[saadkhantareen]

Summary

The auto suggester of a Buffer was only invoked from insert_text. Every text change clears the current suggestion in Buffer._text_changed, so after deleting text (backspace, delete, cut, undo, ...) the suggestion disappeared and was never regenerated until the user typed again. This change asks the auto suggester for a new suggestion on every text change, mirroring how input validation is already re-run from _text_changed.

Fixes #2016

Changes

• src/prompt_toolkit/buffer.py: in Buffer._text_changed, schedule the existing _async_suggester coroutine whenever auto_suggest is set, alongside the existing validation scheduling. This covers all mutation paths that go through _text_changed (deletions, undo/redo, set_document, text assignment), not just insertions. When text changes through insert_text, the suggester can be scheduled twice; that is harmless because the coroutine is guarded to run only one at a time and returns early when a suggestion is already present.
• tests/test_buffer.py: new regression test test_auto_suggest_after_delete with a recording AutoSuggest stub. It asserts that a suggestion is generated after typing, and that after delete_before_cursor a new suggestion is generated for the remaining text.

Tests

• python -m pytest tests/test_buffer.py -v — 10 passed, including the new test_auto_suggest_after_delete (fails without the fix: the suggestion stays None after deletion).
• python -m pytest tests/ -q — 157 passed (full suite, including tests/test_memory_leaks.py).
• python -m black --check src/prompt_toolkit/buffer.py tests/test_buffer.py — both files unchanged (formatting clean).

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