MISSING_CHECKPOINTER: persistence features need a checkpointer on compile()

TL;DR: You used a persistence feature (threads, time travel, interrupts, human-in-the-loop) without passing a checkpointer to compile(). Pass one; the in-memory saver needs no extra install.

The fix

1. Every persistence feature (per-thread history, interrupts, time travel) requires the checkpointer. There is no default.
2. InMemorySaver is for dev and tests. For local durable runs use SqliteSaver (langgraph-checkpoint-sqlite); for production use PostgresSaver (langgraph-checkpoint-postgres).
3. Async graphs need AsyncSqliteSaver / AsyncPostgresSaver.
4. In JS this is the MISSING_CHECKPOINTER error code.

When to use this

• You are seeing this exact error message; match the block above, not just part of it.
• The failing call matches the scenario in the title: MISSING_CHECKPOINTER.
• You want the fastest verified fix before digging through logs.

When not to use this

• Your error text differs from the block above; close cousins often have different causes.
• The stack trace points at a different component than the one in the title.
• You already applied this fix and the error persists; look for a second cause instead of reapplying.

Compatibility

• Not pinned to a specific version; follows current MISSING_CHECKPOINTER behavior.

Error catalog entry grounded in the official MISSINGCHECKPOINTER error page and checkpointers docs, verified 2026-09-26. Error page: https://docs.langchain.com/oss/python/langgraph/errors/MISSINGCHECKPOINTER ; checkpointers: https://docs.langchain.com/oss/python/langgraph/checkpointers