fix(core): applied secrets_map in load to plain string values

[npage902]

Replaces #33618

Description: Fixes the bug in the load() function where secret placeholders in plain dicts were not replaced, even if they match a key in secrets_map, and adds a test case.

Example:

obj = {"api_key": "__SECRET_API_KEY__"}
secret_key = "secret_key_1234"
secrets_map = {"__SECRET_API_KEY__": secret_key}
result = load(obj, secrets_map=secrets_map)

Before this change, printing api_key in result would output "__SECRET_API_KEY__". Now, it will properly output "secret_key_1234".

Issue: Fixes #31804

Dependencies: None

make format, make lint, and make test have all passed on my machine.

[codspeed-hq]

CodSpeed Performance Report

Merging #33678 will not alter performance

_{Comparing npage902:npage902/fix-load-secrets-map (9d15ff9) with master (9383b78)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

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

Summary

✅ 13 untouched
⏩ 21 skipped¹

Footnotes

1. 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. ↩

[npage902]

Apologies for any confusion thanks to my last PR. Now, hopefully everything should be working fine. I'm still learning how to do open source contributions, so please let me know if there are any issues.

[Copilot]

Pull Request Overview

This PR adds support for string-based secret placeholders in the load() function, allowing secrets to be referenced directly as string values (e.g., "__SECRET_API_KEY__") in addition to the existing structured secret format ({"lc": 1, "type": "secret", "id": ["KEY"]}).

Key Changes:

• Enhanced _load() function to check if string values match keys in secrets_map and replace them with the corresponding secret values
• Added a test case demonstrating the new string secret replacement functionality

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
libs/core/langchain_core/load/load.py	Adds string placeholder support by checking if any string value in the object tree matches a key in secrets_map and replacing it with the secret value
libs/langchain/tests/unit_tests/load/test_load.py	Adds basic test case for the new string secrets feature with a simple dictionary example