fix(langchain): keep tool envelopes JSON-serializable for date and decimal rows

[MohammadHijjawi97]

Summary

make_success now passes data through the existing json_safe helper, so wren_query / wren_recall_queries envelopes stay JSON-serializable when rows contain DATE, TIMESTAMP or DECIMAL values. An agent now receives JSON tool output instead of a Python repr.

What failure does this repair?

wren_query stores table.to_pylist() in data.rows, which keeps datetime.date and Decimal objects. LangChain builds the ToolMessage content with json.dumps and falls back to str() when that raises (langchain_core.tools.base._stringify), so the model gets a Python repr. Reproduction: DuckDB project with orders(id INTEGER, order_date DATE, amount DECIMAL(10,2)), tool invoked as an agent would ({"type": "tool_call", ...}):

Before:

ToolMessage.content sent to the LLM:
{'ok': True, 'content': '[{"id": 1, "order_date": "2026-05-06", "amount": "19.99"}]', 'data': {'columns': ['id', 'order_date', 'amount'], 'rows': [{'id': 1, 'order_date': datetime.date(2026, 5, 6), 'amount': Decimal('19.99')}], 'row_count': 1, 'content_truncated': False}, 'warnings': []}
-> not JSON: JSONDecodeError Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
json.dumps(envelope) -> TypeError: Object of type date is not JSON serializable

After:

{"ok": true, "content": "[{\"id\": 1, \"order_date\": \"2026-05-06\", \"amount\": \"19.99\"}]", "data": {"columns": ["id", "order_date", "amount"], "rows": [{"id": 1, "order_date": "2026-05-06", "amount": "19.99"}], "row_count": 1, "content_truncated": false}, "warnings": []}
-> parses as JSON

wren_recall_queries goes through the same path; its LanceDB rows include a created_at datetime. The conversion matches what content already shows (default=str) and what format_error already does for metadata (ISO strings, Decimal as string). Calling the tool directly now also returns these values as strings in data; toolkit.query() is unchanged and still returns Arrow.

How is it tested?

• tests/unit/test_envelope.py::test_make_success_makes_query_rows_json_serializable
• tests/integration/test_runtime_tools.py::test_wren_query_tool_call_returns_json_for_date_and_decimal_rows: real DuckDB project and a real tool call; asserts json.loads(message.content). Not marked slow, so it runs in the sdk-langchain CI job.

Both fail without the change (TypeError / JSONDecodeError) and pass with it. Full pytest in sdk/wren-langchain: 124 passed, 2 deselected (slow). ruff check . and ruff format --check . are clean.

Duplicate check

Checked open and closed PRs and issues for wren-langchain / json_safe / envelope serialization. No open PR touches sdk/wren-langchain.

Summary by CodeRabbit

• Bug Fixes
  • Query results containing dates, timestamps, or decimals can now be returned in a JSON-serializable success response, with these values represented as strings.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 2cd59ef0-fdef-4313-b484-71c21cda9cf2

📥 Commits

Reviewing files that changed from the base of the PR and between caa23ac and e523998.

📒 Files selected for processing: 3

• sdk/wren-langchain/src/wren_langchain/_envelope.py
• sdk/wren-langchain/tests/integration/test_runtime_tools.py
• sdk/wren-langchain/tests/unit/test_envelope.py

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review.

Walkthrough

The success envelope now applies json_safe to its data. Unit and integration tests cover JSON serialization of date, datetime, and decimal values.

Changes

JSON-safe success envelopes

Layer / File(s)	Summary
Convert and validate success envelope data sdk/wren-langchain/src/wren_langchain/_envelope.py, sdk/wren-langchain/tests/unit/test_envelope.py, sdk/wren-langchain/tests/integration/test_runtime_tools.py	make_success applies json_safe to envelope data. Unit tests check JSON serialization of date, datetime, and decimal values. An integration test checks date and decimal values returned through wren_query.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: paulchen79

Merge Risk: ⚪ Minimal · up to e5239

No actionable merge-blocking risk is identified; this is ready for normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly and concisely identifies the main change: keeping LangChain tool envelopes JSON-serializable for date and decimal rows.
Description check		The description includes all required sections. It explains the change, provides a reproduction and actual error output, lists targeted and full test results, and documents the duplicate check.
Docstring Coverage		Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 3 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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_{A rabbit checks the dates in rows,
And sees each decimal string now shows.
JSON carries each value through,
The envelope keeps them safe and true.
The rabbit hops, review is done.}

_{Comment @coderabbitai help to get the list of available commands.}