fix: apply security and correctness review findings across both stacks

Legacy panel:
- upstream body reads now carry their own deadline and a 10 MB byte budget;
  a stalled modem can no longer hang /api/status fan-out forever nor OOM
  the proxy (request headers alone had the timeout, bodies had none)
- add X-Frame-Options DENY / CSP frame-ancestors none / nosniff; the panel
  (delete-instance and confirmed-write dialogs) is no longer clickjackable
- only send a JSON content-type when the API console request has a body, so
  payload-less dangerous writes stop failing with 400 and burning the
  one-use confirmation token
- register a form-urlencoded parser (the proxy branch was unreachable) and
  drop the multipart parser that buffered up to 60 MB before rejecting;
  bodyLimit drops to 2 MB; framework-level 415 keeps the stable error body
- remove /api/sms/send from readable paths: GET bypassed the write
  confirmation for a send endpoint
- /api/instances/:id/login maps upstream failures to a stable 502 instead
  of leaking raw error text
- guard MULTI_SIMADMIN_TIMEOUT_MS parsing (NaN aborted every request);
  prune dead code (buildClients, cookie expando no-op)

Control plane:
- deleting a notification channel detaches it from rules instead of leaving
  dangling ids that made every referencing rule unreadable and silently
  dropped future notifications; rule reads tolerate unknown ids
- startup sweep resets notification_queue rows stranded in 'sending' by a
  crash (mirrors the sms outbox sweep); terminal outbox rows are pruned on
  the retention timer
- /api/v1/metrics no longer emits operator-assigned node names on the
  session-free scrape; login limiter map is bounded and pruned; Secure
  cookie honors the gateway-declared x-forwarded-proto
- webhook delivery sets redirect: manual (signed payloads are not replayed)
- SMTP envelope sender is validated against CR/LF smuggling
- scheduled reboots with delaySeconds != 3 fail fast at the dispatcher with
  a clear reason instead of burning every retry; contract narrowed to the
  pinned baseline

server/core.js

@@ -1,7 +1,13 @@
 
 export { normalizeBaseUrl, normalizeInstance } from './config/schema.js'
 
-export const DEFAULT_TIMEOUT_MS = Number(process.env.MULTI_SIMADMIN_TIMEOUT_MS || 6000)
+function parsePositiveIntEnv(value, fallback) {
+  const parsed = Number(value)
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : fallback
+}
+
+export const DEFAULT_TIMEOUT_MS = parsePositiveIntEnv(process.env.MULTI_SIMADMIN_TIMEOUT_MS, 6000)
+export const DEFAULT_MAX_BODY_BYTES = parsePositiveIntEnv(process.env.MULTI_SIMADMIN_MAX_BODY_BYTES, 10 * 1024 * 1024)
 export function redactInstance(instance) {
   return {
     id: instance.id,
@@ -165,7 +171,6 @@ export function createSimAdminClient(instance, { fetchImpl = fetch, timeoutMs =
     const headers = new Headers(options.headers || {})
     const cookie = jar.header()
     if (cookie && !headers.has('cookie')) headers.set('cookie', cookie)
-    if (headers.has('cookie')) headers.cookie = headers.get('cookie')
     try {
       const response = await fetchImpl(url, { ...options, headers, signal: controller.signal, redirect: options.redirect || 'manual' })
       jar.setFromHeaders(response.headers)
@@ -178,7 +183,7 @@ export function createSimAdminClient(instance, { fetchImpl = fetch, timeoutMs =
   async function fetchJson(endpoint, options = {}) {
     const startedAt = Date.now()
     const response = await request(endpoint, { method: 'GET', ...options, headers: { accept: 'application/json,text/plain,*/*', ...(options.headers || {}) } })
-    const text = await response.text()
+    const text = (await readResponseBody(response, { bodyTimeoutMs: options.timeoutMs || timeoutMs })).toString('utf8')
     let data = null
     try { data = text ? JSON.parse(text) : null } catch {}
     return { ok: response.ok, status: response.status, latencyMs: Date.now() - startedAt, data, text: data ? undefined : text.slice(0, 1000), headers: response.headers }
@@ -212,6 +217,36 @@ export function createSimAdminClient(instance, { fetchImpl = fetch, timeoutMs =
   return { instance, jar, request, fetchJson, ensureAuthenticated, clearEphemeralSecret }
 }
 
-export function buildClients(instances, options = {}) {
-  return new Map(instances.map(instance => [instance.id, createSimAdminClient(instance, options)]))
+// The header timeout ends once headers arrive; body reads need their own
+// deadline and a byte budget so a stalled or hostile upstream can neither hang
+// status aggregation nor exhaust memory.
+export async function readResponseBody(response, { maxBytes = DEFAULT_MAX_BODY_BYTES, bodyTimeoutMs = DEFAULT_TIMEOUT_MS } = {}) {
+  const reader = response.body?.getReader()
+  if (!reader) return Buffer.alloc(0)
+  const chunks = []
+  let size = 0
+  let failure = null
+  const timer = setTimeout(() => {
+    failure = new Error('upstream response body timed out')
+    reader.cancel(failure).catch(() => {})
+  }, bodyTimeoutMs)
+  try {
+    while (true) {
+      const { done, value } = await reader.read()
+      if (done) break
+      size += value.byteLength
+      if (size > maxBytes) {
+        failure = new Error('upstream response body exceeded the size limit')
+        throw failure
+      }
+      chunks.push(Buffer.from(value))
+    }
+  } finally {
+    clearTimeout(timer)
+  }
+  if (failure) {
+    await reader.cancel(failure).catch(() => {})
+    throw failure
+  }
+  return Buffer.concat(chunks)
 }