docs(architecture): fix OQ-05 — multi-connectivity endpoint, not multi-transport
Correct the conflation of quinn/TLS/iroh as interchangeable transports. They are complementary connectivity modes serving different deployment contexts: quinn (public IP + TLS), iroh (NAT traversal via relay), TCP (handler-specific, not core). Clarify that TLS cert = network identity, not auth identity. Map stealth mode to HTTP handler on standard ALPNs instead of byte-peeking. Resolve OQ-05 as one-way door. SendStream/ RecvStream now use internal enum dispatch for both quinn and iroh streams.
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@@ -6,36 +6,59 @@ Proposed
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## Context
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ADR-001 establishes ALPN-based protocol dispatch: a single QUIC+TLS endpoint accepts connections, and the ALPN negotiated during the TLS handshake routes each connection to the correct `ProtocolHandler`. ADR-002 defines the `ProtocolHandler` trait. ADR-006 establishes one ALPN per connection. ADR-007 defines `Connection` and `BiStream`.
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ADR-001 establishes ALPN-based protocol dispatch: a single endpoint accepts connections, and the ALPN negotiated during the TLS handshake routes each connection to the correct `ProtocolHandler`. ADR-002 defines the `ProtocolHandler` trait. ADR-006 establishes one ALPN per connection. ADR-007 defines `Connection` and `BiStream`.
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The question now is: **how does the endpoint work?** What accepts QUIC connections, negotiates ALPN, and hands connections to handlers? This is the central runtime piece of alknet-core — every handler depends on it.
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The question now is: **how does the endpoint work?** What accepts connections, negotiates ALPN, and hands connections to handlers? This is the central runtime piece of alknet-core — every handler depends on it.
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The reference implementation (`alknet-main`) uses a `Server` struct that binds a `TransportAcceptor`, runs an accept loop, and dispatches to a `ServerHandler` based on transport type and interface kind. This has three problems that the ALPN model solves:
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### Multiple connectivity modes, not multiple transports
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1. **Multiple listener types**: `ListenerConfig` has three variants (Stream, Http, Dns) with per-variant configuration and validation. ALPN eliminates this — one endpoint, one listener, ALPN does the routing.
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2. **Protocol detection by byte-peeking**: The `stealth` module reads the first bytes to detect SSH vs HTTP. ALPN negotiation makes this unnecessary — the TLS handshake tells you the protocol before any application bytes are read.
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3. **SSH-centric accept loop**: The current `handle_connection` immediately enters `russh::server::run_stream`. In the new model, the accept loop is ALPN-agnostic — it doesn't know or care what protocol the handler speaks.
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The reference implementation supports three connectivity modes that serve **fundamentally different deployment contexts**:
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### iroh's pattern
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1. **QUIC+TLS (public)** — The node has a public IP and open ports. TLS provides protocol routing via ALPN negotiation. The TLS certificate is the node's **network-facing identity** — it's what clients verify when connecting to `alknet.example.com:4433`. This is the mode for replicators, VPS hosts, service providers. SSH key auth still handles **authentication** — the TLS cert is not the auth identity, it's the network identity.
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iroh's `Router` registers `ProtocolHandler` instances with ALPN strings, then calls `endpoint.accept()` in a loop. For each incoming connection, it reads the negotiated ALPN, looks up the handler, and calls `handler.accept(connection)`. This is clean and proven.
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2. **iroh P2P (NAT traversal)** — The node has no public IP or open ports. iroh's relay handles NAT traversal and connection brokering. Node identity comes from iroh's `NodeId` (Ed25519 key pair). The relay is a signaling service, not a proxy — it helps peers establish direct QUIC connections. This is the mode for home servers, IoT devices, anything behind NAT.
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3. **TCP (local/dev)** — Bare SSH over TCP. Port 22. No TLS, no ALPN, no certs. SSH key exchange handles both identity and authentication. This is the mode for local network access and development.
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These are not interchangeable "transports" to be abstracted behind a trait. They are **different ways a node can be reached**, each with different identity and authentication implications:
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| Mode | Identity source | Auth mechanism | Requires public IP | Use case |
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|------|-----------------|----------------|-------------------|----------|
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| QUIC+TLS | TLS cert (network) + SSH key (auth) | SSH key, API key | Yes | VPS, replicators |
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| iroh P2P | NodeId (Ed25519) | NodeId, SSH key | No | Home servers, NAT |
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| TCP | SSH host key | SSH key | Yes (local) | Dev, LAN |
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### What the old "stealth mode" actually was
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The reference implementation's "stealth mode" is **SSH-over-TLS on port 443**. The TLS cert is NOT the node's identity — it's **camouflage**. The purpose is to make port 443 look like a web server to port scanners and DPI systems. Non-SSH traffic gets a fake nginx 404. SSH auth still happens via SSH key exchange *inside* the TLS tunnel.
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In the new ALPN model, this concept maps to: the endpoint speaks QUIC+TLS with ALPN, and the `alknet/http` handler can serve a decoy website on `h2`/`http/1.1` while real services use `alknet/ssh`, `alknet/call`, etc. The ALPN router does the "stealth" job — unknown ALPNs get the HTTP handler, which can serve whatever fronting content is desired. No byte-peeking needed.
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### iroh produces QUIC connections
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iroh's `Endpoint::accept()` produces incoming QUIC connections. These connections have ALPNs. They can feed directly into the same `HandlerRegistry` dispatch. The iroh endpoint and the quinn endpoint both produce QUIC connections — the difference is how they're established (relay-assisted vs direct), not how handlers consume them.
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This means: **the ALPN router is transport-agnostic**. It dispatches by ALPN string. It doesn't care whether the connection came from a quinn endpoint or an iroh endpoint. Both produce connections that handlers can use via the same `Connection` type.
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### Key design questions
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1. **Handler registration**: Static (at startup) or dynamic (at runtime)?
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2. **TLS certificate management**: How does the endpoint get TLS certs? Where does ACME fit?
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3. **Connection lifecycle**: Who owns the `quinn::Endpoint`? How does graceful shutdown work?
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1. **How many endpoints can a node have?** A node may need to listen on quinn (public QUIC+TLS) AND iroh (P2P relay) simultaneously. These are not alternatives — they're complementary connectivity modes.
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2. **Handler registration**: Static (at startup) or dynamic (at runtime)?
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3. **Connection lifecycle**: Who owns the endpoints? How does graceful shutdown work?
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4. **Error handling**: What happens when a handler panics? When ALPN negotiation fails?
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## Decision
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### Endpoint owns the QUIC endpoint
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### A node can have multiple endpoints
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`alknet-core` owns the `quinn::Endpoint` directly. The endpoint binds to a single address, configures TLS with a `rustls::ServerConfig` that includes the ALPN strings from all registered handlers, and accepts connections in a loop.
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`AlknetEndpoint` manages one or more QUIC connection sources. Each source produces connections that feed into the same `HandlerRegistry`:
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```rust
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pub struct AlknetEndpoint {
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endpoint: quinn::Endpoint,
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// One or more QUIC connection sources
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quinn: Option<quinn::Endpoint>, // Public QUIC+TLS
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iroh: Option<iroh::Endpoint>, // P2P relay-assisted
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handlers: Arc<HandlerRegistry>,
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dynamic: Arc<ArcSwap<DynamicConfig>>,
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identity_provider: Arc<dyn IdentityProvider>,
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@@ -43,7 +66,9 @@ pub struct AlknetEndpoint {
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}
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```
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There is no `TransportAcceptor` trait, no `TransportKind` enum, no `ListenerConfig` enum. QUIC+TLS+ALPN replaces all of that.
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A node that has a public IP runs with `quinn: Some(...)` — it listens on a public address with TLS+ALPN. A node behind NAT runs with `iroh: Some(...)` — it connects to a relay and accepts P2P connections. A node that has both runs with both — it's reachable via either path, and both feed into the same ALPN router.
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**TCP mode is not an endpoint concern.** TCP mode in the reference implementation is SSH over raw TCP on port 22. This is not QUIC and doesn't have ALPN. In the new model, TCP access to SSH is handled by the SSH handler directly — it can listen on a TCP socket independently of the ALPN endpoint. This is a handler-specific concern, not a core endpoint concern.
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### HandlerRegistry maps ALPN strings to ProtocolHandler instances
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@@ -53,44 +78,52 @@ pub struct HandlerRegistry {
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}
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```
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Registration is static at startup. The CLI binary constructs a `HandlerRegistry` by inserting handlers for each ALPN, then passes it to `AlknetEndpoint::new()`. The ALPN strings in the TLS `ServerConfig` are derived from the registry's keys.
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Registration is static at startup (OQ-04). The CLI binary constructs a `HandlerRegistry`, inserts handlers, and passes it to `AlknetEndpoint::new()`.
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This is a two-way door (OQ-04): starting static is simple. If dynamic registration is needed later, the registry can be wrapped in `ArcSwap<HandlerRegistry>` and the TLS `ServerConfig` can be regenerated. But ALPN negotiation happens during the TLS handshake, so adding a handler at runtime requires the next connection to use the new ALPN — which the client already has to know about. Dynamic registration has limited value for v1.
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The ALPN strings for the quinn endpoint's TLS `ServerConfig` are derived from the registry's keys. The iroh endpoint's ALPN strings are also derived from the registry — both endpoints advertise the same set of ALPNs.
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### Accept loop: connect, dispatch, spawn
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### Accept loop: accept from all sources, dispatch by ALPN
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The endpoint runs accept loops for each active connection source. All loops dispatch through the same `HandlerRegistry`:
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```
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// Quinn accept loop (if configured)
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loop {
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incoming = endpoint.accept().await
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incoming = quinn_endpoint.accept().await
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connection = incoming.await // TLS handshake + ALPN negotiation
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dispatch(connection)
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}
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// iroh accept loop (if configured)
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loop {
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incoming = iroh_endpoint.accept().await
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connection = incoming.await // iroh QUIC connection + ALPN
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dispatch(connection)
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}
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fn dispatch(connection) {
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alpn = connection.alpn()
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handler = registry.get(alpn)
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match handler {
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Some(h) => {
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auth = resolve_endpoint_auth(connection) // TLS client cert, etc.
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tokio::spawn(h.handle(connection, &auth))
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auth = AuthContext::from_connection(&connection)
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conn = Connection::new(connection)
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tokio::spawn(h.handle(conn, &auth))
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}
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None => connection.close()
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}
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}
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```
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Key behaviors:
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- **ALPN mismatch**: The TLS handshake fails. This is correct — the client and server have no protocol in common.
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- **Handler not found**: Should not happen — the `ServerConfig` only advertises ALPNs that have registered handlers. If somehow a connection negotiates an ALPN with no handler, the connection is closed with an error log.
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- **Handler panic**: The handler runs in a spawned tokio task. If it panics, the task is caught by tokio's panic handler. The connection is dropped. Other connections are unaffected.
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- **Graceful shutdown**: A `watch::Sender<bool>` signals the accept loop to stop accepting new connections. Existing connections are given a drain timeout (2 seconds default), then forcefully closed.
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Both accept loops are `tokio::select!`-ed against the shutdown signal.
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### TLS certificate configuration
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### TLS certificate and the distinction between network identity and auth identity
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TLS certs come from `StaticConfig`:
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- File paths (`tls_cert`, `tls_key`) for manual provisioning
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- Self-signed for development
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For the quinn endpoint, the TLS cert serves as **network-facing identity** — it's what clients verify when connecting to a domain name. It is NOT the node's authentication identity. Authentication is handled by handlers (SSH key exchange, API tokens, etc.).
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The `rustls::ServerConfig` is built from the cert + key + ALPN list at startup. The ALPN list is derived from `HandlerRegistry::alpn_strings()`.
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This is the same model as the reference implementation's TLS mode: the cert makes the port look legitimate and encrypts traffic, but SSH key exchange handles the actual authentication. The ALPN model extends this: the cert + ALPN routing is the network layer, handler-specific auth is the application layer.
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ACME auto-provisioning (Let's Encrypt) is not in scope for v1. It will be added as a feature later (see OQ-12).
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For the iroh endpoint, the `NodeId` serves as network identity. No TLS cert is needed — iroh's QUIC uses the NodeId for connection verification.
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### Error taxonomy
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@@ -115,18 +148,18 @@ pub enum HandlerError {
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## Consequences
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**Positive:**
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- Single accept loop replaces multiple listener types and byte-peeking
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- ALPN negotiation happens at the TLS layer — no application-level protocol detection
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- A node can be reachable via multiple paths simultaneously (public QUIC+TLS, iroh P2P)
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- ALPN router is transport-agnostic — dispatches by ALPN string regardless of connection source
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- Adding a handler is registering an ALPN string — no endpoint code changes
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- Handler panics are isolated — one bad handler can't take down the endpoint
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- `quinn::Endpoint` is the only transport — no TransportAcceptor trait needed for v1
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- The endpoint is testable: give it mock handlers and a test ALPN, verify dispatch
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- "Stealth mode" maps naturally to the HTTP handler serving decoy content on `h2`/`http/1.1`
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- Both iroh and quinn produce QUIC connections — same `Connection` type works for both
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**Negative:**
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- Direct quinn dependency in alknet-core — WASM targets can't use quinn (mitigated: WASM clients don't run endpoints, they connect to them; the WASM door is for client-side handlers, not the endpoint itself)
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- No runtime handler registration without regenerating the TLS config (mitigated: two-way door, start static, add ArcSwap later if needed)
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- alknet-core depends on both quinn and iroh (mitigated: both are feature-gated; a node that only needs one doesn't compile the other)
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- The endpoint is more complex than a single quinn listener — it manages multiple accept loops
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- TLS cert provisioning is manual (file paths) for v1 — ACME auto-provisioning is a future feature (OQ-12)
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- One address per endpoint — if you need to listen on multiple addresses, run multiple endpoints (acceptable for v1)
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- No runtime handler registration without regenerating the TLS config (mitigated: two-way door, start static, add ArcSwap later if needed)
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## References
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@@ -136,6 +169,8 @@ pub enum HandlerError {
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- ADR-007: BiStream type definition (Connection, SendStream, RecvStream)
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- ADR-009: One-way door decision framework
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- OQ-04: Dynamic handler registration (two-way door, start static)
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- OQ-05: Multi-transport endpoint (two-way door, start with quinn)
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- OQ-05: Multi-transport endpoint (now: multi-connectivity endpoint)
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- iroh Router pattern: `docs/research/references/iroh/`
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- Reference implementation: `alknet-main/crates/alknet-core/src/server/serve.rs`
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- Reference implementation: `alknet-main/crates/alknet-core/src/server/serve.rs`
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- Reference stealth mode: `alknet-main/crates/alknet-core/src/server/stealth.rs`
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- Reference iroh transport: `alknet-main/crates/alknet-core/src/transport/iroh_transport.rs`
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