[mrcsin]

Problem

Slice 6a typed only the connection-lost fault. The rest of the PLC producer surface stayed English:

• NotConnectedError / ProtocolVersionMismatchError were internal — invisible to ReasonLocalizer.
• The recipe-active, write-verification and not-committed faults were free-text new Error(...) / Result.Fail(string).
• PlcSyncExecutor laundered typed inners — it re-wrapped a typed inner's .Message into a fresh untyped Error before emitting the fault, discarding the type so the localizing seam could not reach it.

On the diagnostics side, PlcTransactionExecutor's five catch { return Result.Fail(ex.Message); } sites kept only the message string — the exception type and stack were gone before any log sink, and nothing walks Result.Reasons. This is the second half of #120 ("exception type/stack lost at Result.Fail(ex.Message)").

What changed

Type the PLC producer surface, un-launder the fault forwarding, and land the exception in a log.

Six typed faults localize by type (2 made public, 4 new), each with a ReasonLocalizer arm, en/ru resx, Designer accessor, and a coverage sample:

Class	en	note
NotConnectedError	Not connected to PLC	made public + fieldless
ProtocolVersionMismatchError	PLC protocol version {0} does not match expected {1}	made public + Expected/Actual props
RecipeActiveError	Recipe is being executed on PLC	new leaf
WriteVerificationFailedError	Recipe write verification failed after {0} attempts	new leaf (Attempts)
RecipeNotCommittedError	Recipe not committed on PLC	new leaf
PlcCommandFailedError	PLC command failed	new Rule-B envelope (CausedBy(ex))

Un-laundering — PlcSyncExecutor now forwards the typed inner directly (reportFault(Errors[0]), return activeResult.ToResult()) so it localizes through the 6a ReportFailure(IError) seam; the recipe-active and exception-stringify sites are typed.

Diagnostics (#120, second half) — the five PlcTransactionExecutor catches return PlcCommandFailedError().CausedBy(ex) and log the exception once (writes at Error, reads at Warning). The PlcExecutionMonitor poll-error line is guarded to skip PlcCommandFailedError (already logged at the catch) while still surfacing the decode-Result.Fail path — exactly-once logging, no silenced failure.

Behavior-preserving for English except PlcCommandFailedError, which replaces the raw ex.Message headline with a localized "PLC command failed" and keeps the exception on CausedBy plus the log. HasError<T> type assertions survive the make-public.

Deferred to 6c (documented in error-reporting.md): the #120 cancellation threading (part 1), the short protocol-version-read diagnostic, the enable catch, and the codec decode-Result.Fail forwarding — all left English by design.

Verification

• dotnet build SemiStep.slnx — 0 warnings.
• dotnet test SemiStep/SemiStep.Tests/SemiStep.Tests.csproj — 1661 passed, 0 failed.
• ReasonLocalizerTests pins the ru render of all six types (e.g. ProtocolVersionMismatchError(2,1) → "Версия протокола ПЛК 1 не соответствует ожидаемой 2") + en Localize == .Message; CoreErrorLocalizationCoverageTests auto-enrolls the public types; ResourceSyncTests enforces en/ru/Designer key + placeholder parity.
• ResultReportingExtensionsTests drives NotConnectedError/RecipeActiveError/PlcCommandFailedError through the seam and asserts Russian in the operation slot. PlcSyncCoordinatorTests pins the RecipeActiveError production path and PlcCommandFailedError carrying the exception on .Reasons.
• Review chain: comprehensive (5 agents) → critical re-check → smells → comment audit → critical, all clean after fixes. The reviews caught a real diagnostics hole (deleting the monitor poll-error line silenced the decode-Result.Fail path — restored guarded) and a symmetric write-path double-log (guarded).
• Manual test (operator): passed.

Addresses #120 (second half; part 1 — cancellation threading — deferred to 6c).

Per-task commits before collapse

69a01fa docs(plan): record exec branch and verify steps for 6b
f2c6fd5 style: separate ProtocolVersionMismatchError properties with blank line
3efbf7a fix: skip redundant write-failure log for typed command failures
7d577a3 fix: address review findings (monitor log, RecipeActive test, doc counts)
4036bb7 test(l10n): cover PLC error localization end-to-end
10f9e9c feat(l10n): type PLC command failures and log the exception
1c802ea feat(l10n): type PLC producer errors and un-launder faults

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