feat: governed function runtime + billing drain
GCAP-SPEC-FUNCTION-DESCRIPTOR-0001 implementation.
Mirrors connector runtime pattern exactly.
FunctionPlugin — trigger_events, handle(), descriptor(), knative_manifest()
FunctionRegistry — trigger_index for event-driven routing
FunctionRuntime — invoke() + dispatch() with Chronicle lineage
governed_function decorator — SDK surface for function authors
BillingProcessor — GSAP_CR_RECEIVED → billable event with Chronicle CID
EchoFunction — dev/test
API: /functions/ catalogue, invoke, dispatch, manifest, health
8 tests passing.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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