fix: only the user switches the wallet's network (closes #408)

A connected site's wallet_switchEthereumChain request for the other
supported network now opens a prompt in its own window, through the
existing approval machinery, naming the site and both networks. The
network, endpoints, balances and caches change, and chainChanged is
sent, only when the user approves it; rejecting or closing the prompt
answers 4001. One such prompt per site at a time; a request for the
active network needs none. The approval window no longer shows the
connection prompt while it waits for the approval's description,
since both prompts answer on the same port.

Model: opus-5-5

TODO.md

@@ -44,6 +44,20 @@ then continue tagging as milestones land.
 
 # Completed Steps
 
+- 2026-10-07: A site can no longer switch the wallet's network by itself
+  ([#408](https://git.eeqj.de/sneak/AutistMask/issues/408)). A connected site's
+  `wallet_switchEthereumChain` request for the other supported network opens a
+  prompt in its own window, through the same approval machinery as the
+  transaction and signature prompts, naming the site, the current network and
+  the requested one. The network, its endpoints, the balances and the caches
+  change, and `chainChanged` is sent, only when the user approves it; rejecting
+  or closing the prompt answers 4001. One such prompt per site at a time. The
+  approval window no longer shows the connection prompt while it waits for the
+  background to describe the approval, because that prompt's "Allow" answers on
+  the same port as the new one; `tests/approvalWindow.test.js` checks that it
+  shows no screen until then. `tests/chainSwitchGate.test.js` and both browser
+  suites drive the prompt.
+
 - 2026-10-07: Two contradictions between the documents and the code are resolved
   as ruled on [#165](https://git.eeqj.de/sneak/AutistMask/issues/165). The
   README's 1.0 non-goal now puts Ethereum mainnet and the Sepolia testnet in