delta-channel-dump

Recover messages (and other channels) from a Postgres-backed LangGraph thread written by langgraph >= 1.2 (DeltaChannel format) — including LangGraph Server / langgraph-api deployments on the Postgres runtime, deepagents 0.6.x, or any OSS app using PostgresSaver — before rolling back to an older runtime such as deepagents 0.5.x / langgraph < 1.2.

langgraph-api uses the same checkpoints / checkpoint_blobs / checkpoint_writes schema as OSS checkpoint-postgres; this script reads those tables directly.

On the older runtime, add_messages does not understand the EXT_DELTA_SNAPSHOT msgpack ext code and silently returns an empty list for affected channels. This tool reads the raw checkpoint blobs from Postgres and emits JSON you can inspect and re-apply via update_state (LangGraph Server SDK) or graph.update_state (OSS).

Install

bash

pip install "psycopg[binary]" ormsgpack

Run

bash

export DATABASE_URI=postgres://user:pass@host:5432/dbname
python3 dump.py \
    --thread-id <uuid> \
    --channel messages \
    [--channel files ...] \
    [--checkpoint-id <uuid>] \
    [--checkpoint-ns ""] \
    --output recovery.json

--thread-id (required): thread UUID
--channel (required, repeatable): channel names to recover
--checkpoint-id (optional): target checkpoint; defaults to latest
--checkpoint-ns (optional): namespace; defaults to ""
--database-uri (optional): Postgres URI; defaults to DATABASE_URI env var
--output (optional): output file; defaults to stdout

Output

json

{
  "thread_id": "...",
  "checkpoint_ns": "",
  "target_checkpoint_id": "...",
  "parent_checkpoint_id": "...",
  "channels": {
    "messages": {
      "delta_kind": "snapshot",
      "seed_checkpoint_id": "...",
      "seed_version": "...",
      "seed": [{ "type": "ai", "content": "...", "id": "ai-0" }],
      "writes": [
        {
          "checkpoint_id": "...",
          "task_id": "...",
          "idx": 0,
          "value": [{ "type": "ai", "content": "...", "id": "ai-10" }]
        }
      ]
    }
  }
}

delta_kind is one of:

snapshot — DeltaChannel snapshot blob (channel_values[ch] == true)
legacy_plain — pre-DeltaChannel inline or blob value
no_seed — walked to root without finding a populated ancestor

writes are ordered oldest-to-newest (the order a reducer would replay them).

Reducing back to a single list

For deepagents-style messages, combine seed and writes, then deduplicate:

python

import json

data = json.load(open("recovery.json"))
ch = data["channels"]["messages"]
messages = list(ch["seed"] or [])
for w in ch["writes"]:
    messages.extend(w["value"] or [])

# Dedup by id, keep last; drop RemoveMessage tombstones
by_id = {}
for m in messages:
    if isinstance(m, dict) and m.get("type") == "remove":
        by_id.pop(m.get("id"), None)
    elif isinstance(m, dict) and m.get("id"):
        by_id[m["id"]] = m
    else:
        by_id[id(m)] = m
reduced = list(by_id.values())

This approximates _messages_delta_reducer semantics; adjust for your graph.

Re-applying

python

from langgraph_sdk import get_client

client = get_client(url="http://localhost:8123")
await client.threads.update_state(
    thread_id,
    values={"messages": reduced},
)

Review the recovered JSON before calling update_state. This tool is read-only and intentionally does not mutate the database.

Scope / non-goals (v1)

Postgres only — OSS PostgresSaver or langgraph-api Postgres runtime; not inmem, gRPC core, Mongo, or Redis checkpointer backends
No AES decryption (LANGGRAPH_AES_KEY) or custom encryption
No reducer — raw seed + writes only
No automatic update_state — operator applies manually

Copying

dump.py is self-contained. Copy it anywhere; only psycopg[binary] and ormsgpack are required at runtime. No langgraph imports.