Session Vault Phase B: hosted vault on overdeck.ai (encrypted, user-keyed) #4297

Part of PAN-2350 (Overdeck Anywhere). Split out of PAN-2609 on 2026-09-28, as its PRD directs ("Phase B … separate issue; do not build under PAN-2609").

PRD: .pan/drafts/pan-2609.md, section "Phase B — hosted vault on overdeck.ai"

What

A hosted Session Vault backend on overdeck.ai: pan vault setup overdeck://… stores the vault's encrypted chunks and refs at overdeck.ai instead of in a user-owned git remote. The service stores ciphertext it cannot read; the vault key stays on the user's devices.

Architecture from the PRD (decision D-4: an object store with a compare-and-swap ref service, not a git server):

• storage: Cloudflare R2 (no egress fees; adoption and restore are download-heavy);
• refs and CAS: one Cloudflare Durable Object per vault;
• API: a Worker at vault.overdeck.ai implementing VaultStore over HTTPS (PUT/GET/HEAD /objects/:id, GET/PUT /refs/:name with If-Match: <version>);
• identity and billing: the shared overdeck.ai account and the Anywhere subscription (sold through Creem as merchant of record); quota on stored bytes.

Why

Phase A (PAN-2609) needs the user to own and configure a private git remote. A hosted backend makes the vault one command for users who don't want to run storage, and it is the anchor product of the Anywhere subscription.

Requirements (carried from the PRD)

• HB-1 The overdeck:// backend passes the same VaultStore contract tests as git and dir.
• HB-2 The server never receives plaintext or the vault key (acceptance by traffic capture).
• HB-3 Account deletion deletes all objects within 24 h.
• HB-4 Export: pan vault migrate <new-backend> copies every object and ref, so users are never locked in.
• HB-5 Web viewing, if ever built, decrypts in the browser with the key entered locally and never uploads it.

Dependencies

• PAN-2609 Phase A (format, encryption, VaultStore interface).
• PAN-4293 overdeck.ai account service.
• PAN-4294 subscription and billing.
• Epic decision D-7 as amended 2026-09-28: overdeck.ai may store encrypted, user-keyed data it cannot read (PAN-2350).
• Pricing: decided 2026-09-28; see "Pricing" below. (The earlier ~$5/month placeholder is superseded.)
• Order: step 6 (paid tier) of the PAN-2350 sequence, after the account service and billing, before the PAN-2356 relay.

Pricing (decided 2026-09-28)

Operator-approved. Not yet available.

• The vault is not sold separately; it anchors the one Anywhere subscription.
• Payment provider: Creem as merchant of record. Creem is the legal seller and collects and remits VAT, GST and sales tax. Fees: 3.9% + $0.40 per successful charge, no international card fee; payouts on the 1st and 15th at the higher of $7 or 1% of the payout (pricing, payouts, checked 2026-09-28).
• Fees per charge: $96/yr: $4.14 (4.3%); $60/yr: $2.74 (4.6%); $10/mo: $0.79 (7.9%). A $5 monthly price would lose 11.9%, which is why the plan pushes annual billing.
• Cost basis: Cloudflare R2 at $0.015/GB-month; all-in cost per user is about $0.10-0.24/month at 5 GB and $1.52-1.66/month at 100 GB. A heavy user adds about 4 GB stored per month (zstd about 3.2x).
• Margins (vault only, Creem fees with payout at 1%): Anywhere annual about 92% typical / 74% at the 100 GB cap; $10 monthly 89% / 75%; founding 90% / 61%. Relay and push cost is not modeled yet and will lower the bundle margin.
• At the cap nothing is deleted: uploads stop, local copies stay, and the user is offered a retention rule, the add-on, or migration. Version history is never gated.
• Public reasoning, for operator review before publishing: docs page PR #4309.
• PRD: .pan/drafts/pan-2609.md "Phase B pricing (decided 2026-09-28)".

Part of PAN-2350.