feat(webapp): completing spans server-side no longer write-after-read, improving efficiency and perf #3531

Job	Run time
e2e / 🧪 CLI v3 tests (ubuntu-latest - npm)	2m 25s
typecheck / typecheck	6m 5s
e2e / 🧪 CLI v3 tests (ubuntu-latest - pnpm)	2m 30s
e2e / 🧪 CLI v3 tests (windows-latest - npm)	5m 24s
e2e / 🧪 CLI v3 tests (windows-latest - pnpm)	5m 58s
units / webapp / 🧪 Unit Tests: Webapp (4, 8)	5m 22s
units / webapp / 🧪 Unit Tests: Webapp (5, 8)	2m 51s
units / internal / 🧪 Unit Tests: Internal (2, 8)	4m 27s
units / internal / 🧪 Unit Tests: Internal (3, 8)	3m 50s
units / webapp / 🧪 Unit Tests: Webapp (1, 8)	5m 24s
units / webapp / 🧪 Unit Tests: Webapp (6, 8)	6m 54s
units / internal / 🧪 Unit Tests: Internal (4, 8)	4m 51s
units / webapp / 🧪 Unit Tests: Webapp (8, 8)	5m 29s
units / webapp / 🧪 Unit Tests: Webapp (3, 8)	2m 36s
units / webapp / 🧪 Unit Tests: Webapp (7, 8)	2m 20s
units / webapp / 🧪 Unit Tests: Webapp (2, 8)	3m 24s
units / internal / 🧪 Unit Tests: Internal (8, 8)	2m 4s
units / internal / 🧪 Unit Tests: Internal (1, 8)	5m 39s
units / internal / 🧪 Unit Tests: Internal (5, 8)	4m 17s
units / internal / 🧪 Unit Tests: Internal (6, 8)	3m 21s
units / internal / 🧪 Unit Tests: Internal (7, 8)	4m 1s
units / packages / 🧪 Unit Tests: Packages (1, 1)	3m 35s
units / packages / 📊 Merge Reports	20s
units / internal / 📊 Merge Reports	20s
units / webapp / 📊 Merge Reports	48s
	1h 34m 15s

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