Persist Agent Run spools across worker replacement

[ppXD]

Summary

• mount the Agent Run spool on a named volume in the local app topology
• mirror the same durability contract in the API/worker E2E topology
• pin both compose files with a YAML topology test

Scope

This closes same-host worker replacement/recreate loss. Multi-host deployments still require an RWX spool or later object-backed source; this PR does not claim cross-host durability and does not change completion or harness semantics.

Validation

• focused durable-root/topology unit tests: 11 passed
• docker compose config validation for app and E2E files
• git diff --check