Per-tag opt-in for write-retry per docs/v2/plan.md decisions #44, #45, #143.
Default is false — writes never auto-retry unless the driver author has marked
the tag as safe to replay.
Core.Abstractions:
- DriverAttributeInfo gains `bool WriteIdempotent = false` at the end of the
positional record (back-compatible; every existing call site uses the default).
Driver.Modbus:
- ModbusTagDefinition gains `bool WriteIdempotent = false`. Safe candidates
documented in the param XML: holding-register set-points, configuration
registers. Unsafe: edge-triggered coils, counter-increment addresses.
- ModbusDriver.DiscoverAsync propagates t.WriteIdempotent into
DriverAttributeInfo.WriteIdempotent.
Driver.S7:
- S7TagDefinition gains `bool WriteIdempotent = false`. Safe candidates:
DB word/dword set-points, configuration DBs. Unsafe: M/Q bits that drive
edge-triggered program routines.
- S7Driver.DiscoverAsync propagates the flag.
Stream A.5 integration tests (FlakeyDriverIntegrationTests, 4 new) exercise
the invoker + flaky-driver contract the plan enumerates:
- Read with 5 transient failures succeeds on the 6th attempt (RetryCount=10).
- Non-idempotent write with RetryCount=5 configured still fails on the first
failure — no replay (decision #44 guard at the ExecuteWriteAsync surface).
- Idempotent write with 2 transient failures succeeds on the 3rd attempt.
- Two hosts on the same driver have independent breakers — dead-host trips
its breaker but live-host's first call still succeeds.
Propagation tests:
- ModbusDriverTests: SetPoint WriteIdempotent=true flows into
DriverAttributeInfo; PulseCoil default=false.
- S7DiscoveryAndSubscribeTests: same pattern for DBx SetPoint vs M-bit.
Full solution dotnet test: 947 passing (baseline 906, +41 net across Stream A
so far). Pre-existing Client.CLI Subscribe flake unchanged.
Stream A's remaining work (wiring CapabilityInvoker into DriverNodeManager's
OnReadValue / OnWriteValue / History / Subscribe dispatch paths) is the
server-side integration piece + needs DI wiring for the pipeline builder —
lands in the next PR on this branch.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
One invoker per (DriverInstance, IDriver) pair; calls ExecuteAsync(capability,
host, callSite) and the invoker resolves the correct pipeline from the shared
DriverResiliencePipelineBuilder. The options accessor is a Func so Admin-edit
+ pipeline-invalidate takes effect without restarting the invoker or the
driver host.
ExecuteWriteAsync(isIdempotent) is the explicit write-safety surface:
- isIdempotent=false routes through a side pipeline with RetryCount=0 regardless
of what the caller configured. The cache key carries a "::non-idempotent"
suffix so it never collides with the retry-enabled write pipeline.
- isIdempotent=true routes through the normal Write pipeline. If the user has
configured Write retries (opt-in), the idempotent tag gets them; otherwise
default-0 still wins.
The server dispatch layer (next PR) reads WriteIdempotentAttribute on each tag
definition once at driver-init time and feeds the boolean into ExecuteWriteAsync.
Tests (6 new):
- Read retries on transient failure; returns value from call site.
- Write non-idempotent does NOT retry even when policy has 3 retries configured
(the explicit decision-#44 guard at the dispatch surface).
- Write idempotent retries when policy allows.
- Write with default tier-A policy (RetryCount=0) never retries regardless of
idempotency flag.
- Different hosts get independent pipelines.
Core.Tests now 44 passing (was 38). Invoker doc-refs completed (the XML comment
on WriteIdempotentAttribute no longer references a non-existent type).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Lands the first chunk of the Phase 6.1 Stream A resilience layer per
docs/v2/implementation/phase-6-1-resilience-and-observability.md §Stream A.
Downstream CapabilityInvoker (A.3) + driver-dispatch wiring land in follow-up
PRs on the same branch.
Core.Abstractions additions:
- WriteIdempotentAttribute — marker for tag-definition records that opt into
auto-retry on IWritable.WriteAsync. Absence = no retry per decisions #44, #45,
#143. Read once via reflection at driver-init time; no per-write cost.
- DriverCapability enum — enumerates the 8 capability surface points
(Read / Write / Discover / Subscribe / Probe / AlarmSubscribe / AlarmAcknowledge
/ HistoryRead). AlarmAcknowledge is write-shaped (no retry by default).
- DriverTier enum — A/B/C per driver-stability.md §2-4. Stream B.1 wires this
into DriverTypeMetadata; surfaced here because the resilience policy defaults
key on it.
Core.Resilience new namespace:
- DriverResilienceOptions — per-tier × per-capability policy defaults.
GetTierDefaults(tier) is the source of truth:
* Tier A: Read 2s/3 retries, Write 2s/0 retries, breaker threshold 5
* Tier B: Read 4s/3, Write 4s/0, breaker threshold 5
* Tier C: Read 10s/1, Write 10s/0, breaker threshold 0 (supervisor handles
process-level breaker per decision #68)
Resolve(capability) overlays CapabilityPolicies on top of the defaults.
- DriverResiliencePipelineBuilder — composes Timeout → Retry (capability-
permitting, never on cancellation) → CircuitBreaker (tier-permitting) →
Bulkhead. Pipelines cached in a lock-free ConcurrentDictionary keyed on
(DriverInstanceId, HostName, DriverCapability) per decision #144 — one dead
PLC behind a multi-device driver does not open the breaker for healthy
siblings. Invalidate(driverInstanceId) supports Admin-triggered reload.
Tests (30 new, all pass):
- DriverResilienceOptionsTests: tier-default coverage for every capability,
Write + AlarmAcknowledge never retry at any tier, Tier C disables breaker,
resolve-with-override layering.
- DriverResiliencePipelineBuilderTests: Read retries transients, Write does NOT
retry on failure (decision #44 guard), dead-host isolation from sibling hosts,
pipeline reuse for same triple, per-capability isolation, breaker opens after
threshold on Tier A, timeout fires, cancellation is not retried,
invalidation scoped to matching instance.
Polly.Core 8.6.6 added to Core.csproj. Full solution dotnet test: 936 passing
(baseline 906 + 30 new). One pre-existing Client.CLI Subscribe flake unchanged
by this PR.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty