evolving_agent

Example: evolving_agent

A minimal end-to-end demo of LangMigrate's lazy online migration, using LangGraph's InMemorySaver so it runs with no database.

The schema evolution

Revision	Change	Safety
a1c0 (add_context)	add context dict with a default	Safe
b2d1 (rename_msgs)	rename msgs → messages, coerce count str → int	Unsafe (handled)

A "v0" thread persisted before any of this has {"msgs": [...], "count": "3"} and no revision tag.

Run it

uv run python examples/evolving_agent/demo.py

You'll see a legacy v0 checkpoint loaded through a MigrationInterceptor, upgraded through the cascade v0 → a1c0 → b2d1, and the database self-healed by the idempotent write-back (same checkpoint id preserved).

Inspect with the CLI

cd examples/evolving_agent
uv run langmigrate history
uv run langmigrate check
uv run langmigrate current

Try it on Postgres

docker compose up -d          # from the repo root
export LANGMIGRATE_URL="postgresql://langmigrate:langmigrate@localhost:5442/langmigrate"
# wire a PostgresSaver into your graph, wrap it with MigrationInterceptor,
# or run a proactive batch:  uv run langmigrate upgrade head