Discord: "Connect a Discord server" OAuth UI (server-26#225 S7)

- /discord/connected: Discord's OAuth redirect target. Stashes code/state
  in sessionStorage, strips them from the URL (replaceState), no-referrer
  (metadata + response header), sends a signed-out user to
  /login?next=/discord/connected and resumes, access_denied = "Nothing
  changed", result card "Linked X: N ready, M need a fix".
- middleware.ts: the callback path joins NO_SESSION_COOKIE_GATE (plan
  finding 2). Also needed for signed-in users: drb_session is
  SameSite=Strict, so it is not sent on the cross-site redirect back from
  discord.com.
- /login honours ?next= for an allowlist of one path (no open redirect).
- DiscordServersCard: Connect is the primary action with a radio-bot
  picker (automatic / the bot for a system / the org's own bots); the
  /drb link code moves to a collapsed secondary option and opens itself
  when /discord/oauth/start answers 404.
- RadioBotsPanel: write-only client-secret field per bot (PUT/DELETE
  /tokens/{id}/oauth), "Connect on/off", "N of 100 servers" with the
  pool cap (90) warning.
- lib/discordOAuth.ts: the S6 client, kept out of c2api.ts; only ever
  navigates to a discord.com /oauth2/authorize URL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/components/discord/RadioBotsPanel.tsx

@@ -3,6 +3,8 @@
 import { useState } from "react";
 import { c2api } from "@/lib/c2api";
 import {
+  DISCORD_UNVERIFIED_GUILD_LIMIT,
+  POOL_BOT_GUILD_CAP,
   type DiscordAdminOverview,
   type RadioBot,
   type RadioBotAddResult,
@@ -13,12 +15,13 @@ import {
   shortId,
 } from "@/lib/discord";
 import { Button } from "@/components/ui/Button";
+import { clearBotOAuthSecret, setBotOAuthSecret } from "@/lib/discordOAuth";
 import { DIM, Field, INPUT, Panel, Status, Table, TD } from "./ui";
 
 // Radio bots = the bot_tokens pool (routers/tokens.py). Used by the Discord
 // admin page's "Radio bots" tab and by /tokens. Every action here is a real
 // platform-admin route: POST /tokens, POST /tokens/{id}/refresh,
-// DELETE /tokens/{id}, POST /tokens/flush.
+// DELETE /tokens/{id}, POST /tokens/flush, PUT /tokens/{id}/oauth.
 
 function Checks({ t }: { t: RadioBot }) {
   if (t.valid === false) {
@@ -46,6 +49,101 @@ function Checks({ t }: { t: RadioBot }) {
   );
 }
 
+/** "N of 100 servers" — Discord caps an unverified bot at 100; Connect stops
+ *  picking a pool bot at the cap (owner ruling Q3), so a full one needs a sibling. */
+function ServerCount({ t, cap }: { t: RadioBot; cap: number }) {
+  if (t.guild_ids == null) return null;
+  const n = t.guild_ids.length;
+  const full = t.org_id == null && n >= cap;
+  return (
+    <div className={`text-xs mb-1 ${full || n >= DISCORD_UNVERIFIED_GUILD_LIMIT ? "text-sev-moderate" : "text-ink-muted"}`}>
+      {n} of {DISCORD_UNVERIFIED_GUILD_LIMIT} servers
+      {full && ` · full at ${cap}: Connect skips it, add another pool bot`}
+    </div>
+  );
+}
+
+/**
+ * The bot app's OAuth client secret, which turns on "Connect a Discord server"
+ * for it (server-26#225 S6/S7, owner ruling Q1: per-bot OAuth). Write-only:
+ * c2-core checks it with Discord and stores it server-side; this form never
+ * reads it back, and the field is cleared as soon as it is sent.
+ */
+function ConnectSetting({ t, onChanged }: { t: RadioBot; onChanged: () => Promise<void> | void }) {
+  const [open, setOpen] = useState(false);
+  const [secret, setSecret] = useState("");
+  const [saving, setSaving] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const on = !!t.oauth_enabled;
+
+  async function save(e: React.FormEvent) {
+    e.preventDefault();
+    const value = secret.trim();
+    setSecret("");
+    if (!value) return;
+    setSaving(true);
+    setError(null);
+    try {
+      await setBotOAuthSecret(t.token_id, value);
+      setOpen(false);
+      await onChanged();
+    } catch (err) {
+      setError(parseC2Error(err).message);
+    } finally {
+      setSaving(false);
+    }
+  }
+
+  async function turnOff() {
+    if (!confirm(`Turn off Connect for ${t.name}? Its stored client secret is deleted. Plain invite links keep working.`)) return;
+    setSaving(true);
+    setError(null);
+    try {
+      await clearBotOAuthSecret(t.token_id);
+      await onChanged();
+    } catch (err) {
+      setError(parseC2Error(err).message);
+    } finally {
+      setSaving(false);
+    }
+  }
+
+  return (
+    <div className="mt-2">
+      <div className="flex flex-wrap items-center gap-x-2 gap-y-1">
+        <Status health={on ? "ok" : "off"}>{on ? "Connect on" : "Connect off"}</Status>
+        <button type="button" className="text-xs text-accent hover:underline" onClick={() => { setOpen((v) => !v); setError(null); }}>
+          {open ? "Cancel" : on ? "Replace secret" : "Set client secret"}
+        </button>
+        {on && !open && (
+          <button type="button" disabled={saving} className="text-xs text-sev-major hover:underline disabled:opacity-40" onClick={turnOff}>
+            Turn off
+          </button>
+        )}
+      </div>
+      {open && (
+        <form onSubmit={save} className="mt-1.5 flex flex-wrap items-center gap-1.5 max-w-[18rem]">
+          <input
+            value={secret}
+            onChange={(e) => setSecret(e.target.value)}
+            type="password"
+            autoComplete="off"
+            spellCheck={false}
+            aria-label={`OAuth client secret for ${t.name}`}
+            placeholder="Client secret"
+            className={`${INPUT} font-mono flex-1 min-w-0`}
+          />
+          <Button type="submit" size="sm" disabled={saving || !secret.trim()}>{saving ? "Checking…" : "Save"}</Button>
+          <p className={`${DIM} w-full`}>
+            From the Discord Developer Portal → this bot&apos;s app → OAuth2. Checked with Discord, stored server-side, never shown again.
+          </p>
+        </form>
+      )}
+      {error && <div className="text-xs text-sev-major mt-1 max-w-[18rem]">{error}</div>}
+    </div>
+  );
+}
+
 function Membership({ t, overview }: { t: RadioBot; overview: DiscordAdminOverview | null }) {
   if (t.guild_ids == null) return <span className={DIM}>unknown — refresh</span>;
   const known = new Map((overview?.guilds ?? []).map((g) => [g.guild_id, g]));
@@ -54,34 +152,38 @@ function Membership({ t, overview }: { t: RadioBot; overview: DiscordAdminOvervi
   const missing = (overview?.guilds ?? []).filter(
     (g) => !members.includes(g.guild_id) && (t.org_id == null || g.acting_org_id === t.org_id),
   );
+  const cap = overview?.limits.pool_bot_guild_cap ?? POOL_BOT_GUILD_CAP;
   if (!members.length && !missing.length) return <span className={DIM}>no servers</span>;
   return (
-    <div className="flex flex-wrap gap-1 max-w-[22rem]">
-      {members.map((gid) => (
-        <span key={gid} className="text-[11px] rounded px-1.5 py-px bg-raised border border-line text-ink-2">
-          {known.has(gid) ? guildLabel(known.get(gid)!) : `server ${shortId(gid)}`}
-        </span>
-      ))}
-      {missing.map((g) => {
-        const href = inviteForGuild(t.invite_url, g.guild_id);
-        const label = `${guildLabel(g)} ✕`;
-        return href ? (
-          <a
-            key={g.guild_id}
-            href={href}
-            target="_blank"
-            rel="noopener noreferrer"
-            title={`Not in ${guildLabel(g)} — invite it`}
-            className="text-[11px] rounded px-1.5 py-px border border-dashed border-sev-moderate text-sev-moderate hover:underline"
-          >
-            {label}
-          </a>
-        ) : (
-          <span key={g.guild_id} className="text-[11px] rounded px-1.5 py-px border border-dashed border-sev-moderate text-sev-moderate">
-            {label}
+    <div className="max-w-[22rem]">
+      <ServerCount t={t} cap={cap} />
+      <div className="flex flex-wrap gap-1">
+        {members.map((gid) => (
+          <span key={gid} className="text-[11px] rounded px-1.5 py-px bg-raised border border-line text-ink-2">
+            {known.has(gid) ? guildLabel(known.get(gid)!) : `server ${shortId(gid)}`}
           </span>
-        );
-      })}
+        ))}
+        {missing.map((g) => {
+          const href = inviteForGuild(t.invite_url, g.guild_id);
+          const label = `${guildLabel(g)} ✕`;
+          return href ? (
+            <a
+              key={g.guild_id}
+              href={href}
+              target="_blank"
+              rel="noopener noreferrer"
+              title={`Not in ${guildLabel(g)} — invite it`}
+              className="text-[11px] rounded px-1.5 py-px border border-dashed border-sev-moderate text-sev-moderate hover:underline"
+            >
+              {label}
+            </a>
+          ) : (
+            <span key={g.guild_id} className="text-[11px] rounded px-1.5 py-px border border-dashed border-sev-moderate text-sev-moderate">
+              {label}
+            </span>
+          );
+        })}
+      </div>
     </div>
   );
 }
@@ -286,6 +388,7 @@ export function RadioBotsPanel({
                 </td>
                 <td className={TD}>
                   <Checks t={t} />
+                  <ConnectSetting t={t} onChanged={onChanged} />
                 </td>
                 <td className={`${TD} text-right whitespace-nowrap`}>
                   <div className="flex flex-col items-end gap-1">