diff --git a/docs/upgrading.md b/docs/upgrading.md
index a762d99..4dff2bd 100644
--- a/docs/upgrading.md
+++ b/docs/upgrading.md
@@ -2,7 +2,9 @@
 
 This guide covers upgrading from a previous MeshCore Hub release to the current version. Check the relevant version section below before upgrading.
 
-## Unreleased — Security hardening (fail-closed defaults)
+## v0.18.0
+
+### Security hardening (fail-closed defaults)
 
 Four behaviour changes tighten default security. **Two are potentially breaking for existing deployments — read before upgrading.**
 
@@ -18,7 +20,7 @@ Four behaviour changes tighten default security. **Two are potentially breaking
 
 **CORS credentials tightened.** An unset `CORS_ORIGINS` still allows all origins for compatibility with external API consumers, but no longer advertises `allow-credentials` (wildcard origins are never valid with credentials in browsers anyway). Explicit origin lists are unchanged.
 
-## Unreleased — Route evaluator performance remediation
+### Route evaluator performance remediation
 
 The background route evaluator was triggering a multi-second `packet_path_hops` scan per route per sweep, flooding the slow-query log and blocking route saves on the same scan. This release reduces load across four orthogonal levers. **Two are destructive / behaviour-changing — read before upgrading.**
 
@@ -34,6 +36,25 @@ The background route evaluator was triggering a multi-second `packet_path_hops`
 
 **Performance rationale:** EXPLAIN analysis showed both candidate query plans (Merge Join full scan and forced Nested Loop) cost ~10–15 s at 6.4 M `packet_path_hops` rows; no SQL rewrite, stats change, or CTE trick could avoid the scan. The fix is purely data-volume pressure: smaller table (retention), smaller candidate set (window cap), index-only scan (covering index), and less frequent sweeps. See `docs/routes.md` for the updated evaluator contract.
 
+### Operational hardening (health probes, maintenance mode, webhooks)
+
+A set of correctness fixes around readiness, maintenance mode, and webhook delivery. **One change affects monitoring setups — read before upgrading.**
+
+**⚠️ Monitoring change: `/health/ready` now returns 503 when not ready.** Both the API and web tiers previously answered HTTP 200 with a `{"status": "not_ready", ...}` body while the database/API backend was down — probes that judge by status code (Docker healthchecks, Kubernetes readiness, most load balancers) kept the instance in rotation. The endpoint now returns **503** when not ready and 200 when ready. **Action:** only needed if you run a custom probe that parsed the response body while relying on the 200 — switch it to status-code semantics. The body also no longer echoes raw backend error text (just the exception type).
+
+**Maintenance mode now actually blocks API calls.** `SYSTEM_MAINTENANCE=true` was documented to "prevent all API calls", but only the React UI was gated — the web tier's `/api/*` proxy kept forwarding to the backend. The proxy now returns `503 {"detail": "Site is in maintenance mode", "code": "MAINTENANCE"}` for every API request while maintenance mode is on. **Action:** scripts or automation that call the API through the web tier during maintenance windows will now see 503s — which is the intended behaviour; schedule them outside the window.
+
+**Webhook delivery: fail-fast on permanent errors, bounded queue.**
+
+- Permanent client errors (any 4xx except `408`/`429` — e.g. a mistyped URL, expired auth, or rejected payload) are **no longer retried**. Previously every non-2xx response burned the full retry cycle (up to 4 attempts with backoff), so one misconfigured endpoint stalled the dispatch pipeline for ~14–45 s per event. Server errors (5xx), timeouts, and transport failures are still retried as before.
+- The internal webhook queue is now **capped at 1000 events**. When endpoints are down or too slow, the oldest queued events are dropped with a `WARNING` log (including the dropped count) instead of growing memory without bound. Nothing changes on healthy meshes.
+
+**Channel changes invalidate dependent caches.** Creating, updating, or deleting a channel now also drops the cached `messages`, `packets`, `packet-groups`, and dashboard responses (previously only the channels list itself). A channel demoted from community to member visibility — or deleted — no longer serves its messages to lower-privileged roles for up to the remaining cache TTL (up to 1 h for the dashboard). No action required.
+
+**API survives Postgres restarts (async engine hardening).** The API's async connection pool now matches the sync engine's sizing (`pool_size=20`, `max_overflow=30`) and uses `pool_pre_ping`, so a Postgres restart or failover no longer leaves stale pooled connections that error as 500s until they churn. Shutdown also correctly closes async-pooled connections (previously leaked). No action required; SQLite deployments are unchanged.
+
+**Web UI fixes.** Dashboard chart date labels and route-match timestamps now render in the configured timezone — chart labels were off by one day for users in negative UTC offsets, and route-match times were off by the user's UTC offset. Expired OIDC sessions now redirect to the login flow on any API GET (previously only writes did; reads spun forever). No action required.
+
 ## v0.17.0
 
 ### React Web UI
diff --git a/e2e/docker-compose.test.yml b/e2e/docker-compose.test.yml
index 35fe72c..fe0e13f 100644
--- a/e2e/docker-compose.test.yml
+++ b/e2e/docker-compose.test.yml
@@ -135,7 +135,8 @@ services:
       - DATABASE_PASSWORD=e2epassword
     command: ["collector"]
     healthcheck:
-      test: ["CMD", "pgrep", "-f", "meshcore-hub"]
+      # Same probe as the main compose file — the image has no pgrep.
+      test: ["CMD", "meshcore-hub", "health", "collector"]
       interval: 5s
       timeout: 5s
       retries: 3
diff --git a/src/meshcore_hub/api/app.py b/src/meshcore_hub/api/app.py
index 6fcb160..4b3d1be 100644
--- a/src/meshcore_hub/api/app.py
+++ b/src/meshcore_hub/api/app.py
@@ -6,6 +6,7 @@ from typing import Any, AsyncGenerator
 
 from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import JSONResponse
 from sqlalchemy import text
 
 from meshcore_hub import __version__
@@ -63,7 +64,9 @@ async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
     if _cache is not None and hasattr(_cache, "close"):
         _cache.close()
     if _db_manager:
-        _db_manager.dispose()
+        # adispose: the async engine's pooled connections must be closed
+        # from this (running) event loop.
+        await _db_manager.adispose()
         _db_manager = None
     logger.info("Database connection closed")
 
@@ -288,15 +291,19 @@ def create_app(
         return {"status": "healthy", "version": __version__}
 
     @app.get("/health/ready", tags=["Health"])
-    def health_ready() -> dict:
-        """Readiness check including database and optional Redis."""
+    def health_ready() -> JSONResponse:
+        """Readiness check including database and optional Redis.
+
+        Returns 503 when not ready so Docker/Kubernetes readiness probes
+        (which judge by HTTP status code) pull the instance from rotation.
+        """
         try:
             db = get_db_manager()
             with db.session_scope() as session:
                 session.execute(text("SELECT 1"))
             result: dict[str, str] = {"status": "ready", "database": "connected"}
         except Exception as e:
-            result = {"status": "not_ready", "database": str(e)}
+            result = {"status": "not_ready", "database": type(e).__name__}
 
         redis_cache = getattr(app.state, "redis_cache", None)
         redis_enabled = getattr(app.state, "redis_enabled", False)
@@ -306,7 +313,8 @@ def create_app(
             else:
                 result["redis"] = "unreachable"
 
-        return result
+        status_code = 200 if result.get("status") == "ready" else 503
+        return JSONResponse(content=result, status_code=status_code)
 
     return app
 
diff --git a/src/meshcore_hub/api/cache_invalidation.py b/src/meshcore_hub/api/cache_invalidation.py
index 62d0ac7..48a770e 100644
--- a/src/meshcore_hub/api/cache_invalidation.py
+++ b/src/meshcore_hub/api/cache_invalidation.py
@@ -79,8 +79,24 @@ def _drop(request: Request, prefix: str) -> None:
 
 
 def invalidate_channels(request: Request) -> None:
-    """Drop cached ``GET /channels`` responses (role-aware, URL-path keys)."""
+    """Drop cached ``GET /channels`` responses (role-aware, URL-path keys).
+
+    Channel visibility also drives role-based redaction and per-channel
+    breakdowns in several other cached endpoints, so they must be dropped
+    alongside the channel list or they serve stale data until their own TTL
+    expires (up to one hour for the dashboard):
+
+    - ``GET /messages`` — visible-channel filtering (URL-path keys)
+    - ``GET /packets`` and ``GET /packet-groups`` — channel/event metadata
+      derived from channel visibility (endpoint-name-style prefixes)
+    - ``GET /dashboard/*`` — ``channel_message_counts`` in ``stats`` and the
+      per-channel series in ``message-activity``
+    """
     _drop(request, "/api/v1/channels")
+    _drop(request, "/api/v1/messages")
+    _drop(request, "packets")
+    _drop(request, "packet_groups")
+    invalidate_dashboard(request)
 
 
 def invalidate_routes(request: Request) -> None:
diff --git a/src/meshcore_hub/collector/subscriber.py b/src/meshcore_hub/collector/subscriber.py
index 0151658..282ae4f 100644
--- a/src/meshcore_hub/collector/subscriber.py
+++ b/src/meshcore_hub/collector/subscriber.py
@@ -15,6 +15,7 @@ import signal
 import threading
 import time
 import uuid
+from collections import deque
 from datetime import datetime, timezone
 from typing import Any, Callable, Optional, TYPE_CHECKING
 
@@ -80,8 +81,11 @@ class Subscriber(LetsMeshNormalizer):
         self._handlers: dict[str, EventHandler] = {}
         self._db_connected = False
         self._health_reporter: Optional[HealthReporter] = None
-        # Webhook processing
-        self._webhook_queue: list[tuple[str, dict[str, Any], str]] = []
+        # Webhook processing. The queue is bounded: a dead endpoint slows
+        # the dispatch thread, and an unbounded queue would grow without
+        # limit on a busy mesh — drop the oldest events instead.
+        self._webhook_queue: deque[tuple[str, dict[str, Any], str]] = deque()
+        self._webhook_queue_max: int = 1000
         self._webhook_lock = threading.Lock()
         self._webhook_thread: Optional[threading.Thread] = None
         # Data cleanup
@@ -377,6 +381,18 @@ class Subscriber(LetsMeshNormalizer):
             public_key: Source node public key
         """
         with self._webhook_lock:
+            if len(self._webhook_queue) >= self._webhook_queue_max:
+                dropped = len(self._webhook_queue) - self._webhook_queue_max + 1
+                # Drop oldest: the slowest path to recovery is a backlog of
+                # stale events; newest events are the most useful.
+                while len(self._webhook_queue) >= self._webhook_queue_max:
+                    self._webhook_queue.popleft()
+                logger.warning(
+                    "Webhook queue full (%d events); dropped %d oldest "
+                    "events (webhook endpoint too slow or down?)",
+                    self._webhook_queue_max,
+                    dropped,
+                )
             self._webhook_queue.append((event_type, payload, public_key))
 
     def _start_webhook_processor(self) -> None:
@@ -398,7 +414,7 @@ class Subscriber(LetsMeshNormalizer):
 
                 while self._running:
                     # Get queued events
-                    events_to_process: list[tuple[str, dict[str, Any], str]] = []
+                    events_to_process: deque[tuple[str, dict[str, Any], str]] = deque()
                     with self._webhook_lock:
                         if self._webhook_queue:
                             events_to_process = self._webhook_queue.copy()
@@ -419,6 +435,14 @@ class Subscriber(LetsMeshNormalizer):
             finally:
                 loop.run_until_complete(dispatcher.stop())
                 loop.close()
+                with self._webhook_lock:
+                    if self._webhook_queue:
+                        logger.warning(
+                            "Webhook processor stopped with %d events still "
+                            "queued (dropped)",
+                            len(self._webhook_queue),
+                        )
+                        self._webhook_queue.clear()
                 logger.info("Webhook processor stopped")
 
         self._webhook_thread = threading.Thread(
diff --git a/src/meshcore_hub/collector/webhook.py b/src/meshcore_hub/collector/webhook.py
index 3b7bb32..0471b35 100644
--- a/src/meshcore_hub/collector/webhook.py
+++ b/src/meshcore_hub/collector/webhook.py
@@ -243,24 +243,19 @@ class WebhookDispatcher:
 
         results: dict[str, bool] = {}
 
-        # Dispatch to all matching webhooks concurrently
-        tasks = []
-        for webhook in self.webhooks:
-            if not webhook.enabled:
-                continue
-            if webhook.matches_event(event_type, payload):
-                tasks.append(self._send_webhook(webhook, event_data))
+        # Dispatch to all matching webhooks concurrently. Evaluate
+        # matches_event once — re-running it for the zip would double the
+        # filter work and risk desynchronizing results from tasks.
+        matched = [
+            webhook
+            for webhook in self.webhooks
+            if webhook.enabled and webhook.matches_event(event_type, payload)
+        ]
+        tasks = [self._send_webhook(webhook, event_data) for webhook in matched]
 
         if tasks:
             task_results = await asyncio.gather(*tasks, return_exceptions=True)
-            for webhook, result in zip(
-                [
-                    w
-                    for w in self.webhooks
-                    if w.enabled and w.matches_event(event_type, payload)
-                ],
-                task_results,
-            ):
+            for webhook, result in zip(matched, task_results):
                 if isinstance(result, Exception):
                     results[webhook.name] = False
                     logger.error(f"Webhook {webhook.name} failed: {result}")
@@ -312,11 +307,25 @@ class WebhookDispatcher:
                         f"(status={response.status_code})"
                     )
                     return True
-                else:
-                    logger.warning(
-                        f"Webhook {webhook.name} returned status {response.status_code}"
+
+                last_error = Exception(f"HTTP {response.status_code}")
+
+                # Permanent client errors (bad URL, auth, payload rejected)
+                # will never succeed on retry — fail fast instead of
+                # multiplying the outage window. 408/429 are retryable.
+                if 400 <= response.status_code < 500 and response.status_code not in (
+                    408,
+                    429,
+                ):
+                    logger.error(
+                        f"Webhook {webhook.name} returned status "
+                        f"{response.status_code}; not retryable"
                     )
-                    last_error = Exception(f"HTTP {response.status_code}")
+                    return False
+
+                logger.warning(
+                    f"Webhook {webhook.name} returned status " f"{response.status_code}"
+                )
 
             except httpx.TimeoutException as e:
                 logger.warning(f"Webhook {webhook.name} timed out: {e}")
diff --git a/src/meshcore_hub/common/database.py b/src/meshcore_hub/common/database.py
index 02ebfd3..f875daf 100644
--- a/src/meshcore_hub/common/database.py
+++ b/src/meshcore_hub/common/database.py
@@ -1,5 +1,7 @@
 """Database connection and session management."""
 
+import asyncio
+import logging
 import os
 from contextlib import asynccontextmanager, contextmanager
 from typing import Any, AsyncGenerator, Generator
@@ -11,6 +13,8 @@ from sqlalchemy.orm import Session, sessionmaker
 
 from meshcore_hub.common.models.base import Base
 
+logger = logging.getLogger(__name__)
+
 
 def _resolve_pg_schema(database_url: str, schema: str | None) -> str | None:
     """Resolve the Postgres schema to scope a connection to (search_path).
@@ -212,8 +216,25 @@ class DatabaseManager:
             if self._schema:
                 server_settings["search_path"] = self._schema
             async_connect_args["server_settings"] = server_settings
+
+        # Mirror the sync engine's pool configuration (see
+        # create_database_engine): without pool_pre_ping a Postgres restart
+        # leaves stale asyncpg connections in the pool that error on next
+        # use. In-memory SQLite uses a non-overflow pool, so skip there.
+        is_memory_sqlite = self.database_url in (
+            "sqlite+aiosqlite://",
+            "sqlite+aiosqlite:///:memory:",
+        )
+        async_engine_kwargs: dict[str, Any] = {"pool_pre_ping": True}
+        if not is_memory_sqlite:
+            async_engine_kwargs["pool_size"] = 20
+            async_engine_kwargs["max_overflow"] = 30
+
         self._async_engine = create_async_engine(
-            async_url, echo=self._echo, connect_args=async_connect_args
+            async_url,
+            echo=self._echo,
+            connect_args=async_connect_args,
+            **async_engine_kwargs,
         )
 
         # Apply the same SQLite pragmas as the sync engine (see
@@ -293,10 +314,36 @@ class DatabaseManager:
             yield session
 
     def dispose(self) -> None:
-        """Dispose of the database engine and connection pool."""
-        self.engine.dispose()
+        """Dispose of the database engines and connection pools.
+
+        The async engine's pooled connections can only be closed from a
+        running event loop. When this method is called outside any loop
+        (e.g. a CLI that used ``async_session`` via ``asyncio.run``), the
+        async engine is disposed on a temporary loop. Inside a running
+        loop, use :meth:`adispose` instead — the async engine is then left
+        for that call and a warning is logged.
+        """
         if self._async_engine is not None:
-            self._async_engine.sync_engine.dispose()
+            try:
+                asyncio.get_running_loop()
+            except RuntimeError:
+                asyncio.run(self._async_engine.dispose())
+                self._async_engine = None
+                self._async_session_factory = None
+            else:
+                logger.warning(
+                    "dispose() called inside a running event loop; async "
+                    "engine not closed — use adispose()"
+                )
+        self.engine.dispose()
+
+    async def adispose(self) -> None:
+        """Dispose both engines from an async context (e.g. app lifespan)."""
+        if self._async_engine is not None:
+            await self._async_engine.dispose()
+            self._async_engine = None
+            self._async_session_factory = None
+        self.engine.dispose()
 
 
 # Global database manager instance (initialized at runtime)
diff --git a/src/meshcore_hub/web/app.py b/src/meshcore_hub/web/app.py
index d834a03..6777298 100644
--- a/src/meshcore_hub/web/app.py
+++ b/src/meshcore_hub/web/app.py
@@ -828,6 +828,11 @@ def create_app(
     )
     async def api_proxy(request: Request, path: str) -> Response:
         """Proxy API requests to the backend API server."""
+        if getattr(request.app.state, "system_maintenance", False):
+            return JSONResponse(
+                {"detail": "Site is in maintenance mode", "code": "MAINTENANCE"},
+                status_code=503,
+            )
         oidc_enabled = getattr(request.app.state, "oidc_enabled", False)
         user_roles: frozenset[str] = frozenset()
         user_id: str | None = None
@@ -1129,15 +1134,25 @@ def create_app(
         return {"status": "healthy", "version": __version__}
 
     @app.get("/health/ready", tags=["Health"])
-    async def health_ready(request: Request) -> dict:
-        """Readiness check including API connectivity."""
+    async def health_ready(request: Request) -> JSONResponse:
+        """Readiness check including API connectivity.
+
+        Returns 503 when not ready so Docker/Kubernetes readiness probes
+        (which judge by HTTP status code) pull the instance from rotation.
+        """
         try:
             response = await request.app.state.http_client.get("/health")
             if response.status_code == 200:
-                return {"status": "ready", "api": "connected"}
-            return {"status": "not_ready", "api": f"status {response.status_code}"}
+                return JSONResponse({"status": "ready", "api": "connected"})
+            return JSONResponse(
+                {"status": "not_ready", "api": f"status {response.status_code}"},
+                status_code=503,
+            )
         except Exception as e:
-            return {"status": "not_ready", "api": str(e)}
+            return JSONResponse(
+                {"status": "not_ready", "api": type(e).__name__},
+                status_code=503,
+            )
 
     # --- SEO Endpoints ---
     def _get_https_base_url(request: Request) -> str:
diff --git a/src/meshcore_hub/web/static/js/spa-react/pages/Routes.tsx b/src/meshcore_hub/web/static/js/spa-react/pages/Routes.tsx
index 6728886..12f8541 100644
--- a/src/meshcore_hub/web/static/js/spa-react/pages/Routes.tsx
+++ b/src/meshcore_hub/web/static/js/spa-react/pages/Routes.tsx
@@ -11,6 +11,7 @@ import { Link, useNavigate, useSearchParams } from "react-router";
 
 import { useAppConfig, hasRole } from "@/context/AppConfigContext";
 import { apiGet, apiPost, apiPut, apiDelete } from "@/utils/api";
+import { useFormatDateTime } from "@/utils/format";
 import { qk, invalidate } from "@/utils/queryKeys";
 import { usePageTitle } from "@/hooks/usePageTitle";
 import { Loading, ErrorAlert } from "@/components/Alerts";
@@ -372,6 +373,7 @@ function MatchRow({
   onNavigate: (url: string) => void;
 }) {
   const { t } = useTranslation();
+  const { formatDateTime } = useFormatDateTime();
   const prefixLen = 2 * (route.match_width || 1);
   const pathLookup = new Map(
     (route.route_nodes || []).map((rn) => [
@@ -439,7 +441,7 @@ function MatchRow({
       })}
       {match.received_at && (
         <span className="ml-auto opacity-40 whitespace-nowrap">
-          {new Date(match.received_at).toLocaleString()}
+          {formatDateTime(match.received_at)}
         </span>
       )}
     </div>
@@ -474,9 +476,9 @@ function DetailContent({
                 <span key={d.date} className="flex-1 text-center min-w-0 truncate">
                   {i === historyData.length - 1
                     ? t("common.now")
-                    : new Date(`${d.date}T00:00:00`).toLocaleDateString(
+                    : new Date(`${d.date}T00:00:00Z`).toLocaleDateString(
                         undefined,
-                        { day: "2-digit", month: "2-digit" },
+                        { day: "2-digit", month: "2-digit", timeZone: "UTC" },
                       )}
                 </span>
               ))}
diff --git a/src/meshcore_hub/web/static/js/spa-react/utils/api.test.ts b/src/meshcore_hub/web/static/js/spa-react/utils/api.test.ts
new file mode 100644
index 0000000..7650d27
--- /dev/null
+++ b/src/meshcore_hub/web/static/js/spa-react/utils/api.test.ts
@@ -0,0 +1,56 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { apiGet } from "./api";
+
+function setOidcEnabled(enabled: boolean) {
+  window.__APP_CONFIG__ = {
+    ...(window.__APP_CONFIG__ ?? {}),
+    oidc_enabled: enabled,
+  } as typeof window.__APP_CONFIG__;
+}
+
+describe("apiGet auth redirect", () => {
+  beforeEach(() => {
+    // A real URL object's href setter rejects relative URLs, so stub a
+    // minimal window.location instead.
+    const locationStub = {
+      href: "http://localhost/nodes?page=2",
+      pathname: "/nodes",
+      search: "?page=2",
+      origin: "http://localhost",
+    };
+    vi.stubGlobal("location", locationStub);
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it("redirects to the login flow on 401 when OIDC is enabled", async () => {
+    setOidcEnabled(true);
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockResolvedValue(
+        new Response("unauthorized", { status: 401 }),
+      ),
+    );
+
+    await expect(apiGet("/api/v1/nodes")).rejects.toThrow("API error: 401");
+    expect(window.location.href).toBe(
+      "/auth/login?next=%2Fnodes%3Fpage%3D2",
+    );
+  });
+
+  it("does not redirect on 401 when OIDC is disabled", async () => {
+    setOidcEnabled(false);
+    const originalHref = window.location.href;
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockResolvedValue(
+        new Response("unauthorized", { status: 401 }),
+      ),
+    );
+
+    await expect(apiGet("/api/v1/nodes")).rejects.toThrow("API error: 401");
+    expect(window.location.href).toBe(originalHref);
+  });
+});
diff --git a/src/meshcore_hub/web/static/js/spa-react/utils/api.ts b/src/meshcore_hub/web/static/js/spa-react/utils/api.ts
index 1b89017..4180185 100644
--- a/src/meshcore_hub/web/static/js/spa-react/utils/api.ts
+++ b/src/meshcore_hub/web/static/js/spa-react/utils/api.ts
@@ -30,6 +30,7 @@ export async function apiGet<T = unknown>(
     }
   }
   const response = await fetch(url, { signal });
+  checkAuthResponse(response);
   if (!response.ok) {
     throw new Error(`API error: ${response.status} ${response.statusText}`);
   }
@@ -91,6 +92,7 @@ export async function apiPostForm<T = unknown>(
     headers: { "Content-Type": "application/x-www-form-urlencoded" },
     body: body.toString(),
   });
+  checkAuthResponse(response);
   if (!response.ok) {
     const text = await response.text();
     throw new Error(`API error: ${response.status} - ${text}`);
diff --git a/src/meshcore_hub/web/static/js/spa-react/utils/charts.test.ts b/src/meshcore_hub/web/static/js/spa-react/utils/charts.test.ts
index 08e3e37..81540bf 100644
--- a/src/meshcore_hub/web/static/js/spa-react/utils/charts.test.ts
+++ b/src/meshcore_hub/web/static/js/spa-react/utils/charts.test.ts
@@ -18,9 +18,10 @@ import {
 const t = ((key: string) => key) as unknown as TFunction;
 
 const dayLabel = (date: string) =>
-  new Date(date).toLocaleDateString("en-GB", {
+  new Date(`${date}T00:00:00Z`).toLocaleDateString("en-GB", {
     day: "numeric",
     month: "short",
+    timeZone: "UTC",
   });
 
 const series = (counts: number[]): ActivitySeries => ({
diff --git a/src/meshcore_hub/web/static/js/spa-react/utils/charts.ts b/src/meshcore_hub/web/static/js/spa-react/utils/charts.ts
index 0627da6..5a72447 100644
--- a/src/meshcore_hub/web/static/js/spa-react/utils/charts.ts
+++ b/src/meshcore_hub/web/static/js/spa-react/utils/charts.ts
@@ -183,11 +183,16 @@ function createChartOptions(showLegend: boolean): ChartOptions<"line"> {
 }
 
 function formatDateLabels(data: { date: string }[]): string[] {
+  // Backend buckets are UTC date-only strings ("%Y-%m-%d"). Parse them as
+  // UTC and format with an explicit timeZone so users in negative UTC
+  // offsets don't see every label shifted to the previous day.
   return data.map((d) => {
-    const date = new Date(d.date);
+    const date = new Date(`${d.date}T00:00:00Z`);
+    if (Number.isNaN(date.getTime())) return d.date;
     return date.toLocaleDateString("en-GB", {
       day: "numeric",
       month: "short",
+      timeZone: "UTC",
     });
   });
 }
diff --git a/tests/test_api/test_cache.py b/tests/test_api/test_cache.py
index 77c0d94..d3d9d99 100644
--- a/tests/test_api/test_cache.py
+++ b/tests/test_api/test_cache.py
@@ -1,7 +1,7 @@
 """Tests for API cache layer."""
 
 import json
-from unittest.mock import MagicMock, patch
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 from fastapi import FastAPI, Request
@@ -1012,7 +1012,9 @@ class TestLifespanRedis:
         app.state.redis_enabled = False
         app_module._db_manager = None
 
-        with patch.object(app_module, "DatabaseManager", return_value=MagicMock()):
+        mock_db = MagicMock()
+        mock_db.adispose = AsyncMock()
+        with patch.object(app_module, "DatabaseManager", return_value=mock_db):
             async with lifespan(app):
                 assert isinstance(app.state.redis_cache, NullCache)
 
@@ -1030,7 +1032,9 @@ class TestLifespanRedis:
         app.state.redis_key_prefix = "myprefix"
         app_module._db_manager = None
 
-        with patch.object(app_module, "DatabaseManager", return_value=MagicMock()):
+        mock_db = MagicMock()
+        mock_db.adispose = AsyncMock()
+        with patch.object(app_module, "DatabaseManager", return_value=mock_db):
             with patch("meshcore_hub.common.redis.RedisCacheBackend") as mock_cls:
                 mock_instance = MagicMock()
                 mock_cls.return_value = mock_instance
@@ -1054,6 +1058,7 @@ class TestLifespanRedis:
 
         mock_cache = MagicMock()
         mock_db_manager = MagicMock()
+        mock_db_manager.adispose = AsyncMock()
         app_module._db_manager = None
 
         with patch.object(app_module, "DatabaseManager", return_value=mock_db_manager):
@@ -1064,7 +1069,7 @@ class TestLifespanRedis:
                 async with lifespan(app):
                     pass
                 mock_cache.close.assert_called_once()
-                mock_db_manager.dispose.assert_called_once()
+                mock_db_manager.adispose.assert_awaited_once()
 
 
 class TestXCacheMiddleware:
@@ -1121,6 +1126,25 @@ class TestHealthReadyRedis:
         assert response.status_code == 200
         assert response.json()["redis"] == "unreachable"
 
+    def test_health_ready_returns_503_when_db_down(self, client_no_auth):
+        """Readiness probes judge by status code: DB down must be a 503."""
+        import meshcore_hub.api.app as app_module
+
+        def _raise():
+            raise RuntimeError("db down")
+
+        original = app_module.get_db_manager
+        app_module.get_db_manager = _raise
+        try:
+            response = client_no_auth.get("/health/ready")
+        finally:
+            app_module.get_db_manager = original
+        assert response.status_code == 503
+        data = response.json()
+        assert data["status"] == "not_ready"
+        # Error detail is reduced to the exception type, not the raw message.
+        assert data["database"] == "RuntimeError"
+
 
 class TestCliRedis:
     def test_redis_enabled_shows_banner(self):
@@ -1414,7 +1438,19 @@ class TestCacheInvalidationHelpers:
 
         cache = MagicMock()
         invalidate_channels(_make_request_with_cache(cache))
-        cache.delete.assert_called_once_with("/api/v1/channels")
+        # Channel list itself (URL-path keys)...
+        cache.delete.assert_any_call("/api/v1/channels")
+        # ...plus every dependent namespace: messages/packets redaction is
+        # visibility-driven and dashboard counts embed per-channel series.
+        for prefix in (
+            "/api/v1/messages",
+            "packets",
+            "packet_groups",
+            "dashboard",
+            "/api/v1/dashboard",
+        ):
+            cache.delete.assert_any_call(prefix)
+        assert cache.delete.call_count == 6
 
     def test_invalidate_routes_drops_url_path_prefix(self):
         from meshcore_hub.api.cache_invalidation import invalidate_routes
@@ -1504,6 +1540,18 @@ class TestMutationInvalidationIntegration:
 
     # --- Channels ---------------------------------------------------------
 
+    def _assert_channel_dependent_drops(self, mock_cache: MagicMock) -> None:
+        """Channel visibility drives redaction/counts in these cached reads."""
+        for prefix in (
+            "/api/v1/channels",
+            "/api/v1/messages",
+            "packets",
+            "packet_groups",
+            "dashboard",
+            "/api/v1/dashboard",
+        ):
+            mock_cache.delete.assert_any_call(prefix)
+
     def test_create_channel_invalidates_channels(self, client_no_auth, api_db_session):
         mock_cache = self._install_mock_cache(client_no_auth)
         resp = client_no_auth.post(
@@ -1517,6 +1565,7 @@ class TestMutationInvalidationIntegration:
         )
         assert resp.status_code == 201
         mock_cache.delete.assert_any_call("/api/v1/channels")
+        self._assert_channel_dependent_drops(mock_cache)
 
     def test_update_channel_invalidates_channels(self, client_no_auth, sample_channel):
         mock_cache = self._install_mock_cache(client_no_auth)
@@ -1526,12 +1575,14 @@ class TestMutationInvalidationIntegration:
         )
         assert resp.status_code == 200
         mock_cache.delete.assert_any_call("/api/v1/channels")
+        self._assert_channel_dependent_drops(mock_cache)
 
     def test_delete_channel_invalidates_channels(self, client_no_auth, sample_channel):
         mock_cache = self._install_mock_cache(client_no_auth)
         resp = client_no_auth.delete(f"/api/v1/channels/{sample_channel.id}")
         assert resp.status_code == 204
         mock_cache.delete.assert_any_call("/api/v1/channels")
+        self._assert_channel_dependent_drops(mock_cache)
 
     # --- Routes -----------------------------------------------------------
 
diff --git a/tests/test_collector/test_subscriber.py b/tests/test_collector/test_subscriber.py
index b080a98..01ec733 100644
--- a/tests/test_collector/test_subscriber.py
+++ b/tests/test_collector/test_subscriber.py
@@ -1288,6 +1288,17 @@ class TestSubscriberDispatch:
 
         assert len(subscriber._webhook_queue) == 0
 
+    def test_webhook_queue_is_bounded_and_drops_oldest(self, subscriber):
+        """A full queue drops the oldest events instead of growing forever."""
+        subscriber._webhook_queue_max = 3
+        for i in range(5):
+            subscriber._queue_webhook_event("test_event", {"seq": i}, "a" * 64)
+
+        assert len(subscriber._webhook_queue) == 3
+        # Oldest two events were dropped; the newest remain in order.
+        remaining = [payload["seq"] for _, payload, _ in subscriber._webhook_queue]
+        assert remaining == [2, 3, 4]
+
     def test_start_with_mqtt_retry(self, mock_mqtt_client, db_manager):
         """MQTT connection is retried on failure."""
         mock_mqtt_client.connect.side_effect = [
diff --git a/tests/test_collector/test_webhook.py b/tests/test_collector/test_webhook.py
index 11a87c2..7fb18e0 100644
--- a/tests/test_collector/test_webhook.py
+++ b/tests/test_collector/test_webhook.py
@@ -318,6 +318,51 @@ class TestWebhookDispatcher:
 
         await dispatcher.stop()
 
+    @pytest.mark.asyncio
+    async def test_dispatch_4xx_not_retried(self, dispatcher):
+        """Permanent client errors must fail fast instead of retrying."""
+        webhook = WebhookConfig(
+            url="https://example.com/webhook",
+            name="notfound-webhook",
+            max_retries=3,
+            retry_backoff=0.01,
+        )
+        dispatcher.add_webhook(webhook)
+        await dispatcher.start()
+
+        mock_response = AsyncMock()
+        mock_response.status_code = 404
+
+        with patch.object(dispatcher._client, "post", return_value=mock_response) as m:
+            result = await dispatcher.dispatch("event", {"data": "test"})
+            assert result == {"notfound-webhook": False}
+            # Exactly one request despite max_retries=3.
+            assert m.call_count == 1
+
+        await dispatcher.stop()
+
+    @pytest.mark.asyncio
+    async def test_dispatch_5xx_retried(self, dispatcher):
+        """Server errors are still retried."""
+        webhook = WebhookConfig(
+            url="https://example.com/webhook",
+            name="server-error-webhook",
+            max_retries=2,
+            retry_backoff=0.01,
+        )
+        dispatcher.add_webhook(webhook)
+        await dispatcher.start()
+
+        mock_response = AsyncMock()
+        mock_response.status_code = 503
+
+        with patch.object(dispatcher._client, "post", return_value=mock_response) as m:
+            result = await dispatcher.dispatch("event", {"data": "test"})
+            assert result == {"server-error-webhook": False}
+            assert m.call_count == 3  # initial + 2 retries
+
+        await dispatcher.stop()
+
     @pytest.mark.asyncio
     async def test_dispatch_timeout(self, dispatcher):
         """Test dispatch handles timeouts."""
diff --git a/tests/test_common/test_database.py b/tests/test_common/test_database.py
index 05afee4..38b8ae2 100644
--- a/tests/test_common/test_database.py
+++ b/tests/test_common/test_database.py
@@ -1,7 +1,7 @@
 """Tests for database engine configuration."""
 
 from pathlib import Path
-from unittest.mock import patch
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 from sqlalchemy import text
@@ -149,3 +149,78 @@ class TestPostgresSessionTimezone:
         server_settings = kwargs["connect_args"]["server_settings"]
         assert server_settings["timezone"] == "UTC"
         assert server_settings["search_path"] == "meshcorehub"
+
+    def test_async_engine_gets_pool_pre_ping_and_sizing(self) -> None:
+        """Async engine mirrors the sync engine's pool config."""
+        manager = DatabaseManager.__new__(DatabaseManager)
+        manager.database_url = "postgresql://u:p@h/db"
+        manager._echo = False
+        manager._schema = None
+        manager._async_engine = None
+        manager._async_session_factory = None
+
+        with patch("meshcore_hub.common.database.create_async_engine") as mock_async:
+            manager._ensure_async_engine()
+        _, kwargs = mock_async.call_args
+        assert kwargs["pool_pre_ping"] is True
+        assert kwargs["pool_size"] == 20
+        assert kwargs["max_overflow"] == 30
+
+    def test_async_engine_skips_pool_args_for_memory_sqlite(self) -> None:
+        """In-memory SQLite uses a non-overflow pool; sizing args must be omitted."""
+        manager = DatabaseManager.__new__(DatabaseManager)
+        manager.database_url = "sqlite+aiosqlite:///:memory:"
+        manager._echo = False
+        manager._schema = None
+        manager._async_engine = None
+        manager._async_session_factory = None
+
+        with (
+            patch("meshcore_hub.common.database.create_async_engine") as mock_async,
+            patch("meshcore_hub.common.database.event.listens_for"),
+        ):
+            manager._ensure_async_engine()
+        _, kwargs = mock_async.call_args
+        assert "pool_size" not in kwargs
+        assert "max_overflow" not in kwargs
+
+    async def test_adispose_closes_async_engine(self) -> None:
+        """adispose awaits the async engine dispose and clears it."""
+        manager = DatabaseManager.__new__(DatabaseManager)
+        manager.database_url = "sqlite+aiosqlite:///:memory:"
+        manager._echo = False
+        manager._schema = None
+        mock_async_engine = AsyncMock()
+        manager._async_engine = mock_async_engine
+        manager._async_session_factory = object()
+        manager.engine = MagicMock()
+
+        await manager.adispose()
+
+        mock_async_engine.dispose.assert_awaited_once()
+        manager.engine.dispose.assert_called_once()
+        assert manager._async_engine is None
+        assert manager._async_session_factory is None
+
+    def test_dispose_sync_context_closes_async_engine_via_temp_loop(self) -> None:
+        """Outside a running loop, dispose() drains the async engine too."""
+        manager = DatabaseManager.__new__(DatabaseManager)
+        manager.database_url = "sqlite+aiosqlite:///:memory:"
+        manager._echo = False
+        manager._schema = None
+        disposed = []
+
+        async def _fake_async_dispose() -> None:
+            disposed.append(True)
+
+        mock_async_engine = MagicMock()
+        mock_async_engine.dispose = _fake_async_dispose
+        manager._async_engine = mock_async_engine
+        manager._async_session_factory = object()
+        manager.engine = MagicMock()
+
+        manager.dispose()
+
+        assert disposed == [True]
+        manager.engine.dispose.assert_called_once()
+        assert manager._async_engine is None
diff --git a/tests/test_web/conftest.py b/tests/test_web/conftest.py
index a43b3c7..688f1b8 100644
--- a/tests/test_web/conftest.py
+++ b/tests/test_web/conftest.py
@@ -247,7 +247,12 @@ class MockHttpClient:
         }
 
     def set_response(
-        self, method: str, path: str, status_code: int = 200, json_data: Any = None
+        self,
+        method: str,
+        path: str,
+        status_code: int = 200,
+        json_data: Any = None,
+        exc: Exception | None = None,
     ) -> None:
         """Set a custom response for a specific endpoint.
 
@@ -256,11 +261,14 @@ class MockHttpClient:
             path: URL path
             status_code: Response status code
             json_data: JSON response body
+            exc: When set, the client raises this instead of responding
+                (simulates an unreachable backend)
         """
         key = f"{method}:{path}"
         self._responses[key] = {
             "status_code": status_code,
             "json": json_data,
+            "exc": exc,
         }
 
     def set_paged_response(self, method: str, path: str, handler: Any) -> None:
@@ -292,6 +300,8 @@ class MockHttpClient:
             return self._response_from_data(
                 {"status_code": 404, "json": {"detail": "Not found"}}
             )
+        if response_data.get("exc") is not None:
+            raise response_data["exc"]
         return self._response_from_data(response_data)
 
     async def request(
diff --git a/tests/test_web/test_app.py b/tests/test_web/test_app.py
index fdcaed0..95094fd 100644
--- a/tests/test_web/test_app.py
+++ b/tests/test_web/test_app.py
@@ -552,6 +552,25 @@ class TestSystemMaintenance:
 
         assert '"system_maintenance": true' in client.get("/").text
 
+    def test_maintenance_blocks_api_proxy(
+        self, mock_http_client: MockHttpClient
+    ) -> None:
+        """Maintenance mode must gate the API proxy, not just the SPA UI."""
+        app = create_app(
+            api_url="http://localhost:8000",
+            api_key="test-api-key",
+            system_maintenance=True,
+            features=ALL_FEATURES_ENABLED,
+        )
+        app.state.http_client = mock_http_client
+        client = TestClient(app, raise_server_exceptions=True)
+
+        response = client.get("/api/v1/nodes")
+        assert response.status_code == 503
+        assert response.json()["code"] == "MAINTENANCE"
+        # The proxy must not have forwarded anything to the backend.
+        assert mock_http_client.last_request_params is None
+
     def test_maintenance_off_by_default(self, client: TestClient) -> None:
         """Without maintenance, nav links render normally (regression)."""
         html = client.get("/").text
diff --git a/tests/test_web/test_health.py b/tests/test_web/test_health.py
index bcd31f9..a6e9816 100644
--- a/tests/test_web/test_health.py
+++ b/tests/test_web/test_health.py
@@ -64,7 +64,7 @@ class TestHealthReadyEndpoint:
         client = TestClient(web_app, raise_server_exceptions=True)
         response = client.get("/health/ready")
 
-        assert response.status_code == 200
+        assert response.status_code == 503
         data = response.json()
         assert data["status"] == "not_ready"
         assert "status 500" in data["api"]
@@ -81,7 +81,24 @@ class TestHealthReadyEndpoint:
         client = TestClient(web_app, raise_server_exceptions=True)
         response = client.get("/health/ready")
 
-        assert response.status_code == 200
+        assert response.status_code == 503
         data = response.json()
         assert data["status"] == "not_ready"
         assert "status 404" in data["api"]
+
+    def test_health_ready_with_api_unreachable(
+        self, web_app: Any, mock_http_client: MockHttpClient
+    ) -> None:
+        """Test that health/ready returns 503 when the API call raises."""
+        web_app.state.http_client = mock_http_client
+        mock_http_client.set_response(
+            "GET", "/health", exc=RuntimeError("connection refused")
+        )
+
+        client = TestClient(web_app, raise_server_exceptions=True)
+        response = client.get("/health/ready")
+
+        assert response.status_code == 503
+        data = response.json()
+        assert data["status"] == "not_ready"
+        assert data["api"] == "RuntimeError"