docs(legal): evidence chain roadmap

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 # Evidence chain · roadmap
 The evidence chain is the set of cryptographic + procedural mechanisms that make a Blocao clip **third-party verifiable** as an authentic, untampered record of what happened at a specific time and place.
 This is a separate workstream from the MVP. See [ADR-0007](../../decisions/0007-evidence-chain-postpone.md) for the rationale.
 ## Two layers
 The roadmap is split into:
 - **Layer 1 (MVP)**: enough to demonstrate good-faith integrity. Ships in the demo path.
 - **Layer 2 (post-MVP)**: third-party-verifiable, eIDAS-aligned, suitable for legal proceedings.
 ## Layer 1 (MVP) — Good-faith integrity
 Ships by end of Sprint 4 in the basic flow, end of Sprint 7 fully polished.
 ### What it provides
 For every recorded clip:
 - **SHA256** computed at write time, stored in the manifest.
 - **Manifest JSON** with: cam_id, sha_clip, sha_keyframe, ts_local, ts_nts, model_sha, site_id, operator_id (when manually pinned).
 - **Cell-local signature** over the manifest, using a key generated at first boot.
 - **NTS-anchored timestamp** (Network Time Security, RFC 8915) so the clock is trustworthy.
 - **Append-only manifest log** in the Cell, replicated to the hub.
 ### What it doesn't provide
 - Timestamp not from a third-party TSA (just NTS — better than naive NTP, less than RFC 3161).
 - Signature key not customer-controlled (BYOK is L2).
 - No transparency log replication to a third party.
 - No FIDO2-attested operator actions.
 ### Sufficient for
 - Internal investigations.
 - Insurance claims (most insurers).
 - "Show me what happened" forensic playback.
 - Customers who trust Blocao Labs as the issuer.
 ### Not sufficient for
 - Court evidence in jurisdictions requiring eIDAS-qualified TSA.
 - Adversarial proceedings where the evidence will be challenged.
 - Regulated industries with specific evidence-chain requirements.
 ## Layer 2 (post-MVP) — Legal-grade
 Targeted for end of Year 1 / start of Year 2.
 ### What L2 adds
 - **RFC 3161 TSA timestamps**: each manifest is signed by a third-party Time Stamp Authority (eIDAS-qualified TSA in EU; ANSSI-recognized for FR; equivalent in other jurisdictions).
 - **Transparency log replication**: manifests append to a public-or-private transparency log (Sigstore-style or custom). External parties can verify "this manifest was published by date X".
 - **BYOK (Bring Your Own Key)**: customer-controlled root key, sealed with Tang+Clevis or HashiCorp Vault. Blocao Labs never sees the key.
 - **FIDO2-attested operator actions**: when an operator pins a clip to a case or exports an evidence pack, the action is attested with a FIDO2 hardware token. Provides non-repudiation.
 - **Tamper-evident export packages**: evidence packs are sealed with a reproducible hash chain that any verifier can check independently.
 ### What this enables
 - Court-grade evidence in EU jurisdictions accepting eIDAS qualified electronic signatures.
 - Defensible chain of custody in adversarial proceedings.
 - Regulated-industry compliance (banking, healthcare with specific evidence rules).
 - Independent third-party verification ("I have this clip, was it created by Blocao on date X?" verifiable without trusting Blocao Labs or the customer).
 ### What it still doesn't provide
 - Proof that what's recorded is not staged or manipulated *at the source* (no AI/CGI detection).
 - Identity of people in frame (separate workstream — facial recognition, with its own legal complexity).
 ## Implementation notes
 ### TSA selection
 For EU operations: select a qualified TSA from the EU Trusted List (e.g., one of the certificate authorities recognized under eIDAS). Multiple TSAs supported for redundancy.
 For Argentina / LATAM: ONTI-recognized TSA where available, fall back to international TSA with documented basis.
 ### Transparency log
 Two options:
 1. **Public log** (Sigstore-style Rekor instance): maximum transparency, but exposes site_id metadata.
 2. **Private log** (customer-operated or Blocao-operated, audited): reasonable transparency, less metadata exposure.
 Default: customer-operated private log on the hub, with optional mirror to public log when customer policy allows.
 ### BYOK key custody
 Three patterns:
 1. **Customer-managed root** with Tang+Clevis: customer holds the unlock policy, Cells decrypt at boot.
 2. **HashiCorp Vault** integration: customer's Vault server provides unsealing.
 3. **HSM-based** (rare): customer has a hardware HSM, Cells request signatures over network.
 Pattern 1 is the default and easiest to operate. Pattern 2/3 for higher-security customers.
 ### FIDO2 attestation flow
 Operator clicks "PIN TO CASE" → console requests FIDO2 attestation from operator's hardware token (YubiKey or platform authenticator) → attestation included in the action's MQTT publish + manifest annotation.
 Without FIDO2 token: action is logged but not attested. Higher-tier customers may require FIDO2 for all sensitive operations.
 ## Roadmap timing
 | Phase | Milestone | Target |
 |---|---|---|
 | L1 basic | SHA + manifest + Cell signature | End of Sprint 4 |
 | L1 polish | NTS-anchored ts in manifest, append-only log replicated to hub | End of Sprint 7 |
 | L2 alpha | RFC 3161 TSA integration, single TSA | Year 1 Q4 |
 | L2 beta | Transparency log replication, BYOK | Year 2 Q1 |
 | L2 GA | FIDO2-attested operator actions, full eIDAS alignment | Year 2 Q2 |
 ## Sales conversation patterns
 **Customer asks**: "Are your clips court-admissible?"
 **Today**: "We sign every clip with a manifest including content hash and trusted-time anchor. For most use cases — internal investigations, insurance claims, civil proceedings where evidence isn't strenuously challenged — that's been sufficient. For criminal proceedings or aggressive civil challenges, evidence chain v2 with RFC 3161 timestamps and transparency log is on our Year 2 roadmap."
 **Customer asks**: "Can the customer hold their own keys?"
 **Today**: "BYOK is on our Year 2 roadmap. Today, the keys are managed by the Cell with a customer-recoverable seal. Discuss your specific requirements with us."
 **Customer asks**: "Do you support eIDAS qualified electronic signatures?"
 **Today**: "Not yet at the qualified-TSA level. Our Year 2 roadmap is explicitly building toward eIDAS alignment. If this is a deal requirement, let's discuss whether we can prioritize for your deployment."
 ## Why L1 is enough for MVP
 The vast majority of forensic use cases don't go to court. Most surveillance recordings are reviewed internally, used for insurance, or for operational decisions. L1 is sufficient for these.
 Going to court is rare; when it happens, courts increasingly accept "best-effort cryptographic chain" with appropriate expert witness explanation. L1 supports that.
 L2 is the fortress version, for the customers who need it. We build it as a platform feature available on demand, not as a prerequisite.