amadan
docs: instance contexts — one engine, different social defaults (#204)
Capture the plan for context-specific defaults (Family / Friends / Community, plus later Team / Business / Club / Other). A context is a named preset over a few orthogonal social-structure knobs (admission, default channels, member-created open channels, discovery, DM scope) — not a mode the engine branches on. We store the resolved knobs, not the context, since instances drift; "Other / Custom" always exists. Flags the two knobs that move the trust model rather than being cosmetic: admission (open join-link changes who you trust) and open-channel confidentiality (instance-key encryption → membership is subscription, not access). Notes scale limits and that Business/compliance conflicts with E2EE.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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| +# Instance contexts — one engine, different social defaults |
| + |
| +Status: **design** (not built). Builds on `docs/threads-and-dms.md` and |
| +`docs/invite-redesign.md`. Nothing here weakens the E2EE invariant: the server |
| +still only ever stores ciphertext and key-blobs it cannot open. |
| + |
| +## The idea |
| + |
| +Different kinds of instances — a family, a friend group, a community — share |
| +~80% of what they need and differ in ~20%. The shared 80% is the **messaging |
| +core**: threads, per-thread AES-GCM keys, the instance key, DMs, attachments, |
| +mini-apps, the whole crypto model. None of it changes across kinds. |
| + |
| +The 20% that differs is entirely **social structure**: who may cross the trust |
| +boundary, who can see whom, and which channels exist by default. So "context" is |
| +**not a mode the engine branches on** — it's a *named preset* over a handful of |
| +orthogonal knobs, plus tailored onboarding copy and channel scaffolding. |
| + |
| +- **A context is a template chosen at instance creation.** It expands into |
| + concrete values on the knobs below, seeds a channel or two, and sets the |
| + onboarding language. |
| +- **We store the resolved knobs, not the context.** Real instances drift — a |
| + family later wants a General; a friend group wants restricted DMs for the one |
| + kid. The admin console exposes the dials directly; the context only seeds them. |
| +- **"Other / Custom" always exists** — the dials with no preset. Future contexts |
| + (Team, Club, Business) are new template rows, not engine changes. |
| + |
| +## The knobs |
| + |
| +| Knob | Options | Backing | |
| +|---|---|---| |
| +| **1. Admission** — who adds a *person* to the instance | admin-only · members-can-invite · open join-link | `usersCanInvite` / `user_invites_enabled` (exists); open join-link is new | |
| +| **2. Default channels** | none · one "General" · several topic channels | instance-key–encrypted threads, auto-created | |
| +| **3. Member-created open channels** | off · on | deferred *"group join links, instance-members-only"* (`threads-and-dms.md`) | |
| +| **4. Discovery / roster visibility** | full-open · restricted (e.g. kids ↔ parents only) | deferred *"restricted discovery"* | |
| +| **5. Who can DM whom** | anyone ↔ anyone · restricted | same restricted-discovery lever | |
| + |
| +Everything else (composing, reactions, attachments, mini-apps) is the shared |
| +core and is identical in every context. |
| + |
| +## Contexts as presets |
| + |
| +| | Admission | Default channels | Member open channels | Discovery / DMs | |
| +|---|---|---|---|---| |
| +| **Family** | admin-only (parents) | none | off | restricted (kids ↔ parents), else open | |
| +| **Friends** | members-can-invite | one General | maybe | full-open | |
| +| **Community** | members-invite or open-link | several topic channels | on | full-open (role-gated later) | |
| +| **Other** | fully custom | — | — | — | |
| +| *Team (later)* | domain/SSO-gated | per-project | on | open within org | |
| +| *Business (later)* | admin/SSO | departmental | on | + retention/audit ⚠️ (see below) | |
| +| *Club (later)* | invite or open-link | few | on | open | |
| + |
| +Each row is a starting point on those five dials, nothing more. |
| + |
| +## Two knobs that aren't cosmetic |
| + |
| +Most knobs are defaults you can flip freely. Two change the **trust model** and |
| +must be designed as first-class features, not preset side effects. |
| + |
| +### Admission is the security posture |
| + |
| +Family's "admin-only" *is* the safety model: a parent vets everyone who can read |
| +anything. Community's "open join-link" means unvetted people get keys wrapped to |
| +them. That is not a preference — it changes who you are trusting. The open |
| +join-link is its own carefully-gated feature (expiring links, optional |
| +admin-approval step), never something a preset silently turns on. |
| + |
| +### Open channels: subscription vs. access |
| + |
| +An "open" channel (General, topic channels) is cleanest **encrypted with the |
| +instance key**: every member already holds it, and new members get it |
| +auto-granted via the existing nudge-and-wrap flow (`instance-key/nudge` → |
| +`grantInstanceKeyTo`), so the channel is instantly readable with zero per-member |
| +re-wrap. That gives a clean split: |
| + |
| +- **Open channels** → instance-key encrypted. *Any member can read* (even browse |
| + before joining). Membership here is a **subscription** — it controls what's in |
| + your list and what notifies you, not access. |
| +- **Private groups / DMs** → per-thread key. Membership is **access** — you |
| + cannot decrypt without being wrapped in. |
| + |
| +Honest limitation: an open channel is cryptographically readable by every |
| +current and future instance member, forever. "Leaving" one is unsubscribing, not |
| +losing the ability to decrypt. For a community that is usually the intended |
| +meaning of "open." A channel that is open-to-join but revocable-on-leave needs a |
| +per-channel key + rekey-on-leave, which costs an online key-holder and O(members) |
| +re-wraps — a bill that grows with size. |
| + |
| +## Cross-cutting concerns (not knobs) |
| + |
| +- **Scale is the silent axis.** Family (~5) and Friends (~20) sit in the model's |
| + sweet spot. Community (100s) strains two mechanics: the nudge-and-grant |
| + instance-key handshake assumes a holder is reachable, and remove-a-member rekey |
| + is O(members) and needs someone online. Decide how far up the size curve each |
| + context is meant to go before designing it. |
| +- **Business bends the model.** Team and Club are basically Community + roles. |
| + Business drags in retention, compliance, and admin-visible audit — several of |
| + which *directly conflict* with E2EE (you cannot hand a compliance officer |
| + plaintext the server never sees). Business needs its own trust-model |
| + conversation; it is not a preset. |
| + |
| +## Status / next steps |
| + |
| +Design only — nothing here is built. Natural build order once we commit: |
| + |
| +1. Land the knobs as instance config + admin-console dials (extends the existing |
| + `user_invites_enabled` pattern). |
| +2. Instance-key–encrypted "General" / open channels + the subscription-vs-access |
| + split. |
| +3. Member-created open channels (the deferred group-join-links design). |
| +4. Restricted discovery (kids ↔ parents). |
| +5. Context templates + onboarding copy on top, once the dials exist. |