refactor(gateway): move egress entrypoint into gateway/egress

egress_entrypoint.sh is the mitmdump launcher for the egress data plane,
so it belongs with the gateway egress service, not at the package root.
Moved to bot_bottle/gateway/egress/entrypoint.sh (prefix stripped now
that the package namespaces it).

Only the Dockerfile.gateway COPY source changes; the runtime target
(/app/egress-entrypoint.sh, referenced by bootstrap's egress DaemonSpec)
is unchanged, and the infra images inherit it via FROM gateway. Updated
the test that resolves the script path and the infra-artifact docstring
example. Full unit suite green (2243).

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

bot_bottle/gateway/egress/entrypoint.sh

@@ -0,0 +1,77 @@
+#!/bin/sh
+# Egress daemon entrypoint inside the gateway (PRD 0024).
+#
+# Extracted verbatim from Dockerfile.egress's prior inline `sh -c`
+# ENTRYPOINT so the supervisor in bot_bottle/gateway_init.py can
+# call it as a normal child. Behavior is unchanged:
+#
+#   * Upstream proxy: when EGRESS_UPSTREAM_PROXY is set, switch
+#     to `--mode upstream:URL` to chain through an upstream proxy.
+#     mitmproxy does NOT honor HTTPS_PROXY on its outbound side,
+#     so the upstream wiring has to be the mitmproxy mode flag,
+#     not env.
+#   * Upstream trust: when EGRESS_UPSTREAM_CA is set, build a
+#     combined trust bundle (system roots + upstream CA) and point
+#     mitmproxy at it. The option REPLACES mitmproxy's default
+#     trust store, so passing the upstream CA alone would break
+#     non-chained hosts.
+#   * `-s /app/egress_addon.py` loads the addon that resolves each
+#     request's policy from the orchestrator control plane by source
+#     IP (PRD 0070). There is no static routes file.
+
+set -e
+
+# Fail closed on a missing policy source. The addon itself raises at
+# load when BOT_BOTTLE_ORCHESTRATOR_URL is unset (so mitmdump exits via
+# its errorcheck addon), but that leaves the fail-closed guarantee at the
+# mercy of a mitmproxy version keeping that behavior. Refuse here too, so
+# a misconfigured gateway can never come up as a bare TLS-bumping open
+# proxy with no policy — independent of mitmproxy's startup-error handling.
+if [ -z "$BOT_BOTTLE_ORCHESTRATOR_URL" ]; then
+  echo "egress: BOT_BOTTLE_ORCHESTRATOR_URL is required (no static routes fallback)" >&2
+  exit 1
+fi
+
+# Pin mitmproxy's config dir to the bind-mount location of its CA
+# regardless of which user mitmdump runs as. In the legacy
+# four-daemon setup (Dockerfile.egress, USER mitmproxy) this
+# resolved naturally to `~mitmproxy/.mitmproxy`. In the PRD 0024
+# bundle (USER root) `~root/.mitmproxy` is empty, so without this
+# flag mitmdump would generate a fresh CA on the wrong path and
+# the agent's installed trust anchor would no longer match the
+# bumped leaf certs.
+CONFDIR=/home/mitmproxy/.mitmproxy
+CONFDIR_FLAG="--set confdir=$CONFDIR"
+
+MODE="--mode regular@9099"
+if [ -n "$EGRESS_UPSTREAM_PROXY" ]; then
+  MODE="--mode upstream:$EGRESS_UPSTREAM_PROXY --listen-port 9099"
+fi
+
+# Bind address. Docker backend wants `0.0.0.0` (agent dials egress
+# directly via the docker network alias). A VM backend uses
+# EGRESS_LISTEN_HOST when a non-default binding is needed.
+LISTEN_HOST_FLAG=""
+if [ -n "$EGRESS_LISTEN_HOST" ]; then
+  LISTEN_HOST_FLAG="--listen-host $EGRESS_LISTEN_HOST"
+fi
+
+TRUST_FLAG=""
+if [ -n "$EGRESS_UPSTREAM_CA" ] && [ -f "$EGRESS_UPSTREAM_CA" ]; then
+  COMBINED=$CONFDIR/combined-trust.pem
+  cat /etc/ssl/certs/ca-certificates.crt "$EGRESS_UPSTREAM_CA" > "$COMBINED"
+  TRUST_FLAG="--set ssl_verify_upstream_trusted_ca=$COMBINED"
+fi
+
+# Scope the proxy env to this process tree only. In the bundle
+# image (PRD 0024) multiple daemons share one container — setting
+# HTTPS_PROXY at the container level would route git-gate's git
+# pushes through an upstream proxy unintentionally. Setting them
+# here means only mitmdump's subprocess inherits them.
+if [ -n "$EGRESS_UPSTREAM_PROXY" ]; then
+  export HTTPS_PROXY="$EGRESS_UPSTREAM_PROXY"
+  export HTTP_PROXY="$EGRESS_UPSTREAM_PROXY"
+  export NO_PROXY="localhost,127.0.0.1"
+fi
+
+exec mitmdump $CONFDIR_FLAG $MODE $LISTEN_HOST_FLAG $TRUST_FLAG -s /app/egress_addon.py