diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1706d6c..e2fb684 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -35,7 +35,7 @@ jobs:
           key: ${{ runner.os }}-stack-${{ hashFiles('stack.yaml.lock') }}-${{ hashFiles('trypurescript.cabal') }}
 
       - name: Build server code
-        run: stack --no-terminal -j1 build
+        run: stack --no-terminal build
 
       - name: Build server assets
         if: github.event_name == 'release'
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2dcb65..d2a4149 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ New features:
 Bugfixes:
 
 Other improvements:
+- Bump the Stackage resolver from `lts-20.9` to `lts-20.26` (GHC 9.2.5 → 9.2.8), the newest snapshot compatible with `purescript-0.15.15` (#322 by @thomashoneyman)
+- Modernize the server build: `cabal-version: 2.4`, build with `-Wall -Werror` (with attendant cleanup in `server/Main.hs`), remove unused dependencies and the redundant `Setup.hs` (#322 by @thomashoneyman)
+- Speed up CI server builds by removing the `-j1` limit; runners have had 4 vCPUs and 16GB of RAM for years (#322 by @thomashoneyman)
+- Serve the site and the compiled `/output` modules with `Cache-Control: no-cache` so browsers revalidate via ETag instead of heuristically caching a stale client for months after a deploy (#322 by @thomashoneyman)
 
 ## [v2026-07-05.1](https://github.com/purescript/trypurescript/releases/tag/v2026-07-05.1)
 
diff --git a/Setup.hs b/Setup.hs
deleted file mode 100644
index 9a994af..0000000
--- a/Setup.hs
+++ /dev/null
@@ -1,2 +0,0 @@
-import Distribution.Simple
-main = defaultMain
diff --git a/deploy/nginx.conf b/deploy/nginx.conf
index 606f317..778fc36 100644
--- a/deploy/nginx.conf
+++ b/deploy/nginx.conf
@@ -44,6 +44,10 @@ server {
 
     location / {
       root /var/www/trypurescript/public;
+      # Always revalidate (cheap ETag 304s): the HTML references the bundle by
+      # a fixed name, so without this browsers heuristically cache the site
+      # and can serve a stale client for months after a deploy.
+      add_header Cache-Control "no-cache";
     }
 
 }
@@ -86,6 +90,10 @@ server {
     # match to ensure that we only serve JS files.
     location ~ ^/output/(.+\.js)$ {
       add_header Access-Control-Allow-Origin *;
+      # Module URLs are generated by the compiler and change content when the
+      # package set or compiler changes; revalidate so browsers never mix
+      # modules from different deploys.
+      add_header Cache-Control "no-cache";
       alias /var/www/trypurescript/staging/.psci_modules/$1;
     }
 }
diff --git a/server/Main.hs b/server/Main.hs
index fdbbb74..a87da6b 100644
--- a/server/Main.hs
+++ b/server/Main.hs
@@ -6,18 +6,15 @@
 
 module Main (main) where
 
-import           Control.Monad (unless, foldM)
-import           Control.Monad.Error.Class (throwError)
+import           Control.Monad (foldM)
 import           Control.Monad.IO.Class (liftIO)
-import           Control.Monad.Logger (runLogger')
 import qualified Control.Monad.State as State
 import           Control.Monad.Trans (lift)
 import           Control.Monad.Trans.Except (ExceptT(..), runExceptT)
-import           Control.Monad.Trans.Reader (runReaderT)
 import           Control.Monad.Writer.Strict (runWriterT)
 import qualified Data.Aeson as A
 import           Data.Aeson ((.=))
-import           Data.Bifunctor (first, second, bimap)
+import           Data.Bifunctor (second, bimap)
 import qualified Data.ByteString.Lazy as BL
 import           Data.Default (def)
 import           Data.Function (on)
@@ -25,7 +22,6 @@ import qualified Data.IORef as IORef
 import           Data.List (nubBy)
 import qualified Data.List.NonEmpty as NE
 import qualified Data.Map as M
-import           Data.Set (Set)
 import qualified Data.Set as Set
 import           Data.Text (Text)
 import qualified Data.Text as T
@@ -50,6 +46,7 @@ import           System.Environment (getArgs)
 import           System.Exit (exitFailure)
 import           System.FilePath.Glob (glob)
 import qualified System.IO as IO
+import           Text.Read (readMaybe)
 import           Web.Scotty
 import qualified Web.Scotty as Scotty
 
@@ -204,9 +201,9 @@ lookupAllConstructors env = P.everywhereOnTypesM $ \case
     other -> pure other
   where
     lookupConstructor :: P.Environment -> P.ProperName 'P.TypeName -> [P.Qualified (P.ProperName 'P.TypeName)]
-    lookupConstructor env nm =
+    lookupConstructor env' nm =
       [ q
-      | (q@(P.Qualified (N.ByModuleName _) thisNm), _) <- M.toList (P.types env)
+      | (q@(P.Qualified (N.ByModuleName _) thisNm), _) <- M.toList (P.types env')
       , thisNm == nm
       ]
 
@@ -216,15 +213,15 @@ lookupAllConstructors env = P.everywhereOnTypesM $ \case
 replaceTypeVariablesAndDesugar :: (Text -> Int -> P.SourceType) -> P.SourceType -> P.SourceType
 replaceTypeVariablesAndDesugar f ty = State.evalState (P.everywhereOnTypesM go ty) (0, M.empty) where
   go = \case
-    P.ParensInType _ ty -> pure ty
+    P.ParensInType _ inner -> pure inner
     P.TypeVar _ s -> do
-      (next, m) <- State.get
+      (n, m) <- State.get
       case M.lookup s m of
         Nothing -> do
-          let ty = f s next
-          State.put (next + 1, M.insert s ty m)
-          pure ty
-        Just ty -> pure ty
+          let unknown = f s n
+          State.put (n + 1, M.insert s unknown m)
+          pure unknown
+        Just unknown -> pure unknown
     other -> pure other
 
 tryParseType :: Text -> Maybe P.SourceType
@@ -242,16 +239,24 @@ main :: IO ()
 main = do
   -- Stop mangled "Compiling ModuleName" text
   IO.hSetBuffering IO.stderr IO.LineBuffering
-  (portString : inputGlobs) <- getArgs
-  let port = read portString
-  inputFiles <- concat <$> traverse glob inputGlobs
-  e <- runExceptT $ do
-    modules <- ExceptT $ I.loadAllModules inputFiles
-    (exts, env) <- ExceptT . I.runMake . I.make $ map (second CST.pureResult) modules
-    namesEnv <- fmap fst . runWriterT $ foldM P.externsEnv P.primEnv exts
-    let
-      allModuleNames = fmap (P.getModuleName . snd) modules
-    pure (allModuleNames, exts, namesEnv, env)
-  case e of
-    Left err -> print err >> exitFailure
-    Right (allModuleNames, exts, namesEnv, env) -> server allModuleNames exts namesEnv env port
+  args <- getArgs
+  case args of
+    portString : inputGlobs
+      | Just port <- readMaybe portString -> run port inputGlobs
+    _ -> do
+      IO.hPutStrLn IO.stderr "Usage: trypurescript PORT INPUT_GLOB..."
+      exitFailure
+  where
+  run :: Int -> [String] -> IO ()
+  run port inputGlobs = do
+    inputFiles <- concat <$> traverse glob inputGlobs
+    e <- runExceptT $ do
+      modules <- ExceptT $ I.loadAllModules inputFiles
+      (exts, env) <- ExceptT . I.runMake . I.make $ map (second CST.pureResult) modules
+      namesEnv <- fmap fst . runWriterT $ foldM P.externsEnv P.primEnv exts
+      let
+        allModuleNames = fmap (P.getModuleName . snd) modules
+      pure (allModuleNames, exts, namesEnv, env)
+    case e of
+      Left err -> print err >> exitFailure
+      Right (allModuleNames, exts, namesEnv, env) -> server allModuleNames exts namesEnv env port
diff --git a/stack.yaml b/stack.yaml
index 207ddd5..a8de960 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,4 @@
-resolver: lts-20.9
+resolver: lts-20.26
 packages:
   - "."
 
@@ -8,8 +8,11 @@ extra-deps:
   - process-1.6.13.1
   # The Cabal library is not in Stackage
   - Cabal-3.6.3.0
-  # Protolude is not yet in resolver snapshot
-  - protolude-0.3.1
+  # Protolude is not in the resolver snapshot; 0.3.3 (not 0.3.1) is needed
+  # for compatibility with the bytestring version in lts-20.26
+  - protolude-0.3.3
+  # purescript pins happy ==1.20.0, but lts-20.26 ships happy-1.20.1.1
+  - happy-1.20.0
 
 flags:
   these:
diff --git a/stack.yaml.lock b/stack.yaml.lock
index 795f79c..1e49384 100644
--- a/stack.yaml.lock
+++ b/stack.yaml.lock
@@ -1,7 +1,7 @@
 # This file was autogenerated by Stack.
 # You should not edit this file by hand.
 # For more information, please see the documentation at:
-#   https://docs.haskellstack.org/en/stable/lock_files
+#   https://docs.haskellstack.org/en/stable/topics/lock_files
 
 packages:
 - completed:
@@ -33,15 +33,22 @@ packages:
   original:
     hackage: Cabal-3.6.3.0
 - completed:
-    hackage: protolude-0.3.1@sha256:1cc9e5a5c26c33a43c52b554443dd9779fef13974eaa0beec7ca6d2551b400da,2647
+    hackage: protolude-0.3.3@sha256:0106615f6fe08de16fe512852c728797db17374d36b4a4ec8187563e924b2439,2261
     pantry-tree:
-      sha256: 6452a6ca8d395f7d810139779bb0fd16fc1dbb00f1862630bc08ef5a100430f9
-      size: 1645
+      sha256: 174c107f3c3af1dc23330ff4431445830aac4b4fdba326e3e654eb491d6e9ca6
+      size: 1594
   original:
-    hackage: protolude-0.3.1
+    hackage: protolude-0.3.3
+- completed:
+    hackage: happy-1.20.0@sha256:5d47dc221a9fe964e36aaaa2e1ab7e8f085a225fd6528d6eff310b92360bbe99,5732
+    pantry-tree:
+      sha256: ff2e7df7cfe8746eedc6f69c225fa8c899c26d28f1c4964eeb00a5d757d30351
+      size: 8749
+  original:
+    hackage: happy-1.20.0
 snapshots:
 - completed:
-    sha256: c11fcbeb1aa12761044755b1109d16952ede2cb6147ebde777dd5cb38f784501
-    size: 649333
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/20/9.yaml
-  original: lts-20.9
+    sha256: 5a59b2a405b3aba3c00188453be172b85893cab8ebc352b1ef58b0eae5d248a2
+    size: 650475
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/20/26.yaml
+  original: lts-20.26
diff --git a/trypurescript.cabal b/trypurescript.cabal
index 0e54ac3..c19ee3c 100644
--- a/trypurescript.cabal
+++ b/trypurescript.cabal
@@ -1,8 +1,8 @@
+cabal-version: 2.4
 name: trypurescript
 version: 1.0.0
-cabal-version: >=1.8
 build-type: Simple
-license: BSD3
+license: BSD-3-Clause
 license-file: LICENSE
 copyright: (c) Phil Freeman 2013
 maintainer: paf31@cantab.net
@@ -10,32 +10,27 @@ synopsis: Interactive PureScript in the Browser
 description: A simple web app for trying out the PureScript compiler
 category: Web
 author: Phil Freeman
-data-dir: ""
 
 executable trypurescript
     -- Since no one depends on this project as a library,
-    -- packages below are `-any` because their versions are determined
-    -- by the `stack.yml` file. Versions correspond to the ones
-    -- specified in the resolver (i.e. the package set)
+    -- packages below are unbounded because their versions are
+    -- determined by the `stack.yaml` file. Versions correspond to the
+    -- ones specified in the resolver (i.e. the package set)
     -- unless it is a versioned library added via `extra-deps` field.
-    build-depends: base -any,
-                   aeson -any,
-                   bytestring -any,
-                   data-default -any,
-                   directory -any,
-                   filepath -any,
-                   Glob -any,
-                   scotty -any,
+    build-depends: base,
+                   aeson,
+                   bytestring,
+                   containers,
+                   data-default,
+                   Glob,
+                   mtl,
                    purescript,
-                   containers -any,
-                   http-types -any,
-                   transformers -any,
-                   mtl -any,
-                   text -any,
-                   time -any,
-                   warp -any
+                   scotty,
+                   text,
+                   time,
+                   transformers,
+                   warp
     hs-source-dirs: server
     main-is: Main.hs
-    buildable: True
-    other-modules: Main
-    ghc-options: -Werror -O2 -threaded -rtsopts
+    default-language: Haskell2010
+    ghc-options: -Wall -Werror -O2 -threaded -rtsopts