experimental: migrate to external repo (#26879)

security scanners can't distinguish monorepo sources from each other.
this will resolve issues for folks trying to use e.g. langchain-core but
getting security issues from experimental flagged!

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
 Thank you for contributing to LangChain!
 
 - [ ] **PR title**: "package: description"
-  - Where "package" is whichever of langchain, community, core, experimental, etc. is being modified. Use "docs: ..." for purely docs changes, "templates: ..." for template changes, "infra: ..." for CI changes.
+  - Where "package" is whichever of langchain, community, core, etc. is being modified. Use "docs: ..." for purely docs changes, "templates: ..." for template changes, "infra: ..." for CI changes.
   - Example: "community: add foobar LLM"
 
 

.github/scripts/check_diff.py

@@ -15,7 +15,6 @@ LANGCHAIN_DIRS = [
     "libs/text-splitters",
     "libs/langchain",
     "libs/community",
-    "libs/experimental",
 ]
 
 # when set to True, we are ignoring core dependents
@@ -153,14 +152,19 @@ def _get_pydantic_test_configs(
     core_min_pydantic_version = get_min_version_from_toml(
         "./libs/core/pyproject.toml", "release", python_version, include=["pydantic"]
     )["pydantic"]
-    core_min_pydantic_minor = core_min_pydantic_version.split(".")[1] if "." in core_min_pydantic_version else "0"
-    dir_min_pydantic_version = (
-        get_min_version_from_toml(
-            f"./{dir_}/pyproject.toml", "release", python_version, include=["pydantic"]
-        )
-        .get("pydantic", "0.0.0")
+    core_min_pydantic_minor = (
+        core_min_pydantic_version.split(".")[1]
+        if "." in core_min_pydantic_version
+        else "0"
+    )
+    dir_min_pydantic_version = get_min_version_from_toml(
+        f"./{dir_}/pyproject.toml", "release", python_version, include=["pydantic"]
+    ).get("pydantic", "0.0.0")
+    dir_min_pydantic_minor = (
+        dir_min_pydantic_version.split(".")[1]
+        if "." in dir_min_pydantic_version
+        else "0"
     )
-    dir_min_pydantic_minor = dir_min_pydantic_version.split(".")[1] if "." in dir_min_pydantic_version else "0"
 
     custom_mins = {
         # depends on pydantic-settings 2.4 which requires pydantic 2.7

.github/workflows/_test_doc_imports.yml

@@ -31,7 +31,7 @@ jobs:
 
       - name: Install langchain editable
         run: |
-          poetry run pip install -e libs/core libs/langchain libs/community libs/experimental
+          poetry run pip install -e libs/core libs/langchain libs/community
 
       - name: Check doc imports
         shell: bash