List agent-touched file paths under a workspace root

The durable agent-touched set (the paths the interactive kernel's file_write / file_edit / file_delete / move / copy / observed exec-class executions mutated) whose path lies under root — prefix match on root + "/", or exact. The late-subscriber replay for the explorer surfaces' agent-touch decorations: a tree mounting after a kernel run — or after a ToolPiper restart — learns the touched set without having listened to the live agent.file-touched events on GET /v1/events. Path-only by design; the captured old/new mutation content rides GET /v1/agent/touched/review. Touches persist on disk until reviewed, bounded by an explicit retention policy (30-day age at boot, 64 runs, 32 MB of snapshot bytes — content degrades oldest-first, rows survive).