docs: resolve the server + web questions — iroh retires the Go server

Decisions banked after the iroh spike (M1/M2 proven) + reviewing iroh's WASM
browser support:
- The Go server is retired entirely post-iroh. iroh subsumes every networking
  role (STUN/TURN→holepunch+relay, signaling→connect(), SSE→iroh relay,
  presence→iroh-gossip). Replacement is off-the-shelf: self-hosted iroh-relay
  (supernode #1) + a tiny account→{EndpointId} rendezvous for gossip bootstrap.
- Web is not a reason to keep a server. The future web client is tethercore
  compiled to wasm32 as a relay-only iroh peer (no holepunch in-browser; reaches
  peers via the relay, E2E). iroh-gossip compiles to WASM, so discovery works
  in-browser unchanged. The MeshEvent seam makes it a build target, not a
  project: feature-gate transports → web build is "engine + IrohTransport only".
- Migration is graceful: IrohTransport runs alongside SSE/RTC/LAN as another
  MeshEvent source until it wins, then they retire.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ARCHITECTURE.md

@@ -199,7 +199,14 @@ prefer-direct (relay saw only presence), and E2E (relay carried only ciphertext)
   `/api/turn-cred` (HMAC ephemeral creds) + web client. **⚠ The deployed binary
   is ahead of this source** (integrated TURN, advanced web client, built from an
   uncommitted tree ~2026-05-21). Do **not** redeploy `server/` as-is — it would
-  regress TURN. Recovering that source is an open task.
+  regress TURN. **Decided (post-iroh): the Go server is retired entirely.** iroh
+  subsumes every networking role it has — STUN/TURN → holepunch + relay,
+  RTC signaling → `endpoint.connect()` (gone), SSE relay → iroh relay, presence
+  → `iroh-gossip`. Its replacement is *off-the-shelf*: a self-hosted **iroh-relay**
+  on the homelab (supernode #1) + a tiny `account → {EndpointId}` rendezvous for
+  gossip bootstrap. Web is not a reason to keep it (§6.3: web = WASM build of the
+  core). Migration is graceful, not big-bang — `IrohTransport` runs *alongside*
+  SSE/RTC/LAN as another `MeshEvent` source until it wins, then they retire.
 
 What's **Mesh** today: identity (weak), LAN/RTC/SSE transports, mDNS + relay
 discovery, E2E channel, presence/reachability. What's **Sync** today: message
@@ -253,10 +260,17 @@ The hard networking kernel exists. To become a general substrate:
    stateless message-passing; a backbone is replicated state.
 2. **An app API / SDK.** A clean surface: declare data, subscribe, send. The
    thing a developer building app #2 actually touches.
-3. **Web target = WASM.** The Rust core compiles to WASM, but the browser
-   sandbox limits web peers to WebRTC / WebSocket / WebTransport (no raw
-   UDP/TCP/mDNS — same wall as iOS's multicast entitlement). Web is a
-   first-class but transport-limited peer.
+3. **Web target = WASM (resolved by iroh).** The future web client is just
+   `tethercore` compiled to `wasm32` as a **relay-only iroh peer** — same core,
+   no bespoke server bridge ever. A browser iroh endpoint can't holepunch
+   (sandbox: no UDP), so it always reaches peers *through the relay* (E2E, relay
+   blind); `iroh-gossip` compiles to WASM too, so discovery (§ M3) works
+   in-browser unchanged. The `MeshEvent` seam makes this a *build target, not a
+   project*: native transports (LAN/mdns, webrtc-rs, reqwest) don't compile to
+   WASM and don't need to — feature-gate the transports and the web build is
+   "engine + `IrohTransport` only, `default-features=false`, `wasm32`." Cost:
+   browser peers lean on the relay (no P2P offload) — trivial for clipboard,
+   relay-carried for big files.
 4. **Capabilities / permissions (target).** Multi-user needs object-capabilities
    (UCAN), not ACLs.
 5. **Persistence / offline-first (target).** Local store + sync-on-reconnect
@@ -335,7 +349,12 @@ and crypto and getting it subtly wrong.
 - [ ] DHT + multi-supernode peer-relay (mostly *adopted* via Iroh/libp2p, not built).
 - [ ] Rotatable rooms/keys/identities + stable-handle directory indirection.
 - [ ] Private discovery (OPRF/PSI lookup; ZKP ownership proofs).
-- [ ] Capability model (UCAN); offline mailbox; web (WASM) peer.
+- [ ] Capability model (UCAN); offline mailbox.
+- [ ] **Web client = `tethercore` on `wasm32`** — relay-only iroh peer, same
+      core, no server bridge. Gated on feature-gating the transports (iroh-only
+      build) + the IrohTransport (M4). A build target, not a project.
+- [ ] **Retire the Go server** once IrohTransport wins — replace with a
+      self-hosted iroh-relay (supernode #1) + a tiny gossip-bootstrap rendezvous.
 
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