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.

electron/main/app-menu.ts

@@ -32,6 +32,9 @@ export function rebuildAppMenu(): void {
     buildAppMenu()
 }
 
+// Number of the latest preset switch
+let lastSwitch = 0
+
 /**
  * Apply a preset and restart the server so it takes effect.
  * If the restart fails, go back to the previous preset and restart again,
@@ -41,6 +44,7 @@ export function rebuildAppMenu(): void {
 export async function switchPreset(
     id: string,
 ): Promise<Record<string, string>> {
+    const switchNumber = ++lastSwitch
     const previousPresetId = getCurrentPresetId()
     const env = applyPresetToEnv(id)
     if (!env) {
@@ -60,8 +64,9 @@ export async function switchPreset(
         console.error("Failed to restart server:", error)
         const reason = error instanceof Error ? error.message : String(error)
 
-        // Another preset was chosen meanwhile: its own restart follows
-        if (getCurrentPresetId() !== id) {
+        // A newer switch started meanwhile (also of this same preset): its
+        // own restart follows, and undoing would lose that choice
+        if (switchNumber !== lastSwitch) {
             throw new Error(
                 `The server could not be restarted.\n\nError: ${reason}`,
             )

electron/main/env-loader.ts

@@ -28,6 +28,20 @@ export function loadEnvFile(): void {
     console.log("No .env file found, using system environment variables")
 }
 
+/**
+ * Index of the quote that closes a value starting with a quote, or -1. A
+ * backslash before the quote character escapes it, as in dotenv; the
+ * backslash stays in the value.
+ */
+function findClosingQuote(value: string): number {
+    const quote = value[0]
+    for (let i = 1; i < value.length; i++) {
+        if (value[i] === "\\" && value[i + 1] === quote) i++
+        else if (value[i] === quote) return i
+    }
+    return -1
+}
+
 /**
  * Parse and load environment variables from a file
  */
@@ -50,7 +64,7 @@ function loadEnvFromFile(filePath: string): void {
 
             const quote = value[0]
             const closingQuote =
-                quote === '"' || quote === "'" ? value.indexOf(quote, 1) : -1
+                quote === '"' || quote === "'" ? findClosingQuote(value) : -1
             if (
                 closingQuote > 0 &&
                 /^\s*(#.*)?$/.test(value.slice(closingQuote + 1))