feat(libcuframes): packet ring buffer implementation (v0.2 Step 2)
Реализация encoded packet ring per docs/protocol.md §10.
Files:
- internal.h: cuframes_pkt_slot_t (64b packed), cuframes_pkt_header_t
(0x1040 fixed header), cuframes_pkt_ring_t handle, constants for
default sizing, packet flags, helper inline functions for slot/data
pointer arithmetic.
- packet_ring.c (new, ~290 LOC): create/open/publish/read/destroy.
Stale recovery симметрично frames SHM (pid liveness check). Seqlock
pattern для subscriber защиты от overrun mid-read (post-check seq
после copy). Wraparound memcpy helpers для variable-length data ring.
- utils.c: cuframes_internal_pkt_shm_name helper + strerror entries.
- cuframes.h: 4 новых error codes (PACKET_OVERSIZED, NO_PACKET_RING,
NO_CODEC_PARAMS, PACKET_OVERRUN).
- CMakeLists.txt: src/packet_ring.c в sources.
API внутренний (cuframes_internal_pkt_ring_*) — publicly exposed
функции будут в Step 3 (cuframes.h API extension).
Связано: #2 (v0.2), PR #4 (draft).
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