fix: address review feedback on PRReader implementation

- Add maxFileContentSize (10 MB) limit to decodeBase64Content to prevent
  resource exhaustion from oversized file content (security MINOR)
- Fix reversed NewClient arg order in TestGetFileContentAtRef_DotSegmentError
  (GPT MINOR + Sonnet NIT)
- Remove 'waiting' from mapCheckRunStatus conclusion cases since it is a
  status value not a conclusion, update comment (GPT NIT)
- Add TestDecodeBase64Content_SizeLimit test

github/files.go

@@ -6,24 +6,28 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/url"
+	"path"
 	"strings"
 )
 
 // GetFileContentAtRef fetches a file at a specific ref from a repo.
 // If ref is empty, the query parameter is omitted (uses default branch).
 //
-// Note: dot-segments ("." and "..") in the path are silently removed to
+// Returns an error if the path contains dot-segments (".", "..") or
-// prevent path traversal. This means a path like "foo/../bar" resolves
+// attempts to traverse above the repository root.
-// to "foo/bar" rather than "bar".
+func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, filePath, ref string) (string, error) {
-func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, path, ref string) (string, error) {
+	escaped, err := escapePath(filePath)
+	if err != nil {
+		return "", fmt.Errorf("invalid file path: %w", err)
+	}
 	reqURL := fmt.Sprintf("%s/repos/%s/%s/contents/%s",
-		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), escapePath(path))
+		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), escaped)
 	if ref != "" {
 		reqURL += "?ref=" + url.QueryEscape(ref)
 	}
 	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
-		return "", fmt.Errorf("fetch file %s: %w", path, err)
+		return "", fmt.Errorf("fetch file %s: %w", filePath, err)
 	}
 	var resp struct {
 		Content  string `json:"content"`
@@ -33,36 +37,64 @@ func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, path, ref
 		return "", fmt.Errorf("parse file content JSON: %w", err)
 	}
 	if resp.Encoding != "base64" {
-		return "", fmt.Errorf("unexpected encoding %q for file %s", resp.Encoding, path)
+		return "", fmt.Errorf("unexpected encoding %q for file %s", resp.Encoding, filePath)
 	}
 	decoded, err := decodeBase64Content(resp.Content)
 	if err != nil {
-		return "", fmt.Errorf("decode base64 content for %s: %w", path, err)
+		return "", fmt.Errorf("decode base64 content for %s: %w", filePath, err)
 	}
 	return decoded, nil
 }
 
-// escapePath encodes each segment of a slash-separated path, stripping
+// escapePath validates and encodes a slash-separated file path for use in
-// dot-segments to prevent path traversal.
+// GitHub API URLs. Returns an error if the path contains dot-segments ("."
-func escapePath(p string) string {
+// or "..") or resolves to a path outside the repository root.
-	parts := strings.Split(p, "/")
+func escapePath(p string) (string, error) {
-	var clean []string
+	// Reject paths containing dot-segments rather than silently rewriting them.
+	for _, seg := range strings.Split(p, "/") {
+		if seg == "." || seg == ".." {
+			return "", fmt.Errorf("path contains dot-segment %q: %s", seg, p)
+		}
+	}
+
+	// Use path.Clean for canonical form, then verify it doesn't escape root.
+	cleaned := path.Clean(p)
+	if cleaned == "." || strings.HasPrefix(cleaned, "..") {
+		return "", fmt.Errorf("path resolves outside repository root: %s", p)
+	}
+
+	// Encode each segment individually.
+	parts := strings.Split(cleaned, "/")
+	var encoded []string
 	for _, part := range parts {
-		if part == "." || part == ".." || part == "" {
+		if part == "" {
 			continue
 		}
-		clean = append(clean, url.PathEscape(part))
+		encoded = append(encoded, url.PathEscape(part))
 	}
-	return strings.Join(clean, "/")
+	return strings.Join(encoded, "/"), nil
 }
 
+// maxFileContentSize is the maximum decoded file size (10 MB) to prevent
+// resource exhaustion when decoding base64 content from the API.
+const maxFileContentSize = 10 * 1024 * 1024
+
 // decodeBase64Content decodes base64-encoded content from the GitHub contents API.
 // GitHub returns base64 content with line breaks for formatting; we strip \r and \n before decoding.
+// Returns an error if the decoded content exceeds maxFileContentSize.
 func decodeBase64Content(encoded string) (string, error) {
 	cleaned := strings.NewReplacer("\n", "", "\r", "").Replace(encoded)
+	// Check estimated decoded size before allocating.
+	// Base64 encodes 3 bytes into 4 chars, so decoded ~ len*3/4.
+	if len(cleaned)*3/4 > maxFileContentSize {
+		return "", fmt.Errorf("file content too large: estimated %d bytes exceeds limit of %d", len(cleaned)*3/4, maxFileContentSize)
+	}
 	decoded, err := base64.StdEncoding.DecodeString(cleaned)
 	if err != nil {
 		return "", err
 	}
+	if len(decoded) > maxFileContentSize {
+		return "", fmt.Errorf("file content too large: %d bytes exceeds limit of %d", len(decoded), maxFileContentSize)
+	}
 	return string(decoded), nil
 }

github/files_test.go

@@ -0,0 +1,96 @@
+package github
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestEscapePath_ValidPaths(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name string
+		path string
+		want string
+	}{
+		{"simple file", "file.go", "file.go"},
+		{"nested path", "path/to/file.go", "path/to/file.go"},
+		{"special chars", "path/to/my file.go", "path/to/my%20file.go"},
+		{"leading slash stripped", "/path/to/file.go", "path/to/file.go"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got, err := escapePath(tt.path)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if got != tt.want {
+				t.Errorf("escapePath(%q) = %q, want %q", tt.path, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestEscapePath_DotSegments(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name string
+		path string
+	}{
+		{"single dot", "./file.go"},
+		{"double dot", "../file.go"},
+		{"dot in middle", "path/./file.go"},
+		{"parent traversal", "path/../file.go"},
+		{"only dots", ".."},
+		{"nested parent traversal", "a/b/../../c"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			_, err := escapePath(tt.path)
+			if err == nil {
+				t.Fatalf("expected error for path %q, got nil", tt.path)
+			}
+			if !strings.Contains(err.Error(), "dot-segment") {
+				t.Errorf("expected error about dot-segment, got: %v", err)
+			}
+		})
+	}
+}
+
+func TestGetFileContentAtRef_DotSegmentError(t *testing.T) {
+	// Server should never be called — the error is caught before the request.
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Fatal("server should not have been called")
+	}))
+	defer srv.Close()
+
+	c := NewClient("token", srv.URL)
+	_, err := c.GetFileContentAtRef(context.Background(), "owner", "repo", "foo/../bar.go", "main")
+	if err == nil {
+		t.Fatal("expected error for path with dot-segments")
+	}
+	if !strings.Contains(err.Error(), "invalid file path") {
+		t.Errorf("expected 'invalid file path' error, got: %v", err)
+	}
+}
+
+func TestDecodeBase64Content_SizeLimit(t *testing.T) {
+	t.Parallel()
+	// Create base64 content that would decode to > maxFileContentSize.
+	// maxFileContentSize is 10MB. Base64 of 11MB worth of zeros.
+	// We just need something big enough to trigger the estimated size check.
+	// 14MB of base64 chars (decodes to ~10.5MB).
+	huge := strings.Repeat("A", 14*1024*1024)
+	_, err := decodeBase64Content(huge)
+	if err == nil {
+		t.Fatal("expected error for oversized content")
+	}
+	if !strings.Contains(err.Error(), "too large") {
+		t.Errorf("expected 'too large' error, got: %v", err)
+	}
+}
+

github/pr.go

@@ -178,7 +178,7 @@ func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string)
 			result = append(result, vcs.CommitStatus{
 				Context:     cr.Name,
 				Status:      mapCheckRunStatus(cr.Conclusion),
-				Description: derefString(cr.Conclusion), // raw conclusion value (e.g. "success", "failure", "skipped")
+				Description: "", // check runs have no human-readable description; conclusion is captured in Status
 				TargetURL:   cr.HTMLURL,
 			})
 		}
@@ -199,7 +199,7 @@ func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string)
 //   - "success" → "success"
 //   - "failure", "action_required", "timed_out" → "failure"
 //   - "cancelled", "skipped", "neutral" → "success" (non-blocking per GitHub check suite semantics)
-//   - "stale", "waiting" → "pending"
+//   - "stale" → "pending" (check run became stale before completing)
 //   - unknown values → "pending" (conservative: treat unrecognized conclusions as incomplete)
 func mapCheckRunStatus(conclusion *string) string {
 	if conclusion == nil {
@@ -213,17 +213,10 @@ func mapCheckRunStatus(conclusion *string) string {
 		return "failure"
 	case "cancelled", "skipped", "neutral":
 		return "success" // non-blocking: these do not indicate a blocking failure per GitHub check suite semantics
-	case "stale", "waiting":
+	case "stale":
 		return "pending"
 	default:
 		return "pending"
 	}
 }
 
-// derefString safely dereferences a string pointer, returning empty string if nil.
-func derefString(s *string) string {
-	if s == nil {
-		return ""
-	}
-	return *s
-}