Add a configurable MaxDiffSize field to Client that limits how much
data GetPullRequestDiff will read into memory. The default is 10 MB
(DefaultMaxDiffSize). When the diff exceeds the limit, ErrDiffTooLarge
is returned, allowing callers to skip position translation gracefully.

Implementation uses io.LimitReader to read maxBytes+1, detecting
overflow without buffering the entire response. Setting MaxDiffSize
to -1 disables the limit entirely.

Closes #92

@@ -130,1 +142,3 @@
-	body, err := c.doGet(ctx, reqURL)
+
+	maxSize := c.MaxDiffSize
+	if maxSize == 0 {

@@ -413,6 +440,86 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 	return nil, lastErr

@@ -0,0 +19,4 @@
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")

@@ -62,2 +68,4 @@
 	// Modifying it while requests are in flight is not safe.
 	RetryBackoff []time.Duration
+
+	// MaxDiffSize is the maximum number of bytes allowed when fetching a PR diff.

@@ -416,0 +487,4 @@
+			if attempt < maxAttempts-1 && isTemporaryNetError(err) {
+				slog.Warn("temporary network error, will retry",
+					"attempt", attempt+1,
+					"url", redactURL(reqURL),

@@ -61,6 +67,10 @@ type Client struct {
 	// This field must be configured before the first request is made.

@@ -413,6 +440,86 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 	return nil, lastErr

@@ -131,0 +153,4 @@
+			return "", fmt.Errorf("fetch diff: %w", err)
+		}
+		return string(body), nil
+	}

@@ -413,6 +441,92 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 	return nil, lastErr

@@ -0,0 +22,4 @@
+	client := NewClient(server.URL, "test-token")
+	client.MaxDiffSize = 100 // 100 bytes limit
+	client.RetryBackoff = []time.Duration{} // no delay in tests
+

@@ -416,0 +469,4 @@
+
+				timer := time.NewTimer(delay)
+				select {
+				case <-timer.C:

@@ -61,6 +68,10 @@ type Client struct {
 	// This field must be configured before the first request is made.

@@ -413,6 +441,92 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 	return nil, lastErr

@@ -0,0 +1,143 @@
+package gitea

@@ -131,0 +158,4 @@
+		return string(body), nil
+	}
+
+	body, err := c.doGetLimited(ctx, reqURL, maxSize)

@@ -413,6 +444,92 @@ func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
 	return nil, lastErr

@@ -416,0 +455,4 @@
+		backoff = []time.Duration{1 * time.Second, 2 * time.Second}
+	}
+	const maxErrorBodyBytes = 64 * 1024
+

@@ -416,0 +489,4 @@
+		resp, err := c.http.Do(req)
+		if err != nil {
+			lastErr = err
+			if attempt < maxAttempts-1 && isTemporaryNetError(err) {

@@ -130,1 +147,3 @@
-	body, err := c.doGet(ctx, reqURL)
+
+	maxSize := c.MaxDiffSize
+	if maxSize == 0 {

@@ -416,0 +467,4 @@
+		limitBytes := maxBytes + 1
+		if limitBytes <= 0 {
+			limitBytes = math.MaxInt64
+		}

@@ -0,0 +69,4 @@
+				w.Write([]byte(tt.diff)) //nolint:errcheck // test handler
+			}))
+			defer server.Close()
+

@@ -61,6 +68,14 @@ type Client struct {
 	// This field must be configured before the first request is made.

@@ -125,9 +140,28 @@ func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number
 }

@@ -64,3 +78,4 @@
+	MaxDiffSize int64
 }
 
 // NewClient creates a new Gitea API client.

@@ -416,0 +464,4 @@
+		defer body.Close()
+		// Read up to maxBytes+1 to detect overflow.
+		// Clamp to prevent integer overflow when maxBytes == math.MaxInt64.
+		limitBytes := maxBytes + 1

@@ -0,0 +72,4 @@
+
+			client := NewClient(server.URL, "test-token")
+			client.MaxDiffSize = tt.maxDiffSize
+			client.RetryBackoff = []time.Duration{}

@@ -47,6 +48,12 @@ func IsServerError(err error) bool {
 	return errors.As(err, &apiErr) && apiErr.StatusCode >= 500 && apiErr.StatusCode < 600

@@ -62,2 +69,4 @@
 	// Modifying it while requests are in flight is not safe.
 	RetryBackoff []time.Duration
+
+	// MaxDiffSize is the maximum number of bytes allowed when fetching a PR diff.

@@ -131,0 +147,4 @@
+
+	maxSize := c.MaxDiffSize
+	if maxSize == 0 {
+		maxSize = DefaultMaxDiffSize