Draft: add FogVault/FogCompute schema scaffolds

[mdheller]

Summary

This PR captures the first SourceOS/SociOS Fog Layer contract scaffolds in the canonical typed-contract repo.

It adds:

• FogVault storage/topic schemas:
  • Topic.json
  • TopicEnvelope.json
  • ReplicationPolicy.json
  • ContentRef.json
• FogCompute compute/evidence schemas:
  • Offer.json
  • WorkOrder.json
  • UsageReceipt.json
  • SettlementEvent.json
• matching example payloads for each new schema
• docs/FOG_LAYER.md as the initial narrative/spec anchor

Why this belongs here

sourceos-spec is the canonical machine-readable contract layer for SourceOS/SociOS. The Fog layer should start here before any substrate, ignition, or runtime implementation lands downstream.

Scope intentionally included

• additive schema scaffolds only
• additive examples only
• no runtime implementation
• no ignition/systemd/bootstrap changes
• no marketplace backend lock-in

Scope intentionally deferred

Follow-up PRs should add:

1. canonical signing/canonicalization rules for fog envelopes and receipts
2. OpenAPI / AsyncAPI fog surfaces
3. JSON-LD / semantic overlay extensions for topic / offer / receipt vocabulary
4. stricter cross-schema references once downstream execution semantics are finalized
5. schema catalog / root README family index updates

Review notes

• This is a draft because the schemas are v0 scaffolds meant to establish the contract surface, not the final semantics.
• The branch was originally cut from an earlier main commit and is now behind the current branch head. The diff is additive (new files only), but the branch should be refreshed/rebased before merge so we do not accumulate avoidable divergence.

Files added

Docs

• docs/FOG_LAYER.md

Schemas

• schemas/ContentRef.json
• schemas/Offer.json
• schemas/ReplicationPolicy.json
• schemas/SettlementEvent.json
• schemas/Topic.json
• schemas/TopicEnvelope.json
• schemas/UsageReceipt.json
• schemas/WorkOrder.json

Examples

• examples/content_ref.json
• examples/offer.json
• examples/replication_policy.json
• examples/settlement_event.json
• examples/topic.json
• examples/topic_envelope.json
• examples/usage_receipt.json
• examples/workorder.json