fix(core): merge strategy and per-call sampling requirements

[ajbozarth]

Pull Request

Issue

Fixes #1698

Description

SamplingStrategy._merge_requirements resolved strategy-level and per-call requirements by supersede rather than merge: when the strategy had its own requirements they won outright and the per-call list was silently dropped (and when it had none, the per-call list was used). The two lists were never combined. This contradicted both the method name and the sample() requirements docstring, which have described the lists as "merged with global requirements" since sampling was first added — a quiet correctness footgun where a requirement the caller configured could go unenforced with no error or warning.

This changes _merge_requirements to return the union of both lists (deduplicated, order-preserving), so every requirement configured on the strategy or at the call site is enforced. Because Requirement has no value equality, deduplication is by object identity: two distinct Requirement instances are always kept and validated, and a real duplicate only arises when the same instance appears in both lists (where which copy is kept is immaterial). The strategy class docstrings (SamplingStrategy, BaseSamplingStrategy, BaseMBRDSampling) are aligned with the merge semantics.

Because this changes released behavior for act() / aact() / instruct() / sample() that has shipped for ~13 months, it was split out of #1697 into its own issue (#1698) and reviewed before implementing.

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Inverted the existing test_global_requirements_override_per_call (now test_global_and_per_call_requirements_are_merged) to assert both lists are evaluated, and added test_merged_requirements_dedup_shared_instance covering identity-based deduplication of a requirement present in both lists.

Attribution

• AI coding assistants used

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Adding a new component, requirement, sampling strategy, or tool?

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• Component
• Requirement
• Sampling Strategy
• Tool