refactor: return Either from loadConfig, add Config tests

test/Roux/ConfigSpec.hs

@@ -0,0 +1,55 @@
+module Roux.ConfigSpec (spec) where
+
+import System.FilePath ((</>))
+import System.IO.Temp (withSystemTempDirectory)
+import Test.Hspec (Spec, describe, expectationFailure, it, shouldBe)
+
+import Roux.Config
+
+spec :: Spec
+spec = describe "loadConfig" $ do
+    it "returns Nothing config when file doesn't exist" $ do
+        result <- loadConfig "/tmp/nonexistent-config-file-for-roux-test.yaml"
+        result `shouldBe` Right (RouxConfig Nothing)
+
+    it "parses a minimal config with api_key" $ do
+        withSystemTempDirectory "roux-test" $ \dir -> do
+            let path = dir </> "config.yaml"
+            writeFile path "anthropic:\n  api_key: sk-test-123\n"
+            result <- loadConfig path
+            case result of
+                Right (RouxConfig (Just ac)) -> do
+                    acApiKey ac `shouldBe` "sk-test-123"
+                    acBaseUrl ac `shouldBe` Nothing
+                    acModel ac `shouldBe` Nothing
+                _ -> expectationFailure "Expected Right config"
+
+    it "parses a full config with all fields" $ do
+        withSystemTempDirectory "roux-test" $ \dir -> do
+            let path = dir </> "config.yaml"
+            writeFile path "anthropic:\n  api_key: sk-test-456\n  base_url: http://localhost:11434/v1\n  model: local-model\n"
+            result <- loadConfig path
+            case result of
+                Right (RouxConfig (Just ac)) -> do
+                    acApiKey ac `shouldBe` "sk-test-456"
+                    acBaseUrl ac `shouldBe` Just "http://localhost:11434/v1"
+                    acModel ac `shouldBe` Just "local-model"
+                _ -> expectationFailure "Expected Right config"
+
+    it "returns Left for malformed YAML" $ do
+        withSystemTempDirectory "roux-test" $ \dir -> do
+            let path = dir </> "config.yaml"
+            writeFile path "{{{{ invalid yaml }}}}\n"
+            result <- loadConfig path
+            case result of
+                Left _ -> pure () -- expected
+                Right _ -> expectationFailure "Expected Left error"
+
+    it "returns Left when api_key is missing" $ do
+        withSystemTempDirectory "roux-test" $ \dir -> do
+            let path = dir </> "config.yaml"
+            writeFile path "anthropic:\n  model: foo\n"
+            result <- loadConfig path
+            case result of
+                Left _ -> pure () -- expected
+                Right _ -> expectationFailure "Expected Left error"