[FanWu-ai]

Summary

Dispatch events over a snapshot of registered handlers. A callback that removes itself no longer skips the following callback, and callbacks added while dispatching are deferred until the next firing. Nested dispatch uses its own fresh snapshot; exception propagation is unchanged.

Validation

• Seven regression cases, including Buffer.on_text_changed integration: five fail on pristine source and two controls pass.
• Pristine complete suite: 156 passed. Final complete suite: 163 passed (CPython 3.12.14, Linux).
• All 12 configured pre-commit hooks pass, plus standalone typos, Ruff lint/format and strict Mypy for win32/linux/darwin.
• Sdist/wheel build and git diff --check pass.
• Independent AI review approved the patch and reran all 163 tests.

AI-assisted implementation and review; no human review is claimed. Hosted CI is separate and not yet verified.