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ADR-0061: Execution Context Accessor Pattern

Status: Accepted
Date: 2026-05-24
Decision Owner: Architecture
Evolith disposition: Proposed for Evolith adoption — zero UMS-specific dependencies; applicable to any .NET satellite
Related:

Context

Command handlers, AOP aspects, background services, and outbox dispatchers all need access to the same request-scoped observability signals: CorrelationId, SessionTrackingId, TraceId, and SpanId.

Before this ADR, each component resolved these independently:

MelLogger read from Activity.Current directly
CorrelationIdMiddleware wrote to HttpContext.TraceIdentifier
SerilogLogger used the static Log.ForContext() without request state

This created three problems:

Inconsistency — different components used different resolution strategies; logs from the same request could carry different CorrelationId values depending on which code path ran.
HTTP coupling — any code needing CorrelationId had to depend on IHttpContextAccessor, leaking Presentation infrastructure into Application or Infrastructure layers.
Background-service blind spot — Activity.Current is null in outbox dispatchers and background services; there was no way to carry forward the originating request context.

Alternatives considered

Option	Problem
`IHttpContextAccessor` everywhere	Couples Application/Infrastructure to HTTP
`AsyncLocal<T>` flow	Breaks across `Task.Run` boundaries and `ConfigureAwait(false)`
Static `Activity.Current` only	Null in background services; no SessionTrackingId
Scoped `RequestContextAccessor`	Writable by middleware, readable by any scoped service — no HTTP dependency

Decision

Introduce a scoped RequestContextAccessor that is written by middleware and read by any component in the request scope without coupling to HTTP.

Types

Ums.Shell.Aop.Aspects.Logger.Serilog   (shell library — generic, no UMS dependency)
├── ExecutionContextSnapshot            record(CorrelationId, SessionTrackingId, TraceId, SpanId)
├── IExecutionContextAccessor           interface { Current; Set(snapshot) }
├── ObservabilityHeaders                static class — HTTP header name constants
│     CorrelationId     = "X-Correlation-Id"
│     SessionTrackingId = "X-Session-Tracking-Id"
└── ObservabilityKeys                   static class — OTel baggage/tag key constants
      CorrelationId     = "correlation.id"
      SessionTrackingId = "session.tracking_id"

Ums.Application.Common.Interfaces
└── IRequestContext                     read-only port for Application layer
      SessionTrackingId, CorrelationId, TraceId, SpanId (all string?)

Ums.Infrastructure.Services
└── RequestContextAccessor              implements IRequestContext + IExecutionContextAccessor
      registered as IRequestContext (read-only) and IExecutionContextAccessor (writable)

Propagation chain

[HTTP Request arrives]
      │
      ▼
CorrelationIdMiddleware
  – reads / generates X-Correlation-Id header
  – writes to Activity.Current baggage ("correlation.id")
  – writes to ILogger scope ("CorrelationId")
      │
      ▼
SessionTrackingMiddleware
  – reads / generates X-Session-Tracking-Id header
  – writes to Activity.Current baggage ("session.tracking_id")
  – calls RequestContextAccessor.Set(new ExecutionContextSnapshot(...))
  – writes to ILogger scope ("SessionTrackingId")
      │
      ▼
RequestContextAccessor (scoped)
  – holds snapshot for remainder of request
  – readable by AOP aspects, handlers, background handoffs
      │
      ▼
UmsSerilogLogger / StructuredAopLoggerBase
  – calls ResolveExecutionContext() → reads RequestContextAccessor.Current
  – falls back to Activity.Current if snapshot is empty (background service path)

Resolution priority in `StructuredAopLoggerBase.ResolveExecutionContext()`

RequestContextAccessor.Current (set by SessionTrackingMiddleware)
Activity.Current baggage (fallback for non-HTTP contexts)
requestId parameter from [LoggerAspect] attribute
Empty string

DI registration

// Ums.Infrastructure/DependencyInjection.cs
services.AddScoped<RequestContextAccessor>();
services.AddScoped<IRequestContext>(sp => sp.GetRequiredService<RequestContextAccessor>());
services.AddScoped<IExecutionContextAccessor>(sp => sp.GetRequiredService<RequestContextAccessor>());

Layer rules

Layer	May use	May NOT use
`Ums.Domain`	— (no context needed)	`IRequestContext`, `IExecutionContextAccessor`
`Ums.Application`	`IRequestContext` (read-only port)	`IExecutionContextAccessor`, `RequestContextAccessor`
`Ums.Infrastructure`	`IExecutionContextAccessor` (AOP adapters)	direct `RequestContextAccessor` (inject via interface)
`Ums.Presentation`	Both interfaces via DI; `RequestContextAccessor` in middleware	—

Consequences

Positive

Single source of truth for all observability signals — one snapshot per request scope
Application layer has zero HTTP dependency for correlation context
Background services and outbox dispatchers can carry forwarded context by receiving an ExecutionContextSnapshot at handoff time
StructuredAopLoggerBase in the shell library uses this pattern without any UMS-specific import
ObservabilityHeaders and ObservabilityKeys constants prevent string-literal proliferation across middleware

Trade-offs

RequestContextAccessor is writable by any code with IExecutionContextAccessor — the contract is by convention, not enforced. Middleware should be the only writer.
Snapshot is captured once per request at SessionTrackingMiddleware position in the pipeline; spans that start later in the pipeline get a stale SpanId in the snapshot. AOP aspects compensate by reading Activity.Current.SpanId as fallback.

Evolith Extraction Checklist

The following types are in Ums.Shell.Aop.Aspects.Logger.Serilog with no UMS-specific import:

ExecutionContextSnapshot — generic record, no product references
IExecutionContextAccessor — generic interface
ObservabilityHeaders — constants, rename prefix as appropriate
ObservabilityKeys — constants, rename prefix as appropriate
StructuredAopLoggerBase — depends only on IExecutionContextAccessor and IJoinPoint

IRequestContext and RequestContextAccessor are UMS-namespaced but trivially portable to any satellite.

ADR Registry

CP-05 Execution Context

ADR-0053 OTel

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