fix: don't hide async exceptions in logs

Fixes #4646. Using the repro on #4646, this now produces the log:

```
11/Feb/2026:09:40:08 -0500: Warp server error: stack overflow
```

When:
```
$ curl localhost:3000/
curl: (52) Empty reply from server
```

CHANGELOG.md

@@ -15,6 +15,8 @@ All notable changes to this project will be documented in this file. From versio
 
 ### Fixed
 
+- Don't hide async exceptions in logs by @stevechavez in #4646
+
 ### Changed
 
 - Log error when `db-schemas` config contains schema `pg_catalog` or `information_schema` by @taimoorzaeem in #4359

src/PostgREST/App.hs

@@ -9,18 +9,24 @@ Some of its functionality includes:
 - Producing HTTP Headers according to RFCs.
 - Content Negotiation
 -}
-{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE RecordWildCards     #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE ViewPatterns        #-}
 module PostgREST.App
   ( postgrest
   , run
   ) where
 
 
+import GHC.IO.Exception (IOErrorType (..))
+import System.IO.Error  (ioeGetErrorType)
+
 import Control.Monad.Except     (liftEither)
 import Data.Either.Combinators  (mapLeft, whenLeft)
 import Data.Maybe               (fromJust)
 import Data.String              (IsString (..))
-import Network.Wai.Handler.Warp (defaultSettings, setHost, setPort,
+import Network.Wai.Handler.Warp (defaultSettings, setHost,
+                                 setOnException, setPort,
                                  setServerName)
 
 import qualified Data.Text.Encoding       as T
@@ -63,7 +69,6 @@ type Handler = ExceptT Error
 
 run :: AppState -> IO ()
 run appState = do
-  let observer = AppState.getObserver appState
   conf@AppConfig{..} <- AppState.getConfig appState
 
   AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
@@ -79,7 +84,24 @@ run appState = do
     address <- resolveSocketToAddress (AppState.getSocketREST appState)
     observer $ AppServerAddressObs address
 
-  Warp.runSettingsSocket (serverSettings conf) (AppState.getSocketREST appState) app
+  Warp.runSettingsSocket (serverSettings conf & setOnException onWarpException) (AppState.getSocketREST appState) app
+  where
+    observer = AppState.getObserver appState
+
+    onWarpException :: Maybe Wai.Request -> SomeException -> IO ()
+    onWarpException _ ex =
+      when (shouldDisplayException ex) $
+        observer $ WarpErrorObs $ show ex
+
+    -- Similar to wai defaultShouldDisplayException in
+    -- https://github.com/yesodweb/wai//blob/8c3882c60f6abe043889fc20c7efd3fa9747fa4a/warp/Network/Wai/Handler/Warp/Settings.hs#L251-L258
+    -- but without omitting AsyncException since it's important to log for ThreadKilled, StackOverflow and other cases.
+    -- We want to reuse this to avoid flooding the logs for some transient failure cases.
+    shouldDisplayException :: SomeException -> Bool
+    shouldDisplayException se
+        | Just (_ :: Warp.InvalidRequest) <- fromException se = False
+        | Just (ioeGetErrorType -> et) <- fromException se, et == ResourceVanished || et == InvalidArgument = False
+        | otherwise = True
 
 serverSettings :: AppConfig -> Warp.Settings
 serverSettings AppConfig{..} =

src/PostgREST/Observation.hs

@@ -65,6 +65,7 @@ data Observation
   | PoolRequestFullfilled
   | JwtCacheLookup Bool
   | JwtCacheEviction
+  | WarpErrorObs Text
 
 data ObsFatalError = ServerAuthError | ServerPgrstBug | ServerError42P05 | ServerError08P01
 
@@ -161,6 +162,8 @@ observationMessage = \case
     "Looked up a JWT in JWT cache"
   JwtCacheEviction ->
     "Evicted entry from JWT cache"
+  WarpErrorObs txt ->
+    "Warp server error: " <> txt
   where
     showMillis :: Double -> Text
     showMillis x = toS $ showFFloat (Just 1) x ""

test/io/test_big_schema.py

@@ -3,6 +3,7 @@
 import re
 
 import pytest
+import requests
 
 from postgrest import run
 
@@ -54,6 +55,25 @@ def test_openapi_in_big_schema(defaultenv):
         assert response.status_code == 200
 
 
+def test_stackoverflow_is_logged(defaultenv):
+    "Stack overflow errors should be logged with the Warp error message"
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_SCHEMAS": "apflora",
+        "PGRST_DB_ANON_ROLE": "postgrest_test_anonymous",
+    }
+
+    with run(env=env, wait_max_seconds=30, no_startup_stdout=False) as postgrest:
+        with pytest.raises(requests.exceptions.ConnectionError):
+            postgrest.session.get("/")
+
+        output = postgrest.read_stdout(nlines=10)
+        output.extend(postgrest.read_stdout(nlines=10))
+
+        assert any("Warp server error: stack overflow" in line for line in output)
+
+
 # See: https://github.com/PostgREST/postgrest/issues/3329
 def test_should_not_fail_with_stack_overflow(defaultenv):
     "requesting a non-existent relationship should not fail with stack overflow due to fuzzy search of candidates"