feat: implement Table 30 Row-2 evt[2:0] validation — PWM_IN (3rd endpoint type)

[SoundMatt]

Direct follow-up to the merged pilot (#114, I2C) and its ADC follow-up (#115), which established the shared Table 33 Row 2 evt[2:0] classifier (rcp::endpoint::evt_row2_kind_of, EvtRow2Kind{Plain,ConfigWrite,Reserved}) and wired I2C then ADC into mock::Server::dispatch(). This PR applies the identical pattern to PWM_IN, the third of the row's 8 endpoint types ({ADC, PWM_IN, I2C, LIN, CAN, UART, ISELED, MDIO}). PWM_OUT (GPIO/PWM_OUT's own Table 33 row, already conformant via endpoint::WriteSemantics) shares rcp/pwm.hpp with PWM_IN but is untouched by this change.

Changes

• include/rcp/pwm.hpp: add PwmInEndpoint::handle_request(evt_op, out_value), PWM_IN's request-decode entry point, mirroring I2cEndpoint::handle_request's and AdcEndpoint::handle_request's shape exactly.

  • Plain (evt[2:0]==000b) delegates to the existing handle_read() (PWM_IN's response-only read model, unchanged): the most recently recorded measurement, or PwmErrc::no_signal if none has ever been captured.
  • Reserved returns endpoint::EndpointErrc::reserved_evt_row2 without touching out_value.
  • ConfigWrite returns the new PwmErrc::config_write_not_supported — full §12.7.1 config-write handling (EP_functional-config wiring) is deliberately deferred, the same scope decision I2C's and ADC's own handle_request made, since PWM_IN has no EP_functional-config wiring in this codebase either.
  • PWM_IN's own request-handling section (§13.7.6.3) explicitly defers to §13.5's evt-bit table rather than redescribing it, so this classification is PWM_IN's own wiring of an already-stated rule, not a new spec fact.

• include/rcp/mock.hpp: wire PwmInEndpoint into mock::Server::dispatch() at endpoint id/byte_bus_id 5, following the I2C/ADC pattern exactly (operational-request gating, wire_error_code_for mapping, a set_pwm_in_response() scripting hook). Unlike ADC's FIFO sample queue, PWM_IN's read model reports the most recently recorded measurement persistently (not consume-once), so set_pwm_in_response() scripts it by calling PwmInEndpoint::record_measurement directly rather than modeling a queue. Also maps PwmErrc::no_signal to acf::WireErrorCode::PwmInNoSignal — unlike ADC's no_signal (which has no TC18-defined wire code and falls back to EpError), Table 27 defines a real numbered PWM_IN_NO_SIGNAL(9) code, so this maps to it directly. Register map now describes 5 endpoints instead of 4.

• .fusa-reqs.json: REQ-PWM-008/REQ-PWM-009 (handle_request Plain/Reserved/ConfigWrite), REQ-MOCK-015/REQ-MOCK-016 (PWM_IN dispatch wiring + operational gating), REQ-MOCK-001 updated for the 5-endpoint map.

  • REQ-PWM-008/REQ-MOCK-015 reuse tc18_master_id: TC18-13.5-001 — verified against RELAY's docs/tc18-master-catalog.json before linking: its own title is "EP-specific usage of evt-field" and its summary explicitly names the ADC/PWM_IN/I2C/... Row 2 rule these requirements are actually about, unlike cpp-RCP feat: implement Table 30 Row-2 evt[2:0] validation — ADC (2nd endpoint type) #115's original REQ-ADC-007 mistake, which linked an unrelated wire-format fact to this same master id and had to be corrected in review.
  • REQ-PWM-009 reuses TC18-12.7.1-001 (the config-write shape, same master entry I2C/ADC's own config-write-not-supported requirements cite).
  • No new wire-codec requirement was needed: PWM_IN reuses the existing shared pwm::encode_pwm_payload/PwmValue codec REQ-PWM-001 already covers (checked RELAY's catalog entry TC18-13.7.6.3-001, "pwmi request format" — PWM_IN's own two-16-bit-value payload figure — before concluding no new citation was needed for the codec itself).

• REQ-PWM-008 tagged severity: cybersecurity (the PWM_IN-level "reject a reserved evt[2:0] value with UNSUPPORTED_CMD rather than silently accepting it" property, same class as REQ-ENDPOINT-007's/REQ-ADC-008's tag): adding 4 new requirements with none cybersecurity-tagged would have diluted the sec-tested ratio from 66/386 (17.10%→17%) to 66/390 (16.92%→16%), tripping the ≥17% CI gate. Tagging REQ-PWM-008 restores it to 67/390 = 17% (integer division, matching CI's own shell arithmetic).

• New unit tests: tests/test_pwm.cpp gets a "Table 33 Row 2 evt[2:0] validation (handle_request)" section mirroring tests/test_i2c.cpp's and tests/test_adc.cpp's shape. tests/test_mock.cpp gets a "PWM_IN" section mirroring the "I2C"/"ADC" sections (plain request answers the scripted measurement, repeated plain requests keep answering the same scripted value since PWM_IN is not consume-once unlike ADC, PwmInNoSignal before any measurement is scripted, all 6 reserved evt values rejected with UNSUPPORTED_CMD without disturbing the scripted measurement, config-write rejected with UNSUPPORTED_CMD, pre-RCP_CONFIGURED gating). Predicate-level Plain/Reserved/ConfigWrite classification for all 8 evt_op values is already covered by tests/test_endpoint.cpp's existing case from the pilot — not duplicated here.

Verification

• Full local build (Ninja, C++17): passes.
• ctest --test-dir build --output-on-failure -j1: 53/53 pass.
• cpfusa v0.18.0 check: 0 errors.
• cpfusa v0.18.0 trace --format json: 390/390 (100%) requirement traceability; secTestedRequirements/totalRequirements = 67/390 = 17% (integer division), meeting the ≥17% CI gate.

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