Restrict upgrade of sample decision in composite sampler#13
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Summary
Fix CompositeSampler to enforce restrict-only semantics: later samplers can only
restrict the sampling decision, never upgrade it.
Problem
CompositeSampler used a "last wins" strategy — the loop unconditionally overwrote
the result with each sampler's decision, only short-circuiting on Drop. This allowed
a later sampler to upgrade a prior restriction:
RecordOnly → RecordAndSample → final: RecordAndSample (wrong)
Solution
The loop now tracks the strictest (minimum) decision seen so far, using the OTel SDK's
enum ordering (Drop < RecordOnly < RecordAndSample). A later sampler can only tighten
the decision, never loosen it:
RecordOnly → RecordAndSample → final: RecordOnly (correct)
Tests
Breaking Change
Callers relying on the old "last sampler wins" behavior will see different results.
This is intentional — the old behavior was a bug.