fix: show the settings card, and make an edit actually take effect

`mode` and `extraRoots` carried no `volatile()` marker, so the framework's
form projection dropped the whole entry from `settings.describe` and the plugin
had no card under Plugins at all. The marker is what creates the card.

It is also what turns each field into a reference rather than a value: the
resolved config hands `apply` a `{get(), [write]}` per volatile field, which is
how a settings write lands in a running plugin without re-applying it. So the
policy and the guard now read both fields at the point of use instead of
snapshotting them at mount, and `sectionOrder`/`contextOrder` stay unmarked
because a prompt section cannot be re-ordered without a remount.

A section is also registered once as a plain string, so the rule could not
follow a live `mode` without freezing at load. The mode-specific sentence moved
into the binding, which is a callback.

index.js

@@ -16,10 +16,12 @@
  * published once here and consumed there, which is also why the preset can be
  * swapped without touching any of this.
  *
- * There is deliberately no `settings` namespace. A facet grant is a statement
- * about one conversation, so the only thing worth persisting is the deployment's
- * standing grants, and those belong in the profile patch — the layer where this
- * machine's facts already live.
+ * There is deliberately no `settings` *namespace* of our own: a facet grant is a
+ * statement about one conversation, so the only thing worth persisting is the
+ * deployment's standing grants, and those belong in the profile patch — the
+ * layer where this machine's facts already live. What the framework projects
+ * onto this row is the {@link Config} schema below, which is the same patch
+ * layer reached through the Web UI rather than a second place to store things.
  */
 
 import Schema from '@deepseek-ai/schemastery'
@@ -28,21 +30,42 @@ import { createFacetPolicy } from './lib/policy.js'
 
 export const name = 'dsh-facet'
 
-/** Every configuration field this plugin exposes. */
+/**
+ * Every configuration field this plugin exposes.
+ *
+ * `mode` and `extraRoots` are marked `volatile()`, and that marker is doing two
+ * jobs rather than one. It is what puts them on the settings page at all — the
+ * framework's form projection keeps only fields under a volatile ancestor, and
+ * drops an entry with no such field from `settings.describe` entirely, so
+ * without it this row has no card. It is also what makes an edit *live*: a
+ * volatile field is handed to {@link apply} as a reference rather than a value,
+ * and the framework commits an edit into that reference without re-applying the
+ * plugin.
+ *
+ * The second job is why every reader of these two fields goes through
+ * `configValue()` in `./lib/policy.js` and reads at the point of use. A plugin
+ * that takes the reference for a string gets a settings card that appears to
+ * work and changes nothing.
+ *
+ * `sectionOrder` and `contextOrder` are deliberately NOT volatile. They place
+ * the rule and the binding among the other prompt sections, which is settled
+ * once at load; making them volatile would put two knobs nobody should touch on
+ * the card, and a section cannot be re-ordered without a remount anyway.
+ */
 export const Config = Schema.object({
   /**
    * How a call outside the facet is handled. `ask` questions the user, `deny`
    * refuses outright, `off` disables enforcement while leaving the preset in
    * place — useful for telling a scoping problem from an unrelated one.
    */
-  mode: Schema.union(['ask', 'deny', 'off']).default('ask'),
+  mode: Schema.union(['ask', 'deny', 'off']).default('ask').volatile(),
 
   /**
    * Paths always in scope, for code a module legitimately depends on — shared
    * types, a common test harness. Relative paths resolve against each session's
    * own directory, so the same list is meaningful in every workspace.
    */
-  extraRoots: Schema.array(String).default([]),
+  extraRoots: Schema.array(String).default([]).volatile(),
 
   /** Placement of the invariant rule in the system prompt. */
   sectionOrder: Schema.number().default(100),