feat(mcp-client): auto-reconnect with bounded backoff after transport close

A per-instance connection supervisor restarts the original server config
with exponential backoff when the transport closes, re-runs tool discovery
on success, and atomically replaces the previous generation. Default policy
retries for ~2.5 minutes (10 attempts, 500ms→30s doubling) before giving up
and unregistering the server's tools.

New config block reconnect { enabled, initialDelayMs, maxDelayMs, maxAttempts }
on both transports; misconfiguration fails plugin load. A connection that
survives past the stability window (maxDelayMs) resets the attempt budget,
so occasional crashes recover indefinitely while a crash loop still exhausts
the cap.

Integrates with the upstream failOnStartupError: the initial sync uses
registrationFailure:'throw' when that flag is set so a squatted namespace
still rejects activation.

Fixes #1746

packages/mcp/mcp-client/tests/fixture-server.ts

@@ -51,6 +51,17 @@ server.registerTool('image', {
   ],
 }))
 
+server.registerTool('crash', {
+  title: 'Crash Tool',
+  description: 'Replies, then exits the server process (crash-recovery test).',
+  inputSchema: {},
+}, async () => {
+  // Exit AFTER the response flushes so the caller observes a clean result
+  // followed by a transport close, like a real post-reply crash.
+  setTimeout(() => process.exit(7), 25)
+  return { content: [{ type: 'text', text: 'crashing' }] }
+})
+
 // Dotted name: legal in MCP, illegal in the DeepSeek function-name contract.
 // Exercises the bridge's normalize-and-hash public-name path end to end.
 server.registerTool('admin.reset', {