Gateway-lifecycle SANDBOX CAPABILITY: ONE shared loopback egress proxy and ONE
ephemeral MITM CA for the WHOLE daemon, keyed PER SESSION.

Why shared, not per-session (turn 32): the gateway is multi-tenant — many
clients/sessions hit one daemon. A per-session proxy+CA thrashes listeners and
mints a fresh CA per session; worse, every child would carry a different trust
root. Instead there is ONE listener and ONE CA (the "same certs" property —
every child trusts the same root), plus a REGISTRY mapping a per-session TOKEN →
that session's live policy fn.

How a connection is attributed to a session: the jailed child's proxy env carries
its unguessable token in the proxy URL userinfo (`http://<token>@127.0.0.1:<port>`);
curl/git/requests/… send it back as `Proxy-Authorization: Basic base64(<token>:)`;
the proxy hands the token to `resolve-policy`, which looks up the registry.

FAIL-CLOSED: a request whose token is missing or not registered to a LIVE session
is DENIED (a `:deny-all?` sentinel policy) — the shared door never serves a policy
it cannot attribute. The token is a random UUID, so one session cannot reach
another's (broader) policy by guessing.

Lazy: the proxy listener and the CA keygen happen only on first `ensure-proxy!` /
`ensure-ca!` — a gateway that never jails a shell child opens neither.

Cross-process gateway event bus.

The gateway's live event log + SSE fan-out (`gateway.state`) is a
PROCESS-LOCAL in-memory registry: `append-event!` only reaches
subscribers inside the SAME JVM. That is why a turn streaming in the
TUI process is invisible to another process watching the SAME
conversation — each process has its own registry, and the only thing
they share is the persisted DB (which lands whole turns, not the live
token stream). So two watchers never stream together.

This bus closes that gap with the simplest transport that needs no
schema change and no always-on daemon: a shared append-only journal
under `~/.vis/gateway/events/<sid>.ndjson`. Every LOCALLY-produced
gateway event is `publish!`ed there (one JSON line, tagged with this
process's `producer` id). A background tailer in each process follows
those files and re-delivers FOREIGN events (producer != self) into the
local registry via a delivery fn wired by `gateway.state` — so every
process's subscribers see the same stream, live.

Ordering/seq: exactly ONE turn runs per session at a time, so at any
moment a single producer owns the stream and its monotonic `:seq` is
authoritative for every watcher. The producer truncates the journal at
each `turn.started`, bounding a file to one turn's worth of deltas;
consumers detect the truncation (offset past EOF) and rewind.

Degrades safely: any IO failure is swallowed and the process falls
back to today's in-process-only behavior.

HTTP/SSE client for the long-lived gateway daemon.

Interactive channels call this facade instead of `gateway.state` directly. It
discover-or-starts the one daemon for the current DB, then speaks the same
HTTP/SSE API every other client uses. This is the thin-client half of the
gateway-daemon plan: token refresh, turn execution, and live streaming happen
in ONE process.

Gateway daemon discovery + registry (build order step 1).

One long-lived gateway per DB owns execution; every TUI/web/whatever is a
thin client of it. This namespace answers the boot-time question: "is a
gateway already running for my DB — attach; else spawn one, DETACHED (nobody's
child), then hand back where to connect."

Registry: one EDN file per DB at `~/.vis/gateway/registry/<sha256(db)>.edn`
holding `{:pid :port :host :secret :db :created-at}`. Freshness = the recorded
`:pid` is still alive AND a caller-supplied `probe` confirms the port+secret
are really OUR daemon (guards OS pid reuse — see D4/Q3 in TODO-gateway-daemon).

Design decisions (locked, see TODO-gateway-daemon.md):
- Q2 registry key = the DB path (two dirs sharing `--db` share one daemon).
- Q3 race = port-bind winner is the daemon; the loser attaches. The daemon
  SELF-REGISTERS on startup (via [[register-self!]] from `serve-main!`), so a
  spawner never needs the child pid — it just polls for a fresh registry.
- Q5 `:memory` never registers/spawns (headless one-shot stays in-process).

Effects (`spawn`, `probe`, pid-liveness) are injectable so the orchestration
in [[discover-or-start!]] is unit-testable without a real process.

Android push (Firebase Cloud Messaging HTTP v1).

Apple's APNs lives in `gateway.push`; this is its Android twin and the two
are dispatched on the registered device's `:platform`. Credentials are a
Google service-account JSON — from the macOS keychain (service `vis-fcm`,
account `service_account`), from the environment, or from a file under
`~/.vis/fcm/`. Key material is never returned, logged or sent over the wire.

Gateway pairing helpers for remote clients.

The QR payload is deliberately tiny and URL-shaped so native apps can scan it
without an HTTP round trip:

  vis://gateway?url=http%3A%2F%2F100.64.0.10%3A7890&token=...

Tailscale fits naturally: if a 100.64.0.0/10 interface is present we prefer it
over LAN addresses, otherwise we fall back to site-local IPv4 addresses.

THE single source of truth for gateway <-> client version compatibility.

Vis ships three INDEPENDENTLY updatable halves that share one HTTP/SSE
wire: the gateway daemon, the TUI/CLI client, and the Vis Companion app.
Any of them can lag. A daemon started by yesterday's binary keeps running
across `brew upgrade`; a phone holds a cached web build for weeks; a
Tailscale peer runs last month's release. Without an explicit contract a
breaking wire change surfaces as a mystery 404, a missing field, or an
event type nobody renders.

So every peer publishes two numbers next to its human release version:

  `protocol`     the wire protocol IT speaks
  `min-*`        the OLDEST counterpart it still speaks to

Compatibility is then a pure comparison ([[verdict]]) — never feature
sniffing, never guessing from a release string. Both halves advertise, both
halves judge, so whichever side is newer can explain the mismatch even when
the other side is too old to know the concept exists.

Bump [[protocol-version]] on any BREAKING wire change (a removed field, a
renamed event type, a changed status shape). Raise [[min-client-protocol]]
or [[min-gateway-protocol]] only when the old shape genuinely stops
working — additive changes keep the number and are negotiated through
`/v1/capabilities` features instead.

Wire shape (snake_case strings, per the gateway wire contract):

  {"protocol": 1, "min_client": 1, "min_gateway": 1, "version": "0.1.5"}

Native push notifications (Apple Push Notification service).

ONE job: when a turn finishes on this gateway, wake the phone that asked
to be woken. Everything here is server-side; the app only ever hands us a
device token.

Three moving parts:

1. **Credentials.** A token-based APNs auth key (`.p8`, ES256) plus its key
   id, the Apple team id and the app's bundle id (the APNs *topic*).
   Resolved from `VIS_APNS_KEY_PATH` / `VIS_APNS_KEY_ID` / `VIS_APNS_TEAM_ID`
   / `VIS_APNS_TOPIC`, else auto-discovered from `~/.vis/apns/AuthKey_<kid>.p8`
   (the key id is read off the filename) with the team/topic still from env
   or `~/.vis/apns/apns.edn`. No credentials = push silently OFF; the gateway
   keeps working exactly as before.

2. **A device registry** at `~/.vis/devices.edn` — device token -> platform,
   APNs environment, client label/version, timestamps. Registration is
   idempotent on the token. Tokens are SECRETS: nothing here logs more than
   a masked prefix.

3. **A sender** — a signed ES256 JWT (cached, refreshed well inside Apple's
   one-hour window) over HTTP/2 to `api.push.apple.com`. A device that
   registered with the wrong environment is retried once against the other
   host, and an APNs `BadDeviceToken`/`Unregistered` verdict evicts the
   device so a stale token cannot accumulate.

The wire surface lives in `gateway.server` (`/v1/devices`); this namespace
knows nothing about Ring.

Gateway HTTP/SSE server.

Clojure-native stack: reitit-ring routes -> Ring middleware -> the
Ring Jetty adapter on JDK virtual threads (`:virtual-threads? true`).
SSE is a Ring `StreamableResponseBody` whose virtual thread is the
connection's SINGLE socket writer: replay rides first, then it drains a
bounded per-connection event queue that `state/fan-out!` enqueues onto,
emitting a heartbeat comment on idle to keep the pipe warm and detect
dead clients.

This is internal plumbing, not a channel: it registers no channel
descriptor and owns no renderer - it ships canonical IR and the
client renders (§4.1). Any host process (the `vis gateway start` daemon, a
TUI run, an embedded caller) can start it alongside whatever else it
is doing via `start!`.

Gateway session manager.

One process-global registry over the live session fleet: per-session
ordered event log (monotonic `:seq`, ring-buffered), SSE subscriber
fan-out, async turn submission with idempotency keys, cancellation,
and turn/cost metrics.

The engine is reached ONLY through the same internal surfaces the
TUI channel uses: `loop/create!`-`send!`-`close!` for the
lifecycle, `:hooks {:on-chunk ...}` phased chunks for the live
stream, `ctx-loop/session-snapshot` for the context. No engine state
lives here - this namespace owns wire bookkeeping (events, turn
records, subscribers), nothing else.

Wire encoding for the HTTP gateway.

One dumb, deterministic boundary: engine EDN -> JSON. Keyword/symbol
keys become snake_case strings (namespace dropped), keyword VALUES keep
their full `ns/name` (a badge role like `:tool-color/search` must survive
the hop — dropping the namespace made the remote TUI see `:search` while
the hop), non-JSON leaves fall back to `str`. The walker makes zero semantic
or rendering decisions. Canonical message content is already a string-keyed
vector of typed block maps before it reaches this boundary.

`canonical` is the SAME shape on the Clojure side: by definition what
`parse-json` ∘ `json-str` yields — snake_case STRING keys — serve it from
a facade and in-process readers see exactly what a remote client sees.