feat(sdk): AI SDK custom useChat transport & chat.task harness #5439

Job	Run time
sdk-compat / Node.js 20.20 (ubuntu-latest)	2m 4s
typecheck / typecheck	6m 46s
sdk-compat / Bun Runtime	2m 12s
sdk-compat / Node.js 22.12 (ubuntu-latest)	2m 2s
e2e / 🧪 CLI v3 tests (ubuntu-latest - npm)	1m 55s
sdk-compat / Deno Runtime	2m 5s
sdk-compat / Cloudflare Workers	2m 16s
e2e / 🧪 CLI v3 tests (windows-latest - pnpm)	5m 14s
e2e / 🧪 CLI v3 tests (windows-latest - npm)	3m 7s
e2e / 🧪 CLI v3 tests (ubuntu-latest - pnpm)	1m 54s
units / packages / 🧪 Unit Tests: Packages (1, 1)	8m 51s
units / webapp / 🧪 Unit Tests: Webapp (3, 8)	3m 18s
units / webapp / 🧪 Unit Tests: Webapp (7, 8)	2m 42s
units / webapp / 🧪 Unit Tests: Webapp (5, 8)	4m 36s
units / webapp / 🧪 Unit Tests: Webapp (6, 8)	8m 2s
units / webapp / 🧪 Unit Tests: Webapp (1, 8)	5m 56s
units / internal / 🧪 Unit Tests: Internal (6, 8)	4m 24s
units / internal / 🧪 Unit Tests: Internal (2, 8)	4m 24s
units / webapp / 🧪 Unit Tests: Webapp (8, 8)	7m 33s
units / webapp / 🧪 Unit Tests: Webapp (4, 8)	6m 30s
units / internal / 🧪 Unit Tests: Internal (1, 8)	4m 8s
units / internal / 🧪 Unit Tests: Internal (7, 8)	4m 24s
units / internal / 🧪 Unit Tests: Internal (4, 8)	4m 28s
units / internal / 🧪 Unit Tests: Internal (3, 8)	4m 23s
units / internal / 🧪 Unit Tests: Internal (8, 8)	2m 38s
units / internal / 🧪 Unit Tests: Internal (5, 8)	4m 24s
units / webapp / 🧪 Unit Tests: Webapp (2, 8)	4m 9s
units / internal / 📊 Merge Reports	26s
units / webapp / 📊 Merge Reports	47s
units / packages / 📊 Merge Reports	21s
	1h 55m 59s

Provide feedback