fix(assets): a busy shard is not a broken one, and a column that reached no existing install (Phase 9a)

Two defects the Phase 9 acceptance walk found on a real rig, one of them ours and
one of them released (docs/link/v8.md §17.14).

## "The shard is not answering for client files" about a shard that was fine

The status call exhausts its 425 backoff whenever something else holds the
shard's single asset slot -- an import the operator started, or the item-art warm
pass refilling itself after a client patch. Phase 8's panel rendered that with
the same banner as a shard that is down or has the plane switched off, and left
it standing, because the page only re-reads after an action. On the rig it was up
for a quarter of an hour while the warm pass refilled 313 pictures and every
direct call to the same route answered normally.

BUSY now says what it is, and one automatic re-read four seconds later clears the
ordinary case. One per mount, guarded by a ref: a page that retried forever would
be holding the slot it is waiting for. DOWN, DISABLED and NO_IMAGING read exactly
as they did.

## Every spawn-atlas import on an upgraded install has failed since v1.2.0

`shard_spawn_points.unique_id` (Events Phase 12b) was added to the CREATE TABLE
and nowhere else. `CREATE TABLE IF NOT EXISTS` does not add a column to a table
that already exists -- which is what the twenty-odd `ADD COLUMN IF NOT EXISTS`
lines in this same file are for -- so it reached fresh installs and no existing
one, and `replaceAtlas` inserts the column unconditionally:

    Unknown column 'unique_id' in 'INSERT INTO'

No bestiary refresh, no spawn map, no champion altars, on every install whose
tables predate 12b. A fresh install cannot reproduce it and neither can a test
whose schema is this file applied to an empty database; it took a rig with old
tables. Org lead, weighing that it is already released: it ships here on edge
rather than as a hotfix to main.

Verified by dropping the column, rebooting, watching the replay put it back, and
importing 6,455 spawners over the bridge.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016wDDVXWMDz82WqE1i969r4

client/src/routes/admin/ClientFiles.jsx

@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useState } from 'react'
+import { useCallback, useEffect, useRef, useState } from 'react'
 import api from '../../api.js'
 import { ErrorState, Loading } from '../../core.js'
 import Row from '../../components/DetailRow.jsx'
@@ -245,6 +245,28 @@ export default function ClientFiles() {
     load()
   }, [load])
 
+  // One automatic re-read when the shard answered BUSY (§3.2's single slot),
+  // and exactly one per mount.
+  //
+  // BUSY is not a fault and it is not sticky on the shard — it means something
+  // else held the asset slot for longer than the client's own 425 backoff, and
+  // the two things that hold it are both ordinary: an import the operator
+  // started, and the item-art warm pass refilling itself after a client patch.
+  // The panel does not poll, so without this the operator is left reading a
+  // refusal about a shard that was free again seconds later, until they think to
+  // reload. A second read clears the common case; if it is still busy, the
+  // sentence says to come back, because a page that retried forever would be
+  // holding the slot it is waiting for.
+  const retried = useRef(false)
+  useEffect(() => {
+    if (retried.current || busy) return
+    const stillBusy = assets?.code === 'BUSY' || clilocs?.code === 'BUSY'
+    if (!stillBusy) return
+    retried.current = true
+    const t = setTimeout(() => load({ quiet: true }), 4000)
+    return () => clearTimeout(t)
+  }, [assets, clilocs, busy, load])
+
   // Every action shares this: run it, say what it said, then re-read status so
   // the panel reflects the world rather than what we assumed happened.
   async function run(section, table, fn) {
@@ -347,9 +369,22 @@ export default function ClientFiles() {
           style={{ border: '1px solid var(--line)', borderRadius: 10, padding: 16 }}
           className="sans"
         >
-          <strong style={{ color: 'var(--head)' }}>The shard is not answering for client files.</strong>
+          {/* BUSY is the one code here that is not a fault, and saying "the shard
+              is not answering" about it sends an operator to check a shard that is
+              working. The slot is held by something ordinary — an import running,
+              or the warm pass — and it frees itself. */}
+          <strong style={{ color: 'var(--head)' }}>
+            {assets.code === 'BUSY'
+              ? 'The shard is busy with another client-file request.'
+              : 'The shard is not answering for client files.'}
+          </strong>
           <p style={{ margin: '6px 0 0', color: 'var(--muted)', fontSize: '0.86rem', lineHeight: 1.6 }}>
-            {assets.reason}
+            {assets.code === 'BUSY'
+              ? 'The shard serves one of these at a time, so an import running now — or the' +
+                ' item-picture pass refilling itself after a client patch — holds it until it is' +
+                ' done. This page re-reads once on its own; if the counts below are still missing' +
+                ' after that, reload in a moment.'
+              : assets.reason}
             {assets.code === 'DISABLED' &&
               ' — set Bridge.AssetsEnabled on the shard to allow it to read its own client files.'}
           </p>