task: record the I2b failed-unknown attempt row

Why: receipt row for follow-up unit attempt 1.
Evidence: /tmp/o2i2-20261020/o2-i2b-receipt.json
Impact: task card only.
Refs: AGENT-EXECUTION.md
Co-authored-by: Cursor <cursoragent@cursor.com>

.task/feature-fast-slow-o2-i2-backend.md

@@ -31,6 +31,7 @@
 |---|---|---|---|---|---|---|---|---|---|---|
 | o2-i2-backend-route-contract-config | deps/agent-native、internal/runtime/、internal/settings/ | AGENT-EXECUTION.md | implementation | cursor→antigravity→pi | 1 | — | invalid-config（host 把写单元包与派发并行执行，执行器读包时文件尚不存在；attempts 为空，无任何改动；fail-stop） | 未集成 | never | /tmp/o2i2-20261020/o2-i2-receipt.attempt1-invalid-config.json |
 | o2-i2-backend-route-contract-config | 同上 | AGENT-EXECUTION.md | implementation | cursor→antigravity→pi | 2（用户 2026-10-20 授权全新重跑） | cursor / auto | success | `e1a90a5`（ref refs/agent-exec/8eed31d0…/d97e9636，parent b5eb89c），`agent-exec apply` 快进集成 | never | /tmp/o2i2-20261020/o2-i2-receipt.json |
+| o2-i2b-eval-receipt-route-contract | internal/runtime/llm.go、internal/server/work_checkpoint_eval_test.go、internal/server/work_checkpoint_eval_route_contract_test.go | AGENT-EXECUTION.md | implementation | cursor→antigravity→pi | 1 | cursor / auto | failed-unknown（worker exit 1，原始日志末尾 `RetriableError: [internal] HTTP/2 keepalive ping timed out after 5000ms`；变更仅在允许路径内但未完成，执行器无法机械对账外部副作用；fail-stop，未换候选） | 未集成 | never | /tmp/o2i2-20261020/o2-i2b-receipt.json |
 
 ## 关联方向与规划