fix(plugin): clear brokered session state on logout

sessionStorage outlives a logout inside the same tab, so the keys stay readable
after the next user signs in. They are namespaced by user id, which stops the new
user's plugins from reading them, but the data is still sitting in the tab — the
same reason logout already drops the appearance snapshot, the SW caches and the
user-scoped offline DB. Purge them there too.

Three things around it, from reading the handlers next to the new ones:

- The inactive-plugin purge ran before the store was updated, so a sessionStorage
  failure cost us the plugin list we had just fetched. Commit first, purge after.
- The session handlers answered without checking requestId, unlike confirm and
  geolocation — an answer the frame can never match is worth skipping.
- The mock host threw plain Errors while the real bridge rejects with .code set,
  and checked the key before the trip scope where the host does the reverse, so a
  plugin's error handling could pass its tests and still break in the app.

plugin-sdk/src/mock-host.ts

@@ -242,17 +242,28 @@ export function createMockHost(opts: MockHostOptions = {}): MockHost {
   const emitted: MockHost['emitted'] = [];
   const notifications: MockHost['notifications'] = [];
   const sessionValues = new Map<string, string>();
+  // The real bridge rejects with a plain Error carrying the code on `.code`
+  // (ui/kit.ts). Keep the `CODE: message` text the rest of this mock uses, but
+  // attach `.code` too, so a plugin that branches on it behaves the same here.
+  const sessionError = (code: string, message: string) => {
+    const err = new Error(`${code}: ${message}`) as Error & { code: string };
+    err.code = code;
+    return err;
+  };
   const sessionPrefix = (scope: 'plugin' | 'trip') => {
     if (scope === 'trip' && opts.sessionTripId === undefined) {
-      throw new Error('NO_TRIP_CONTEXT: trip session storage requires a trip context');
+      throw sessionError('NO_TRIP_CONTEXT', 'trip session storage requires a trip context');
     }
     return scope === 'trip' ? `trip:${opts.sessionTripId}:` : 'plugin:';
   };
   const sessionKey = (key: string, scope: 'plugin' | 'trip') => {
+    // Scope before key, in the host's order — otherwise the same bad call
+    // reports a different code here than it does in the app.
+    const prefix = sessionPrefix(scope);
     if (!key || key.length > PLUGIN_SESSION_MAX_KEY_LENGTH) {
-      throw new Error(`SESSION_INVALID_KEY: session key must be 1-${PLUGIN_SESSION_MAX_KEY_LENGTH} characters`);
+      throw sessionError('SESSION_INVALID_KEY', `session key must be 1-${PLUGIN_SESSION_MAX_KEY_LENGTH} characters`);
     }
-    return `${sessionPrefix(scope)}${key}`;
+    return `${prefix}${key}`;
   };
   const session: PluginSessionStorage = {
     async get(key, options) {
@@ -262,15 +273,15 @@ export function createMockHost(opts: MockHostOptions = {}): MockHost {
     async set(key, value, options) {
       const fullKey = sessionKey(key, options?.scope === 'trip' ? 'trip' : 'plugin');
       const serialized = JSON.stringify(value);
-      if (serialized === undefined) throw new Error('SESSION_INVALID_VALUE: session value must be JSON-serialisable');
+      if (serialized === undefined) throw sessionError('SESSION_INVALID_VALUE', 'session value must be JSON-serialisable');
       const valueBytes = Buffer.byteLength(serialized, 'utf8');
       if (valueBytes > PLUGIN_SESSION_MAX_VALUE_BYTES) {
-        throw new Error(`SESSION_VALUE_TOO_LARGE: session value exceeds ${PLUGIN_SESSION_MAX_VALUE_BYTES} bytes`);
+        throw sessionError('SESSION_VALUE_TOO_LARGE', `session value exceeds ${PLUGIN_SESSION_MAX_VALUE_BYTES} bytes`);
       }
       const prefix = sessionPrefix(options?.scope === 'trip' ? 'trip' : 'plugin');
       const scopedKeyCount = [...sessionValues.keys()].filter((storedKey) => storedKey.startsWith(prefix)).length;
       if (!sessionValues.has(fullKey) && scopedKeyCount >= PLUGIN_SESSION_MAX_KEYS) {
-        throw new Error(`SESSION_KEY_LIMIT: plugin session storage allows at most ${PLUGIN_SESSION_MAX_KEYS} keys`);
+        throw sessionError('SESSION_KEY_LIMIT', `plugin session storage allows at most ${PLUGIN_SESSION_MAX_KEYS} keys`);
       }
       sessionValues.set(fullKey, serialized);
     },