Enable errorlint linter and fix 18 issues

Fix three categories of error handling issues:
- Use errors.Is instead of == for error comparison (6 fixes)
  io.EOF, sql.ErrNoRows, http.ErrServerClosed, context.Canceled
- Use errors.As instead of type assertion on errors (4 fixes)
  *exec.ExitError, *environment.RequiredEnvError, cli.RuntimeError
- Use %w instead of %v in fmt.Errorf for proper wrapping (8 fixes)
  api.go, eval.go, store.go, sqliteutil.go

Assisted-By: cagent

Author: dgageot

.golangci.yml

@@ -14,6 +14,7 @@ linters:
     - durationcheck
     - errcheck
     - errname
+    - errorlint
     - exptostd
     - fatcontext
     - forbidigo

cmd/root/run.go

@@ -2,6 +2,7 @@ package root
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -422,7 +423,8 @@ func (f *runExecFlags) handleExecMode(ctx context.Context, out *cli.Printer, rt
 		OutputJSON:     f.outputJSON,
 		AutoApprove:    f.autoApprove,
 	}, rt, sess, execArgs)
-	if cliErr, ok := err.(cli.RuntimeError); ok {
+	var cliErr cli.RuntimeError
+	if errors.As(err, &cliErr) {
 		return RuntimeError{Err: cliErr.Err}
 	}
 	return err

pkg/config/config_test.go

@@ -271,7 +271,9 @@ func TestCheckRequiredEnvVars(t *testing.T) {
 				require.NoError(t, err)
 			} else {
 				require.Error(t, err)
-				assert.Equal(t, test.expectedMissing, err.(*environment.RequiredEnvError).Missing)
+				var reqErr *environment.RequiredEnvError
+				require.ErrorAs(t, err, &reqErr)
+				assert.Equal(t, test.expectedMissing, reqErr.Missing)
 			}
 		})
 	}

pkg/evaluation/eval.go

@@ -272,7 +272,7 @@ func (r *Runner) preBuildImages(ctx context.Context, out io.Writer, evals []Inpu
 	}
 
 	if len(errs) > 0 {
-		return fmt.Errorf("failed to build %d image(s): %v", len(errs), errs[0])
+		return fmt.Errorf("failed to build %d image(s): %w", len(errs), errs[0])
 	}
 
 	return nil

pkg/fake/proxy.go

@@ -6,6 +6,7 @@ import (
 	"bufio"
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -428,7 +429,7 @@ func StreamCopy(c echo.Context, resp *http.Response) error {
 			}
 			if result.err != nil {
 				// io.EOF or context canceled means normal completion
-				if result.err == io.EOF || ctx.Err() != nil {
+				if errors.Is(result.err, io.EOF) || ctx.Err() != nil {
 					return nil //nolint:nilerr // EOF and context cancellation are normal stream termination
 				}
 				slog.ErrorContext(ctx, "stream read error", "error", result.err)

pkg/fsx/fs.go

@@ -2,6 +2,7 @@ package fsx
 
 import (
 	"context"
+	"errors"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -209,7 +210,7 @@ func WalkFiles(ctx context.Context, root string, opts WalkFilesOptions) ([]strin
 		return nil
 	})
 
-	if err != nil && err != context.Canceled && err != context.DeadlineExceeded {
+	if err != nil && !errors.Is(err, context.Canceled) && !errors.Is(err, context.DeadlineExceeded) {
 		return files, err
 	}
 

pkg/hooks/executor.go

@@ -5,6 +5,7 @@ import (
 	"cmp"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -264,7 +265,8 @@ func (e *Executor) executeHook(ctx context.Context, hook Hook, inputJSON []byte)
 
 	exitCode := 0
 	if err != nil {
-		if exitErr, ok := err.(*exec.ExitError); ok {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) {
 			exitCode = exitErr.ExitCode()
 		} else {
 			return nil, stdout.String(), stderr.String(), -1, err

pkg/mcp/server.go

@@ -3,6 +3,7 @@ package mcp
 import (
 	"cmp"
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"net"
@@ -74,7 +75,7 @@ func StartHTTPServer(ctx context.Context, agentFilename, agentName string, runCo
 	case <-ctx.Done():
 		return httpServer.Shutdown(context.Background())
 	case err := <-errCh:
-		if err == http.ErrServerClosed {
+		if errors.Is(err, http.ErrServerClosed) {
 			return nil
 		}
 		return err

pkg/model/provider/custom_provider_test.go

@@ -3,6 +3,7 @@ package provider
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -502,7 +503,7 @@ func drainStream(t *testing.T, stream chat.MessageStream) {
 	t.Helper()
 	for {
 		_, err := stream.Recv()
-		if err == io.EOF {
+		if errors.Is(err, io.EOF) {
 			return
 		}
 		if err != nil {

pkg/rag/strategy/bm25_database.go

@@ -3,6 +3,7 @@ package strategy
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -96,7 +97,7 @@ func (d *bm25DB) AddDocument(ctx context.Context, doc database.Document) error {
 		fmt.Sprintf("SELECT 1 FROM %s WHERE source_path = ? AND chunk_index = ?", d.docsTable),
 		doc.SourcePath, doc.ChunkIndex).Scan(&exists)
 
-	if err != nil && err != sql.ErrNoRows {
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
 		return fmt.Errorf("failed to check existing document: %w", err)
 	}