refactor(github): extract doRequestCore, address review feedback

- MAJOR: Extract doRequestCore to eliminate doRequest/doRequestWithBody
  duplication. Both now delegate to a shared implementation with the
  retry/backoff logic in a single place.

- MINOR: Replace custom containsStr/containsSubstring helpers with
  strings.Contains in review_test.go.

- MINOR: Use http.Method* constants (MethodPost, MethodDelete, MethodPut)
  in review.go for consistency with doGet.

- MINOR: Remove redundant APPROVED/DISMISSED cases from
  translateGitHubReviewState that were identical to the default passthrough.

- NIT: Clarify DeleteReview comment about COMMENTED being a GitHub API
  state name.

- DismissReview Event field verified as required by GitHub API docs;
  kept as-is.

github/client.go

@@ -193,10 +193,24 @@ func (c *Client) SetRetryBackoff(d []time.Duration) error {
 	return nil
 }
 
-// doRequest performs an HTTP request with retry on 429 rate limit responses.
-// It respects the Retry-After header when present (capped at maxRetryAfter).
-// Transport errors (network failures, context cancellation) are not retried.
-func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept string) ([]byte, error) {
+// requestOptions holds per-request configuration for doRequestCore.
+type requestOptions struct {
+	// bodyFn returns a fresh io.Reader for the request body on each attempt.
+	// Must be non-nil for requests that carry a body (POST, PUT, PATCH).
+	// Returning a fresh reader on each call allows retries to re-send the body.
+	bodyFn func() io.Reader
+
+	// accept overrides the default Accept header. Empty means "application/vnd.github+json".
+	accept string
+
+	// extraHeaders are additional headers to set on each request attempt.
+	extraHeaders map[string]string
+}
+
+// doRequestCore is the shared implementation for all HTTP requests with retry
+// on 429 rate limit responses. It respects the Retry-After header when present
+// (capped at maxRetryAfter). Transport errors are not retried.
+func (c *Client) doRequestCore(ctx context.Context, method, reqURL string, opts requestOptions) ([]byte, error) {
 	const maxRetryAfter = 120 * time.Second
 
 	// backoff holds per-attempt delays: backoff[i] is the delay before attempt i+1.
@@ -247,7 +261,11 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 			}
 		}
 
-		req, err := http.NewRequestWithContext(ctx, method, reqURL, nil)
+		var body io.Reader
+		if opts.bodyFn != nil {
+			body = opts.bodyFn()
+		}
+		req, err := http.NewRequestWithContext(ctx, method, reqURL, body)
 		if err != nil {
 			return nil, fmt.Errorf("create request: %w", err)
 		}
@@ -258,11 +276,14 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 			req.Header.Set("Authorization", "Bearer "+c.token)
 		}
 		req.Header.Set("User-Agent", userAgent)
-		if accept != "" {
-			req.Header.Set("Accept", accept)
+		if opts.accept != "" {
+			req.Header.Set("Accept", opts.accept)
 		} else {
 			req.Header.Set("Accept", "application/vnd.github+json")
 		}
+		for k, v := range opts.extraHeaders {
+			req.Header.Set(k, v)
+		}
 
 		resp, err := c.httpClient.Do(req)
 		if err != nil {
@@ -273,11 +294,11 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 		respStatus := resp.StatusCode
 		retryAfterHeader := resp.Header.Get("Retry-After")
 
-		body, done, err := c.handleResponse(resp, maxResponseBytes, maxErrorBodyBytes)
+		respBody, done, handleErr := c.handleResponse(resp, maxResponseBytes, maxErrorBodyBytes)
 		if done {
-			return body, err
+			return respBody, handleErr
 		}
-		lastErr = err
+		lastErr = handleErr
 
 		// Retry on 429 rate limit
 		if respStatus == http.StatusTooManyRequests && attempt < maxRetryAttempts-1 {
@@ -315,6 +336,13 @@ func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept st
 	return nil, lastErr
 }
 
+// doRequest performs an HTTP request with retry on 429 rate limit responses.
+// It respects the Retry-After header when present (capped at maxRetryAfter).
+// Transport errors (network failures, context cancellation) are not retried.
+func (c *Client) doRequest(ctx context.Context, method, reqURL string, accept string) ([]byte, error) {
+	return c.doRequestCore(ctx, method, reqURL, requestOptions{accept: accept})
+}
+
 // handleResponse reads and closes the response body, returning the result.
 // It uses defer to ensure the body is always closed regardless of code path.
 // Returns (body, done, err) where done=true means the caller should return immediately.
@@ -347,109 +375,11 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 // doRequestWithBody is like doRequest but sends a request body.
 // It accepts the raw body bytes and sets Content-Type to application/json.
 // Retry semantics match doRequest (retries on 429 with Retry-After support).
-func (c *Client) doRequestWithBody(ctx context.Context, method, reqURL string, body []byte) ([]byte, error) {
-	const maxRetryAfter = 120 * time.Second
-
-	defaultBackoff := []time.Duration{1 * time.Second, 2 * time.Second}
-	var backoff []time.Duration
-	if c.retryBackoff != nil && len(c.retryBackoff) == maxRetryAttempts-1 {
-		backoff = make([]time.Duration, len(c.retryBackoff))
-		copy(backoff, c.retryBackoff)
-	} else {
-		backoff = make([]time.Duration, len(defaultBackoff))
-		copy(backoff, defaultBackoff)
+func (c *Client) doRequestWithBody(ctx context.Context, method, reqURL string, reqBody []byte) ([]byte, error) {
+	var opts requestOptions
+	if reqBody != nil {
+		opts.bodyFn = func() io.Reader { return bytes.NewReader(reqBody) }
+		opts.extraHeaders = map[string]string{"Content-Type": "application/json"}
 	}
-
-	const maxErrorBodyBytes = 4 * 1024
-
-	if c.token != "" && !c.allowInsecureHTTP {
-		parsed, err := url.Parse(reqURL)
-		if err != nil {
-			return nil, fmt.Errorf("parse request URL: %w", err)
-		}
-		if !strings.EqualFold(parsed.Scheme, "https") {
-			return nil, fmt.Errorf("refusing to send credentials over non-HTTPS URL %q (use AllowInsecureHTTP option for trusted networks)", reqURL)
-		}
-	}
-
-	var lastErr error
-	for attempt := 0; attempt < maxRetryAttempts; attempt++ {
-		if attempt > 0 {
-			var delay time.Duration
-			if attempt-1 < len(backoff) {
-				delay = backoff[attempt-1]
-			}
-			if delay > 0 {
-				timer := time.NewTimer(delay)
-				select {
-				case <-timer.C:
-					timer.Stop()
-				case <-ctx.Done():
-					timer.Stop()
-					return nil, ctx.Err()
-				}
-			}
-		}
-
-		var bodyReader io.Reader
-		if body != nil {
-			bodyReader = bytes.NewReader(body)
-		}
-		req, err := http.NewRequestWithContext(ctx, method, reqURL, bodyReader)
-		if err != nil {
-			return nil, fmt.Errorf("create request: %w", err)
-		}
-		if c.token != "" {
-			req.Header.Set("Authorization", "Bearer "+c.token)
-		}
-		req.Header.Set("User-Agent", userAgent)
-		req.Header.Set("Accept", "application/vnd.github+json")
-		if body != nil {
-			req.Header.Set("Content-Type", "application/json")
-		}
-
-		resp, err := c.httpClient.Do(req)
-		if err != nil {
-			return nil, fmt.Errorf("do request: %w", err)
-		}
-
-		respStatus := resp.StatusCode
-		retryAfterHeader := resp.Header.Get("Retry-After")
-
-		respBody, done, handleErr := c.handleResponse(resp, maxResponseBytes, maxErrorBodyBytes)
-		if done {
-			return respBody, handleErr
-		}
-		lastErr = handleErr
-
-		if respStatus == http.StatusTooManyRequests && attempt < maxRetryAttempts-1 {
-			if ra := retryAfterHeader; ra != "" {
-				if seconds, err := strconv.Atoi(ra); err == nil && seconds > 0 {
-					delay := time.Duration(seconds) * time.Second
-					if delay > maxRetryAfter {
-						delay = maxRetryAfter
-					}
-					if attempt < len(backoff) {
-						backoff[attempt] = delay
-					}
-				} else if retryAt, err := http.ParseTime(ra); err == nil {
-					delay := time.Until(retryAt)
-					if delay < 0 {
-						delay = 0
-					}
-					if delay > maxRetryAfter {
-						delay = maxRetryAfter
-					}
-					if attempt < len(backoff) {
-						backoff[attempt] = delay
-					}
-				}
-			}
-			continue
-		}
-
-		return nil, lastErr
-	}
-
-	return nil, lastErr
+	return c.doRequestCore(ctx, method, reqURL, opts)
 }