feat(endpoint): decompose Phase 2 into 9 tasks for alknet-endpoint crate extraction

- endpoint/crate-init: initialize crate, Cargo.toml, module skeleton
- endpoint/registry: extract HandlerRegistry (~50 lines)
- endpoint/endpoint-core: AlknetEndpoint fresh build against ADR-083 shape
- endpoint/dispatch: public dispatch, build_auth_context, ACME guard
- endpoint/accept-quinn: quinn accept loop + extractors (extracted)
- endpoint/accept-iroh: iroh accept loop + extractors (extracted)
- endpoint/accept-tcp-tls: TCP+TLS accept loop (new code)
- endpoint/tests: move + adapt 17 tests
- endpoint/review-endpoint: review checkpoint

7 generations, 3 parallel tasks (accept loops), no cycles.
Depends on tls/review-tls (Phase 1 complete).

tasks/endpoint/registry.md

@@ -0,0 +1,99 @@
+---
+id: endpoint/registry
+name: Extract HandlerRegistry from alknet-core/endpoint.rs into alknet-endpoint
+status: pending
+depends_on: [endpoint/crate-init]
+scope: narrow
+risk: low
+impact: component
+level: implementation
+---
+
+## Description
+
+Phase 2, Task 2 of the crate extraction. Extract the `HandlerRegistry` type from
+`crates/alknet-core/src/endpoint.rs` (lines 66-116) into `crates/alknet-endpoint/src/registry.rs`.
+
+The old code **stays** in `endpoint.rs` (duplicated) — no breakage. The new crate is
+self-contained and builds standalone.
+
+### Types to extract
+
+From `endpoint.rs` lines 66-116:
+
+| Type/Function | Lines | Destination |
+|---------------|-------|-------------|
+| `HandlerRegistry` struct | 66-68 | `registry.rs` |
+| `HandlerRegistry::new()` | 71-75 | `registry.rs` |
+| `HandlerRegistry::register()` | 77-86 | `registry.rs` |
+| `HandlerRegistry::get()` | 88-90 | `registry.rs` |
+| `HandlerRegistry::alpn_strings()` | 92-94 | `registry.rs` |
+| `impl Default for HandlerRegistry` | 97-101 | `registry.rs` |
+| `impl Debug for HandlerRegistry` | 103-116 | `registry.rs` |
+
+### Adaptations
+
+1. **Imports**: Update `crate::types::ProtocolHandler` to `alknet_core::types::ProtocolHandler`.
+2. **No other changes**: The `HandlerRegistry` is a pure data structure with no transport deps.
+   It maps ALPN byte strings to `ProtocolHandler` instances. No feature gates needed — it's
+   always available regardless of which transports are enabled.
+
+### Public API
+
+```rust
+// registry.rs
+
+/// Maps ALPN byte strings to `ProtocolHandler` instances.
+/// Registered statically at startup by the assembly layer; the endpoint
+/// dispatches by looking up the negotiated ALPN.
+pub struct HandlerRegistry {
+    handlers: HashMap<&'static [u8], Arc<dyn ProtocolHandler>>,
+}
+
+impl HandlerRegistry {
+    pub fn new() -> Self;
+    /// Insert a handler. Panics if the ALPN is already registered.
+    pub fn register(&mut self, handler: Arc<dyn ProtocolHandler>);
+    /// Look up a handler by ALPN string.
+    pub fn get(&self, alpn: &[u8]) -> Option<&Arc<dyn ProtocolHandler>>;
+    /// Return all registered ALPN strings.
+    pub fn alpn_strings(&self) -> Vec<Vec<u8>>;
+}
+```
+
+### What stays in core
+
+The old `HandlerRegistry` in `endpoint.rs` lines 66-116 is **not deleted** — it stays as a
+duplicate. The prune happens in Phase 4. This task only adds code to `alknet-endpoint`.
+
+## Acceptance Criteria
+
+- [ ] `crates/alknet-endpoint/src/registry.rs` contains `HandlerRegistry` with all methods
+- [ ] `HandlerRegistry::new()` creates an empty registry
+- [ ] `HandlerRegistry::register()` inserts a handler, panics on duplicate ALPN
+- [ ] `HandlerRegistry::get()` looks up by ALPN, returns `None` for unknown
+- [ ] `HandlerRegistry::alpn_strings()` returns all registered ALPNs
+- [ ] `Default` impl delegates to `new()`
+- [ ] `Debug` impl lists ALPNs without exposing handler internals
+- [ ] All imports use `alknet_core::` (not `crate::`)
+- [ ] No feature gates (always available)
+- [ ] `cargo check -p alknet-endpoint` succeeds
+- [ ] `cargo clippy -p alknet-endpoint` succeeds with no warnings
+- [ ] `cargo test -p alknet-core` still passes (old code untouched)
+
+## References
+
+- docs/research/alknet-crate-extraction/findings.md — Phase 2, registry module
+- docs/architecture/crates/endpoint/README.md — HandlerRegistry spec
+- crates/alknet-core/src/endpoint.rs — lines 66-116 (source code to extract)
+
+## Notes
+
+> This is the simplest extraction in Phase 2 — ~50 lines of pure data structure.
+> `HandlerRegistry` has no transport deps and no feature gates. It's extracted
+> first because `AlknetEndpoint::new()` takes it as a parameter. The old code in
+> `endpoint.rs` is NOT deleted — that's Phase 4.
+
+## Summary
+
+> To be filled on completion