docs(hook_streaming): correct why _sum_cost_usd is not foundation's sum_cost_usd - #156
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Salil Das (sadlilas) merged 1 commit intoAug 26, 2026
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…um_cost_usd The docstring described this function as "replicated inline (not imported) ... to keep this hook free of foundation coupling." That is false: this package declares amplifier-foundation as a dependency and imports it in eleven places across src/, including elsewhere in this same bundle package. There is no boundary here to protect. The real reason is that this function differs from foundation's in two ways that a "de-duplicate this into the import" pass would silently regress: it returns a str (sessionCostTotal is a decimal string on the wire) and it skips non-finite values (foundation's has no such guard). Neither regression would fail a type check, because _emit takes dict[str, Any]. The docstring now says that, and points at the existing is_finite comment rather than restating it. Docstring only. No code change. Generated with [Amplifier](https://github.com/microsoft/amplifier) Co-Authored-By: Amplifier <240397093+microsoft-amplifier@users.noreply.github.com>
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Summary
_sum_cost_usdinhook_streaming.pycarried this rationale:That is false, and it invites a refactor that would introduce a real bug. Docstring only — no code change.
Coupling is not the reason
This package declares
amplifier-foundationas a dependency inpyproject.tomland imports it in eleven places acrosssrc/, including elsewhere in this same bundle package. There is no boundary here to protect.The actual reason: two differences a de-duplication pass would erase
str, not aDecimal.sessionCostTotalis a decimal string on the wire (docs/spec/wire-protocol.md).Decimal("NaN")andDecimal("Infinity")are validDecimals that do not raiseInvalidOperation, andx + NaNisNaN. Foundation's helper has no such guard. That reasoning is already recorded in the comment on theis_finitecheck itself, so the docstring points there rather than restating it.Neither regression would fail a type check:
_emittakesdict[str, Any], so aDecimalwould reach the wire unchecked, and there are no unit tests over this function.Verification
Zero executable lines changed.
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