cli: release host.lock on a late fork or send throw; retry a vanishing lock (row 106, #1600)

Darkwing round 1, approved by Dewey in #1600 comment 28319 on manifest
ae38cbe280aa5885aec7648d38143920753db86ea1ca3934d0a8885fb61e5105.
Sage gate rerun on f63c965f9 plus build.patch: every package suite and
every scripts/test-*.sh green (cli 168, harness 73, test-release 14).
readHostState now treats a host.json that vanishes mid-read as no host
for stopHost and hostStatus too (Dewey note b); Sage accepts it as
correct. Nothing goes live until a re-pin under Mos's go.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/cli/README.md

@@ -181,8 +181,10 @@ mosaic bus status [--json]      host state file, socket, writer.lock
    <business> (pid <pid>)`. A lock whose host no longer runs is taken over
    whatever its age: it is moved aside, checked to be the file that was
    read, and removed; if another host's claim was moved aside in that race,
-   it goes back. Each refusal below removes `host.lock` again, so a host
-   that didn't start leaves no file.
+   it goes back. Of three starts racing one stale lock, two can both claim
+   it, and then the broker's `writer.lock` refuses the second broker. Each
+   refusal below removes `host.lock` again, so a host that didn't start
+   leaves no file.
 4. It forks `packages/bus/src/process.mjs` and waits up to 30 s for the boot
    reply. If the broker answers `{ok: false, error}`, the host exits 3 and
    prints `broker refused to start: <code>`. A timeout or an early exit