Implement FileReader conformance on the GitHub client: GetFileContent,
ListContents, path helpers, base64 decode. Includes compile-time
conformance checks for both PRReader and FileReader.

Requires PR B (#102). Part 3 of 3 for #80.

@@ -0,0 +13,4 @@
+
+// GetFileContent fetches a file from a repo at the given ref.
+// Delegates to GetFileContentAtRef with the provided ref.
+func (c *Client) GetFileContent(ctx context.Context, owner, repo, path, ref string) (string, error) {

@@ -0,0 +92,4 @@
+	}
+
+	result := make([]vcs.ContentEntry, len(entries))
+	for i, e := range entries {

@@ -0,0 +106,4 @@
+// Slashes are preserved as path separators; other special characters are escaped.
+// Dot-segments ("." and "..") and empty segments (from consecutive slashes like
+// "a//b") are silently removed to prevent path traversal and produce canonical
+// paths. This is intentional: callers may receive a different path than requested

@@ -0,0 +127,4 @@
+func decodeBase64Content(encoded string) (string, error) {
+	// GitHub inserts newlines in base64 content
+	cleaned := strings.NewReplacer("\n", "", "\r", "").Replace(encoded)
+	decoded, err := base64.StdEncoding.DecodeString(cleaned)

@@ -0,0 +1,637 @@
+package github

@@ -0,0 +14,4 @@
+// GetFileContent fetches a file from a repo at the given ref.
+// Delegates to GetFileContentAtRef with the provided ref.
+func (c *Client) GetFileContent(ctx context.Context, owner, repo, path, ref string) (string, error) {
+	return c.GetFileContentAtRef(ctx, owner, repo, path, ref)

@@ -0,0 +83,4 @@
+		if err2 := json.Unmarshal(body, &single); err2 != nil {
+			return nil, fmt.Errorf("parse contents JSON: as array: %v; as object: %w", err, err2)
+		}
+		// Guard against empty objects ({}) or unexpected shapes that

@@ -0,0 +196,4 @@
+
+func TestListContents_401(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(401)

@@ -0,0 +1,637 @@
+package github

@@ -0,0 +7,4 @@
+
+// Compile-time interface conformance assertions.
+// These verify github.Client satisfies vcs.PRReader and vcs.FileReader.
+var (

@@ -0,0 +80,4 @@
+	var entries []entry
+	if err := json.Unmarshal(body, &entries); err != nil {
+		var single entry
+		if err2 := json.Unmarshal(body, &single); err2 != nil {

@@ -0,0 +84,4 @@
+			return nil, fmt.Errorf("parse contents JSON: as array: %v; as object: %w", err, err2)
+		}
+		// Guard against empty objects ({}) or unexpected shapes that
+		// unmarshal successfully but carry no useful data.

@@ -12,1 +14,4 @@
 
+// GetFileContent fetches a file from a repo at the given ref.
+// Delegates to GetFileContentAtRef with the provided ref.
+func (c *Client) GetFileContent(ctx context.Context, owner, repo, filePath, ref string) (string, error) {

@@ -49,0 +90,4 @@
+		// Guard against empty objects ({}) or unexpected shapes that
+		// unmarshal successfully but carry no useful data.
+		if single.Name == "" && single.Path == "" && single.Type == "" {
+			return nil, fmt.Errorf("parse contents JSON: unexpected response format")

@@ -11,0 +18,4 @@
+			"content":  "dGVzdA==", // "test" in base64
+			"encoding": "base64",
+		})
+	}))

@@ -11,0 +175,4 @@
+		t.Errorf("expected name 'lib', got %q", entries[1].Name)
+	}
+	if entries[1].Type != "dir" {
+		t.Errorf("expected type 'dir', got %q", entries[1].Type)

@@ -5,6 +5,9 @@ import (
 	"gitea.weiker.me/rodin/review-bot/vcs"
 )

@@ -46,6 +54,58 @@ func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, filePath,
 	return decoded, nil

@@ -49,0 +76,4 @@
+		Path string `json:"path"`
+		Type string `json:"type"`
+	}
+

@@ -49,0 +90,4 @@
+		// Guard against empty objects ({}) or unexpected shapes that
+		// unmarshal successfully but carry no useful data.
+		if single.Name == "" && single.Path == "" && single.Type == "" {
+			return nil, fmt.Errorf("parse contents JSON: unexpected response format")

@@ -49,0 +101,4 @@
+			Name: e.Name,
+			Path: e.Path,
+			Type: e.Type,
+		}

@@ -11,0 +18,4 @@
+			"content":  "dGVzdA==", // "test" in base64
+			"encoding": "base64",
+		})
+	}))

@@ -46,6 +54,58 @@ func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, filePath,
 	return decoded, nil
 }
 

@@ -49,0 +73,4 @@
+
+	type entry struct {
+		Name string `json:"name"`
+		Path string `json:"path"`

@@ -81,2 +389,4 @@
+}
+
 func TestDecodeBase64Content_SizeLimit(t *testing.T) {
 	t.Parallel()