# Client architecture — decisions > **Superseded by `MESHBAY_DESIGN.md`.** This was the client architecture decisions; its design > content now lives in §14.2 (D1–D4). > > It is kept because code comments, tests and other documents cite its > sections and its labels, and because it records reasoning a synthesis > compresses. **Where it disagrees with `MESHBAY_DESIGN.md`, the design > document is right; where either disagrees with the code, the code is.** > `MESHBAY_DESIGN.md` §16 maps every section reference here onto its > replacement, and §13 defines every label. > Created 2026-08-13 after the second security review. D1/D2/D3 decided the same day; > D4 (hub minimization) deferred. Fold into `meshbay-draft-v5.md`. > The analysis below is kept as the rationale behind the decisions, not as open questions. --- ## Status | # | Decision | State | |---|---|---| | D1 | Does the hub keep serving the web UI? | ✅ **DECIDED 2026-08-13 — yes** | | D2 | Browser extension, native desktop client, or both? | ✅ **DECIDED 2026-08-13 — native client, offered alongside the hub-served SPA.** Shell revised 2026-08-17: **Electron**, see `desktop-client-v1.md` | | D3 | Transport: aiortc primary, QUIC at parity, TCP+HTTP removed | ✅ Decided 2026-08-13. Unchanged for the **node**; the desktop client uses Chromium's WebRTC rather than aiortc, and QUIC via a Python sidecar | | D4 | Hub minimization (old Phase 12) | ⏸️ **Deferred, may be dropped** | > **2026-08-17 — the browser-extension options are no longer live.** 12.2 (signed digest > of the served bundle) is what Option A needed, and it remains scheduled; nothing else > from A or B is planned. The desktop client is the answer to T3 for users who want one. **What was decided.** The hub keeps serving the web UI — that is the zero-install path and it stays. A native desktop client is offered *in addition*, not as a replacement. Hub minimization is off the critical path and may be dropped entirely. **What that means, stated once and then respected.** Keeping the hub in the trusted path is a legitimate product call, and this project is not obliged to defend against its own operator. But two consequences should be carried deliberately rather than by accident: 1. **T3 is accepted permanently for browser users.** A hub that serves the code can exfiltrate keys from the page regardless of what the protocol does. The native client gives users who care an alternative; browser users are trusting meshbay.org, and the docs should say so plainly rather than claiming end-to-end integrity. 2. **H3 was the last open High finding and its only fix lived in the dropped phase.** The hub is the public key directory: substituting a key during an invite hands it the group key, silently, with no forgery and no code injection. So key transparency and safety numbers were kept and are now Phase 12.1 — everything else from hub minimization is dropped. If Phase 12 is later dropped too, H3 stays open by choice, and "unreadable by other parties, even the hub" stops being a claim the project can make about an adversarial hub. The honest framing that survives all of this: **the hub cannot read your content unless it actively attacks you.** That is still a strong property, and it is defensible. ## Rationale — why the native client is not a T3 fix The second review recommended a native client and claimed *"T3 disappears — code integrity stops depending on the hub."* **That claim was wrong and has been corrected** in `second-review.md` §9. If the hub operator is the adversary, a native client downloaded from `meshbay.org` and signed with a key that operator holds does not remove the trust — it relocates it from "the JS they serve" to "the binary they serve." What actually changes is **detectability**: - **Browser:** an attack is one HTTP response, targeted at one user, leaving no artifact. Undetectable in principle. - **Native:** an attack requires shipping a build. That build is an artifact — hashable, archivable, comparable between users, reversible. Targeting one user means giving them a different binary, which reproducible builds and published hashes make detectable. That is a real improvement, but **the value lives in the verification machinery (reproducible builds, published hashes, independent rebuilds — Phase 18.7), not in the packaging format.** Without it, a native client from meshbay.org is only marginally more trustworthy than the SPA from meshbay.org. Native also has real costs that were under-weighted: loss of the browser sandbox (a Python process with full user privileges vs a seccomp-confined renderer), ownership of patch velocity for WebKitGTK and every bundled dependency, and new attack surface (loopback media server, IPC bridge, update client). **Conclusion recorded:** the native client is justified on *product* grounds — durable keys, no browser tab, background connectivity, better video, hub-less `group://` access over QUIC. It should not be justified as the fix for T3 unless 18.7 ships with it. --- ## D1 rationale — hub keeps serving the UI ✅ Keeping it is defensible. It is how anyone tries the platform without installing anything, and it stays the fallback when a device has no client installed. What must be true now that it stays (Phase 12.2/12.3): - strict CSP and Subresource Integrity on the bundle - the hub publishes a **signed digest** of the served bundle, so any third party — an extension, a native client, a curious user — can verify it - `/app/` carries an explicit, visible "reduced trust: this hub serves this code" notice - the docs never claim end-to-end integrity for the hub-served SPA path The honest framing: hub-served SPA is a **convenience tier**, not the secure tier. --- ## D2 rationale — native chosen; extension not taken up Three shapes, cheapest first: **Option A — Extension as a verifier (hub still serves the UI)** The extension does not ship the UI. It hashes the bundle the hub served and compares it against a digest signed by the project. Mismatch → visible alarm, optionally block. Converts a silent targeted injection into a loud one. Small effort, keeps today's architecture, compatible with D1 = yes. **Option B — Extension ships the UI (hub serves the API only)** The UI lives in the extension, distributed and signed by Mozilla/Chrome — a channel **the hub operator does not control**. Manifest V3 forbids remote code, which works in our favour: the structure enforces exactly what we want. Keys live in extension storage, isolated from page JS. Moderate effort. **Option C — Native desktop client** ← **CHOSEN** Phase 13. Full control, durable keys in an OS keystore, QUIC, hub-less access, best UX. Highest effort, and the security argument depends on 18.7. > **Shell revised 2026-08-17: Electron, not pywebview** (+ an optional Python sidecar for > `group://` over QUIC). See `desktop-client-v1.md` §2. The comparison table below > was written against pywebview and **two of its rows are wrong for the chosen shell**: > > - *Browser sandbox* — Electron with `sandbox` and `contextIsolation` **keeps** the > Chromium renderer sandbox. The row reads "❌ None (partial under Flatpak)"; that was > WebKitGTK's property, not native's. > - *Crypto available* — the client keeps WebCrypto **and** gains local Argon2id/ChaCha20 > in the main process; the row implied WebCrypto is lost with the browser engine. > > The row that gets *worse*: **patch velocity**. "You own it" is more true of Chromium > than of a distro-maintained WebKitGTK, and the renderer parses attacker-controlled > content from nodes. That is the real cost and it is accepted deliberately. ### Comparison | | Hub-served SPA (today) | A: extension verifies | B: extension ships UI | C: native desktop | |---|---|---|---|---| | Code distribution channel | Hub (the adversary) | Hub, but **verified** | Store (independent) | Hub download + own signing key | | Silent targeted injection | Undetectable | **Detected** | Not possible | Detectable *if* 18.7 | | Browser sandbox | ✅ Full | ✅ Full | ✅ Full | ❌ None (partial under Flatpak) | | Patch velocity | Browser auto-updates | Browser auto-updates | Browser + store review latency | **You own it** (WebKitGTK, Python deps) | | Key storage | IndexedDB, page-reachable | unchanged | Extension storage, page-isolated | **OS keystore** | | Crypto available | WebCrypto only (no ChaCha20/Argon2id) | unchanged | unchanged | **Full** (ChaCha20, Argon2id 256 MB) | | Transport | WebRTC | WebRTC | WebRTC | WebRTC **+ QUIC** | | Large file → disk | Chrome only (FS Access API) | unchanged | unchanged | **Native, unlimited** | | Hub-less `group://` | ❌ | ❌ | ❌ | ✅ | | New attack surface | — | negligible | negligible | loopback server, IPC, updater | | Platforms to maintain | 0 | 2 stores | 2 stores | 3 OSes | | Effort | 0 | Low | Moderate | High | ### Observations for the decision - **A and B are not exclusive with C.** A/B protect browser users; C serves users who want a real application. "Both" is coherent — just sequence them. - **B gives most of C's security benefit at a fraction of the cost**, because the win was never the packaging format — it was getting the code off the adversary's distribution channel — and the extension keeps the browser sandbox while doing it. - **Store review latency is the one place B is worse than C**: a critical fix waits on Mozilla/Google. Mitigate with a version-pinned kill switch. - **For node operators specifically, Phase 14 (CLI) beats all three.** The operator is the highest-value target — holds the GEK, is the content authority — and today must use hub-served JS to initialize GEKs and invite members. The CLI removes that dependency at a fraction of any client's cost. If only one thing gets built for T3, it should be the CLI. - If **D1 = yes** (hub keeps serving the UI), Option A is the natural companion and is nearly free once 12.6 publishes the signed digest. ### Not yet investigated - Whether AMO/Chrome Web Store policy accepts an extension whose purpose is P2P file sharing - Whether MV3 service-worker lifetimes can hold a long-lived WebRTC DataChannel (may need an offscreen document — worth a spike before committing to B) - Safari/iOS: no extension route comparable to AMO; likely out of scope either way --- ## Impact on the roadmap | Decision | If yes | If no | |---|---|---| | D1 hub serves UI | Phase 12.6 as written (CSP, SRI, signed digest, reduced-trust notice) | 12.6 shrinks to removing `/app/`; hub becomes API-only | | D2 = A | Small new phase; 12.6 is a prerequisite | — | | D2 = B | New phase, ~Phase 13-sized; 13.1 platform split is reused directly | — | | D2 = C | Phase 13 as written (13.2–13.11), + 18.7 for the security claim to hold | Phase 13 reduces to 13.1 only | **13.1 (platform adapter split) is worth doing regardless of D2.** It is pure refactoring whose acceptance criterion is "the browser SPA behaves identically," and it is the prerequisite for A, B and C alike.