What problems was I solving

The repository contained three dead-code exports in the event-handler-agent package: EventHandlerModelCallPurpose.SessionBriefing was introduced but never passed to eventHandlerModelCallMetadata; THREAD_EXPANSION_MAX_NON_THREADS_COMPONENTS had no remaining external consumers after its previous use was removed; and ThreadExpansionRuleConfig was only used as a type annotation for a single local constant.

What user-facing changes did I ship

There are no user-facing changes. This change only removes unreachable code; runtime behavior, component limits, and model-call attribution metadata remain identical.

How I implemented it

Removed the SessionBriefing enum member and its map entries from model-call-attribution.ts, and removed the exported constant THREAD_EXPANSION_MAX_NON_THREADS_COMPONENTS and interface ThreadExpansionRuleConfig from thread-expansion-rules.ts. The literal value 2 is now inlined as maxNonThreadsComponents in THREAD_EXPANSION_RULE_CONFIG, whose inferred type preserves the same shape.

Description for the changelog

Cleans up dead exports from event-handler-agent by removing the unused SessionBriefing model-call purpose, the unreferenced THREAD_EXPANSION_MAX_NON_THREADS_COMPONENTS constant, and the ThreadExpansionRuleConfig interface. No behavior or public API contracts change because no external code consumed these exports.