fix: older defects (batch C) and the second batch's review

Chats:
- New Chat right after an answer saves that chat once. Saves run one at
  a time and read the chat on screen when their turn comes; a save
  scheduled for a chat that is no longer on screen is dropped. A chat
  whose id was still on its way to the URL no longer comes back after
  New Chat (the next answer went into it).
- Crossing the 768 px breakpoint keeps the chat panel: a streaming answer,
  unsaved messages and attachments stay. The panel gets the sizes of each
  side, and a panel collapsed on desktop opens on mobile.
- The chat's export waits for its own reply: an edit's history export
  still on its way no longer answers it with the older diagram, and two
  file saves at once no longer swap results.
- A second edit in one answer is previewed on the first edit's result.
- Stop also ends a running screenshot check; a chat that cannot be saved
  (storage full) can be left with "Continue without saving".
- Small diagrams with shapes count as diagrams; the tool card no longer
  crashes on malformed operations.

Quota and providers:
- Requests that reach the server's own endpoints count toward the quota:
  EdgeOne (always its own endpoint now), a private base URL whatever key
  header is sent, keyless Ollama without a URL. With the quota on, a
  redirect is followed only to a public address. The output cap applies
  to these requests too.
- Stop records the tokens of the steps that finished; the screenshot check
  counts its tokens without counting a request.
- EdgeOne configured only by AI_PROVIDER works, also in the admin Test,
  which forwards the access code. Azure set up only in the admin panel
  works in chat. The Test sends a Bedrock session token.
- The admin panel's Test of an entry without a URL uses the server's URL
  as the server does (no private address check for it); the admin panel
  no longer writes an Ollama URL.

MCP server:
- Write tools and start_session run one at a time, so two at once never
  drop each other's change; a cancelled call waiting its turn is skipped.
  get_diagram and export_diagram keep the session they started with.
- Export to .drawio first gets the user's latest edits from the browser.
- History thumbnails: one that arrives after the next AI write is
  dropped; a sync reply keeps the image; a version that changed only page
  settings is its own entry.
- A diagram over the 10 MB limit is saved without its image, or the user
  is told to download it (the server now answers 413 instead of cutting
  the connection).
- Labels holding text like id='1' or parent='1' are no longer read as
  attributes (a layer or a parent was deleted). A broken bare
  <mxGraphModel> file is refused.
- After a sync reply the tab no longer sends its autosave copy again.

Desktop and files:
- A newer switch of the same preset is not rolled back by an older one
  that failed. .env values with escaped quotes are read whole.
- MCP saved files: a file that could not be read stays protected while a
  folder without permission hides it, and is saved again once deleted.
- The desktop app reports "no chats" only when the count was read and no
  model settings are stored.

app/api/validate-diagram/route.ts

@@ -6,6 +6,12 @@
 import { Output, streamText } from "ai"
 import { checkAccessCode, rejectCrossSite } from "@/lib/access-code"
 import { getValidationModel } from "@/lib/ai-providers"
+import {
+    checkAndIncrementRequest,
+    isQuotaEnabled,
+    recordTokenUsage,
+} from "@/lib/dynamo-quota-manager"
+import { getUserIdFromRequest } from "@/lib/user-id"
 import { VALIDATION_SYSTEM_PROMPT } from "@/lib/validation-prompts"
 import {
     type ValidationResult,
@@ -78,6 +84,35 @@ export async function POST(req: Request): Promise<Response> {
             )
         }
 
+        // It runs the server's vision model: with the quota on, the daily
+        // and per-minute token limits apply, and its tokens are counted. Not
+        // the request limit, which is for chats: the day's last chat still
+        // gets its check, and a check does not count as a chat.
+        const userId = getUserIdFromRequest(req)
+        const countsQuota = isQuotaEnabled() && userId !== "anonymous"
+        if (countsQuota) {
+            const quotaCheck = await checkAndIncrementRequest(
+                userId,
+                {
+                    requests: 0,
+                    tokens: Number(process.env.DAILY_TOKEN_LIMIT) || 200000,
+                    tpm: Number(process.env.TPM_LIMIT) || 20000,
+                },
+                0,
+            )
+            if (!quotaCheck.allowed) {
+                return Response.json(
+                    {
+                        error: quotaCheck.error,
+                        type: quotaCheck.type,
+                        used: quotaCheck.used,
+                        limit: quotaCheck.limit,
+                    },
+                    { status: 429 },
+                )
+            }
+        }
+
         // Get the validation model
         let model
         try {
@@ -120,7 +155,14 @@ export async function POST(req: Request): Promise<Response> {
             ],
             maxOutputTokens: 1024,
             abortSignal: AbortSignal.timeout(timeout),
-            onFinish: ({ output }) => {
+            onFinish: ({ output, totalUsage }) => {
+                if (countsQuota && totalUsage) {
+                    recordTokenUsage(
+                        userId,
+                        (totalUsage.inputTokens || 0) +
+                            (totalUsage.outputTokens || 0),
+                    )
+                }
                 if (sessionId && output) {
                     console.log(
                         `[validate-diagram] Session ${sessionId}: valid=${output.valid}, issues=${output.issues?.length ?? 0}`,