fix(discord): show the real reason a thread fails, keep the gateway across a save, refund the rate limit for a refused file

src/discord-bridge.ts

@@ -286,6 +286,9 @@ function coerce(raw: unknown): DiscordConfig {
   };
 }
 
+/** A failure with a reason worth showing as it is (unlike a network error, whose text is not). */
+class BridgeProblem extends Error {}
+
 export async function readDiscordConfig(configDir: string): Promise<DiscordConfig> {
   try {
     return coerce(JSON.parse(await fs.readFile(discordConfigPath(configDir), 'utf-8')));
@@ -674,6 +677,8 @@ export class DiscordBridge {
   private threads: Record<string, string> = {};
   private loaded = false;
   private gateway: DiscordGateway | null = null;
+  /** The token the running gateway was started with ('' when none). */
+  private gatewayToken = '';
   private lastSent = new Map<string, number>();
   private lastReply = new Map<string, number>();
   /** The last name seen per session, so only a real rename touches the thread. */
@@ -762,10 +767,14 @@ export class DiscordBridge {
       this.threadsParent = parent;
       await this.persistThreads();
     }
+    activeStartupHint = this.cfg.enabled && this.cfg.token && this.cfg.startupHint ? DISCORD_STARTUP_HINT : undefined;
+    // A save that changed neither the switch nor the token keeps the gateway session, so it can resume.
+    const want = this.cfg.enabled && this.cfg.token && !this.held ? this.cfg.token : '';
+    if (this.gateway && want && want === this.gatewayToken) return;
     this.gateway?.stop();
     this.gateway = null;
-    activeStartupHint = this.cfg.enabled && this.cfg.token && this.cfg.startupHint ? DISCORD_STARTUP_HINT : undefined;
-    if (this.cfg.enabled && this.cfg.token && !this.held) {
+    this.gatewayToken = want;
+    if (want) {
       this.gateway = new DiscordGateway(
         () => this.cfg.token,
         (m) => void this.onGatewayMessage(m).catch(() => undefined),
@@ -779,6 +788,7 @@ export class DiscordBridge {
   stop(): void {
     this.gateway?.stop();
     this.gateway = null;
+    this.gatewayToken = '';
     activeStartupHint = undefined;
     this.lastSent.clear();
     this.lastReply.clear();
@@ -799,9 +809,11 @@ export class DiscordBridge {
             ? 'Channel not found (check the IDs)'
             : status
               ? `HTTP ${status}`
-              : (err as { name?: string })?.name === 'TimeoutError'
-                ? 'Timed out'
-                : 'Network error';
+              : err instanceof BridgeProblem
+                ? err.message
+                : (err as { name?: string })?.name === 'TimeoutError'
+                  ? 'Timed out'
+                  : 'Network error';
     return { ok: false, status, error, at: this.now() };
   }
 
@@ -823,12 +835,12 @@ export class DiscordBridge {
     const p = (mine.p = (async () => {
       try {
         const t = await this.api.createThread(parent, threadNameFor(name, sessionId));
-        if (!t?.id) return this.fail(new Error('Discord did not return a thread'));
+        if (!t?.id) return this.fail(new BridgeProblem('Discord did not return a thread'));
         // A save moved the bridge to another channel meanwhile: this thread belongs to the old one.
-        if (parent !== this.cfg.parentChannelId) return this.fail(new Error('The parent channel changed'));
+        if (parent !== this.cfg.parentChannelId) return this.fail(new BridgeProblem('The parent channel changed'));
         if (this.closedWhilePending.has(sessionId)) {
           await this.closeThread(t.id);
-          return this.fail(new Error('The tab was closed'));
+          return this.fail(new BridgeProblem('The tab was closed'));
         }
         this.threads[sessionId] = t.id;
         await this.persistThreads();

src/web/routes/discord-routes.ts

@@ -77,6 +77,12 @@ function consumeNotifyToken(sessionId: string, now: number = Date.now()): boolea
   return true;
 }
 
+/** Give back a token spent on a request that was refused before anything was posted. */
+function refundNotifyToken(sessionId: string): void {
+  const b = notifyBuckets.get(sessionId);
+  if (b) b.tokens = Math.min(NOTIFY_PER_MINUTE, b.tokens + 1);
+}
+
 /** Test hook: forget every bucket between runs. */
 export function _resetNotifyBuckets(): void {
   notifyBuckets.clear();
@@ -197,6 +203,7 @@ export function registerDiscordRoutes(app: FastifyInstance, deps: DiscordRouteDe
     if (file !== undefined) {
       const problem = await fileProblem(session.workingDir, !!session.remote, file);
       if (typeof problem === 'string') {
+        refundNotifyToken(session.id);
         reply.code(400);
         return createErrorResponse(ApiErrorCode.INVALID_INPUT, problem);
       }

test/discord-bridge.test.ts

@@ -582,7 +582,20 @@ describe('DiscordBridge', () => {
   it('names a thread that Discord answers without an id, instead of reporting an old result', async () => {
     const b = bridge({}, async (url) => (String(url).endsWith('/threads') ? jsonRes({}) : jsonRes({ id: 'msg' })));
     const r = await b.notify(MSG);
-    expect(r).toMatchObject({ ok: false });
+    expect(r).toMatchObject({ ok: false, error: 'Discord did not return a thread' });
+    b.stop();
+  });
+
+  it('keeps the gateway session across a save that changes neither the switch nor the token', async () => {
+    const b = bridge();
+    await b.reload();
+    const first = (b as unknown as { gateway: unknown }).gateway;
+    expect(first).not.toBeNull();
+    await b.reload();
+    expect((b as unknown as { gateway: unknown }).gateway).toBe(first);
+    await writeDiscordConfig(dir, { ...CFG, token: 'another-token' });
+    await b.reload();
+    expect((b as unknown as { gateway: unknown }).gateway).not.toBe(first);
     b.stop();
   });
 
@@ -692,8 +705,9 @@ describe('DiscordBridge', () => {
       await vi.waitFor(() => expect(posts.some((p) => p.path.endsWith('/threads'))).toBe(true));
       await b.sessionDeleted('s1');
       release();
-      await first;
+      const out = await first;
       expect(posts).toContainEqual({ path: `/channels/${THREAD}`, method: 'PATCH', body: { archived: true } });
+      expect(out).toMatchObject({ ok: false, error: 'The tab was closed' });
       expect(await readThreadMap(dir)).toEqual({});
       b.stop();
     });

test/routes/discord-routes.test.ts

@@ -216,6 +216,17 @@ describe('POST /api/sessions/:id/discord-notify', () => {
     bridge.stop();
   });
 
+  it('does not spend rate-limit tokens on a request refused for its file', async () => {
+    const { app, bridge } = await harness();
+    await app.inject({ method: 'PUT', url: '/api/discord', payload: FULL });
+    for (let i = 0; i < 8; i++) {
+      const bad = await app.inject({ method: 'POST', url, payload: { message: 'x', file: 'no-such-file.txt' } });
+      expect(bad.statusCode).toBe(400);
+    }
+    expect((await app.inject({ method: 'POST', url, payload: { message: 'still allowed' } })).statusCode).toBe(200);
+    bridge.stop();
+  });
+
   it('rejects an empty or oversized message', async () => {
     const { app } = await harness();
     const url = `/api/sessions/test-session-1/discord-notify`;