René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ExceptionGroup wrapping obscures real errors from task groups","articleBody":"## Summary\n\nWhen SDK internal anyio task group tasks fail, the real error is wrapped in a `BaseExceptionGroup` alongside `Cancelled` exceptions from cancelled sibling tasks. This makes error classification extremely difficult for callers — they cannot reliably determine the root cause of a failure.\n\nThere are 16 `create_task_group()` usages across the SDK with no `except*` syntax or ExceptionGroup unwrapping anywhere.\n\n## Expected Behavior\n\n- Callers should receive the original exception, not an ExceptionGroup wrapping it alongside cancellation noise\n- When a task group has one real failure and N cancelled siblings, only the real failure should propagate\n\n## Current Behavior\n\n- A single connection failure produces a `BaseExceptionGroup` containing the real error plus multiple `Cancelled` exceptions\n- Callers must manually unwrap exception groups to find the root cause\n- This affects ~80+ call sites across the SDK where task groups are used\n\n## Affected Code\n\n- `src/mcp/shared/session.py` (session task groups)\n- `src/mcp/client/streamable_http.py` (transport task groups)\n- All other `create_task_group()` sites\n\n## Related\n\n- #1742 — broader typed error classes design\n- #1830 — CancelledError indistinguishable from external cancellation (closed but related)\n\n---\n\n\u003csub\u003e[AI Disclaimer](https://gist.github.com/maxisbey/6123d132484e4c533eab519a2800693d)\u003c/sub\u003e","author":{"url":"https://github.com/maxisbey","@type":"Person","name":"maxisbey"},"datePublished":"2026-02-19T21:52:58.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/2114/python-sdk/issues/2114"}