a manifest cannot ask for a particular port

A preference sounds helpful and fails silently. When the wished-for number is
taken the plugin is handed a different one, the install succeeds, and whatever
was configured against the old number goes on pointing at nothing - with nobody
told. This afternoon that nearly happened: 3011 was only free because fofos-dev
had been stopped twenty minutes earlier, and had it still been running the site
would have been given a random port behind an nginx host still aimed at 3011.

So the number is always drawn fresh and always kept. Always drawn means it is
never something you can assume; always kept means the proxy host is configured
against it exactly once. The failure mode that remains - having to go and read
the number - is one that announces itself, which the other one did not.

isFree went with it; it existed only to test a wish.

src/databases/officer_db/src/plugins/queries.ts

@@ -77,17 +77,6 @@ export async function getPluginPorts(appName: string): Promise<Record<string, nu
  * remembered port must say so loudly rather than quietly choosing another, because the number is written
  * down in configuration this database cannot see.
  */
-/** Can we bind it right now? The only honest test, and true only for this instant. */
-async function isFree(port: number): Promise<boolean> {
-  try {
-    const probe = Bun.serve({ port, hostname: '127.0.0.1', fetch: () => new Response('') });
-    probe.stop(true);
-    return true;
-  } catch {
-    return false;
-  }
-}
-
 async function freePort(taken: Set<number>): Promise<number> {
   for (let attempt = 0; attempt < 20; attempt++) {
     const probe = Bun.serve({ port: 0, hostname: '127.0.0.1', fetch: () => new Response('') });
@@ -105,7 +94,7 @@ async function freePort(taken: Set<number>): Promise<number> {
  * point — see the note on `pluginPorts`. Re-installing, upgrading and restarting all return what was
  * given the first time.
  */
-export async function allocatePluginPort(appName: string, name: string, preferred?: number): Promise<number> {
+export async function allocatePluginPort(appName: string, name: string): Promise<number> {
   const [existing] = await db
     .select()
     .from(pluginPorts)
@@ -120,16 +109,7 @@ export async function allocatePluginPort(appName: string, name: string, preferre
   */
   for (let attempt = 0; attempt < 5; attempt++) {
     const taken = new Set((await db.select().from(pluginPorts)).map((r) => r.port));
-    /*
-      The wish first, and only on the first attempt.
-
-      A preferred port that is already spoken for, or that something else on this machine is listening
-      on, is not an error — it is a plugin arriving somewhere its ideal address is taken, which is
-      ordinary. It falls back to any free one rather than failing, because an install that refuses over
-      a preference would make `preferred` a claim.
-    */
-    const wish = attempt === 0 && preferred && !taken.has(preferred) && (await isFree(preferred)) ? preferred : null;
-    const port = wish ?? (await freePort(taken));
+    const port = await freePort(taken);
     try {
       const [row] = await db.insert(pluginPorts).values({ appName, name, port }).returning();
       return row!.port;