test(j1939tp): a paced BAM round trip does not gate on the receiver's default T1

[dborgards]

What does this change?

Closes #277. Eight tests in J1939TpTests round-trip a BAM paced at 5 ms on the real clock and assert the reassembled datagram, not timing. Their receivers kept the default T1 of 750 ms, re-armed per TP.DT, while every DT crosses a thread-pool confirmation hop, an actor post and the spacing timer on its way. A host stall longer than 750 ms between any two packets turned a reassembly test into a T1 abort, which is what the macOS leg of #276 produced.

Five tests in the class already pin T1 high for this reason (t1: TimeSpan.FromSeconds(5) "T1 must not fire first", and 30 s elsewhere). The eight now share one PacedRoundtripOptions() with T1 at 30 s, so ShortTimeout is their only clock, and the comment on it names the quantity the host perturbs and the margin that remains. Parallel_Bam_And_TwoCm_Sessions_Do_Not_Interfere lifts T2 and T3 the same way, since its CM sessions run on the same clock. T1 keeps its own tests (Bam_Receiver_T1Timeout_FaultsReceiveAsyncWhenDtStops and the virtual-clock ones), which is where a timer that is the subject belongs.

Not taken from #277: the abort message naming the packet index. That is product code and a fix release for a diagnostic this change makes unnecessary in the suite; if it is wanted for the field, it is a separate decision.

No mutation check: this change removes an incidental gate rather than adding a detection claim. The eight tests' reassembly assertions are unchanged.

Type of change

• feat — new behaviour (minor release)
• fix / perf — bug or performance fix (patch release)
• docs / test / refactor / chore / ci — no release
• Breaking change (! in the title, plus a BREAKING CHANGE: footer explaining the migration)

Checklist

• dotnet build CanKit.Pro.sln -c Release succeeds — with -p:CI=true
• dotnet test CanKit.Pro.sln -c Release passes — 1532/1532 on net10.0; dotnet format --verify-no-changes and dotnet pack + eng/verify-packages.py also run
• Public API changes are documented with XML comments — n/a
• New behaviour is covered by a test — n/a
• The requirement or ADR this relates to is referenced (e.g. FR-RAW-031, ADR-7), if any — Bam_Roundtrip_ReceiverReassemblesIdenticalPayload failed once on macos-latest with a T1 timeout #277, Three wall-clock-dependent tests fail intermittently across all three CI legs #92

🤖 Generated with Claude Code

https://claude.ai/code/session_01NPLBiJfQ9po3gRXbWpiQn6

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Generated by Claude Code

[cursor]

PR Summary

Low Risk
Test-only changes to J1939Tp integration options; no runtime or public API impact.

Overview
Stabilizes eight J1939-TP virtual-loopback tests that round-trip a 5 ms paced BAM and assert reassembly, not timing (#277). They previously kept the default 750 ms T1, which re-arms on every TP.DT; on loaded hosts (e.g. macOS CI) a stall between packets could abort reassembly instead of failing the intended assertion.

Adds shared PacedRoundtripOptions() — 5 ms bamPacketSpacing and 30 s t1 — so ShortTimeout is the only meaningful clock for those tests. Parallel_Bam_And_TwoCm_Sessions_Do_Not_Interfere uses the same helper and also sets T2/T3 to 30 s for concurrent CM sessions. T1 timeout behavior stays covered by dedicated tests. No production code changes; reassembly assertions are unchanged.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-04T18:39:47.465757Z	1f879ab	PR opened

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