feat(core,partners): add package version tracking to tracing metadata (#35295)

Following on the heels of #35293

TODO:
- Packages outside of this repo (e.g. LiteLLM, Nvidia, Google, AWS)

---

## Summary

Surface partner package versions in `metadata.versions` on LangSmith
traces. Mirrors the JS SDK's `_addVersion()` pattern
([langchainjs#10106](https://github.com/langchain-ai/langchainjs/pull/10106)).

Each model constructor records its package version via `_add_version()`
on `BaseLanguageModel`. The version dict accumulates through the class
hierarchy — `langchain-core` is added in
`BaseLanguageModel.model_post_init`, `langchain-openai` in
`BaseChatOpenAI._set_openai_chat_version`, and each leaf partner in its
uniquely-named `model_validator`. Traces end up with:

```json
{
  "metadata": {
    "versions": {
      "langchain-core": "1.4.5",
      "langchain-openai": "1.3.0",
      "langchain-xai": "1.2.2"
    }
  }
}
```

### Changes

- `BaseLanguageModel._add_version(pkg, version)` — appends to
`self.metadata["versions"]`; accepts any `Mapping` type; emits a warning
if a non-mapping value is found and replaced
- `BaseLanguageModel.model_post_init` — adds `langchain-core` version;
calls `super()` for MRO safety
- `_merge_metadata_dicts` — one-level-deep (non-recursive) merge for
nested dict metadata keys
- `CallbackManager.add_metadata` — uses `_merge_metadata_dicts` instead
of flat `dict.update()` so nested metadata dicts (like `versions`)
coexist rather than clobber
- `merge_configs` — uses `_merge_metadata_dicts` for config merging

**Partners:**
- Each now calls `self._add_version("langchain-<pkg>", __version__)`

### Design decisions

- **Constructor-based, not `_get_ls_params`-based** — versions flow
through `self.metadata` (local metadata on traces), not through
`LangSmithParams`. This matches JS and makes child-class version
inheritance automatic (no merge/clobber issues).
- **`versions` is local (non-inheritable) metadata** — `self.metadata`
is passed to `CallbackManager.configure` as `local_metadata`
(`add_metadata(..., inherit=False)`), so `versions` is attached **once
per chat-model run** and is **not** propagated to child runs or
duplicated onto every streaming chunk. This is intentionally the
opposite of the inheritable-per-chunk metadata that #36588 was reducing
for performance — `versions` does not regress that path.
- **`add_metadata` deep-merge is a correctness fix, not just for
versions** — previously `add_metadata`/`merge_configs` did a flat
top-level `dict.update`/spread, so any nested metadata dict baked into a
config (e.g. via `.with_config({"metadata": {...}})`) would be wholly
replaced when a caller also passed `metadata`. `_merge_metadata_dicts`
merges one level deep so user-provided `config.metadata.versions` and
model-set `versions` coexist instead of clobbering. The merge runs once
per `configure` (not per chunk), so it is off the streaming hot path.
- **One level deep only** — `_merge_metadata_dicts` is deliberately
*not* a recursive deep merge; values nested more than one level are
last-writer-wins. This covers the `versions` case without the
ambiguity/cost of arbitrary-depth merging.
- **Warn on non-dict `metadata["versions"]`** — if a user sets
`metadata={"versions": "some-string"}`, `_add_version` emits a warning
and replaces the value with the version dict rather than silently
discarding user data or crashing. This is a soft breaking change for
anyone who previously stored non-dict values at this key.

### Follow-ups (tracked separately, out of scope here)

- JS `mergeConfigs` still flat-spreads nested metadata, so
`metadata.versions` can still clobber on the JS side until an equivalent
deep-merge lands.

---

Made by [Open SWE](https://openswe.vercel.app)

---------

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

.github/workflows/check_core_versions.yml

@@ -1,67 +0,0 @@
-# Ensures version numbers in pyproject.toml and version.py stay in sync.
-#
-# (Prevents releases with mismatched version numbers)
-
-name: "🔍 Check Version Equality"
-
-on:
-  pull_request:
-    paths:
-      - "libs/core/pyproject.toml"
-      - "libs/core/langchain_core/version.py"
-      - "libs/partners/anthropic/pyproject.toml"
-      - "libs/partners/anthropic/langchain_anthropic/_version.py"
-
-permissions:
-  contents: read
-
-jobs:
-  check_version_equality:
-    runs-on: ubuntu-latest
-
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
-
-      - name: "✅ Verify pyproject.toml & version.py Match"
-        run: |
-          # Check core versions
-          CORE_PYPROJECT_VERSION=$(grep -Po '(?<=^version = ")[^"]*' libs/core/pyproject.toml)
-          CORE_VERSION_PY_VERSION=$(grep -Po '(?<=^VERSION = ")[^"]*' libs/core/langchain_core/version.py)
-
-          # Compare core versions
-          if [ "$CORE_PYPROJECT_VERSION" != "$CORE_VERSION_PY_VERSION" ]; then
-            echo "langchain-core versions in pyproject.toml and version.py do not match!"
-            echo "pyproject.toml version: $CORE_PYPROJECT_VERSION"
-            echo "version.py version: $CORE_VERSION_PY_VERSION"
-            exit 1
-          else
-            echo "Core versions match: $CORE_PYPROJECT_VERSION"
-          fi
-
-          # Check langchain_v1 versions
-          LANGCHAIN_PYPROJECT_VERSION=$(grep -Po '(?<=^version = ")[^"]*' libs/langchain_v1/pyproject.toml)
-          LANGCHAIN_INIT_PY_VERSION=$(grep -Po '(?<=^__version__ = ")[^"]*' libs/langchain_v1/langchain/__init__.py)
-
-          # Compare langchain_v1 versions
-          if [ "$LANGCHAIN_PYPROJECT_VERSION" != "$LANGCHAIN_INIT_PY_VERSION" ]; then
-            echo "langchain_v1 versions in pyproject.toml and __init__.py do not match!"
-            echo "pyproject.toml version: $LANGCHAIN_PYPROJECT_VERSION"
-            echo "version.py version: $LANGCHAIN_INIT_PY_VERSION"
-            exit 1
-          else
-            echo "Langchain v1 versions match: $LANGCHAIN_PYPROJECT_VERSION"
-          fi
-
-          # Check langchain-anthropic versions
-          ANTHROPIC_PYPROJECT_VERSION=$(grep -Po '(?<=^version = ")[^"]*' libs/partners/anthropic/pyproject.toml)
-          ANTHROPIC_VERSION_PY_VERSION=$(grep -Po '(?<=^__version__ = ")[^"]*' libs/partners/anthropic/langchain_anthropic/_version.py)
-
-          # Compare langchain-anthropic versions
-          if [ "$ANTHROPIC_PYPROJECT_VERSION" != "$ANTHROPIC_VERSION_PY_VERSION" ]; then
-            echo "langchain-anthropic versions in pyproject.toml and _version.py do not match!"
-            echo "pyproject.toml version: $ANTHROPIC_PYPROJECT_VERSION"
-            echo "_version.py version: $ANTHROPIC_VERSION_PY_VERSION"
-            exit 1
-          else
-            echo "Langchain-anthropic versions match: $ANTHROPIC_PYPROJECT_VERSION"
-          fi

.github/workflows/check_versions.yml

@@ -0,0 +1,54 @@
+# Ensures version numbers in pyproject.toml and _version.py stay in sync.
+#
+# (Prevents releases with mismatched version numbers)
+
+name: "Check Version Equality"
+
+on:
+  pull_request:
+    paths:
+      - "libs/core/pyproject.toml"
+      - "libs/core/langchain_core/version.py"
+      - "libs/langchain_v1/pyproject.toml"
+      - "libs/langchain_v1/langchain/__init__.py"
+      - "libs/partners/*/pyproject.toml"
+      - "libs/partners/**/_version.py"
+
+permissions:
+  contents: read
+
+jobs:
+  check_version_equality:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+
+      - uses: astral-sh/setup-uv@0ca8f610542aa7f4acaf39e65cf4eb3c35091883 # v7
+        with:
+          python-version: "3.12"
+
+      - name: "Verify pyproject.toml & version files match"
+        run: |
+          FAILED=0
+
+          for dir in libs/core libs/langchain_v1 libs/partners/*; do
+            [ -f "$dir/Makefile" ] || continue
+            if grep -q '^check_version:' "$dir/Makefile"; then
+              echo "--- $dir ---"
+              make -C "$dir" check_version || FAILED=1
+            elif find "$dir" -maxdepth 2 -name '_version.py' -not -path '*/tests/*' \
+                | grep -q .; then
+              # A package ships a _version.py but has no way to verify it stays
+              # in sync with pyproject.toml. Don't let it pass unchecked.
+              echo "--- $dir ---"
+              echo "Error: $dir has a _version.py but no 'check_version' Makefile target"
+              FAILED=1
+            fi
+          done
+
+          if [ "$FAILED" -ne 0 ]; then
+            echo ""
+            echo "One or more version checks failed!"
+            exit 1
+          fi