Implementation: Fleetd.main's boot composition now lives in FleetdAssembly (fleetd #612)

Figure 2's intro and caption said main assembles the graph; that has not been
true since #620. Adds the seam's contract: FleetdAssembly/FleetdRuntime/
ResourcePorts, why there is deliberately no inert default, and the two traps a
boot test hits — the late attachApp, and the one-FakeHerdr fixture that cannot
tell leadAgents() from memberAgents() when memberHerdrSocket is unset.

9-Implementation.md

@@ -306,7 +306,10 @@ loop (`rest/FleetApp.java:143-158`). **There is no `/events` route**, and the wo
 
 ## Bootstrap wiring
 
-`Fleetd.main` assembles the object graph in dependency order, then starts both faces.
+`Fleetd.main` loads the config, reports it and runs `cfg.validateAll()`. Everything after that —
+the whole object graph, in dependency order, then starting both faces — lives in
+`FleetdAssembly.assembleAndStart(AssemblyInputs, ResourcePorts)` (fleetd #612). `main` is now three
+statements and one call.
 
 ```mermaid
 flowchart LR
@@ -324,11 +327,46 @@ flowchart LR
     mcp --> app["rest.FleetApp<br/>(start Javalin)"]
 ```
 
-*Figure 2 — startup wiring in `Fleetd.main`. The guard asserts the primary's own environment is
-clean before anything else; the two adapters plug into one `CompositePeerLauncher`;
-`reapOrphanWorkers()` clears stale panes left by a prior daemon restart; `CallerResolver` is built
-last among the core services because it needs the live lead and architect bindings that everything
-above it produces.*
+*Figure 2 — startup wiring, now inside `FleetdAssembly.assembleAndStart`. The guard asserts the
+primary's own environment is clean before anything else; the two adapters plug into one
+`CompositePeerLauncher`; `reapOrphanWorkers()` clears stale panes left by a prior daemon restart;
+`CallerResolver` is built last among the core services because it needs the live lead and architect
+bindings that everything above it produces.*
+
+### Why the assembly is a separate method
+
+Nothing used to call `Fleetd.main` far enough to observe what it passed. So any injected wiring
+could be swapped for its inert variant — `X.none()`, `_ -> null`, `() -> Map.of()` — and the whole
+suite stayed green. That is not a theory: #602/#606 shipped exactly that defect, and a later sweep
+found 16 more call sites with the same hole.
+
+Three types carry the fix:
+
+- **`FleetdAssembly.assembleAndStart`** — the same statements `main` used to run inline, in the same
+  order. Construction and start order is preserved deliberately; it was *not* rebuilt into
+  "construct everything, then start everything", because that would change boot timing.
+- **`FleetdRuntime`** — owns the assembled objects and their single ordered `close()`. Its
+  package-private accessors return **the identical instances the running daemon uses**, never a
+  copy. A test that inspected a snapshot built alongside the real objects could pass while
+  production silently received something else, which is the defect being closed.
+- **`ResourcePorts`** — every boot-time side effect a real daemon must do for real and a test must
+  not: read the environment, connect a herdr client, open a broker, read a clock, start a scheduler,
+  register the shutdown hook, bind the HTTP server. `ResourcePorts.system()` is the one production
+  implementation.
+
+**There is deliberately no `ResourcePorts.none()` and no smaller overload of `assembleAndStart`.**
+Adding an inert default, even for tests, would hand a future edit the exact compiling substitute
+this work exists to rule out. A test writes its own fake and owns that choice.
+
+Two consequences worth knowing before you write a boot test:
+
+- One statement could not move without reordering startup. `main` registered its shutdown hook
+  *before* building the Javalin app, so `FleetdRuntime` is built first and the app attached
+  afterwards via `attachApp`, still before HTTP listens. See that field's javadoc.
+- A wiring that differs between the lead and member herdr daemons cannot be pinned by a fixture with
+  one `FakeHerdr`. When `memberHerdrSocket` is unset the assembly falls back to `memberHerdr = herdr`,
+  so `router.leadAgents()` and `router.memberAgents()` become the same object and a test cannot tell
+  them apart. Configure two sockets. This cost two rounds of rework on #612 alone.
 
 ## Flow: forward rendezvous (`fleet_send` → `fleet_reply`)