docs: move the disk-watch auto-created-todo detail out of turn-loop/README.md

The disk_watch todo producer isn't turn-loop-shaped -- it's disk-space
state tracked in persistence.md's State dirs (per agent) section, right
next to hyperhive-todos.sqlite's own description. Leave a lean pointer
in the boot-wiring narrative instead of duplicating the detail.

Fixes #2727

docs/persistence.md

@@ -297,6 +297,17 @@ Under `/var/lib/hyperhive/agents/<name>/`:
     (`HIVE_AGENT_SOCKET`); the harness merges them into `get_loose_ends`
     output and clears a row on `mark_todo_done`. Replaced the old
     file-based `mcp-loose-ends/` scanner.
+
+    The harness itself is also a producer, not just the socket server:
+    boot wiring's `spawn_todo_socket` starts `todo_server::run` (the
+    socket the out-of-process daemons above dial) alongside
+    `disk_watch::run` — an *in-process* todo producer that shares the
+    store + wake `Notify` directly rather than dialling its own socket.
+    `disk_watch` raises a keyed `disk` todo when the filesystem backing
+    this agent's state gets tight, naming the agent's own biggest
+    directories; the summary is bucketed and carries no raw byte
+    counts, so an unchanged situation re-upserts as `changed == false`
+    and never re-wakes.
   - `hyperhive-events.sqlite` — turn-loop event log.
   - `hyperhive-turn-stats.sqlite` — per-turn timing stats.
   - `hyperhive-model` — single-line model name override file.