Billtrim: AWS bill savings

The two tools operate at clearly different granularities: analyze_aws_bill takes a whole CSV export and returns ranked waste findings, while explain_aws_usage_type takes a single usage-type string and returns an explanation. The descriptions even state the routing rule explicitly ('use it when you already have a line item and do not need to analyze a whole file'), leaving no realistic path to misselection.

Both names follow the same verb_noun snake_case convention (analyze_aws_bill, explain_aws_usage_type) with a consistent 'aws' domain qualifier. No mixed casing or stylistic drift between the two.

The surface is genuinely narrow — a stateless bill-analysis helper — so two tools are defensible, but it sits at the thin end where an agent has almost no room to compose a workflow. Two tools is borderline rather than clearly well-scoped.

The domain is covered at both entry points (whole-file analysis and single-line explanation), which are the two natural ways an agent would approach an AWS bill. Minor gaps remain: no way to re-query or drill into a specific finding from a prior analysis, and no comparison across billing periods, but these are workarounds rather than blockers.