Fix contradicting memory loss: ADD new fact when DELETing old one

[joaquinhuigomez]

Summary

• Update DEFAULT_UPDATE_MEMORY_PROMPT to ADD the new fact when DELETing a contradicting old one
• Prevents silent data loss when memory contradictions occur

The DELETE section of the update memory prompt instructed the LLM to delete contradicting memories but never to add the replacement fact. For example, adding "I hate Chinese food" after "I love Chinese food" would delete the old memory and discard the new one, leaving the memory store empty.

The fix updates the prompt instructions and example so the LLM emits both a DELETE for the old memory and an ADD for the new contradicting fact. The memory processing pipeline already handles ADD and DELETE events independently, so no code changes are needed beyond the prompt.

Added a test to verify the prompt contains ADD instructions in the contradiction/DELETE section.

Fixes #4536

[SaharshPatel24]

Good fix for a real bug — the core idea is correct and the pipeline already handles ADD/DELETE independently.

One small suggestion: the new instruction 'For the new ADD entry, generate a new ID' contradicts the existing line 264 which says 'do not generate any new ID'. Also, the pipeline ignores the ID on ADD events anyway — it always generates a fresh UUID internally via _create_memory().

So you could simplify by just omitting the ID field in the ADD example:

{
    "text": "Dislikes cheese pizza",
    "event": "ADD"
}

This keeps it consistent with the existing prompt instruction and avoids confusing the LLM with contradicting rules. Not a blocker, just a cleaner approach.

[joaquinhuigomez]

Good point — removed the id field from the ADD entry. The pipeline ignores it anyway. Updated.

[joaquinhuigomez]

Thanks for the approval — anything else needed to merge?

[kartik-mem0]

Closing as superseded by the v3 memory pipeline (#4805).

The v3 algorithm replaced UPDATE_MEMORY_PROMPT with ADDITIVE_EXTRACTION_PROMPT, which is ADD-only — contradictions are now handled via memory linking instead of DELETE operations. The prompt changes in this PR target code that's no longer in the active code path.

Thank you for the contribution! The underlying issue (#4536) is now resolved by the architectural change in v3.