feat(P06): engine client + sandbox session hook + files/exec routes (Wave 2, task 6-2-01)
Backend: /v1/sandboxes/{id}/files (list/read/write; traversal rejected 422) and
/v1/sandboxes/{id}/exec (bounded command, captured output — CUT-2: no shell relay);
async workspace resolution for tracked + shell layouts; 17 API tests green.
Web: lib/engine-client.ts — typed fetch client for all engines (sandboxes/files/exec/
variants/grade/defense/traces/lab-SSE/proctor) with honest error mapping (503 busy ->
EngineBusyError, 403 not-allowlisted, 429 rate-limited); hooks/use-sandbox-session.ts —
variant->sandbox->starter-files bootstrap, run/test/saveFile/openFile actions, idempotent
destroy on unmount (AbortController), busy/denied/error states surfaced. typecheck 7/7.
---ci---
phase: 6
milestone: v0.3
status: execute
requirements: {covered: [REQ-3-008], partial: []}
---/ci---
CIAgent
c760f9af2b