diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1a5b801..e466b07 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -82,6 +82,10 @@ One flat config at the repo root (`eslint.config.mjs`) covers every package —
 
 `@typescript-eslint/no-explicit-any` is a **warning** under a per-package budget, set in each package's lint script (`eslint src --max-warnings N`). CI fails if the count grows, so a new `any` needs either a real type or a deliberate decision to raise the number. Lower it when you remove one.
 
+Four **type-aware** rules run on `src` (not on tests): `no-floating-promises`, `no-misused-promises`, `await-thenable`, `require-await`. They need a TypeScript program and are slower, so the set is deliberately small — these catch things `tsc` does not, and the rest of `recommendedTypeChecked` mostly duplicates `strict` at the cost of a large style backlog.
+
+`no-floating-promises` is the one that earns its keep here. This SDK does a lot of deliberate fire-and-forget — violation reporting, honeytoken derivation, directory warmup — and an accidental one looks identical to an intentional one. Mark the deliberate ones with `void`, and say in a comment why the rejection is safe to drop.
+
 Format code:
 
 ```bash
diff --git a/eslint.config.mjs b/eslint.config.mjs
index 5f99a7e..9e7a653 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -70,6 +70,36 @@ export default tseslint.config(
     },
   },
 
+  // Type-aware rules, on the source only.
+  //
+  // These need a TypeScript program, which costs real time — so they are scoped
+  // to the rules that actually catch things `tsc` does not. The headline is
+  // no-floating-promises: this SDK does a lot of deliberate fire-and-forget
+  // (violation reporting, honeytoken derivation, directory warmup) where the
+  // intentional ones are marked `void` and an accidental one would look
+  // identical. A detection that silently never reported is the exact failure
+  // this catches.
+  //
+  // The broad `recommendedTypeChecked` preset is deliberately NOT used: most of
+  // it duplicates what `strict` already enforces, at the cost of a much slower
+  // lint and a large backlog of findings that are style rather than defects.
+  {
+    files: ['**/src/**/*.ts'],
+    ignores: ['**/*.test.ts', '**/*.spec.ts'],
+    languageOptions: {
+      parserOptions: {
+        projectService: true,
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+    rules: {
+      '@typescript-eslint/no-floating-promises': 'error',
+      '@typescript-eslint/no-misused-promises': 'error',
+      '@typescript-eslint/await-thenable': 'error',
+      '@typescript-eslint/require-await': 'error',
+    },
+  },
+
   {
     files: ['**/*.test.ts', '**/*.spec.ts'],
     languageOptions: {
diff --git a/packages/client/src/collectors/environment.ts b/packages/client/src/collectors/environment.ts
index 86b4d53..1960ca7 100644
--- a/packages/client/src/collectors/environment.ts
+++ b/packages/client/src/collectors/environment.ts
@@ -265,7 +265,10 @@ export class EnvironmentalCollector {
         state: audioCtx.state,
         baseLatency: audioCtx.baseLatency
       };
-      audioCtx.close();
+      // Not awaited (the info is already gathered) but the rejection has to go
+      // somewhere: `void` alone would leave an unhandled rejection logged in the
+      // user's console, and the try/catch above does not cover it.
+      audioCtx.close().catch(() => {});
       return info;
     } catch {
       return { supported: false, error: true };
diff --git a/packages/client/src/invisible.ts b/packages/client/src/invisible.ts
index c62611a..bdbb7b0 100644
--- a/packages/client/src/invisible.ts
+++ b/packages/client/src/invisible.ts
@@ -108,7 +108,12 @@ export class InvisibleSession {
   }
 
   private _attachToForms(): void {
-    document.addEventListener('submit', async (e) => {
+    // Deliberately a SYNCHRONOUS listener. `e.preventDefault()` below only
+    // works because nothing has awaited yet — once the handler yields, the
+    // browser has already submitted the form and cancelling is a no-op. An
+    // async listener made that a one-line change away from silently breaking,
+    // with no test that would notice.
+    document.addEventListener('submit', (e) => {
       const form = e.target as HTMLFormElement;
       if (form.dataset.webdecoyIgnore) return;
 
@@ -122,28 +127,35 @@ export class InvisibleSession {
 
       if (!this.lastScore || Date.now() - this.lastScore.timestamp > 60000) {
         e.preventDefault();
-
-        try {
-          const result = await this.execute(form.dataset.webdecoyAction || 'form_submit');
-          tokenField.value = result.token || '';
-
-          if (result.success) {
-            form.submit();
-          } else {
-            document.dispatchEvent(
-              new CustomEvent('webdecoy:blocked', { detail: { score: result.score, form } }),
-            );
-          }
-        } catch (error) {
-          console.error('WebDecoy captcha error:', error);
-          form.submit(); // Fail open
-        }
+        void this._scoreThenSubmit(form, tokenField);
       } else {
         tokenField.value = this.lastScore.token || '';
       }
     });
   }
 
+  /** Score the session, then resubmit the form the listener cancelled. */
+  private async _scoreThenSubmit(
+    form: HTMLFormElement,
+    tokenField: HTMLInputElement,
+  ): Promise<void> {
+    try {
+      const result = await this.execute(form.dataset.webdecoyAction || 'form_submit');
+      tokenField.value = result.token || '';
+
+      if (result.success) {
+        form.submit();
+      } else {
+        document.dispatchEvent(
+          new CustomEvent('webdecoy:blocked', { detail: { score: result.score, form } }),
+        );
+      }
+    } catch (error) {
+      console.error('WebDecoy captcha error:', error);
+      form.submit(); // Fail open
+    }
+  }
+
   async execute(action = ''): Promise<VerifyResponse> {
     const elapsed = Date.now() - this.startTime;
     if (elapsed < this.options.minCollectionTime) {
diff --git a/packages/express/src/captcha.ts b/packages/express/src/captcha.ts
index 84871bd..c0be842 100644
--- a/packages/express/src/captcha.ts
+++ b/packages/express/src/captcha.ts
@@ -62,7 +62,15 @@ function normalizeQuery(query: Request['query']): Record<string, string | undefi
 export function webdecoyCaptcha(options?: ExpressCaptchaOptions): RequestHandler {
   const endpoints = createCaptchaEndpoints(options);
 
-  return async (req: Request, res: Response, next: NextFunction): Promise<void> => {
+  return (req: Request, res: Response, next: NextFunction): void => {
+    // Express 4 does not catch a rejected promise from a handler, so an async
+    // handler that throws leaves the request hanging until the client times out
+    // and logs an unhandled rejection instead of a 500. Kept synchronous, with
+    // the rejection routed to the error middleware explicitly.
+    void handle(req, res, next).catch(next);
+  };
+
+  async function handle(req: Request, res: Response, next: NextFunction): Promise<void> {
     const result = await endpoints.handle({
       method: req.method,
       pathname: req.path,
@@ -80,5 +88,5 @@ export function webdecoyCaptcha(options?: ExpressCaptchaOptions): RequestHandler
     res.status(result.status);
     for (const [k, v] of Object.entries(result.headers)) res.setHeader(k, v);
     res.json(result.body);
-  };
+  }
 }
diff --git a/packages/fastify/src/captcha.ts b/packages/fastify/src/captcha.ts
index f0ad83b..df7c4fd 100644
--- a/packages/fastify/src/captcha.ts
+++ b/packages/fastify/src/captcha.ts
@@ -18,6 +18,9 @@ import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
 import fp from 'fastify-plugin';
 import { createCaptchaEndpoints, type CaptchaEndpointsOptions } from '@webdecoy/node';
 
+// fastify-plugin's async contract: the signature is what marks this a plugin,
+// not the body, so there is nothing here to await.
+// eslint-disable-next-line @typescript-eslint/require-await
 async function plugin(fastify: FastifyInstance, options: CaptchaEndpointsOptions): Promise<void> {
   const endpoints = createCaptchaEndpoints(options);
 
diff --git a/packages/webdecoy/src/violation-reporter.ts b/packages/webdecoy/src/violation-reporter.ts
index 0076d5b..20771c4 100644
--- a/packages/webdecoy/src/violation-reporter.ts
+++ b/packages/webdecoy/src/violation-reporter.ts
@@ -29,7 +29,10 @@ export class ViolationReporter {
     this.debug = config.debug ?? false;
 
     const flushInterval = config.flushInterval ?? 5000;
-    this.flushTimer = setInterval(() => this.flush(), flushInterval);
+    // flush() catches everything internally and never rejects, so `void` is the
+    // whole handling. Said out loud because a timer whose callback rejects
+    // keeps firing and every tick adds another unhandled rejection.
+    this.flushTimer = setInterval(() => void this.flush(), flushInterval);
     if (this.flushTimer.unref) {
       this.flushTimer.unref();
     }