fix(convoy): route stranded scan warnings to stderr, not stdout (#2142)

findStrandedConvoys() used style.PrintWarning() which wrote to stdout,
contaminating the JSON output when --json flag was set. The daemon's
JSON parser failed on the warning text (U+26A0 prefix).

Fix: use fmt.Fprintf(os.Stderr, ...) directly for the warning, ensuring
stdout contains only valid JSON when --json is active.

Also improve daemon error message to include raw stdout for debugging
when JSON parsing fails.

Closes #2142

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

internal/cmd/convoy.go

@@ -1267,7 +1267,9 @@ func findStrandedConvoys(townBeads string) ([]strandedConvoyInfo, error) {
 	for _, convoy := range convoys {
 		tracked, err := getTrackedIssues(townBeads, convoy.ID)
 		if err != nil {
-			style.PrintWarning("skipping convoy %s: %v", convoy.ID, err)
+			// Write to stderr explicitly — stdout may be consumed as JSON
+			// by the daemon's JSON parser (fixes #2142).
+			fmt.Fprintf(os.Stderr, "⚠ Warning: skipping convoy %s: %v\n", convoy.ID, err)
 			continue
 		}
 		// Empty convoys (0 tracked issues) are stranded — they need

internal/daemon/convoy_manager.go

@@ -373,7 +373,9 @@ func (m *ConvoyManager) findStranded() ([]strandedConvoyInfo, error) {
 
 	var stranded []strandedConvoyInfo
 	if err := json.Unmarshal(stdout.Bytes(), &stranded); err != nil {
-		return nil, fmt.Errorf("parsing stranded JSON: %w", err)
+		// Include first line of raw output for debugging (e.g., non-JSON warnings on stdout)
+		raw := util.FirstLine(stdout.String())
+		return nil, fmt.Errorf("parsing stranded JSON: %w (raw: %q)", err, raw)
 	}
 
 	return stranded, nil