required by No heap allocation in dispatch (REQ_0060) from the steady-state posture, mirroring Per-channel routing registr... (REQ_0328).