CB-308: resolve the cross-host design review; bump wiki to 36bb865

Six decisions recorded in §7, replacing the matching open questions: signed
messages (identity from the key, extending identity-from-connection across the
broker), target-host-owned profiles advertised via presence, repo provisioning
by pinned forge clone, live-only asks with TTL + TOO_LATE notice, spawn-id
dedup on the target, and broker-outage semantics (local unaffected, remote
fails fast, gateway stays soft-state). §8 keeps what is genuinely still open,
with control *authorization* now separated from the resolved *authenticity*.

The broker-level half (U8 broadcast, exclusive consumers, inbox caps, TLS,
schema version, trace id) lands in wiki chapter 10 §10 — pointer bumped
(also picks up 1710a77, chapter 11 Features).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013ZGgxLQ2VpwZhEYoru8rkf

docs/CB-308-Multi-Host-Federation.md

@@ -1,6 +1,6 @@
 # CB-308 — Multi-Host Federation (Stage 5)
 
-**Status:** design note (proposal)
+**Status:** design note (proposal) — core design decisions resolved 2026-08-10 (§7)
 **Depends on:** CB-307 (broker-based reliable delivery) — CB-308 is the multi-host layer built *on*
 CB-307's broker fabric.
 **Relates to:** CB-401 (`PeerHandle` opaque id), CB-304 (`rosterView`), CB-306 (spawn-readiness),
@@ -143,6 +143,8 @@ extending the same broker from "worker→primary reliability" to "gateway↔gate
 5. **Trust** — the broker connection is now the security boundary. A gateway injects env/tokens at
    daemon privilege (the CB-401 Stage-C concern), so a **remote-triggered spawn/send** needs
    authn/authz: who may act on which host, and which control channels a gateway will honour.
+   *Authenticity* is resolved — signed messages, §7.1; *authorization* (who may do what) remains
+   open — §8.
 
 ## 5. The one thing the broker does NOT dissolve
 
@@ -191,7 +193,44 @@ useful), and build CB-308's items on top once the broker fabric exists. Choose C
 channel naming **multi-host-ready** now (per-agent routing keys, a `roster.*` topic namespace) so
 CB-308 doesn't have to repaint the topology.
 
-## 7. Open questions
+## 7. Resolved design decisions (2026-08-10)
+
+Settled in a design review of this note + wiki chapter 10. The broker-level operational rules
+(inbox caps, TLS + private broker, schema versioning, trace id, exclusive consumers, U8 broadcast)
+are recorded in wiki 10 §10; the CB-308-side decisions are below.
+
+1. **Sender authenticity — sign every message.** Each gateway holds its own signing key and signs
+   what it publishes (sender gid, `msgId`, timestamp). The receiving gateway verifies the
+   signature **and** checks against the roster that the claimed sender lives on the signing
+   gateway's host. This extends the single-host invariant — *identity comes from the connection,
+   never an argument* — across the broker: cross-host, identity comes from the key. Complements
+   (not replaces) per-gateway broker logins over TLS.
+2. **Profiles are owned by the worker's host.** `bridge_spawn(profile, host)` resolves the name in
+   the *target* gateway's `bridged.yaml`. Gateways advertise their profile names in presence
+   heartbeats, so a leader sees what each host offers before spawning; an unknown name is a clear
+   error from the target. Secrets (base URLs, tokens) never leave the host that uses them.
+3. **Repo provisioning — clone from the forge, pinned.** A cross-host spawn names the repo URL and
+   the exact commit. The target gateway clones from the forge into a local cache (first spawn
+   only), then cuts a per-worker worktree — the CB-301-ext flow with a clone step in front,
+   covered by the same repo-scoped forge token (CB-302). Git stays the only channel code moves
+   through.
+4. **Asks are live-only, with expiry.** `ASK`/`ANSWER` (U2) traverse the broker as short-lived
+   (TTL'd) messages carrying the `turn_id`, and are never held durably — the single-host rule
+   kept. An answer arriving after its turn ended is **not** injected; it is dropped and the leader
+   gets a `TOO_LATE` notice, so the one failure case is loud rather than weird. Only terminal
+   replies are durable. Walkthrough: wiki 10 §7.4.
+5. **Spawn dedup — a spawn id, remembered on the target.** The control queue redelivers like any
+   queue; a replayed `SpawnRequest` must not double-spawn. Requests carry a unique spawn id; the
+   target gateway keeps a short memory of handled ids and answers a redelivery with the existing
+   `PeerHandle`. CB-117's orphan reap stays as the backstop.
+6. **Broker down — local unaffected, remote fails fast.** The routing fork (§3.2) means same-host
+   traffic never touches the broker; that is now a written promise. A send to a remote agent while
+   the broker is unreachable **fails immediately** with a clear error — the gateway never buffers
+   on the broker's behalf (it stays soft-state, so a crash cannot lose messages it claimed to
+   deliver). Gateways auto-reconnect; remote hosts read as unknown in the roster meanwhile. Broker
+   HA is a later ops choice, not a design requirement.
+
+## 8. Still open
 
 - **Directory ground-truth:** pure soft-state presence (heartbeats) vs. also treating broker queue
   existence as authoritative. Lean soft-state to preserve the persistence boundary; revisit if
@@ -199,7 +238,9 @@ CB-308 doesn't have to repaint the topology.
 - **Global id scheme:** `<host>/<paneId>` (human-legible, leaks host) vs. opaque UUID (clean, needs
   the directory to resolve host). Probably UUID in the protocol, host as directory metadata.
 - **Gateway discovery:** how gateways find the broker and each other (static config vs. discovery).
-- **Trust model shape:** per-host shared secret vs. mTLS on the broker vs. a capability token per
-  control action — ties into CB-401 Stage-C.
-- **Failure semantics:** a host/gateway dies mid-turn — how the federated roster reaps it (missed
-  heartbeat) and whether in-flight primary-bound messages survive (broker durability = yes).
+- **Control authorization:** signing (§7.1) settles *who sent it*; still open is *who may do
+  what* — which leaders may spawn or stop on which hosts (allowlist vs. a capability token per
+  control action — ties into CB-401 Stage-C).
+- **Gateway death mid-turn:** the roster reaps it by missed heartbeat, and in-flight primary-bound
+  messages survive by broker durability; still open is reconciling *worker* state when the dead
+  gateway's host comes back (orphaned panes vs. still-valid sessions).