refactor(git): improve diff handling to tolerate exit code 1

- Introduce git.Diff function that uses CombinedOutput and treats exit code 1 as success (indicating changes exist).
- Update prdescribe command to use git.Diff and trim whitespace when checking for empty diffs.
- Enhance prdescribe output to include base branch in the status message.

cmd/prdescribe.go

@@ -2,10 +2,12 @@ package cmd
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/fatih/color"
 	"github.com/spf13/cobra"
 	"gmgauthier.com/grokkit/config"
+	"gmgauthier.com/grokkit/internal/git"
 )
 
 var prDescribeCmd = &cobra.Command{
@@ -21,24 +23,26 @@ func init() {
 func runPRDescribe(cmd *cobra.Command, _ []string) {
 	base, _ := cmd.Flags().GetString("base")
 
-	diff, err := gitRun([]string{"diff", fmt.Sprintf("%s..HEAD", base), "--no-color"})
-	if err != nil || diff == "" {
-		diff, err = gitRun([]string{"diff", fmt.Sprintf("origin/%s..HEAD", base), "--no-color"})
+	// Prefer a local base, fallback to origin/<base>. Tolerant of exit code 1.
+	diff, err := git.Diff([]string{"diff", fmt.Sprintf("%s..HEAD", base), "--no-color"})
+	if err != nil || strings.TrimSpace(diff) == "" {
+		diff, err = git.Diff([]string{"diff", fmt.Sprintf("origin/%s..HEAD", base), "--no-color"})
 		if err != nil {
 			color.Red("Failed to get branch diff: %v", err)
 			return
 		}
 	}
-	if diff == "" {
+	if strings.TrimSpace(diff) == "" {
 		color.Yellow("No changes on this branch compared to %s/origin/%s.", base, base)
 		return
 	}
+
 	modelFlag, _ := cmd.Flags().GetString("model")
 	model := config.GetModel("prdescribe", modelFlag)
 
 	client := newGrokClient()
 	messages := buildPRDescribeMessages(diff)
-	color.Yellow("Writing PR description...")
+	color.Yellow("Writing PR description (base=%s)...", base)
 	client.Stream(messages, model)
 }
 

internal/git/git.go

@@ -1,6 +1,7 @@
 package git
 
 import (
+	"errors"
 	"fmt"
 	"os/exec"
 	"strings"
@@ -60,3 +61,24 @@ func LogSince(since string) (string, error) {
 	args := []string{"log", "--pretty=format:%s%n%b%n---", since + "..HEAD"}
 	return Run(args)
 }
+
+// Diff runs `git diff` and tolerates exit code 1 (differences found).
+// This is normal git behavior when there *are* changes — unlike .Output().
+func Diff(args []string) (string, error) {
+	cmdStr := "git " + strings.Join(args, " ")
+	logger.Debug("executing git diff", "command", cmdStr)
+
+	// nolint:gosec // intentional git subprocess
+	cmd := exec.Command("git", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) && exitErr.ExitCode() == 1 {
+			// legitimate diff (changes exist)
+			return string(out), nil
+		}
+		logger.Error("git diff failed", "command", cmdStr, "error", err)
+		return "", fmt.Errorf("git diff failed: %w", err)
+	}
+	return string(out), nil
+}