feat(example)+docs: pvd_tool on the modern stack; chapter 42 teaches the daemon path

C9 — the flagship vendor example now demonstrates the intended integration
shape. examples/pvd_tool/main.cpp: 1093 -> 570 lines. The 466-line
hand-registered handler section and the hand-wired Server/Router/emit
plumbing are gone, replaced by EquipmentRuntime + register_default_handlers
(the example now serves all 56 handlers, up from its hand-picked 51) +
commands.set_handler for the START-runs-the-recipe behaviour (was a
hard-coded S2F41 router override). All domain logic — sensor simulator,
recipe runner, alarm threshold monitor, EPT cycler, Prometheus gauges —
unchanged. pvd's SVIDs 1/2 and CEIDs 400/401 match the roles: defaults, so
the built-ins bind with no config change. Verified: builds clean, boots
("registered 56 handlers", config loaded, EPT cycling), HSMS :5000 accepts,
metrics :9090 answers HTTP 200. logfn flushes per line so docker/CI logs
are visible immediately.

Writing project — new tutorial chapter docs/42_vendor_daemon_and_clients.md:
why a daemon (the host-timer argument), the proto contract and the HCACK-4
command semantics, the Python client walkthrough, EquipmentRuntime +
capability registration + roles:, the threading contract (posting API /
read_sync / hooks-on-io-thread) and primary-vs-observer slots, and a
which-tier-do-I-pick table. Indexed in 00_index Part 4. Refreshed the three
spots that still described pvd_tool's old "51 handlers in ~460 lines" shape
(ch35, ch41, pvd README) — drift killed in the same commit that made it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

examples/pvd_tool/README.md

@@ -21,7 +21,7 @@ customize.  They're written to be a template, not an abstract demo.
 | §3 Recipe runner              | Driving a PJ through SettingUp → Processing → ProcessComplete by walking the recipe body, with per-step CEID emission |
 | §4 Alarm threshold monitor    | Continuous threshold-based alarm logic (chamber pressure, cleaning interval) with set/clear emission |
 | §5 EPT cycling                | E116 state transitions driven by PJ state + safety alarms             |
-| §6 Router handlers            | Every SECS/GEM message a host might send to a PVD tool, 51 handlers in ~460 lines |
+| §6 main()                     | `EquipmentRuntime` + `register_default_handlers` (all 56 GEM handlers in one call) + `commands.set_handler` for the START behaviour |
 | §7 main()                     | Loading YAML → validating → composing → running, including the Prometheus exporter on `:9090` (§7.3) |
 
 ## Running it