bug: predictiveContextCache is not cleared on session reset/end

[compoodment]

Summary

src/context-engine.ts keeps predicted context in a module-level Map keyed by sessionId. Entries are deleted when assembleContext consumes them, but a session can end or reset without a final assemble call.

Impact

• abandoned sessions can leave stale predicted context entries behind;
• recycled sessionId values could receive predictions from an earlier session;
• long-running gateway processes can accumulate cache entries over time.

Scope

Lifecycle/cache hygiene bug. Not an immediate crash.

Fix Path

• Clear predictiveContextCache on before_reset and session_end lifecycle hints.
• Consider a TTL or max-entry cap as a fallback for hosts that do not deliver lifecycle hints reliably.
• Treat cachedIdentity invalidation separately unless live identity/config reload is explicitly supported.

Verification Target

• Unit test for lifecycle hint clearing.
• Unit test proving stale predictions from an ended session are not reused.

A previous broad PR (#218) touched this but was closed for bundling unrelated changes. Bring this back as a focused cache-lifecycle patch.

– Vale