fix: what the third round broke, and the first batch's review

MCP preview after the server lost a session (it expired, or the MCP
process restarted):
- Every server state has an id, made when the state is created. The tab
  notices a new id even when the version numbers happen to match, and
  every push names the state it was based on, so one based on a lost state
  is refused, also when it comes before the tab's first poll (the server
  recovers the saved file first).
- The tab keeps the newest canvas XML, saved or not. When the server knows
  nothing (no file) or exactly what the tab last saved, the canvas wins and
  is saved, so edits made while the server was down are kept. Otherwise
  the server's diagram (an AI write the tab missed, a cleared document
  that was saved) is shown and the tab's copy goes to History.
- Late answers to an old state's push or poll are dropped; a failed push
  says the server is unreachable; Download as .drawio saves the canvas.

Settings and server:
- Saved providers this version does not know stay in storage with their
  keys, and sending no longer trips over them.
- The desktop "Ollama (Local)" preset with a key goes to local Ollama
  again; a server model's Ollama URL variable is read; the admin panel
  writes Ollama Cloud's URL for a key without one.
- Provider error texts show again in the desktop app and for EdgeOne.
- .env: a quoted value followed by a comment ending in a quote is read as
  dotenv reads it; unquoted values are unchanged.
- Desktop app: the next launch opens the port where a chat was last
  saved; a launch elsewhere that saves nothing does not move it, and a
  page with no chats lets the next launch try the other port once.
- The Test button no longer stays busy after another tab changed the key.
- A completed append_diagram is no longer undone by an earlier failed
  edit's preview; a file read once in vain is saved again once it is read
  or gone.

From the first batch's review:
- The admin panel's Test of an entry without a URL now tests the server's
  <P>_BASE_URL, where chat sends the entry's key; chat is unchanged (the
  first fix rerouted working setups).
- The model list ends downloads that are too large, accepts answers
  without a body, and keeps the "redirects are not allowed" explanation.
- A test covers the preview's History rendering.

electron/electron.d.ts

@@ -75,6 +75,10 @@ declare global {
              * preset); returns a function that stops the calls
              */
             onServerRestarted?: (callback: () => void) => () => void
+            /** A chat was saved: open this port next launch */
+            chatSaved?: () => Promise<void>
+            /** The page loaded with this many chats */
+            chatsLoaded?: (count: number) => Promise<void>
         }
 
         /** Settings window Electron API */

electron/main/env-loader.ts

@@ -51,17 +51,25 @@ function loadEnvFromFile(filePath: string): void {
             const quote = value[0]
             const closingQuote =
                 quote === '"' || quote === "'" ? value.indexOf(quote, 1) : -1
-            if (value.length > 1 && value.endsWith(quote) && closingQuote > 0) {
-                // Quoted from start to end: the quotes inside belong to the
-                // value (JSON with an apostrophe), as dotenv reads it
-                value = value.slice(1, -1)
-            } else if (closingQuote > 0) {
-                // Quoted value: keep what's inside the quotes and drop
-                // anything after them (e.g. a comment)
+            if (
+                closingQuote > 0 &&
+                /^\s*(#.*)?$/.test(value.slice(closingQuote + 1))
+            ) {
+                // Quoted value, then nothing or a comment: keep what is
+                // inside the quotes, as dotenv reads it
                 value = value.slice(1, closingQuote)
             } else {
-                // Unquoted value: drop an inline comment ("value  # comment")
+                // Unquoted value: drop an inline comment ("value  # comment").
+                // A value quoted from start to end with quotes inside (JSON
+                // with an apostrophe) loses only the outer two, as in dotenv.
                 value = value.replace(/\s+#.*$/, "")
+                if (
+                    closingQuote > 0 &&
+                    value.length > 1 &&
+                    value.endsWith(quote)
+                ) {
+                    value = value.slice(1, -1)
+                }
             }
 
             // Don't override existing environment variables

electron/main/ipc-handlers.ts

@@ -13,6 +13,7 @@ import {
     updatePreset,
 } from "./config-manager"
 import { restartNextServer } from "./next-server"
+import { noteNoChats, rememberChatPort } from "./port-manager"
 import {
     applyProxyToEnv,
     getProxyConfig,
@@ -77,6 +78,15 @@ export function registerIpcHandlers(): void {
         return app.getVersion()
     })
 
+    // ==================== Where the chats are ====================
+
+    // The page saved a chat, or loaded without any: decides which port
+    // (and so which origin's chats) the next launch opens
+    handle("chat-saved", () => rememberChatPort())
+    handle("chats-loaded", (_event, count: unknown) => {
+        if (count === 0) noteNoChats()
+    })
+
     // ==================== Window Controls ====================
 
     ipcMain.on("window-minimize", (event) => {

electron/main/port-manager.ts

@@ -1,4 +1,4 @@
-import { existsSync } from "node:fs"
+import { existsSync, readFileSync, writeFileSync } from "node:fs"
 import net from "node:net"
 import path from "node:path"
 import { app } from "electron"
@@ -39,6 +39,55 @@ function hasStoredData(port: number): boolean {
     )
 }
 
+// The two fixed production ports, the only ones whose origin (and so its
+// chats and settings) is the same at every launch
+const HOME_PORTS = [PORT_CONFIG.legacyProduction, PORT_CONFIG.production]
+
+const chatPortFile = () => path.join(app.getPath("userData"), "chat-port.json")
+
+/** The fixed port where a chat was last saved, if known */
+function readChatPort(): number | null {
+    try {
+        const { port } = JSON.parse(readFileSync(chatPortFile(), "utf-8"))
+        return HOME_PORTS.includes(port) ? port : null
+    } catch {
+        return null
+    }
+}
+
+function writeChatPort(port: number): void {
+    try {
+        writeFileSync(chatPortFile(), JSON.stringify({ port }))
+    } catch (error) {
+        console.warn("Could not save the chat port:", error)
+    }
+}
+
+/**
+ * The page saved a chat: open on this port next time. Chats of the two
+ * ports cannot be shown together (each origin has its own storage), so the
+ * app opens where the user last worked. A launch that had to use the other
+ * port and saved nothing does not move it.
+ */
+export function rememberChatPort(): void {
+    const port = allocatedPort
+    if (!app.isPackaged || port === null || !HOME_PORTS.includes(port)) return
+    if (readChatPort() !== port) writeChatPort(port)
+}
+
+/**
+ * The page loaded without any chats. Before any chat was saved under this
+ * version (no file yet), the user's chats may be on the other fixed port,
+ * where an older version opened: try it first next time.
+ */
+export function noteNoChats(): void {
+    const port = allocatedPort
+    if (!app.isPackaged || port === null || !HOME_PORTS.includes(port)) return
+    if (existsSync(chatPortFile())) return
+    const other = HOME_PORTS.find((p) => p !== port)
+    if (other !== undefined && hasStoredData(other)) writeChatPort(other)
+}
+
 /**
  * Check if a specific port is available
  */
@@ -86,15 +135,19 @@ export async function findAvailablePort(reuseExisting = true): Promise<number> {
         allocatedPort = null
     }
 
-    // In production, try the legacy port first to preserve existing users'
-    // data, unless only the new port has data: their app started on 13370
-    // while Windows reserved 61337, and 61337 being free now would hide it
+    // In production, first the port where a chat was last saved. Without
+    // one, the legacy port first to preserve existing users' data, unless
+    // only the new port has data: their app started on 13370 while Windows
+    // reserved 61337, and 61337 being free now would hide it
+    const chatPort = isDev ? null : readChatPort()
     const candidates = isDev
         ? [preferredPort]
-        : hasStoredData(PORT_CONFIG.production) &&
-            !hasStoredData(PORT_CONFIG.legacyProduction)
-          ? [PORT_CONFIG.production, PORT_CONFIG.legacyProduction]
-          : [PORT_CONFIG.legacyProduction, PORT_CONFIG.production]
+        : chatPort !== null
+          ? [chatPort, ...HOME_PORTS.filter((p) => p !== chatPort)]
+          : hasStoredData(PORT_CONFIG.production) &&
+              !hasStoredData(PORT_CONFIG.legacyProduction)
+            ? [PORT_CONFIG.production, PORT_CONFIG.legacyProduction]
+            : [PORT_CONFIG.legacyProduction, PORT_CONFIG.production]
     for (const port of candidates) {
         if (await isPortAvailable(port)) {
             allocatedPort = port

electron/preload/index.ts

@@ -28,6 +28,11 @@ contextBridge.exposeInMainWorld("electronAPI", {
     setUserLocale: (locale: string) =>
         ipcRenderer.invoke("set-user-locale", locale),
 
+    // A chat was saved, or the page loaded with this many chats: the next
+    // launch opens the port where the chats are
+    chatSaved: () => ipcRenderer.invoke("chat-saved"),
+    chatsLoaded: (count: number) => ipcRenderer.invoke("chats-loaded", count),
+
     // The server restarted on the same port (another preset)
     onServerRestarted: (callback: () => void) => {
         const listener = () => callback()