24 add insert at operation for inserting into a list at a specific index

[nathanjmcdougall]

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[Copilot]

Pull request overview

This PR adds a new “insert at index” capability for YAML block sequences, exposed through the Python Document/Editor APIs and implemented in the Rust patch-application pipeline to preserve round-tripping behavior (especially comments/formatting).

Changes:

• Add Document.insert(..., index, value) and Editor.insert(..., index, value) with Python list.insert()-style index semantics (negative indices, clamping).
• Introduce a new core operation Op.insert_at implemented as a local (non-yamlpatch) op and routed through apply_patches_impl.
• Add test coverage across core ops, document/editor APIs, and an integration scenario (pre-commit repo insertion).

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/test_integration.py	Adds an end-to-end test for inserting a repo into a pre-commit config list.
tests/test_editor.py	Adds editor-level tests for insert() behavior and persistence to disk.
tests/test_document.py	Adds document-level tests for insert() semantics and error cases.
tests/test_core_ops.py	Adds core operation constructor + apply_patches tests for insert_at.
src/yamltrip/editor.py	Adds Editor.insert() wrapper around Document.insert().
src/yamltrip/document.py	Adds immutable Document.insert() API that emits an Op.insert_at patch.
src/yamltrip/_core.pyi	Updates native-module type stubs with Op.insert_at.
src/ops.rs	Adds LocalOp / OpInner to support local-only ops and implements Op.insert_at.
src/document.rs	Routes local ops in apply_patches_impl and implements apply_insert_at string surgery.
doc/specs/2026-05-19-insert-operation-design.md	Design spec documenting the API, routing approach, and algorithm.

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