CI / CI (push) Successful in 3m7s
**Root cause:** ServiceAdapter dispatcher sets X-Upstream-Path to template strings like `/v1/poimen/executions/{id}/stream` with literal `{id}`. The handler extracted `{id}` as the workflow ID instead of the actual value.
**Fix:** All handlers read `workflow_id` from query params (`?workflow_id=xxx`). Paths changed to flat resource names without path parameters.
**API contract:**
```
GET /executions — list
GET /executions/detail?workflow_id=xxx — describe
GET /executions/history?workflow_id=xxx — history
GET /executions/stream?workflow_id=xxx — SSE
POST /executions/signal?workflow_id=xxx — signal
DELETE /executions/detail?workflow_id=xxx — terminate
```
All accessed via `X-Service: poimen` + `X-Resource: <name>` headers.
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Reviewed-on: #42