## Summary
Replaces the single-roundtrip `UNION ALL` DeltaChannel read with a
two-stage query that avoids fetching unused snapshot blobs, then removes
the old combined path entirely.
### Problem
`_get_channel_writes_history` used a single `UNION ALL` query that
fetched **all** checkpoint metadata, writes, and blobs for a
`(thread_id, channel)` in one shot. With `snapshot_frequency=N`, this
pulled back O(N/freq) full-size snapshot blobs even though only the
nearest one is needed to seed reconstruction. At 500 turns with
`snapshot_frequency=10`, this meant fetching ~100 complete
message-history snapshots per read.
### Solution
Two-stage read:
- **Stage 1** — lightweight scan of `checkpoints` only (no blob bytes):
walks the parent chain from the target checkpoint and stops at the first
ancestor with a snapshot, returning `chain_cids` and `seed_version`
- **Stage 2** — targeted fetch: only the writes for `chain_cids` and the
single seed blob at `seed_version`
The two-stage path is now unconditional — the old combined query and
`LG_DELTA_TWO_STAGE_QUERY` env-var gate have been removed.
### Sentinel cleanup
`DELTA_SENTINEL` is now a pure in-memory signal and is never written to
storage:
- Postgres `put()` already stripped it from `channel_values` before
writing blobs
- Memory saver `put()` now stores `"empty"` instead of serializing the
sentinel
- `EXT_DELTA_SENTINEL` (msgpack ext code 8) removed from
`JsonPlusSerializer`
- `DELTA_SENTINEL` is kept as an in-memory marker:
`DeltaChannel.checkpoint()` returns it so savers know to skip it, and
`_ChannelWritesHistory.seed` uses it to mean "no snapshot found, start
from empty"
## Performance
Benchmarked at `snapshot_frequency=10` on Postgres (`~100 tok/msg`):
| turns | old combined query | two-stage |
|------:|-------------------:|----------:|
| 50 | 6.0ms | 2.8ms (2.1x faster) |
| 100 | 10.1ms | 5.6ms (1.8x faster) |
| 500 | **216.1ms** | 15.3ms (**14x faster**) |
The old query's read time grew super-linearly with turn count because
each read fetched O(N/freq) full snapshot blobs. Two-stage keeps read
depth bounded by `snapshot_frequency` regardless of thread length.
## Test plan
- `make test` in `libs/checkpoint`, `libs/checkpoint-postgres`,
`libs/langgraph`
- Removed `test_delta_sentinel_serde_round_trip` (sentinel no longer
serializable)
- Updated `test_memory.py` — delta channel blobs stored as `"empty"`,
not serialized sentinel
- Updated `test_channels.py` — `channel_values` no longer contains
sentinel key for DeltaChannels
- Deleted `test_delta_channel_two_stage_benchmark.py` (one-stage vs
two-stage comparison; path no longer exists)
---------
Co-authored-by: Sydney Runkle <54324534+sydney-runkle@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
## Summary
Fixes#7498 — `MESSAGE_COERCION_FAILURE` when resuming threads
checkpointed before v1.0.1.
**Root cause:** PR #6269 (v1.0.1) added an `_allowed_json_modules`
security gate to `JsonPlusSerializer._reviver`. The gate defaults to
`None`, so old `"json"`-format checkpoint blobs containing `lc=2`
constructor dicts (the pre-msgpack serialization format for pydantic
objects like `HumanMessage`) are now returned as raw dicts instead of
being reconstructed. Those raw dicts reach `add_messages →
convert_to_messages`, which sees `type="constructor"` and raises
`MESSAGE_COERCION_FAILURE`. Fresh first-turn messages are unaffected
because current `dumps_typed` only writes `"msgpack"` blobs.
**Fix:** `_reviver` now reconstructs `lc=2` blobs whose target class is
already in `SAFE_MSGPACK_TYPES` — the same curated allowlist already
used by the msgpack deserialization path (includes all standard
LangChain message types). Unknown classes are still blocked, preserving
the security intent of #6269.
## Changes
- `libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py` — add
`_is_safe_json_type()` helper; update `_reviver` and
`_check_allowed_json_modules` to allow safe types without an explicit
allowlist
- `libs/checkpoint/tests/test_jsonplus.py` — two new regression tests:
safe-type `lc=2` blobs revive correctly; unknown-type `lc=2` blobs stay
blocked
## Test plan
- [ ] `test_lc2_json_safe_type_revives_without_allowlist` —
`HumanMessage`/`AIMessage` lc=2 JSON blobs round-trip to proper
`BaseMessage` objects with no allowlist configured
- [ ] `test_lc2_json_unknown_type_stays_blocked_without_allowlist` —
`pprint.pprint` lc=2 blob still returns raw dict (not reconstructed)
- [ ] `test_deserde_invalid_module` — existing behaviour unchanged
- [ ] Full `test_jsonplus.py` suite: 93/93 passing
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
bumping core dependency for `langgraph-prebuilt` to `>1.0.0` so that we
can take advantage of internal utils that allow `ToolRuntime` injection.
We were previously bumping the version in lock step with prebuilt (prev
version was 0.3.67), so this pattern is in line with that.
Also updating snapshots accordingly:
* New mermaid syntax for a few graphs
* Removal of `examples` from `AIMessage`
* catching error thrown by asyncio
* using 2nd check for annotations given Pydantic 2.12 changes
* skipping tests for remote graph bc langgraph-api is dependent on
`jsonschema-rs`
* skipping tests w/ pydantic v1 models
```bash
hint: This usually indicates a problem with the package or the build environment.
help: `jsonschema-rs` (v0.29.1) was included because `langgraph:dev` (v1.0.0rc1) depends on `langgraph-cli[inmem]` which
depends on `langgraph-api` (v0.4.29) which depends on `jsonschema-rs`
```
not yet testing for free threaded python, that'll be much more involved!
ended up separating lint / testing deps during this process bc I was
getting a ton of not required deps while testing that were complicating
things :/
* Migrate to `uv`
* Format `pyproject.toml` files properly
* Remove upper bounds on dependencies, and bounds on dev dependencies
(we should be using latest)
* Move to hatch for packaing
In the future we should:
* Set up dependabot / automate lockfile updates and tests
* Add tests for min compatible versions (I'll do this right after merge)
* Use dynamic versioning
* Bump `pydantic` to v2.11.4 in the lockfile, we have some tests failing
* Implement serialization with msgpack library
- encode custom python objects with a msgpack extension type, with constructor path string, and args encoded as nested msgpack doc
* Smaller msgpack extension types
* Update lock files
* lock
* Don't delegate to pydantic json
* Fix kafka serde
- should use our serializer to load, as inputs to subgraphs are serialized using it
* Performance improvements in checkpointer libs
- Use sha1 instead of md5 for hashing (faster in python 3.x)
- Use orjson instead of json for json dumping (sadly can't use for json loading)
* Update tests
* Update
* Use random number instead of hash for get_version_number
* Avoid saving writes for the last task to complete in each step
- only when possible, exceptions for ERROR, INTERRUPT, SEND
* Make Channel.from_checkpoint a regular function
- context manager no longer needed since Context became a managed value
* Use __slots__ for Channels
* Fix for kafka
* Remove unused fil;e
* Add benchmark-fast command for running locally
* Small improvements to jsonplus serializer
* Don't use PregelNode.mapper when schema is a typed dict
- All it would do is create a new copy of same dict
* Avoid copying checkpoint when fetching at beginning of loop
* Fix needs array
* Update tests
