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Get Started Free →jeremylongshore/langchain-langgraph-basics
Build a correct LangGraph 1.0 StateGraph — typed TypedDict state with reducers, nodes, edges, compile, and recursion budgets — without hitting the silent-termination and state-replacement traps.
Passed 20 of 22 test cases with the skill, and 15 of 22 without it.
and 2 more in the full report
5 fixed15 passed either way2 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 5 test cases the skill fixed. Same model, same prompt, with and without the skill.
We recently updated our state graph library package version in production. After the deployment, our application connected to our existing PostgreSQL checkpoint database, but all existing session states are being returned as completely empty objects without throwing any database connection errors. What database maintenance step was missed during the library version upgrade?
| Checked | Without skill | With skill |
|---|---|---|
| The response specifies running PostgresSaver.setup() after upgrading the package version. | Missed | Passed |
The instructions your model reads when the skill loads.
A conditional edge whose router returns a string that is not in path_map halts
the graph without reaching END. No exception. No log line. The invocation just
returns whatever state existed at the halt point — pain-catalog entry P56, and
the single most common reason a newly wired StateGraph "almost works." The
sibling pain: Command(update={"messages": [msg]}) wipes the prior message
history because messages was declared as a plain list[AnyMessage] instead of
Annotated[list[AnyMessage], add_messages] — the reducer is what turns update
into "append" instead of "replace" (P18).
Two more gotchas this skill defuses:
GraphRecursionError: Recursion limit of 25 reached fires on graphs
that never loop, because recursion_limit counts supersteps (one step
per synchronous batch of node executions), not loop iterations. A planner
langgraph silently reads old PostgresSaver checkpoints
as empty state. Checkpoint schemas evolve; PostgresSaver.setup() must be
rerun after every version bump before production traffic.This skill walks through a minimal StateGraph end to end: a TypedDict state
with reducers on every list field, node functions that return partial-state
dicts, edges and defensive conditional edges with END as a fallback in
path_map, compilation with a checkpointer, recursion_limit sizing, and
invocation with an explicit thread_id. Pin: langgraph 1.0.x,
langchain-core 1.0.x. Pain-catalog anchors: P16, P18, P20, P55, P56.
pip install langgraph>=1.0,<2.0 langchain-core>=1.0,<2.0langchain-model-inference), or a pure-logic graph with no LLMpip install langgraph-checkpoint-postgres and a Postgres 14+ instanceTypedDict with reducers on list fieldstest cases passed, vs 15 / 22 without
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