Context Observation

Observation is the non-compacting context policy. Configure it with:

type ContextObservationPolicy struct {
	ReservedOutput content.TokenCount
	SafetyMargin   content.TokenCount
	CountTimeout   time.Duration
}

func WithContextObservation(policy ContextObservationPolicy) Option
func (p ContextObservationPolicy) Validate(
	capability contextcount.CounterCapability,
) error

Every field is explicit. ReservedOutput must be nonzero and CountTimeout must be positive. When the counter quality is CountQualityHeuristicEstimate, SafetyMargin must also be nonzero. Exact provider and exact local counters may use a zero safety margin.

Hard admission

Observation counts the candidate request before admission and compares it to the limit returned by ResolveContextLimits. It does not rewrite the conversation and does not invoke a compaction hustle. If the candidate reaches the limit, the runtime returns a typed *loop.ContextLimitError containing the event.ContextMeasurement and refuses that request.

The option requires the complete context group: WithContextCounter, WithInferenceCapability, and exactly one of observation or compaction. Adding both policies returns DefinitionConflictingContextPolicy; adding a policy without a counter or capability returns the corresponding missing-context error.

%%{init: {"theme":"dark"}}%%
sequenceDiagram
    participant S as session/loop
    participant C as ContextCounter
    participant M as model request
    S->>C: CountContext(candidate, timeout)
    C-->>S: measurement and quality
    S->>S: resolve hard InputLimit
    alt used >= InputLimit
        S-->>M: ContextLimitError
    else below limit
        S->>M: send candidate request
    end

Policy fields and errors

Validate returns *loop.ContextObservationPolicyError; inspect its Field with errors.As. It performs metadata checks only and does not call the counter’s I/O method during definition construction.

Source and proof

• Observation policy type and validation
• Definition context-policy coupling
• Observation policy and admission tests