fix(core): strip message IDs from cache keys using model_copy

[aroun-coumar]

Description:

Closes #33883

Chat model cache keys are generated by serializing messages via dumps(messages). The optional BaseMessage.id field (a UUID used solely for tracing/threading) is included in this serialization, causing functionally identical messages to produce different cache keys. This results in repeated API calls, cache bloat, and degraded performance in production workloads (e.g., agents, RAG chains, long conversations).

This change normalizes messages only for cache key generation by stripping the nonsemantic id field using Pydantic V2’s model_copy(update={"id": None}). The normalization is applied in both synchronous and asynchronous cache paths (_generate_with_cache / _agenerate_with_cache) immediately before dumps().

normalized_messages = [
    msg.model_copy(update={"id": None})
    if getattr(msg, "id", None) is not None
    else msg
    for msg in messages
]
prompt = dumps(normalized_messages)

[codspeed-hq]

CodSpeed Performance Report

Merging #33915 will not alter performance

_{Comparing aroun-coumar:fix/cache-strip-message-ids (608e470) with master (69c7d1b)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched
⏩ 21 skipped¹

Footnotes

1. 21 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩