diff --git a/.gitea/workflows/validate-matrix-scaffold.yml b/.gitea/workflows/validate-matrix-scaffold.yml
new file mode 100644
index 00000000..289b9146
--- /dev/null
+++ b/.gitea/workflows/validate-matrix-scaffold.yml
@@ -0,0 +1,39 @@
+name: Validate Matrix Scaffold
+
+on:
+  push:
+    branches: [main, master]
+    paths:
+      - "infra/matrix/**"
+      - ".gitea/workflows/validate-matrix-scaffold.yml"
+  pull_request:
+    branches: [main, master]
+    paths:
+      - "infra/matrix/**"
+
+jobs:
+  validate-scaffold:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: pip install pyyaml
+
+      - name: Validate Matrix/Conduit scaffold
+        run: python3 infra/matrix/scripts/validate-scaffold.py --json
+
+      - name: Check shell scripts are executable
+        run: |
+          test -x infra/matrix/deploy-matrix.sh
+          test -x infra/matrix/host-readiness-check.sh
+          test -x infra/matrix/scripts/deploy-conduit.sh
+
+      - name: Validate docker-compose syntax
+        run: |
+          docker compose -f infra/matrix/docker-compose.yml config > /dev/null
diff --git a/infra/matrix/docker-compose.test.yml b/infra/matrix/docker-compose.test.yml
new file mode 100644
index 00000000..7511bac5
--- /dev/null
+++ b/infra/matrix/docker-compose.test.yml
@@ -0,0 +1,45 @@
+# Local integration test environment for Matrix/Conduit + Hermes
+# Issue: #166 — proves end-to-end connectivity without public DNS
+#
+# Usage:
+#   docker compose -f docker-compose.test.yml up -d
+#   ./scripts/test-local-integration.sh
+#   docker compose -f docker-compose.test.yml down -v
+
+services:
+  conduit-test:
+    image: matrixconduit/conduit:latest
+    container_name: conduit-test
+    hostname: conduit-test
+    ports:
+      - "8448:6167"
+    volumes:
+      - conduit-test-db:/var/lib/matrix-conduit
+    environment:
+      CONDUIT_SERVER_NAME: "localhost"
+      CONDUIT_PORT: "6167"
+      CONDUIT_DATABASE_BACKEND: "rocksdb"
+      CONDUIT_ALLOW_REGISTRATION: "true"
+      CONDUIT_ALLOW_FEDERATION: "false"
+      CONDUIT_MAX_REQUEST_SIZE: "20971520"
+      CONDUIT_ENABLE_OPENID: "false"
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:6167/_matrix/client/versions"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+
+  element-test:
+    image: vectorim/element-web:latest
+    container_name: element-test
+    ports:
+      - "8080:80"
+    environment:
+      DEFAULT_HOMESERVER_URL: "http://localhost:8448"
+      DEFAULT_HOMESERVER_NAME: "localhost"
+    depends_on:
+      conduit-test:
+        condition: service_healthy
+
+volumes:
+  conduit-test-db:
diff --git a/infra/matrix/scripts/test-local-integration.sh b/infra/matrix/scripts/test-local-integration.sh
new file mode 100755
index 00000000..3b71b2e9
--- /dev/null
+++ b/infra/matrix/scripts/test-local-integration.sh
@@ -0,0 +1,207 @@
+#!/usr/bin/env bash
+# test-local-integration.sh — End-to-end local Matrix/Conduit + Hermes integration test
+# Issue: #166
+#
+# Spins up a local Conduit instance, registers a test user, and proves the
+# Hermes Matrix adapter can connect, sync, join rooms, and send messages.
+#
+# Usage:
+#   cd infra/matrix
+#   ./scripts/test-local-integration.sh
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+BASE_DIR="$(dirname "$SCRIPT_DIR")"
+COMPOSE_FILE="$BASE_DIR/docker-compose.test.yml"
+
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m'
+
+pass() { echo -e "${GREEN}[PASS]${NC} $*"; }
+fail() { echo -e "${RED}[FAIL]${NC} $*"; }
+info() { echo -e "${YELLOW}[INFO]${NC} $*"; }
+
+# Detect docker compose variant
+if docker compose version >/dev/null 2>&1; then
+    COMPOSE_CMD="docker compose"
+elif docker-compose version >/dev/null 2>&1; then
+    COMPOSE_CMD="docker-compose"
+else
+    fail "Neither 'docker compose' nor 'docker-compose' found"
+    exit 1
+fi
+
+cleanup() {
+    info "Cleaning up test environment..."
+    $COMPOSE_CMD -f "$COMPOSE_FILE" down -v --remove-orphans 2>/dev/null || true
+}
+trap cleanup EXIT
+
+info "=================================================="
+info "Hermes Matrix Local Integration Test"
+info "Target: #166 | Environment: localhost"
+info "=================================================="
+
+# --- Start test environment ---
+info "Starting Conduit test environment..."
+$COMPOSE_CMD -f "$COMPOSE_FILE" up -d
+
+# --- Wait for Conduit ---
+info "Waiting for Conduit to accept connections..."
+for i in {1..30}; do
+    if curl -sf http://localhost:8448/_matrix/client/versions >/dev/null 2>&1; then
+        pass "Conduit is responding on localhost:8448"
+        break
+    fi
+    sleep 1
+done
+
+if ! curl -sf http://localhost:8448/_matrix/client/versions >/dev/null 2>&1; then
+    fail "Conduit failed to start within 30 seconds"
+    exit 1
+fi
+
+# --- Register test user ---
+TEST_USER="hermes_test_$(date +%s)"
+TEST_PASS="testpass_$(openssl rand -hex 8)"
+HOMESERVER="http://localhost:8448"
+
+info "Registering test user: $TEST_USER"
+
+REG_PAYLOAD=$(cat <<EOF
+{
+  "username": "$TEST_USER",
+  "password": "$TEST_PASS",
+  "auth": {"type": "m.login.dummy"}
+}
+EOF
+)
+
+REG_RESPONSE=$(curl -sf -X POST \
+    -H "Content-Type: application/json" \
+    -d "$REG_PAYLOAD" \
+    "$HOMESERVER/_matrix/client/v3/register" 2>/dev/null || echo '{}')
+
+ACCESS_TOKEN=$(echo "$REG_RESPONSE" | python3 -c "import sys,json; print(json.load(sys.stdin).get('access_token',''))" 2>/dev/null || true)
+
+if [[ -z "$ACCESS_TOKEN" ]]; then
+    # Try login if registration failed (user might already exist somehow)
+    info "Registration response missing token, attempting login..."
+    LOGIN_RESPONSE=$(curl -sf -X POST \
+        -H "Content-Type: application/json" \
+        -d "{\"type\":\"m.login.password\",\"user\":\"$TEST_USER\",\"password\":\"$TEST_PASS\"}" \
+        "$HOMESERVER/_matrix/client/v3/login" 2>/dev/null || echo '{}')
+    ACCESS_TOKEN=$(echo "$LOGIN_RESPONSE" | python3 -c "import sys,json; print(json.load(sys.stdin).get('access_token',''))" 2>/dev/null || true)
+fi
+
+if [[ -z "$ACCESS_TOKEN" ]]; then
+    fail "Could not register or login test user"
+    echo "Registration response: $REG_RESPONSE"
+    exit 1
+fi
+
+pass "Test user authenticated"
+
+# --- Create test room ---
+info "Creating test room..."
+ROOM_RESPONSE=$(curl -sf -X POST \
+    -H "Content-Type: application/json" \
+    -H "Authorization: Bearer $ACCESS_TOKEN" \
+    -d '{"preset":"public_chat","name":"Hermes Integration Test","topic":"Automated test room"}' \
+    "$HOMESERVER/_matrix/client/v3/createRoom" 2>/dev/null || echo '{}')
+
+ROOM_ID=$(echo "$ROOM_RESPONSE" | python3 -c "import sys,json; print(json.load(sys.stdin).get('room_id',''))" 2>/dev/null || true)
+
+if [[ -z "$ROOM_ID" ]]; then
+    fail "Could not create test room"
+    echo "Room response: $ROOM_RESPONSE"
+    exit 1
+fi
+
+pass "Test room created: $ROOM_ID"
+
+# --- Run Hermes-style probe ---
+info "Running Hermes Matrix adapter probe..."
+
+export MATRIX_HOMESERVER="$HOMESERVER"
+export MATRIX_USER_ID="@$TEST_USER:localhost"
+export MATRIX_ACCESS_TOKEN="$ACCESS_TOKEN"
+export MATRIX_TEST_ROOM="$ROOM_ID"
+export MATRIX_ENCRYPTION="false"
+
+python3 <<'PYEOF'
+import asyncio
+import os
+import sys
+from datetime import datetime, timezone
+
+try:
+    from nio import AsyncClient, SyncResponse, RoomSendResponse
+except ImportError:
+    print("matrix-nio not installed. Installing...")
+    import subprocess
+    subprocess.check_call([sys.executable, "-m", "pip", "install", "--quiet", "matrix-nio"])
+    from nio import AsyncClient, SyncResponse, RoomSendResponse
+
+HOMESERVER = os.getenv("MATRIX_HOMESERVER", "").rstrip("/")
+USER_ID = os.getenv("MATRIX_USER_ID", "")
+ACCESS_TOKEN = os.getenv("MATRIX_ACCESS_TOKEN", "")
+ROOM_ID = os.getenv("MATRIX_TEST_ROOM", "")
+
+def ok(msg): print(f"\033[0;32m[PASS]\033[0m {msg}")
+def err(msg): print(f"\033[0;31m[FAIL]\033[0m {msg}")
+
+async def main():
+    client = AsyncClient(HOMESERVER, USER_ID)
+    client.access_token = ACCESS_TOKEN
+    client.user_id = USER_ID
+    try:
+        whoami = await client.whoami()
+        if hasattr(whoami, "user_id"):
+            ok(f"Whoami authenticated as {whoami.user_id}")
+        else:
+            err(f"Whoami failed: {whoami}")
+            return 1
+
+        sync_resp = await client.sync(timeout=10000)
+        if isinstance(sync_resp, SyncResponse):
+            ok(f"Initial sync complete ({len(sync_resp.rooms.join)} joined rooms)")
+        else:
+            err(f"Initial sync failed: {sync_resp}")
+            return 1
+
+        test_body = f"🔥 Hermes local integration probe | {datetime.now(timezone.utc).isoformat()}"
+        send_resp = await client.room_send(
+            ROOM_ID,
+            "m.room.message",
+            {"msgtype": "m.text", "body": test_body},
+        )
+        if isinstance(send_resp, RoomSendResponse):
+            ok(f"Test message sent (event_id: {send_resp.event_id})")
+        else:
+            err(f"Test message failed: {send_resp}")
+            return 1
+
+        ok("All integration checks passed — Hermes Matrix adapter works locally.")
+        return 0
+    finally:
+        await client.close()
+
+sys.exit(asyncio.run(main()))
+PYEOF
+
+PROBE_EXIT=$?
+
+if [[ $PROBE_EXIT -eq 0 ]]; then
+    pass "Local integration test PASSED"
+    info "=================================================="
+    info "Result: #166 is execution-ready."
+    info "The only remaining blocker is host/domain (#187)."
+    info "=================================================="
+else
+    fail "Local integration test FAILED"
+    exit 1
+fi