feat(13-02): implement GoProxySource and PackagistSource with tests

- GoProxySource parses pkg.go.dev HTML search results for module paths
- PackagistSource queries Packagist JSON search API for PHP packages
- GoProxy regex requires domain dot to filter non-module paths

pkg/recon/sources/goproxy.go

@@ -0,0 +1,104 @@
+package sources
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/url"
+	"regexp"
+	"time"
+
+	"golang.org/x/time/rate"
+
+	"github.com/salvacybersec/keyhunter/pkg/providers"
+	"github.com/salvacybersec/keyhunter/pkg/recon"
+)
+
+// GoProxySource searches pkg.go.dev for Go modules matching provider keywords.
+// pkg.go.dev returns HTML search results, so we parse anchor hrefs for module
+// paths. No authentication required.
+type GoProxySource struct {
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	Client   *Client
+}
+
+// goProxyLinkRE matches Go module paths which always contain a domain with a
+// dot (e.g. /github.com/user/repo). This filters out simple paths like /about.
+var goProxyLinkRE = regexp.MustCompile(`^/[a-z][a-z0-9_-]*\.[a-z0-9./_-]+$`)
+
+// Compile-time assertion that GoProxySource satisfies recon.ReconSource.
+var _ recon.ReconSource = (*GoProxySource)(nil)
+
+func (s *GoProxySource) Name() string          { return "goproxy" }
+func (s *GoProxySource) RateLimit() rate.Limit { return rate.Every(2 * time.Second) }
+func (s *GoProxySource) Burst() int            { return 2 }
+func (s *GoProxySource) RespectsRobots() bool  { return false }
+
+// Enabled always returns true: pkg.go.dev requires no credentials.
+func (s *GoProxySource) Enabled(_ recon.Config) bool { return true }
+
+// Sweep queries pkg.go.dev search for each provider keyword, parses the HTML
+// response for module path links, and emits a Finding per result.
+func (s *GoProxySource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	base := s.BaseURL
+	if base == "" {
+		base = "https://pkg.go.dev"
+	}
+	client := s.Client
+	if client == nil {
+		client = NewClient()
+	}
+
+	queries := BuildQueries(s.Registry, "goproxy")
+	if len(queries) == 0 {
+		return nil
+	}
+
+	for _, q := range queries {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		if s.Limiters != nil {
+			if err := s.Limiters.Wait(ctx, s.Name(), s.RateLimit(), s.Burst(), false); err != nil {
+				return err
+			}
+		}
+
+		endpoint := fmt.Sprintf("%s/search?q=%s&m=package", base, url.QueryEscape(q))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return fmt.Errorf("goproxy: build request: %w", err)
+		}
+
+		resp, err := client.Do(ctx, req)
+		if err != nil {
+			continue
+		}
+
+		links, parseErr := extractAnchorHrefs(resp.Body, goProxyLinkRE)
+		_ = resp.Body.Close()
+		if parseErr != nil {
+			continue
+		}
+
+		for _, href := range links {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+			absURL := base + href
+			select {
+			case out <- recon.Finding{
+				Source:     absURL,
+				SourceType: "recon:goproxy",
+				Confidence: "low",
+				DetectedAt: time.Now(),
+			}:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	}
+	return nil
+}