[boeboe]

Implementations added

Adapter	Upstream	Version	Revision	Pin	Licence	Published	Transports (both roles)
j2mod	steveohara/j2mod	3.4.0	d7861c90f40a7ac219a2dc6987ffa54caa5d47a7	jar sha256 0d4254d2…	Apache-2.0	yes	tcp, udp, rtu-over-tcp
jsmodbus	Cloud-Automation/node-modbus	5.0.0	fdf02b2600b22519ae4e7465e9bec381a1653172 (npm gitHead, untagged)	tarball sha512 integrity	MIT	yes	tcp, rtu-over-tcp
modbusesp	emelianov/modbus-esp8266	4.1.1	299666307a052df52f757f3131e292c2513bb57f	git tag, commit checked; SOURCES.sha256	BSD-3-Clause	yes	tcp, rtu-over-tcp
modbus4j	MangoAutomation/modbus4j	3.1.0	3325a2cbce786989156ba7999d6adc2755f7ea5b	archive sha256 eb20d1fc…	GPL-3.0-or-later	no (built locally, R8.3)	tcp, udp, rtu-over-tcp

Every pin is the latest stable upstream release (scripts/latest-upstream.py reports update=no for all four). Base images are the existing digest pins, plus node:26.13.0-trixie-slim@sha256:5adad64f… for jsmodbus.

modbus-esp8266 in Docker: this works. The library's Modbus sources are compiled unmodified for Linux against a small Arduino-core layer (sockets as Client/Server/Stream) that has no Modbus logic. Four of its documented compile-time settings are changed through an -include overlay; the upstream files are not edited. See adapters/modbusesp/README.md.

Contract 1.2

• --transport tcp|udp|rtu-over-tcp on server and client, plus the capability field transports. The five 1.0 adapters declare tcp only.
• Five new features that every adapter declares. When a pairing lacks one, the affected cases are recorded as unsupported; nothing is waived in tests/known-bugs.tsv.

Feature	False for	Why (spec V1.1b3)
serverIllegalFunction	j2mod, jsmodbus, modbus4j	j2mod over TCP and modbus4j over RTU close or stay silent instead of exception 1 (§7). jsmodbus never answers an undecodable request.
serverRejectedWriteUnchanged	modbus4j	A refused FC15/FC16 has already written its in-range part (§6.11/6.12 state diagrams, FIXTURES rule 2).
serverHighestAddress	modbus-esp8266	addReg off-by-one: address 65535 can't be served (§4.4).
clientLargestRegisterWrites, serverLargestRegisterWrites	jsmodbus	FC16 byte count is capped at 0xF6. The client sends 240 data bytes for 123 registers, and the RTU server stalls (§6.12).

Scenarios

• New: transport.<udp|rtu-over-tcp>.case.*, .agree.*, .values.* (tests/transport-cases.tsv), and values.rejected-write.unchanged.
• Changed: the out-of-range FC15/FC16 cases now get a fresh server each, so a partly written refusal can't change later read-only cases.
• Changed: the FC65, 65535 and largest-write cases and checks are now gated on the features above.

Results

All nine images on linux/arm64, make documents: 9453 pass, 0 fail, 5007 unsupported, 0 not-tested, 0 known-difference, 0 infra-error. Smoke: 46–58 checks per image, 0 failures. make validate lint is clean.

Reproduce: make images documents.

Findings

All findings, with PDUs and spec sections, are in docs/COMPATIBILITY.md#findings and each adapter's README. Highlights beyond the table:

• j2mod: no CRC check on RTU; UDP FC20/FC24 frame lengths are wrong.
• jsmodbus: FC43 exceptions carry the MEI byte; pipelined requests are answered LIFO.
• modbus-esp8266: the FC20 byte count is off by 2, and the server can overflow its heap (the adapter refuses such requests first).
• modbus4j: no answer for another unit or a bad quantity; FC22 is answered with exception 1 by its server.

Docs and policy

• Updated: versions.yaml, THIRD_PARTY_NOTICES.md, README, AGENTS, PLAN, CAPABILITIES, CONTAINER_CONTRACT, FIXTURES, COMPATIBILITY.
• REQUIREMENTS R2.1 (the list of stacks), R8.1 (the GPL adapter is GPL) and R8.3 (GPL images are not published).
• RELEASE.md v0.4.0, interop_version 0.4.0.

CI

• The selftest job's time limit is now 150 min and the release build's 180 min: there are 81 pairings instead of 25, and the local run took about 70 min.
• The upstream drift matrix covers the four new stacks.
• The own-stack workflow takes its reference list from ADAPTERS in the release it tests.

Not done here: the release itself (maintainer), and pinning in go-modbus (follows the release).

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