fix(canopen): grow SDO receive buffers geometrically, report a short RPDO once per run

[dborgards]

What does this change?

Two findings from the deep review (docs/reviews/2026-09-30-deep-review.md, § 2.8):

• C11 — The classic SDO client (sizeless or under-declared upload), the block-download server and the block-upload client grew their receive buffer by exactly one segment, copying everything received so far each time: O(N²). A 64 KiB sizeless transfer allocated ~307 MB; the buffers now double (CanOpenNode.GrowCapacity), clamped to MaxSdoTransferBytes (+7 on the block paths, whose last segment may overshoot by six bytes, CANopen: collected minor findings (boundary OOM, registration leak, RTR DLC, doc drift) #59). Results were already trimmed to Offset, so the slack is never visible.
• C13 — A producer sending a too-short RPDO made the node emit EMCY 8210h for every frame. It is now raised once per run of short frames; a fitting frame or reconfiguring the RPDO ends the run.

C12 (block-download client timer re-armed per sub-block instead of per segment, versus the wording in CanOpenNodeOptions) is not touched; it needs a decision on which side is right.

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 (net10.0; net48 only runs in CI)
• Public API changes are documented with XML comments (none; GrowCapacity is internal)
• New behaviour is covered by a test
• The requirement or ADR this relates to is referenced (FR-CO-002/003/004, FR-CO-024)

Mutation checks: making GrowCapacity return needed fails the three allocation tests and the unit theory; removing the debounce condition, and removing the reset on a fitting frame, each fail the new EMCY test. The reset on RPDO reconfiguration is not covered by a test.

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Touches SDO transfer memory behavior and PDO/EMCY handling on the operational path; changes are bounded by existing caps and protocol rules, with broad new tests.

Overview
Fixes two review findings: O(N²) SDO receive-buffer growth and EMCY storms on repeated short RPDOs.

SDO buffers now grow via internal GrowCapacity (double from at least 8 bytes, clamped to MaxSdoTransferBytes, with +7 slack on block paths). Classic segmented upload client, block-download server, and block-upload client use it instead of resizing to exactly the next segment; realloc copies only bytes received so far (Offset), not the whole old array. Large sizeless transfers drop from ~307 MB allocated (64 KiB) to roughly linear total copy/allocation cost.

Short RPDOs still skip actuation and may raise EMCY 8210h once per continuous run of too-short frames (ShortFrameReported on RpdoRuntime). A frame that meets the mapped length or RPDO reconfiguration clears the flag so the next short frame can report again; disabled EMCY (1014h bit 31) emits nothing and does not consume the debounce state.

Tests cover geometric growth (unit theory + GC allocation bounds on .NET 5+) and FR-CO-024 EMCY debounce behavior.

^{Reviewed by Cursor Bugbot for commit abd93e0. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-03T07:31:35.569061Z	cb1a42b	New commits

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