docs(row321): wait for loopback health before precheck (#1817, F11)

(cherry picked from commit 9aae73ade2)

docs/guides/host-run-sheet.md

@@ -319,7 +319,7 @@ file with `stat -c '%U %a %n' PATH`, never `cat`. `<business>` is the host's bus
 |---|---|---|---|---|---|
 | `/srv/mosaic/.config/mosaic-dev/secrets/` | `claude-session.env`, one line `ZAI_API_KEY=...` | 0600 | mosaic | library | `<path> sets ZAI_API_KEY` |
 | `/srv/mosaic/.config/mosaic-dev/secrets/` | the Console's proof file, the path the args file's `--proof-file` names | 0600 or 0400 | mosaic | library | none. `case2-unit.sh` refuses at render. Precheck line missing. |
-| `/srv/mosaic/.config/mosaic-dev/secrets/<business>/` | `library-gitea` | 0600 | mosaic | library | `case2-precheck.sh --business <business> --library-status`, after the bus is up: `library-last-error library-credential-missing` until it's placed, then `library <project> last fetched ...` |
+| `/srv/mosaic/.config/mosaic-dev/secrets/<business>/` | `library-gitea` | 0600 | mosaic | library | After a unit start, wait for loopback `/healthz` with the bounded retry in section 10 before `case2-precheck.sh --business <business> --library-status`: `library-last-error library-credential-missing` until it's placed, then `library <project> last fetched ...` |
 | `/srv/mosaic/.config/mosaic-dev/secrets/agents/<business>/<agent>/` | one file per service | 0600, dirs 0700 | mosaic | both | none. Filled only by `mosaic credentials issue`, or Approve after #436. Never by hand. |
 
 The installer key, `<configDir>/secrets/hosts/<business>/<hostId>/installer`, is not a slot anyone places.
@@ -355,4 +355,20 @@ Precheck line: `ok      notifier config <dataRoot>/notify/<business>/notify.json
 None by hand. I2's `case2-unit.sh` enables both units, starts the bus, then the Console (Q189, mos-1122).
 `stack-upgrade.sh` stops and starts both units itself.
 
+After a unit start, wait for the Console's loopback `/healthz` to succeed before running
+`case2-precheck.sh`, including `--library-status` in section 9. Replace `<port>` with the installed
+Console unit's `--port`. This retry is bounded to 30 attempts, each with a 2-second timeout, with
+1 second between failed attempts. If it prints STOP, stop here; do not run the precheck or adopt.
+
+```sh
+(
+  attempts=0
+  until curl -fsS --max-time 2 -o /dev/null 'http://127.0.0.1:<port>/healthz'; do
+    attempts=$((attempts + 1))
+    [ "$attempts" -lt 30 ] || { echo "STOP: loopback healthz did not become ready; do not continue" >&2; exit 1; }
+    sleep 1
+  done
+)
+```
+
 Precheck line: none. Both units active after the render: precheck line missing.