rewrite(phase8): batch B — content-parity audit (tsn/powerstate/faultinject/ratelimit/mdns/authz/relay/bridges)

[SoundMatt]

rewrite(phase8): batch B — content-parity audit (tsn/powerstate/faultinject/ratelimit/mdns/authz/relay/bridges)

Part of the v3.0.0 ground-up rewrite (cpp-RCP #129, ROADMAP.md Phase 17),
branch rewrite/v3-from-c-rcp. Phase 8 (remaining modules), batch B of 2:
tsn, powerstate, faultinject, ratelimit, mdns, authz, relay/relay.hpp,
restbridge/grpcbridge -- all already fully implemented+tested from an
earlier untracked pass; this batch is a content-parity audit against
c-RCP, not a rewrite.

Findings, per module

• tsn.hpp: already equivalent within a documented architectural
  divergence (c-RCP wraps a full AVTP transport + raw-frame priority
  classifier; cpp-RCP exposes a primitive apply_priority() called with
  an already-known RequestCategory) -- pre-documented in-header, no
  action. Catalog observation only (c-RCP's REQ-TSN-007/008 have no
  cpp-RCP analog, by design) -- left untouched, Phase 6 is closed.
• powerstate.hpp: no new findings beyond the 8 already-filed pending
  gaps from Phase 6 batch 13 (REQ-PWRMODE-004/012/017/019/021/022/
  026/027) -- confirmed NOT re-litigated. Confirmed wakeup.hpp (not
  powerstate.hpp) carries the actual SleepCMD/WakeUp wire codec
  equivalent to c-RCP's ep_wakeup.h -- a layering difference, not a
  missing capability. No changes.
• faultinject.hpp: capability-equivalent (Drop/Slow/Error/Timeout,
  count-limited rules). Notably its pick_rule() already fixes a real
  use-after-free/data-race an earlier revision had, documented in-file
  as cpp-RCP-D6 -- arguably more correct than c-RCP's own mechanism.
  No action.
• ratelimit.hpp: capability-equivalent (token bucket, safety-tag
  exemption, per-domain keying). Bootstrap/refill semantics match
  exactly. No action.
• mdns.hpp: capability-equivalent (Discoverer/Announcer, StaticDiscoverer,
  make_instance_name). One cosmetic-only divergence (hex case, service
  type string) -- not a wire-interop requirement since mDNS records are
  self-contained. No action.
• authz.hpp: genuine capability-granularity gap found, documented
  in-file rather than ported -- c-RCP keys policy entries on an opaque
  request_type byte (letting a policy distinguish read vs write within
  one request kind); cpp-RCP's RequestCategory taxonomy is coarser and
  cannot express that distinction. Pre-existing since v2.11.0, already
  justified at length in the header's own comment, and changing it
  would break the already-tested PolicyEntry/permit() contract -- out
  of this batch's authority. Documented as a known granularity gap for
  a possible future targeted fix, not force-fit here.
• relay/relay.hpp: confirmed structurally distinct from adapt.hpp
  (relay.hpp is the protocol-agnostic Channel/Context/Node
  abstraction; adapt.hpp is the RCP-specific wiring on top, already
  covered by Phase 6 batch 12). c-RCP's own relay.h header states
  outright it is "a pure-C port of the same subset cpp-RCP's
  include/relay/relay.hpp exposes... not a full RELAY binding" --
  cpp-RCP's version is the reference here, confirmed full parity
  (superset, even -- templated Channel vs one concrete type). No
  action.
• restbridge.hpp/grpcbridge.hpp: both compile-time interface stubs on
  both sides (no backend linked, every call returns not-supported).
  c-RCP's own header comments confirm they mirror cpp-RCP's stub
  behavior. Config shapes and defaults match exactly. No action.

Verification

Independently re-verified: confirmed the c-RCP relay.h "pure-C port of
cpp-RCP's own relay.hpp" claim, the restbridge.h "mirrors cpp-RCP's own
stub" claim, and the faultinject.hpp cpp-RCP-D6 use-after-free-fix
comment all directly against source -- all accurate. Full tree rebuilt
from scratch: 0 errors, 0 warnings, 58/58 ctest suites pass (100%).

include/rcp/authz.hpp: +17 lines (comment only, zero behavior change).
No other files touched.

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