feat: implement Table 30/33 Row-2 evt[2:0] validation — MDIO (8th and LAST endpoint type)

[SoundMatt]

Summary

Implements TC18 (OPEN Alliance TC18 Remote Control Protocol Specification v0.5.1_RC) §13.5 Table 33's "Row 2" evt[2:0] request classification for the MDIO endpoint type (include/rcp/mdio.hpp, MDIO's own section is §13.7.13.3) — the eighth and LAST of the eight endpoint types sharing this row ({ADC, PWM_IN, I2C, LIN, CAN, UART, ISELED, MDIO}), following the pattern established by I2C (#114), ADC (#115), PWM_IN (#116), LIN (#117), CAN (#118), UART (#119), and ISELED (#120).

Classification rule, via the shared rcp::endpoint::evt_row2_kind_of / EndpointErrc::reserved_evt_row2 predicate already in rcp/endpoint.hpp (called, not reinvented):

• evt[2:0] == 000b → Plain: delegates to the existing transaction logic unchanged
• evt[2:0] in 001b-110b → Reserved: rejected with EndpointErrc::reserved_evt_row2 (wire error code UNSUPPORTED_CMD)
• evt[2:0] == 111b → ConfigWrite (§12.7.1, not yet implemented): reported via new MdioErrc::config_write_not_supported

handle_request → transact rename (naming collision)

MdioEndpoint already had a pre-existing method literally named handle_request(MdioRequest, MdioResponse&) — the read/write register transaction logic, predating this milestone entirely and unrelated to evt[2:0] classification.

1. Renamed the existing method to transact(MdioRequest, MdioResponse&), matching the name rcp/iseled.hpp's IseledEndpoint::transact already established for the identical role.
2. Updated all 8 call sites in tests/test_mdio.cpp from .handle_request( to .transact(.
3. Added a new handle_request(uint8_t evt_op, MdioRequest, MdioResponse&) — the evt[2:0] classifier — that delegates Plain to transact() unchanged, rejects Reserved without calling transact(), and rejects ConfigWrite with MdioErrc::config_write_not_supported.

Confirmed clean: grepped the whole repo for .handle_request( on MdioEndpoint/mdio_. — zero remaining 2-argument call sites. mock.hpp had zero prior MDIO wiring at all (verified via grep -n "mdio\|Mdio\|MDIO" include/rcp/mock.hpp on main returning nothing before this PR), so there was nothing else to migrate.

Addressing model — confirmed untouched

include/rcp/mdio.hpp's own header comment documents this header previously modeled MDIO addressing as an invented IEEE 802.3 Clause 22/Clause 45-style PHY-address scheme with no basis in TC18, corrected in issue #72 to the real mdio_mode/mdio_address/mdio_payload model. This PR does NOT touch, reinterpret, or extend MdioRequest's/MdioResponse's field shapes or the mdio_mode/register_key logic in any way. Table 33's evt[2:0] classification is a completely separate, orthogonal concern, and no new MDIO wire encoding is invented anywhere in mdio.hpp itself.

mock.hpp wiring — 10th mock endpoint, byte_bus_id=10

Wires MdioEndpoint into rcp/mock.hpp for the first time, following UART's (#119) and ISELED's (#120) shape:

• byte_bus_id/endpoint id 10, after ISELED's 9; REQ-MOCK-001's endpoint count updated to ten
• new dispatch_mdio(), branching on req.op like dispatch_uart (since MdioRequest::is_write is intrinsic to the request itself)
• Unlike ISELED, no MDIO byte-level wire codec (Figure 43/Table 60) exists anywhere in this codebase — mdio.hpp deliberately stops at the (mode, mdio_address, mdio_payload) struct level. dispatch_mdio makes the same kind of deliberately simple, explicitly disclaimed choice dispatch_can makes for CAN's fixed CanIdentifier/FrameFormat: a fixed representative MdioMode::MmdSingleWord/mdio_address=0, with mdio_payload packed/unpacked via avtp::detail::put_u16/get_u16 (the same generic helper dispatch_ep0 already uses for its own magic-number encoding) purely so the mock has some round-trippable wire value. This is the mock's own simulation choice, not a TC18-derived encoding.
• No set_mdio_response() hook: MDIO's register model is self-contained (a write round-trips straight back out on a subsequent read), unlike I2C/LIN/ISELED's external-bus scripting hooks.

.fusa-reqs.json

Added REQ-MDIO-006/007 and REQ-MOCK-025/026, reusing TC18-13.5-001 and TC18-12.7.1-001 — independently re-verified against RELAY's docs/tc18-master-catalog.json (both entries confirm MDIO by name in Table 33's Row 2 list) and against the actual TC18.txt line ranges cited (both match exactly). Also updated REQ-MDIO-003/004's text for the transact rename. Tagged REQ-MDIO-006 (reserved-value-rejection) severity: cybersecurity; sec-tested ratio after this change is 72/410 = 17.56%, above cpfusa's 17% floor.

Pre-existing citation spot-check (not touched by this diff)

Spot-checked MDIO's own pre-existing TC18.txt citations:

• REQ-MDIO-001 (§13.2 Table 32, L3998-4017): confirmed exact match.
• REQ-MDIO-002 (§13.7.13.3 Table 60, L6080-6088): confirmed exact match.

Unlike ISELED's citations in rust-RCP (found ~400 lines stale, PR #161), MDIO's pre-existing citations show no drift — no corrective action needed.

Separately noted (not a citation issue): REQ-MDIO-005's text still references MdioErrc::phy_address_out_of_range, a symbol that no longer exists in mdio.hpp's enum — an apparent leftover from the pre-issue-#72 addressing model. Not part of this PR's diff; flagged here as a small follow-up rather than silently rewritten.

Testing

• tests/test_mdio.cpp: renamed 8 call sites to transact(); added 6 new TEST_CASEs covering Plain/Reserved(×6)/ConfigWrite/masking/field-independence classification.
• tests/test_mock.cpp: REQ-MOCK-001 updated to ten endpoints; new MDIO section mirroring CAN/UART/ISELED's shape.
• Full build (CMake+Ninja) and ctest --test-dir build: 53/53 suites pass, 0 failures.
• cpfusa check --strict: 0 errors (2 warnings/1 info are pre-existing baseline conditions, confirmed identical on main before this change).
• cpfusa trace: 410/410 requirements, 100% annotated, 100% tested; --sec-tested 17 passes (17.56%).
• Mutation test: temporarily changed the ConfigWrite branch to call transact() instead of returning the error; rebuilt; confirmed 2 test_mdio + 1 test_mock assertions failed as expected; reverted cleanly; confirmed all tests pass again with no leftover (grep -n "MUTATION-TEST" finds nothing).