26: Say what boot() being idempotent costs

docs/configuration.md

@@ -32,6 +32,11 @@ Only the second reason picks 0 out of 0 through 4; if your container is already
 anywhere below 5 works. Order among the configuration calls does not matter, so long as they all
 precede `Absorber::boot()`.
 
+`Absorber::boot()` is idempotent, so calling it from more than one code path is safe — but the
+first call is the one that counts, and the container it saw is the container the library keeps.
+Setting a different one afterwards binds nothing into it, and leaves the accessors asking a
+container that was never taught about this library. Set the container once, before booting.
+
 ## Registering a sub-plugin
 
 | Key | Type | Required | Meaning |

src/Absorber.php

@@ -122,6 +122,13 @@ public static function all(): array {
 	 * Bind the collaborators, then let the scheduler decide when they run. Idempotent — safe to
 	 * call from more than one code path.
 	 *
+	 * Idempotent means the first call wins outright, and the container is part of what it wins.
+	 * A Config::set_container() after this has returned binds nothing: the scheduler keeps the
+	 * container it closed over, while the accessors and the notice trampolines resolve from
+	 * whatever Config holds when they are called, so the two halves would answer to different
+	 * containers and the accessors would ask an unbound one. Set the container first — the
+	 * recommended slot is plugins_loaded priority 0 — and do not replace it afterwards.
+	 *
 	 * The provider is constructed rather than resolved: it is what teaches the container about this
 	 * library, so the container cannot be asked to build it first. It is bound afterwards, and only
 	 * when nothing answers to `Provider_Interface` already, so a host may replace the whole set of