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Elior Nataf LackritzandGitHub
12aeb0fddb
A raw `Pregel` graph whose input channel is a DeltaChannel saved a run's
input to it as a `NULL_TASK_ID` write on the checkpoint the run started
from, under `"sync"` and `"async"` durability. Readers apply a
checkpoint's `NULL_TASK_ID` writes as its own state, so:
- on a new thread that checkpoint is never saved, and the first run's
input was lost for good: after `{"log": [0], "plain": [0], ...}`, `log`
read `[2]` next to `plain` `[0, 2]`;
- the last checkpoint of a run read the next run's input;
- a run with input from an older checkpoint (`checkpoint_id`) leaked its
input into the branch that already grew from it, and read that branch's
input when it had one.
The input's writes now go on the checkpoint the run starts from under a
task id of their own, `uuid5(checkpoint_id, INPUT)`, the one
`update_state` uses for an input update. On a new thread, or a
checkpoint a `checkpoint_id` addressed, which may already have children
that would read them, nothing is stored there and the input checkpoint
snapshots the channel instead. A normal run stores the same write as
before, and `durability="exit"`, which already kept the input right, is
unchanged. Threads saved before this keep the input writes already
stored on their checkpoints.
A `StateGraph` routes its input through its start channel, so only raw
`Pregel` graphs hit this.
JS twin: langchain-ai/langgraphjs#2981
## Tests
`test_delta_channel_run_input.py`, under every durability, with `invoke`
and `ainvoke`: two runs on a new thread, and a run with input from an
older checkpoint whose other branch had DeltaChannel input or none.
Every checkpoint reads the same in the DeltaChannel and a plain channel.
The 12 sync and async cases fail on main, and dropping the task id, the
new-thread snapshot or the addressed-checkpoint snapshot each fails its
own cases. The `langgraph` and `prebuilt` suites pass (without Redis),
and `lint_package` and `lint_tests` are clean.