fix: coerce UUID session_id to string in ChatOutputResponse

[HzaRashid]

Explicitly coerces session_id inChatOutputResponse schema to be a string if a UUID is provided to prevent UUID inputs (common for session ids) from causing validation errors. Added tests covering model-level coercion.

Reproduction (before fix):

1. In an isolated lfx environment, run: lfx run agent.json "hi", where agent.json is the simple agent starter flow.
2. Observe exact failure:
   {"success": false, "type": "error", "exception_type": "ValidationError", "exception_message": "1 validation error for ChatOutputResponse\nsession_id\n Input should be a valid string [type=string_type, input_value=UUID('...'), input_type=UUID]\n For further information visit https://errors.pydantic.dev/2.12/v/string_type"}

Result (after fix):

• Re-running the same command no longer fails on ChatOutputResponse.session_id UUID validation.

This failure occurs in LFX because the graph's session id is not pre-populated as it is in Langflow. See Line 255 in src/lfx/src/lfx/base/agents/agent.py.

Summary by CodeRabbit

• New Features

  • Session identifiers provided as UUIDs are now automatically converted to string format consistently across API responses and data schemas.

• Tests

  • Added comprehensive test coverage for session identifier handling, including coercion validation and error handling for invalid session identifier types across multiple modules.

[coderabbitai]

Important

Review skipped

Auto incremental reviews are disabled on this repository.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

Walkthrough

The changes introduce UUID-to-string coercion for session_id fields across the backend and lfx codebases. A shared utility function coerce_to_str_if_uuid is added to both schema validator modules, with corresponding field validators implemented in ChatOutputResponse and DataOutputResponse schemas to ensure session_id values are consistently converted from UUID to string representation before validation.

Changes

Cohort / File(s)	Summary
Utility Functions src/backend/base/langflow/schema/validators.py, src/lfx/src/lfx/schema/validators.py	Added coerce_to_str_if_uuid helper function that converts UUID instances to strings, leaving other values unchanged.
Backend Schema Validators src/backend/base/langflow/utils/schemas.py	Added field validator coerce_session_id_uuid_to_str and docstring to ChatOutputResponse to coerce UUID session_id values to strings before model validation.
LFX Schema Validators src/lfx/src/lfx/utils/schemas.py	Added field validator coerce_session_id_uuid_to_str and docstring to both ChatOutputResponse and DataOutputResponse to coerce UUID session_id values to strings, with corresponding imports.
LFX Graph Vertex Integration src/lfx/src/lfx/graph/vertex/base.py, src/lfx/src/lfx/graph/vertex/vertex_types.py	Integrated UUID-to-string coercion in extract_messages_from_artifacts using coerce_to_str_if_uuid before constructing ChatOutputResponse instances.
Backend Test Coverage src/backend/tests/unit/utils/test_schemas.py	Added test cases validating UUID session_id coercion to string and rejection of non-string, non-UUID session_id values.
LFX Test Coverage src/lfx/tests/unit/utils/test_schemas.py, src/lfx/tests/unit/graph/vertex/test_vertex_base.py	Added comprehensive tests for UUID session_id coercion, including test doubles with strict validation and monkeypatched schema replacements to verify stringified session_id in message construction.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 6 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Excessive Mock Usage Warning	⚠️ Warning	Test file test_vertex_base.py exhibits excessive mocking: introduces _StrictChatOutputResponse test double, uses monkeypatch to replace schema classes across modules, and dedicates 80+ lines primarily to mock setup rather than testing core UUID coercion logic.	Refactor tests to use real ChatOutputResponse objects with actual UUID inputs instead of test doubles. Extract pure UUID coercion function for focused unit testing, or use integration tests. This reduces mock-heavy setup and validates actual behavior.

✅ Passed checks (6 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 80.95% which is sufficient. The required threshold is 80.00%.
Test Coverage For New Implementations	✅ Passed	PR includes comprehensive test coverage for UUID-to-string coercion implementations across backend and LFX with positive and negative test cases.
Test Quality And Coverage	✅ Passed	Test coverage for UUID session_id coercion functionality is comprehensive, spanning three test files with proper pytest patterns, error handling validation, and monkeypatching for dependency injection.
Test File Naming And Structure	✅ Passed	Test files follow proper pytest conventions with descriptive names and comprehensive coverage including both positive and negative scenarios across backend, LFX schemas, and LFX vertex modules.
Title check	✅ Passed	The title 'fix: coerce UUID session_id to string in ChatOutputResponse' directly addresses the main change: adding UUID-to-string coercion for session_id in ChatOutputResponse and related schemas to fix Pydantic validation failures.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/lfx-chatresp-uuid

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

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

[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	22.87% (7981/34889)	15.45% (4224/27334)	15.6% (1147/7348)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
2611	0 💤	0 ❌	0 🔥	43.757s ⏱️

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.36%. Comparing base (2fc6ca8) to head (6f01c7a).
⚠️ Report is 1 commits behind head on main.

❌ Your project status has failed because the head coverage (42.37%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11958      +/-   ##
==========================================
+ Coverage   37.31%   37.36%   +0.04%     
==========================================
  Files        1592     1592              
  Lines       78280    78304      +24     
  Branches    11824    11826       +2     
==========================================
+ Hits        29212    29256      +44     
+ Misses      47448    47426      -22     
- Partials     1620     1622       +2     

Flag	Coverage Δ
backend	57.39% <100.00%> (+0.06%)	⬆️
frontend	20.49% <ø> (ø)
lfx	42.37% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/backend/base/langflow/utils/schemas.py	100.00% <100.00%> (ø)
src/lfx/src/lfx/utils/schemas.py	63.52% <100.00%> (+5.99%)	⬆️

... and 12 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[coderabbitai]

the helper expects str | UUID | None, but the call site's value for session is not necessarily of those types

🧹 Nitpick comments (1)

src/lfx/src/lfx/graph/vertex/vertex_types.py (1)

170-173: The isinstance check is redundant.

The coerce_to_str_if_uuid function already handles all input types safely (UUID → string, str → passthrough, None → passthrough, other → passthrough). The conditional adds complexity without changing behavior.

Consider simplifying to match base.py (line 449):

♻️ Simplify by removing redundant type check

-            raw_session_id = message_dict.get("session_id")
-            session_id = (
-                coerce_to_str_if_uuid(raw_session_id) if isinstance(raw_session_id, (UUID, str)) else raw_session_id
-            )
+            session_id = coerce_to_str_if_uuid(message_dict.get("session_id"))

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/lfx/src/lfx/graph/vertex/vertex_types.py` around lines 170 - 173, The
isinstance guard around coerce_to_str_if_uuid is redundant; change the
session_id assignment to call coerce_to_str_if_uuid(raw_session_id)
unconditionally (replace the conditional expression that references
raw_session_id, session_id and coerce_to_str_if_uuid with a direct call) so
behavior matches base.py usage and simplifies the code.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@src/lfx/src/lfx/graph/vertex/vertex_types.py`:
- Around line 170-173: The isinstance guard around coerce_to_str_if_uuid is
redundant; change the session_id assignment to call
coerce_to_str_if_uuid(raw_session_id) unconditionally (replace the conditional
expression that references raw_session_id, session_id and coerce_to_str_if_uuid
with a direct call) so behavior matches base.py usage and simplifies the code.

---

ℹ️ Review info

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d602738 and 6ffe0d5.

📒 Files selected for processing (9)

• src/backend/base/langflow/schema/validators.py
• src/backend/base/langflow/utils/schemas.py
• src/backend/tests/unit/utils/test_schemas.py
• src/lfx/src/lfx/graph/vertex/base.py
• src/lfx/src/lfx/graph/vertex/vertex_types.py
• src/lfx/src/lfx/schema/validators.py
• src/lfx/src/lfx/utils/schemas.py
• src/lfx/tests/unit/graph/vertex/test_vertex_base.py
• src/lfx/tests/unit/utils/test_schemas.py

[HzaRashid]

Went for a middle ground approach, by validating session id to be str | uuid | None inside the ‘before’ validator with a more descriptive error message instead of silently coercing to str and then waiting for the ‘after’ check to fail with a generic message