chore: archive web OSM import task

.trellis/tasks/archive/2026-08/08-26-web-osm-import/implement.md

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+# Implementation Plan
+
+1. Read frontend/backend project specs and map the current workbench startup contract.
+2. Extract small, testable helpers for session workspace creation, default `RoadCompilerInput`, and bounded OSM request handling.
+3. Repair `bin/road-workbench.js` to support import-first startup while adapting legacy `--input` files.
+4. Add server endpoints for upload/bootstrap and active-session state, preserving all existing edit routes.
+5. Add a minimal import screen and transition in the existing client; keep the map/editor UI intact.
+6. Add tests for helper validation and an HTTP import smoke path using `test/fixtures/fengshu-er-road.osm`.
+7. Run `npm test`, targeted workbench tests, and manual localhost smoke checks; fix issues found.
+8. Run Trellis quality check, update relevant specs if a durable convention is discovered, then commit.
+
+Validation commands:
+
+- `npm test`
+- `node --check bin/road-workbench.js`
+- `node --check workbench/server.js`
+- targeted workbench test command added by this task
+
+Rollback points: CLI/server changes can be reverted independently of compiler sources; workspace staging ensures an import failure does not alter an existing session.