improvement(trace): billing trace span typing

[icecrasher321]

Summary

Minor typing improvement to make invariants clearer for trace spans.

Type of Change

• Other: Code quality

Testing

N/A

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		May 1, 2026 7:30am

[cursor]

PR Summary

Medium Risk
Touches billing-related cost aggregation and BYOK/segment cost handling, so mistakes could affect what users are charged. Changes are small and covered by targeted unit tests around toolCost and segment recursion.

Overview
Improves trace-span cost handling and typing by making calculateCostSummary operate on a narrowed TraceSpan shape and using type guards to distinguish billable spans and model-breakdown children.

Adds first-class support for toolCost in TraceSpan.cost, preserves it when building spans from provider outputs, and ensures cost summaries attribute tool charges to the parent span while still skipping model-breakdown child spans to avoid double counting. Tests are updated/added to verify toolCost propagation and that non-model (e.g., tool) segment costs are not zeroed for BYOK.

^{Reviewed by Cursor Bugbot for commit dd71d11. Configure here.}

[greptile-apps]

Greptile Summary

This PR extends TraceSpan.cost with an optional toolCost field and threads it through the trace-span pipeline: span-factory.ts now propagates it from provider output (guarded to positive values), logging-factory.ts aggregates it per-model in calculateCostSummary, and both the factory and test files are tightened from any[] to the new CostTraceSpan/BillableTraceSpan narrowed types. The BYOK test is updated to actively exercise tool-segment cost preservation (previously just a future-proofing comment).

Confidence Score: 5/5

Safe to merge — all changes are additive typing improvements with no logic mutations except toolCost propagation, which is gated by a > 0 guard consistent with the provider side.

No bugs identified. The type narrowing is correct, the toolCost > 0 guard is consistent with the existing sumToolCosts guard in providers/index.ts, the BYOK zeroing correctly leaves tool segments intact, and all new behaviour is covered by tests.

No files require special attention.

Important Files Changed

Filename	Overview
apps/sim/lib/logs/types.ts	Adds toolCost?: number to TraceSpan.cost — minimal, correct addition to the existing optional-fields shape.
apps/sim/lib/logs/execution/trace-spans/span-factory.ts	Destructures and conditionally propagates toolCost from provider output into the trace span cost; guarded correctly to only write positive values, consistent with the provider-side sumToolCosts guard.
apps/sim/lib/logs/execution/logging-factory.ts	Replaces any[] in calculateCostSummary with CostTraceSpan/BillableTraceSpan narrowed types; adds hasBillableCost and isModelBreakdownSpan helpers; accepts undefined input gracefully; logic is unchanged.
apps/sim/providers/index.test.ts	Test updated to give the tool time-segment an actual cost and assert it is preserved under BYOK zeroing — correct behavioural test.
apps/sim/lib/logs/execution/logging-factory.test.ts	New test verifies that parent toolCost is preserved in cost summary while model-breakdown children are correctly skipped; assertions are accurate.
apps/sim/lib/logs/execution/trace-spans/trace-spans.test.ts	New concurrent test validates end-to-end that toolCost from a block output is faithfully round-tripped onto the resulting TraceSpan.cost.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Provider response\n(response.cost.toolCost)"] -->|"sumToolCosts()"| B["providers/index.ts\nattaches toolCost to response.cost"]
    B -->|"BYOK: zeroModelSegmentCosts()\n(model segments only — tool preserved)"| C["ProviderTiming.timeSegments"]
    B -->|"enrichWithProviderMetadata()"| D["span-factory.ts\nspan.cost = {input, output, total, toolCost?}"]
    D -->|"toolCost > 0 guard"| E["TraceSpan.cost.toolCost\n(new field in types.ts)"]
    E -->|"calculateCostSummary()"| F["logging-factory.ts\nmodels[model].toolCost accumulator"]
    F --> G["Cost summary\n(totalCost, models[x].toolCost)"]

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