Eval: wire aikit-sdk token usage and TokenUsageLine into artifacts

[aroff]

Summary

FastSkill eval already defines input_tokens / output_tokens on CaseResult and CaseSummary, but the eval runner always sets them to None. aikit-sdk (on goaikit/aikit main, including work such as PR #60 / token usage aggregation) now exposes:

• RunResult.token_usage: Option<TokenUsage> with aggregated input_tokens, output_tokens, optional totals, cache, and reasoning fields.
• AgentEventPayload::TokenUsageLine { usage, source, raw_agent_line_seq } on the streaming callback when RunOptions::emit_token_usage_events is true (default).

This issue tracks updating gofastskill/fastskill so eval runs record that data in artifacts and traces.

Dependency: latest aikit-sdk

• Requirement: Bump the resolved aikit-sdk revision to the current tip of https://github.com/goaikit/aikit branch main (run cargo update -p aikit-sdk and commit Cargo.lock).
• Reference SHA (verify at implementation time): main at e007c0182feefa87ba6a1d405826ae420953ca63 (must be at or after the token-usage merge; e.g. commit 72a69c7d517bb26a1e443d51b273ab126b04e1ce and descendants).
• [dependencies] in Cargo.toml already uses aikit-sdk = { git = "...", branch = "main" }; the important part is refreshing Cargo.lock so CI and local builds pick up the new APIs.

Code changes (FastSkill)

1. src/eval/trace.rs — handle new event variant

• Extend TracePayload with a variant for token usage (e.g. embed usage + source as JSON-friendly structs, or reuse types re-exported from aikit-sdk if appropriate).
• Update agent_events_to_trace to match AgentEventPayload::TokenUsageLine so trace.jsonl includes per-step usage when the SDK emits it.
• Ensure existing consumers (count_raw_json_events, checks on trace) remain correct: token lines should not be counted as raw_json tool commands unless you intentionally change that definition.

2. src/eval/runner.rs — populate CaseResult from RunResult

• On successful run_agent_events / Ok(run_result), map run_result.token_usage into CaseResult:
  • Set input_tokens / output_tokens from TokenUsage when Some.
  • Optionally extend CaseResult (and serde JSON) with optional fields for total_tokens, cache, and reasoning if product wants full detail in result.json; otherwise document that only input/output are stored in the flat fields.

3. eval report / eval score (if applicable)

• Ensure human-readable report shows token totals when present.
• Confirm eval score re-read path still deserializes result.json after any schema extension (backward compatible Option fields).

4. Tests

• Update or add CLI/integration tests under tests/cli/eval_tests.rs (or unit tests with a stub runner) so a fake RunResult with token_usage produces non-null token fields in result.json.
• If the trace format gains a new payload type, add a small serialization test in eval/trace.rs tests.

Acceptance criteria

• Cargo.lock pins aikit-sdk to latest main compatible with TokenUsage / TokenUsageLine.
• fastskill eval run writes non-null input_tokens / output_tokens in per-case result.json when the agent stream includes usage the SDK can aggregate.
• trace.jsonl records token usage events without breaking existing checks that rely on raw_json command counts.
• Docs: short note in skill or repo docs that eval artifacts may include token usage (optional follow-up in gofastskill/skill references/eval.md).

References

• aikit-sdk: TokenUsage, RunResult::token_usage, AgentEventPayload::TokenUsageLine, aggregate_token_usage in aikit-sdk/src/runner.rs.
• fastskill eval: src/eval/runner.rs, src/eval/trace.rs, src/eval/artifacts.rs (CaseResult).

[aroff]

Project board: add this issue to Pipeline and set Status to Draft if it does not land there automatically.

If using gh locally with project scope:

gh auth refresh -s project
gh project item-add 1 --owner gofastskill --url https://github.com/gofastskill/fastskill/issues/118
# Then set Status = Draft via UI, or:
# gh project item-edit --id <ITEM_ID> --project-id PVT_kwDODpSNOs4BRC0y --field-id PVTSSF_lADODpSNOs4BRC0yzg-_RGY --single-select-option-id 58ae43f0

Note: retrieve <ITEM_ID> from the JSON output of item-add --format json after refresh.