feat(journal): two-instance federation harness + trails↔trails Accept fix (§11)

The 11.4 harness — e2e/federation/: postgres (two DBs) + a Caddy with
an internal CA terminating real HTTPS between two complete journal
containers (journal-a.test / journal-b.test), driven by an opt-in
integration test (FEDERATION_TWO_INSTANCE=1, via run.sh). The driver
seeds users straight into each DB, mints a signed session cookie
(known SESSION_SECRET), follows across instances through the real
/follows/outgoing route, and asserts the full pipeline: Follow →
auto-Accept → settle → first outbox poll → bob's public activity
rendered in alice's /feed with @bob@journal-b.test attribution. Plus a
wire-level 11.3 check: unsigned Create(Note) → 4xx, no DB writes.

And the harness immediately earned its keep — it caught a real
trails↔trails bug Mastodon interop never could: our Follow ids are
fragment URIs on OUR domain, so the Follow embedded in another trails
instance's Accept is cross-origin and Fedify rightly distrusts it;
re-fetching the id returns the actor document, getObject() yields a
Person, and the Accept/Reject/Undo listeners bailed silently — follows
stayed Pending forever. The listeners now fall back to the wire
objectId (captured BEFORE getObject(), which memoizes the fetched
document and changes what objectId reports) validated against our
Follow-id shape + the personal inbox's ctx.recipient. Forgery-safe:
settleOutgoingFollow only matches a Pending row toward the
HTTP-Signature-authenticated sender.

Supporting changes:
- federation.server.ts: env-gated allowPrivateAddress
  (FEDERATION_ALLOW_PRIVATE_ADDRESS=true) so the harness's RFC 1918
  Docker network is fetchable — testing only, loudly documented.
- Root .dockerignore: local builds shipped a 1GB+ context and
  overlaid host (darwin) node_modules over the image's own install
  via COPY . . — CI never noticed because it builds from clean
  checkouts. Context is now ~5MB.
- tasks.md: 11.1–11.7 marked with provenance notes; design.md gains
  the cross-origin embedded-object lesson.

Gate: typecheck ✓ lint ✓ unit+integration (FEDERATION_INTEGRATION=1) ✓
e2e 71/72 + known komoot flake green isolated ✓ harness run clean from
scratch (2/2, teardown included) ✓

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

e2e/federation/run.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# Two-instance federation harness runner (social-federation 11.4).
+#
+#   ./e2e/federation/run.sh            # build, test, tear down
+#   KEEP_STACK=1 ./e2e/federation/run.sh   # leave the stack up for poking
+#
+# Brings up two journal instances that federate with each other (see
+# docker-compose.yml), pushes the Drizzle schema into both databases,
+# and runs the driver test. Opt-in and self-contained — nothing here is
+# wired into `pnpm test` or CI.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
+compose() { docker compose -f "$SCRIPT_DIR/docker-compose.yml" "$@"; }
+
+cleanup() {
+  if [[ "${KEEP_STACK:-}" == "1" ]]; then
+    echo "KEEP_STACK=1 — leaving the stack up. Tear down with:"
+    echo "  docker compose -f $SCRIPT_DIR/docker-compose.yml down -v"
+  else
+    compose down -v --remove-orphans >/dev/null 2>&1 || true
+  fi
+}
+trap cleanup EXIT
+
+echo "==> postgres + caddy (internal CA)"
+compose up -d --wait postgres caddy
+
+echo "==> pushing schema into trails_a and trails_b"
+push_schema() {
+  # A transient postgres backend crash mid-introspection has been seen
+  # under Docker Desktop load ("Connection terminated unexpectedly" +
+  # crash recovery). Retry after the healthcheck reports the server
+  # recovered — without hiding a deterministic failure.
+  local url="$1" attempt
+  for attempt in 1 2 3; do
+    if DATABASE_URL="$url" pnpm --dir "$ROOT" db:push; then return 0; fi
+    echo "schema push failed (attempt $attempt) — waiting for postgres to recover"
+    sleep 5
+    compose up -d --wait postgres
+  done
+  return 1
+}
+push_schema postgres://trails:trails@127.0.0.1:5499/trails_a
+push_schema postgres://trails:trails@127.0.0.1:5499/trails_b
+
+echo "==> building the journal image (slow on first run)"
+compose build journal-a
+
+echo "==> journal-a + journal-b"
+compose up -d --wait journal-a journal-b
+
+echo "==> driving the federation flow"
+FEDERATION_TWO_INSTANCE=1 pnpm --dir "$ROOT/apps/journal" exec vitest run app/lib/federation-two-instance.integration.test.ts