fix: tolerate unpickleable Redis cache values

[jynbil1]

Fixes #8476.

Summary

• make Redis cache serialization failures explicit for TypeError/AttributeError/PicklingError before network writes
• keep chat cache type metadata as a string and treat pickle-only cache write failures as cache misses
• apply the same non-fatal cache-write handling to session cache writes so graph execution can continue when Redis cannot serialize runtime objects
• add regression coverage for async chat cache, sync chat cache, session cache, load-session fallback, unrelated TypeError re-raise, and Redis pre-network serialization failure

Validation

• uv run ruff check src/backend/base/langflow/services/cache/service.py src/backend/base/langflow/services/cache/utils.py src/backend/base/langflow/services/chat/service.py src/backend/base/langflow/services/session/service.py src/backend/tests/unit/services/test_cache_serialization.py
• uv run pytest src/backend/tests/unit/services/test_cache_serialization.py
• git diff --check

Summary by CodeRabbit

• Chores

  • Updated langchain_core dependency to version 1.4.0 across all starter projects.

• Bug Fixes

  • Improved cache reliability with enhanced error handling and recovery mechanisms for serialization failures, ensuring smoother operation when caching encounters issues.

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Walkthrough

This PR improves cache serialization robustness to address Celery/Redis deployment failures when flows contain unpickleable objects. Serialization errors are now caught at the Redis level, classified for error-specific handling in ChatService and SessionService, and gracefully degraded (cache write skipped, warning logged). The PR also bumps langchain_core from 1.3.2 to 1.4.0 across 18 starter projects.

Changes

Cache Serialization Resilience

Layer / File(s)	Summary
Redis Cache Validation and Error Detection src/backend/base/langflow/services/cache/service.py, src/backend/base/langflow/services/cache/utils.py	RedisCache.set now serializes explicitly via dill.dumps with comprehensive exception handling for serialization failures, empty data, and Redis write failures. New is_cache_serialization_error utility classifies TypeError messages to distinguish pickle-related failures from unrelated errors by checking for "pickle" or "pickled" substrings.
Chat Service Cache Resilience src/backend/base/langflow/services/chat/service.py	ChatService.set_cache stores cached payloads with string type metadata via _cache_type_name utility instead of raw class objects. Cache write path is wrapped in TypeError handling: serialization-related failures are logged and return False, enabling graceful fallback; unrelated TypeErrors are re-raised.
Session Service Cache Resilience src/backend/base/langflow/services/session/service.py	SessionService introduces _set_cache_value helper for unified async/sync cache writes with serialization error handling. Both load_session and update_session now delegate through this helper, which skips cache writes and logs warnings on serialization failures, allowing sessions to load even with unpickleable state.
Test Infrastructure and Fakes src/backend/tests/unit/services/test_cache_serialization.py (imports and helpers)	Defines async/sync cache service test doubles (RecordingAsyncCache, RejectingAsyncCache, RecordingSyncCache, RejectingSyncCache), UnpickleableValue type for triggering serialization failures, and make_chat_service helper for test dependency injection.
Cache Serialization Test Suite src/backend/tests/unit/services/test_cache_serialization.py (test functions)	Comprehensive tests validating ChatService type name storage and pickle failure handling (async/sync paths), SessionService graceful degradation during update_session and load_session, and RedisCache early rejection of unpickleable values before network calls.

Starter Projects Dependency Bump

Layer / File(s)	Summary
Starter Project langchain_core Updates src/backend/base/langflow/initial_setup/starter_projects/*.json	Consistent version bump of langchain_core from 1.3.2 to 1.4.0 in Agent, File, ApifyActors, MCPTools, and YfinanceComponent nodes across 18 starter project definitions. Each file receives 1–4 dependency version updates matching the components present in that flow.

Sequence Diagram

sequenceDiagram
  participant Caller
  participant ChatService
  participant CacheService
  participant Dill
  participant Logger
  Caller->>ChatService: set_cache(key, data)
  ChatService->>ChatService: type_name = _cache_type_name(data)
  ChatService->>CacheService: upsert(key, {type: type_name, ...})
  alt Pickle/Serialization TypeError
    CacheService->>Dill: dumps(data)
    Dill-->>CacheService: PicklingError or TypeError
    CacheService-->>ChatService: TypeError
    ChatService->>Logger: awarning(pickle error)
    ChatService-->>Caller: False
  else Success
    CacheService->>Dill: dumps(data)
    Dill-->>CacheService: pickled bytes
    CacheService->>CacheService: store in memory/Redis
    CacheService-->>ChatService: success
    ChatService->>CacheService: contains(key)
    ChatService-->>Caller: cache_updated boolean
  else Unrelated TypeError
    CacheService-->>ChatService: TypeError
    ChatService-->>Caller: re-raise
  end

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🎯 3 (Moderate) | ⏱️ ~25 minutes

🚥 Pre-merge checks | ✅ 8 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 6.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (8 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: making the system tolerate unpickleable Redis cache values by handling serialization failures gracefully.
Linked Issues check	✅ Passed	The PR fully addresses issue #8476 by implementing error handling for unpickleable Redis values, treating serialization failures as non-fatal cache misses so flows continue execution.
Out of Scope Changes check	✅ Passed	All changes are in-scope: cache serialization error handling, chat/session cache tolerance logic, and corresponding tests. Version bumps in starter projects are unrelated but minimal and acceptable.
Test Coverage For New Implementations	✅ Passed	Test file test_cache_serialization.py with 8 tests covers cache serialization error handling. Tests follow naming conventions and use proper assertions.
Test Quality And Coverage	✅ Passed	8 async tests cover type caching, pickle handling, graceful degradation. Proper patterns, behavior validation, and all required paths tested.
Test File Naming And Structure	✅ Passed	File meets all requirements: test_*.py pattern, pytest structure with async, unit test directory, descriptive test names, helper classes/setup, edge case coverage, and positive/negative scenarios.
Excessive Mock Usage Warning	✅ Passed	Test doubles are minimal, purpose-specific implementations of cache interfaces. No mock libraries used. 8 tests verify real service behavior with appropriate test doubles for isolated unit testing.

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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[jynbil1]

Maintainer note: the current Update Component Index failure appears to be a fork checkout issue rather than a component-index diff. The job log stops in actions/checkout with A branch or tag with the name 'fix/tolerate-unpickleable-redis-cache' could not be found, which is looking on langflow-ai/langflow instead of the fork branch.

Local verification on the current PR branch still passes:

uv run pytest src/backend/tests/unit/services/test_cache_serialization.py
# 8 passed

git diff --check origin/main...HEAD
# no output

[jynbil1]

CI triage after the latest run:

• Update Component Index failed before running project logic: actions/checkout could not find an upstream branch/tag named fix/tolerate-unpickleable-redis-cache. This appears to be a fork-PR workflow/ref issue rather than a source diff issue.
• Merge Frontend Jest + Playwright Coverage Reports reached Codecov upload, then failed with Token required - not valid tokenless upload, also outside the patch.
• The only test failure is tests/core/integrations/assistant-panel.spec.ts:5 waiting for assistant-input-textarea; this is unrelated to the backend cache/starter-project diff in this PR.

The focused cache serialization changes remain covered by the added unit tests; I can patch source issues quickly if a maintainer sees a diff-related failure.

[jynbil1]

Follow-up after rebasing/merging latest main into the PR branch and pushing 39dbf85:

Local verification on the current branch still passes:

uv run pytest src/backend/tests/unit/services/test_cache_serialization.py
# 8 passed

uv run ruff check src/backend/base/langflow/services/cache/service.py src/backend/base/langflow/services/cache/utils.py src/backend/base/langflow/services/chat/service.py src/backend/base/langflow/services/session/service.py src/backend/tests/unit/services/test_cache_serialization.py
# All checks passed

git diff --check origin/main...HEAD
# no output

The new Docker-image failure appears to be infrastructure cancellation, not a test/build assertion from this patch. The job ends with:

The runner has received a shutdown signal
ERROR: failed to build: failed to receive status: rpc error: code = Unavailable desc = error reading from server: EOF
The operation was canceled.

The other remaining failures are still the fork checkout issue in Update Component Index and the unrelated frontend assistant-panel Playwright shard.