fix: put the recall chip in the header utilities, not the cell the sidebar's expand button owns

The chip registered into `conversation.session.header.corner`, which is a
SINGLE cell the product already occupies: the client catalog lists its
occupants as `client-ui-sidebar-right ExpandButton` and its replaceRisk as
`shadows-shipped-ui`. Two registrations at priority 0 in a single cell are a
hard error inside the slot registry, and the error lands in the OTHER
plugin's `slots.inject()` callback: the renderer's `changed` handler catches
it, calls `stop()` on that inject controller — killing that contribution for
the rest of the fiber's life — and rethrows it from a microtask, which is the
uncaught `single slot ... already has a registration at priority 0 (registered
by dsh-recall)` in the console. So the chip was not merely racing the shipped
right-sidebar expand control; it was taking it down.

It now registers into `conversation.session.header.utilities`, a list cell
(`replaceRisk: none`, right-aligned, same Session scope and therefore the same
`useProjection` prop) as `{ id: 'dsh-recall', order: 20 }`, so it stays at the
right-hand end without competing for a seat.

The suite could not have caught this: the slot stub accepts any registration
and knows nothing about cardinality, keys or collisions. It now asserts the
chip carries a list id and that this plugin registers nothing into the corner.

README.md

@@ -146,18 +146,20 @@ Parameters: `query`, `action`, `limit`, `path` (restrict to a subdirectory),
 
 Two surfaces, both reading a host projection rather than polling:
 
-- a **chip in the session header** — `Recall 3 · 40× · 457 KB kept out`. No price
-  on it, deliberately: at the measured rate a whole conversation's avoided
-  context is a fraction of a penny, and a chip advertising that reads as the tool
-  being useless rather than as the arithmetic being honest. The tooltip carries
-  the full comparison.
+- a **chip in the session header's utilities** — `Recall 3 · 40× · 457 KB kept
+  out`. No price on it, deliberately: at the measured rate a whole conversation's
+  avoided context is a fraction of a penny, and a chip advertising that reads as
+  the tool being useless rather than as the arithmetic being honest. The tooltip
+  carries the full comparison.
 - a **right-sidebar Recall tab** — the same figures with room for what they are
   not: *"An estimate, and an upper bound: it assumes a whole file would have been
   read each time. Token counts are bytes ÷ 4."*
 
 Both render nothing when there is nothing to say — a conversation that never used
-recall costs no layout at all, which matters for the header corner because the
-framework lays it out only while its occupant renders something.
+recall costs no layout at all. The chip is an entry in the header's `utilities`
+list, carrying its own id. The far-right corner is deliberately left alone: it is
+a single cell that the product's own right-sidebar expand control occupies, so a
+registration there shadows shipped UI rather than sitting beside it.
 
 The data path is `presentationMeta` → the `tool/result` event's `meta` → a
 projection unit (`recallUsage`) with a wire view the browser reads through