fix: allow claude CLI provider to run inside Claude Code sessions

Remove CLAUDECODE env var from subprocess environment to allow nesting.
Also parse stdout before checking exit code to handle stderr diagnostic
noise without losing valid JSON output (same pattern as codex provider).

pkg/providers/claude_cli_provider.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"os"
 	"os/exec"
 	"strings"
 )
@@ -41,13 +42,40 @@ func (p *ClaudeCliProvider) Chat(ctx context.Context, messages []Message, tools
 	if p.workspace != "" {
 		cmd.Dir = p.workspace
 	}
+
+	// Remove CLAUDECODE env var to allow nesting (Claude Code blocks
+	// subprocess launches when this variable is set).
+	env := os.Environ()
+	filtered := env[:0]
+	for _, e := range env {
+		if !strings.HasPrefix(e, "CLAUDECODE=") {
+			filtered = append(filtered, e)
+		}
+	}
+	cmd.Env = filtered
+
 	cmd.Stdin = bytes.NewReader([]byte(prompt))
 
 	var stdout, stderr bytes.Buffer
 	cmd.Stdout = &stdout
 	cmd.Stderr = &stderr
 
-	if err := cmd.Run(); err != nil {
+	err := cmd.Run()
+
+	// Parse JSON from stdout even if exit code is non-zero,
+	// because claude writes diagnostic noise to stderr but still
+	// produces valid JSON output.
+	if stdoutStr := stdout.String(); stdoutStr != "" {
+		resp, parseErr := p.parseClaudeCliResponse(stdoutStr)
+		if parseErr == nil && resp != nil && resp.Content != "" {
+			return resp, nil
+		}
+	}
+
+	if err != nil {
+		if ctx.Err() == context.Canceled {
+			return nil, ctx.Err()
+		}
 		if stderrStr := stderr.String(); stderrStr != "" {
 			return nil, fmt.Errorf("claude cli error: %s", stderrStr)
 		}