fix(canopen): hold the peer SDO channel across a foreign PDO snapshot

[dborgards]

What does this change?

Closes #295. ObserveForeignPdoAsync read a peer's COB-IDs and mapping with one public upload each, so a caller to the same peer could take the SDO channel between two of them; the displaced upload was refused as in flight, which the observer took for "live record unavailable", and the observation combined a live COB-ID with the file's mapping. The observer now takes the peer's SDO channel without waiting and holds it for the whole snapshot, the rule #291 gave the SRDO observer: a caller arriving meanwhile is refused as in flight, a safety transaction waits, and a channel busy at the start makes the whole snapshot the file's.

Test: CanOpenForeignPdoObserveTests.A_call_cutting_in_mid_snapshot_is_refused_and_the_snapshot_stays_live — a public upload started in the AfterPdoMatchForTests seam, between the COB-ID match and the mapping read. Red on 2d5ba02 (the mapping came from the file), green after the change. The pinned fallback An_SDO_already_in_flight_falls_back_to_the_file_instead_of_throwing still holds. README (§SDO client, §Observing a peer PDO), the ICanOpenNode remarks and FR-CO-030 say so.

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 (-p:CI=true, 0 warnings)
• dotnet test CanKit.Pro.sln -c Release passes (net10.0: 1884 tests; dotnet format --verify-no-changes clean; pack + verify-packages.py 9 packages ok; requirements traceability 0 new untraced)
• Public API changes are documented with XML comments (no API change; ObserveForeignPdoAsync remarks updated)
• New behaviour is covered by a test
• The requirement or ADR this relates to is referenced: FR-CO-030

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Changes peer SDO concurrency and foreign-PDO decode semantics when the channel is contended; behavior is covered by new and existing tests but affects master-tool timing with safety transactions and concurrent SDO.

Overview
Fixes #295: ObserveForeignPdoAsync could mix a live COB-ID with the EDS/DCF mapping when another SDO call to the same peer ran between the observer’s COB-ID and mapping uploads—the displaced upload was treated as “live unavailable” and fell back to the file.

ObserveForeignPdoAsync now matches the SRDO observer: it claims the peer SDO channel without waiting (PeerSdoChannel, non-blocking Wait(0)) and holds it for the whole live snapshot, routing all COB-ID/mapping reads through a LiveUpload delegate (SdoUploadCoreAsync or synthetic “already in flight”). Concurrent SDO calls to that peer are refused; safety transactions wait; if the channel was busy at the start, the entire snapshot uses the file. Adds test seam AfterPdoMatchForTests and integration test A_call_cutting_in_mid_snapshot_is_refused_and_the_snapshot_stays_live.

FR-CO-030, ICanOpenNode remarks, and README (SDO client + observing peer PDO) document snapshot semantics and in-flight behavior.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-12T10:31:40.136348Z	157e7ad	PR opened

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