feat(dashboard): traces timeline ui

[jog1t]

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[jog1t]

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• feat(dashboard): traces timeline ui #4056 👈 (View in Graphite)
• refactor(rivetkit): make traces server only lib #4051
• feat(frontend): traces ui #4038 : 1 other dependent PR (#4032 )
• feat(rivetkit): traces #4037
• feat(rivetkit): integrate workflows in to actors #4006
• feat(rivetkit): workflows #3734
• feat(rivetkit): add actor run handler #4005 : 1 other dependent PR (#4008 )
• feat: actor messages & queues #3989 : 1 other dependent PR (#4002 )
• main

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[claude]

PR Review: Traces Timeline UI

This PR adds a sophisticated timeline visualization for actor traces. Overall solid implementation with good separation of concerns.

Critical Issues

1. Placeholder implementations throw errors (actor-traces.tsx:272-280) - These throw on every timeline interaction. Need to wire up state management properly.

2. Type inconsistencies in SpanNode (types.ts:10-21) - spanId is nullable but accessed without null checks. endTimeUnixNano and startTimeUnixNano use any instead of proper types. Multiple redundant fields.

3. Incorrect null check (utils.ts:5) - Uses === undefined but type is bigint | null

4. Missing null check (span-sidebar.tsx:118) - spanId passed without null check

5. Unsafe non-null assertions (utils.ts:43, 45) - Could throw runtime errors

Performance Issues

6. Expensive calculations on every render (traces-timeline.tsx:467-471) - Division in render loop
7. Date.now() called repeatedly - Multiple calls in same render
8. Missing React keys (actor-traces.tsx:914-929) - Gap keys could collide

Code Quality

9. Unused import - TracesTimeline imported but never used
10. Duplicate function (actor-traces.tsx:669-1058) - TracesTimelineView appears unused
11. Magic numbers - GAP_THRESHOLD_MS differs between files (500 vs 50)
12. Missing accessibility - No ARIA labels or keyboard navigation

Recommendations

High Priority: Fix issues 1-5 before merging
Medium Priority: Performance optimizations, extract constants, add accessibility
Low Priority: Add tests and documentation

Nice Touches

• Smooth drag-to-pan UX
• Visual gap indicators
• Synchronized scrolling
• Collapsible span tree

Overall: Well-architected feature but needs fixes for incomplete implementation and type safety issues before merging.