Adds validate_caller_dimensions and the two ChatRequest fields that
carry them. Every limit rejects rather than trims: Langfuse drops
metadata values past 200 characters, which leaves the caller believing
something was recorded when nothing was.
Whitespace on tenant_id is refused outright instead of stripped. " t1"
and "t1" compare unequal inside an RLS policy, so silently rewriting the
caller's value would hand them a tenant whose rows they cannot find.
Non-finite floats are refused for a concrete reason: json.dumps writes
them as the bare literals NaN and Infinity, which are not valid JSON and
which JSONB rejects. Letting one through turns a caller's input mistake
into a failed insert, and the telemetry layer degrades failed inserts to
a warning -- so the mistake would surface as missing rows, nowhere else.
The new fields go after sampling so no positional construction of
ChatRequest shifts. Validation is split across three helpers to keep
each one under the complexity gate.
iomgaa
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