docs(prd-0070): record remote-terminal resolution; track detail in #478

Remote terminal is an orchestrator operation, not a data-plane one: the
agent PTY is exec_agent-sourced (ssh -t / container exec --tty / docker
exec), which the orchestrator owns — the gateway never holds a PTY. A
--remote flag publishes a running agent's session; local + remote clients
share it via a session multiplexer (one PTY, many clients),
operator-role-gated, so the split's "one authenticated remote door" holds
for terminals too. Detailed design (multiplexer location, input
arbitration, per-client rendering, always-on vs --remote) tracked in #478.

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

docs/prds/0070-per-host-orchestrator.md

@@ -462,11 +462,15 @@ launch, teardown, list, supervise approvals, policy — is a control-plane
 operation, so the trusted control plane is the single remote entry point. Keep
 it **out of the gateway**: the data plane is the more-exposed, agent-facing
 unit, and a goal of the split is to shrink its surface and keep its image slim
-(no iroh/Rust dependency). Agent-PTY-to-mobile streaming is a *data-plane*
-stream and a separate concern; if it must reach the phone over the same
-endpoint, **relay it through the orchestrator's iroh door** rather than opening
-a second door in the gateway — one authenticated remote entry point, plane
-split intact.
+(no iroh/Rust dependency). Remote **terminal** access rides the same door and is likewise an orchestrator
+operation, not a data-plane one: the agent PTY is `exec_agent`-sourced (`ssh
+-t` / `container exec --tty` / `docker exec`), which the orchestrator owns — the
+gateway never holds a PTY. A `--remote` flag publishes a running agent's
+session; local and remote clients share it through a **session multiplexer**
+(one PTY, many attached clients), operator-role-gated, so the split's "one
+authenticated remote door" holds for terminals too. Detailed design —
+multiplexer location, input arbitration, per-client rendering, always-on vs.
+`--remote` — is tracked in **#478**.
 
 ## Sequencing
 
@@ -555,7 +559,5 @@ Keep the gateway **service one shared thing** throughout.
   plane (add/remove routes/keys/proposals without a restart).
 - **Identity-token delivery:** exactly how the per-bottle token is placed
   where the agent can present it but not swap in another bottle's.
-- **Agent-PTY-to-mobile streaming path:** relay it through the orchestrator's
-  iroh endpoint (default — one authenticated remote door, plane split intact),
-  or give the data-plane stream its own transport. Only matters once remote
-  terminal mirroring lands.
+- **Remote terminal design** (multiplexer location, input arbitration,
+  per-client rendering, always-on vs. `--remote`) is tracked in **#478**.