events.sqlite vacuum moves host-side

retention is a host concern — agents have no business doing their
own cleanup, and a misbehaving harness could skip it. drop
spawn_events_vacuum from both hive-ag3nt and hive-m1nd, drop the
matching Bus::vacuum + EventStore::vacuum methods. new
hive_c0re::events_vacuum module sweeps every existing
agents/<name>/state/hyperhive-events.sqlite on the same hourly
cadence as the broker vacuum. same two-stage delete (older than 7
days, trim to 2000 newest). called from main alongside broker
vacuum.

also: server-side state badge entered into todo.md (today's badge
is derived client-side from sse, fine for idle/thinking but a
state machine that grows compacting/napping wants authoritative
status from the harness).

TODO.md

@@ -34,6 +34,23 @@ Pick anything from here when relevant. Cross-cutting design notes live in
   `napping 😴` once the `/compact` trigger and `nap` tool exist —
   both need a harness signal (an explicit `LiveEvent::StateChange`
   variant or piggyback on Note).
+- **Server-side state badge.** Today the badge is computed client-side
+  from `turn_start`/`turn_end` events. On page reload mid-turn the
+  history replay re-derives it, but with a `compacting` / `napping`
+  state coming and a non-trivial state machine it's better to track
+  authoritative state in the harness and expose it via
+  `GET /api/state` (`status: "thinking" | "idle" | "compacting" |
+  "napping"`). JS just renders. Drops the
+  derive-from-events-and-pray code path.
+- **Terminal: inline diffs for Write/Edit.** Today a `Write` /
+  `Edit` tool-use row just shows the file path. Render the actual
+  change inline in the terminal: for `Edit`, a small `+`/`-`
+  per-line diff between `input.old_string` and `input.new_string`;
+  for `Write`, the first few lines of `input.content` (it's all
+  "+"). Keep collapsed by default (`<details>` like the existing
+  tool_result rollups), expand to full diff on click. Color via
+  the same `.diff-add` / `.diff-del` classes the dashboard
+  approval diff already uses.
 - **Terminal: `/model` slash command.** Operator-typeable model
   override from the terminal. Depends on the model-override work
   above; once an override mechanism exists, wire a `/model <name>`