AMPR-176/#505: ProvenanceCommitted design placeholder

[wow-miley]

Summary

I filed a forward-looking design placeholder for the future MemoryEvent.ProvenanceCommitted event, addressing Gap-5 from the Wave 3 cognitive event audit (AMPR-168). The new docs/design/provenance-event.md sketches the event shape, an Ed25519-over-parent-hash-chain working assumption, three publish-site patterns (with a checkpoint-only recommendation), the OpenAI grant "verifier first vs event first" open question, and explicit promotion criteria for when this gets implemented. I also dropped a TODO(AMPR-176) marker inside sealed interface MemoryEvent so the work is anchored at the right call site. No new event type, no publish site, no tests — code change is the marker only.

Test plan

• ./gradlew ktlintFormat — BUILD SUCCESSFUL
• grep -n "TODO(AMPR-176)" MemoryEvent.kt matches the new marker (line 38)

Closes #505

🤖 Generated with Claude Code

[github-actions]

Concept staleness check — 3 warning(s).

These changes touched files listed under a concept's tracked_sources without updating the concept file. Either update the concept (and bump last_verified) or include a Concept-Verified: <ConceptName> trailer in a commit on this PR.

Validator output

⚠ Concept 'CognitionTrace' may be stale: ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/MemoryEvent.kt matches tracked_sources pattern ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/MemoryEvent.kt but docs/concepts/cognition-trace.md was not modified.
⚠ Concept 'EventSerialBus' may be stale: ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/MemoryEvent.kt matches tracked_sources pattern ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/** but docs/concepts/event-serial-bus.md was not modified.
⚠ Concept 'MemoryProvenance' may be stale: ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/MemoryEvent.kt matches tracked_sources pattern ampere-core/src/commonMain/kotlin/link/socket/ampere/agents/domain/event/MemoryEvent.kt but docs/concepts/memory-provenance.md was not modified.

validate-concepts: 3 warning(s). Validator informs; never blocks.