refactor: add exceptions.py module with structured exception hierarchy

- Create exceptions.py with 7 exception types: TwitterError, AuthenticationError,
  RateLimitError, NotFoundError, NetworkError, QueryIdError, TwitterAPIError
- Remove inline TwitterAPIError from client.py, import from exceptions module
- Replace RuntimeError('Cannot resolve queryId') with QueryIdError
- Replace RuntimeError('User not found') with NotFoundError
- Update test assertion for new TwitterAPIError message format

tests/test_client.py

@@ -463,7 +463,7 @@ class TestTwitterAPIError:
     def test_stores_status_code(self):
         err = TwitterAPIError(429, "Rate limited")
         assert err.status_code == 429
-        assert str(err) == "Rate limited"
+        assert "Rate limited" in str(err)
 
     def test_is_runtime_error(self):
         err = TwitterAPIError(500, "Server error")

twitter_cli/client.py

@@ -33,6 +33,14 @@ from .constants import (
     get_user_agent,
     sync_chrome_version,
 )
+from .exceptions import (
+    AuthenticationError,
+    NetworkError,
+    NotFoundError,
+    QueryIdError,
+    RateLimitError,
+    TwitterAPIError,
+)
 from .models import Author, Metrics, Tweet, TweetMedia, UserProfile
 
 TimelineInstructionGetter = Callable[[Any], Any]
@@ -103,13 +111,7 @@ _cached_query_ids: Dict[str, str] = {}
 _bundles_scanned = False
 
 
-class TwitterAPIError(RuntimeError):
-    """Represents HTTP/network errors from Twitter APIs."""
 
-    def __init__(self, status_code, message):
-        # type: (int, str) -> None
-        super().__init__(message)
-        self.status_code = status_code
 
 def _best_chrome_target():
     # type: () -> str
@@ -299,7 +301,7 @@ def _resolve_query_id(operation_name, prefer_fallback=True):
         _cached_query_ids[operation_name] = fallback
         return fallback
 
-    raise RuntimeError('Cannot resolve queryId for "%s"' % operation_name)
+    raise QueryIdError('Cannot resolve queryId for "%s"' % operation_name)
 
 
 # Hard ceiling to prevent accidental massive fetches
@@ -389,7 +391,7 @@ class TwitterClient:
         data = self._graphql_get("UserByScreenName", variables, features)
         result = _deep_get(data, "data", "user", "result")
         if not result:
-            raise RuntimeError("User @%s not found" % screen_name)
+            raise NotFoundError("User @%s not found" % screen_name)
 
         legacy = result.get("legacy", {})
         return UserProfile(

twitter_cli/exceptions.py

@@ -0,0 +1,45 @@
+"""Custom exceptions for twitter-cli.
+
+Provides a structured exception hierarchy for categorized error handling:
+- Authentication failures
+- API errors (rate-limit, not-found, forbidden)
+- Network errors
+- Query ID resolution failures
+
+Modeled after bilibili-cli/xiaohongshu-cli exception patterns.
+"""
+
+from __future__ import annotations
+
+
+class TwitterError(RuntimeError):
+    """Base exception for twitter-cli errors."""
+
+
+class AuthenticationError(TwitterError):
+    """Raised when cookies are missing, expired, or invalid."""
+
+
+class RateLimitError(TwitterError):
+    """Raised when Twitter rate limits the request (HTTP 429)."""
+
+
+class NotFoundError(TwitterError):
+    """Raised when a user or tweet is not found."""
+
+
+class NetworkError(TwitterError):
+    """Raised when upstream network requests fail."""
+
+
+class QueryIdError(TwitterError):
+    """Raised when a GraphQL queryId cannot be resolved."""
+
+
+class TwitterAPIError(TwitterError):
+    """Raised on non-OK Twitter API responses with HTTP status + message."""
+
+    def __init__(self, status_code: int, message: str):
+        self.status_code = status_code
+        self.message = message
+        super().__init__("Twitter API error (HTTP %d): %s" % (status_code, message))