docs: add Corridor agent instructions (#39839)

Add a repository-wide `<corridor>` block to `AGENTS.md` requiring agents
to plan first and run Corridor `analyzePlan` before generating or
modifying code.

This mirrors langchain-ai/deepagents#5740. The tags are explicit and
balanced so Corridor-specific guidance remains scoped.

---

Validation: `git diff --check` and a tag-balance assertion.

---------

Co-authored-by: langsmith-fleet[bot] <langsmith-fleet[bot]@users.noreply.github.com>

AGENTS.md

@@ -2,6 +2,14 @@
 
 This document provides context to understand the LangChain Python project and assist with development.
 
+<corridor>
+
+## Corridor security analysis
+
+When Corridor's `analyzePlan` tool is available, create a plan and use the tool to analyze it before generating or modifying code. Apply the resulting security guidance before writing code.
+
+</corridor>
+
 ## Project architecture and context
 
 ### Monorepo structure

CLAUDE.md

@@ -2,6 +2,14 @@
 
 This document provides context to understand the LangChain Python project and assist with development.
 
+<corridor>
+
+## Corridor security analysis
+
+When Corridor's `analyzePlan` tool is available, create a plan and use the tool to analyze it before generating or modifying code. Apply the resulting security guidance before writing code.
+
+</corridor>
+
 ## Project architecture and context
 
 ### Monorepo structure