Fix scout traces show rendering span durations ~1000x too small

[quinnmil]

Closes #26

Summary

scout traces show rendered every span's duration ~1000x too small, which silenced the whole visualization: bars always collapsed to the 1-block minimum, the yellow/red color thresholds could never trigger, and the ⚠ slow warning was unreachable.

Root cause: the API reports a span's duration_ms / exclusive_duration_ms in seconds, despite the key name. renderSpan formatted the raw value as milliseconds, so an 8-second span printed "8ms," and the bar-fill ratio against the trace total was always ≈0.001.

Fix

Renamed TraceSpan.DurationMs/ExclusiveDurationMs to DurationSeconds/ExclusiveDurationSeconds so the real unit is explicit in the Go types (JSON tags keep the API's wire names, so --json output is unchanged), and scale to milliseconds once at the point of use in renderSpan for both the printed label and the bar-fill ratio.

Verified live

Checked against real trace data on an authenticated account: before the fix, a span's printed duration and the trace header's total duration disagreed by ~1000x; after, they agree, and a trace's duration_in_seconds matches the sum of its root-span durations to six decimal places across several traces. With the fix, a root span filling the whole trace renders fully red with the slow warning, a span at roughly half the trace's duration renders mostly-filled in yellow with the warning, and a small span renders a single filled block in green with no warning — all three color thresholds and the warning are reachable again.

Tests

• Updated the existing memory-footer test to use internally consistent (seconds) values.
• Added two new tests: one asserting a span's rendered duration matches the trace header when the span spans the whole trace, and one asserting the bar-fill block counts and the slow warning for a 60%-of-trace span versus a 5%-of-trace span.

Test plan

• gofmt -l cmd internal (clean, aside from a pre-existing unrelated file)
• go vet ./...
• go build
• go test -race ./...
• golangci-lint run ./... (0 issues)
• Live verification against real trace data (described above, no account-specific details included)

🤖 Generated with Claude Code

https://claude.ai/code/session_01BK3fzED9ksTWsvoPfsEwpS

[mitchh456]

Verified against the API serializer — duration_ms is seconds, so the scaling direction is right; the bar-fill and slow-threshold paths now have direct test coverage.