fix(core): handle parent/child mustache vars

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Description:

currently mustache_schema("{{x.y}} {{x}}") will error. pr fixes

Issue: na
**Dependencies:**na

[codspeed-hq]

CodSpeed Performance Report

Merging #33346 will improve performances by 29.4%

_{Comparing anika/v03_mustache_schema_fix (2cf8f28) with master (cda3362)¹}

⚠️ Unknown Walltime execution environment detected

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For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

⚡ 1 improvement
✅ 12 untouched
⏩ 21 skipped²

Benchmarks breakdown

	Mode	Benchmark	BASE	HEAD	Change
⚡	WallTime	test_import_time[HumanMessage]	273.8 ms	211.6 ms	+29.4%

Footnotes

1. No successful run was found on v0.3 (809a021) during the generation of this report, so master (cda3362) was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 21 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[Copilot]

Pull Request Overview

This PR fixes a bug in the mustache_schema function where having both parent and child mustache variables (e.g., {{x.y}} and {{x}}) in the same template would cause an error. The fix filters out child variables when their parent is also present.

• Added logic to detect and handle parent/child variable conflicts in mustache templates
• Implemented a helper function to check if one sequence is a subsequence of another
• Added comprehensive test coverage for the parent/child variable scenario

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
libs/core/langchain_core/prompts/string.py	Added parent/child conflict resolution logic and is_subsequence helper function
libs/core/tests/unit_tests/prompts/test_string.py	Added test case for parent/child mustache variable handling