refactor: replace direct error comparisons with errors.Is

Improves correctness when working with wrapped errors

pkg/channels/line.go

@@ -7,6 +7,7 @@ import (
 	"crypto/sha256"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -104,7 +105,7 @@ func (c *LINEChannel) Start(ctx context.Context) error {
 			"addr": addr,
 			"path": path,
 		})
-		if err := c.httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+		if err := c.httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			logger.ErrorCF("line", "Webhook server error", map[string]interface{}{
 				"error": err.Error(),
 			})

pkg/providers/codex_cli_provider.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os/exec"
 	"strings"
@@ -67,7 +68,7 @@ func (p *CodexCliProvider) Chat(ctx context.Context, messages []Message, tools [
 	}
 
 	if err != nil {
-		if ctx.Err() == context.Canceled {
+		if errors.Is(ctx.Err(), context.Canceled) {
 			return nil, ctx.Err()
 		}
 		if stderrStr := stderr.String(); stderrStr != "" {

pkg/providers/codex_provider.go

@@ -91,8 +91,8 @@ func (p *CodexProvider) Chat(ctx context.Context, messages []Message, tools []To
 		if evt.Type == "response.completed" || evt.Type == "response.failed" || evt.Type == "response.incomplete" {
 			evtResp := evt.Response
 			if evtResp.ID != "" {
-				copy := evtResp
-				resp = &copy
+				cp := evtResp
+				resp = &cp
 			}
 		}
 	}

pkg/providers/error_classifier.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"errors"
 	"regexp"
 	"strings"
 )
@@ -102,12 +103,12 @@ func ClassifyError(err error, provider, model string) *FailoverError {
 	}
 
 	// Context cancellation: user abort, never fallback.
-	if err == context.Canceled {
+	if errors.Is(err, context.Canceled) {
 		return nil
 	}
 
 	// Context deadline exceeded: treat as timeout, always fallback.
-	if err == context.DeadlineExceeded {
+	if errors.Is(err, context.DeadlineExceeded) {
 		return &FailoverError{
 			Reason:   FailoverTimeout,
 			Provider: provider,

pkg/providers/error_classifier_test.go

@@ -293,7 +293,7 @@ func TestFailoverError_ErrorString(t *testing.T) {
 func TestFailoverError_Unwrap(t *testing.T) {
 	inner := errors.New("inner error")
 	fe := &FailoverError{Reason: FailoverTimeout, Wrapped: inner}
-	if fe.Unwrap() != inner {
+	if !errors.Is(inner, fe.Unwrap()) {
 		t.Error("Unwrap should return wrapped error")
 	}
 }

pkg/providers/fallback.go

@@ -2,6 +2,7 @@ package providers
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -98,7 +99,7 @@ func (fc *FallbackChain) Execute(
 
 	for i, candidate := range candidates {
 		// Check context before each attempt.
-		if ctx.Err() == context.Canceled {
+		if errors.Is(ctx.Err(), context.Canceled) {
 			return nil, context.Canceled
 		}
 
@@ -130,7 +131,7 @@ func (fc *FallbackChain) Execute(
 		}
 
 		// Context cancellation: abort immediately, no fallback.
-		if ctx.Err() == context.Canceled {
+		if errors.Is(ctx.Err(), context.Canceled) {
 			result.Attempts = append(result.Attempts, FallbackAttempt{
 				Provider: candidate.Provider,
 				Model:    candidate.Model,
@@ -204,7 +205,7 @@ func (fc *FallbackChain) ExecuteImage(
 	}
 
 	for i, candidate := range candidates {
-		if ctx.Err() == context.Canceled {
+		if errors.Is(ctx.Err(), context.Canceled) {
 			return nil, context.Canceled
 		}
 
@@ -219,7 +220,7 @@ func (fc *FallbackChain) ExecuteImage(
 			return result, nil
 		}
 
-		if ctx.Err() == context.Canceled {
+		if errors.Is(ctx.Err(), context.Canceled) {
 			result.Attempts = append(result.Attempts, FallbackAttempt{
 				Provider: candidate.Provider,
 				Model:    candidate.Model,

pkg/providers/fallback_test.go

@@ -122,7 +122,7 @@ func TestFallback_ContextCanceled(t *testing.T) {
 	}
 
 	_, err := fc.Execute(ctx, candidates, run)
-	if err != context.Canceled {
+	if !errors.Is(err, context.Canceled) {
 		t.Errorf("expected context.Canceled, got %v", err)
 	}
 }

pkg/tools/i2c_linux.go

@@ -2,6 +2,7 @@ package tools
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"syscall"
 	"unsafe"
@@ -113,7 +114,7 @@ func (t *I2CTool) scan(args map[string]interface{}) *ToolResult {
 		// Set slave address — EBUSY means a kernel driver owns this address
 		_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), i2cSlave, uintptr(addr))
 		if errno != 0 {
-			if errno == syscall.EBUSY {
+			if errors.Is(errno, syscall.EBUSY) {
 				found = append(found, deviceEntry{
 					Address: fmt.Sprintf("0x%02x", addr),
 					Status:  "busy (in use by kernel driver)",

pkg/tools/message_test.go

@@ -126,7 +126,7 @@ func TestMessageTool_Execute_SendFailure(t *testing.T) {
 	if result.Err == nil {
 		t.Error("Expected Err to be set")
 	}
-	if result.Err != sendErr {
+	if !errors.Is(sendErr, result.Err) {
 		t.Errorf("Expected Err to be sendErr, got %v", result.Err)
 	}
 }

pkg/tools/shell.go

@@ -3,6 +3,7 @@ package tools
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
@@ -188,7 +189,7 @@ func (t *ExecTool) Execute(ctx context.Context, args map[string]interface{}) *To
 	}
 
 	if err != nil {
-		if cmdCtx.Err() == context.DeadlineExceeded {
+		if errors.Is(cmdCtx.Err(), context.DeadlineExceeded) {
 			msg := fmt.Sprintf("Command timed out after %v", t.timeout)
 			return &ToolResult{
 				ForLLM:  msg,