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.

test/guard.test.js

@@ -18,6 +18,15 @@ import { after, before, test } from 'node:test'
 
 import { apply as guard } from '../lib/guard.js'
 import { createFacetPolicy } from '../lib/policy.js'
+import { Config } from '../index.js'
+
+/**
+ * The symbol cosmokit marks a volatile config reference with. A settings write
+ * reaches a running plugin as `target[write](value)` — that is literally what
+ * `updateVolatile` does — so a test can commit an edit the way the framework
+ * does, without a settings service.
+ */
+const VOLATILE_WRITE = Symbol.for('cosmokit.volatile.write')
 
 /** A filesystem provider with `dsh-fs-local`'s two relevant behaviours. */
 const fsLikeLocal = {
@@ -50,8 +59,8 @@ const fsLikeLocal = {
 }
 
 /** Capture what `apply` registered, so the test can drive it. */
-function harness({ mode = 'ask', extraRoots = [], tool = true } = {}) {
-  const policy = createFacetPolicy({ mode, extraRoots })
+function harness({ mode = 'ask', extraRoots = [], tool = true, config } = {}) {
+  const policy = createFacetPolicy(config ?? { mode, extraRoots })
   const captured = { section: undefined, context: undefined, tool: undefined, preExecute: undefined }
   const ctx = {
     facetPolicy: policy,
@@ -217,6 +226,25 @@ test('off mode registers nothing', () => {
   assert.equal(captured.tool, undefined)
 })
 
+test('a live mode edit decides the next call, without the guard being remounted', async () => {
+  // The loader hands the guard the schema-resolved config, so `mode` arrives as
+  // a volatile reference rather than a string. This drives that exact shape.
+  const config = Config({ mode: 'ask' })
+  const { captured } = harness({ config })
+  const outside = { name: 'read', args: { file_path: '../../shared/types.ts' }, agent: agent() }
+
+  assert.equal((await dispatch(captured, outside)).kind, 'ask')
+
+  // What a settings write does: commit into the reference in place, and
+  // deliberately do not re-apply the plugin. One mount, three answers.
+  config.mode[VOLATILE_WRITE]('deny')
+  assert.equal((await dispatch(captured, outside)).kind, 'deny')
+
+  // `off` silences the guard entirely, which is the whole meaning of the mode.
+  config.mode[VOLATILE_WRITE]('off')
+  assert.equal((await dispatch(captured, outside)).kind, 'allow')
+})
+
 test('the guard adds to a decision, never overrides one', async () => {
   const { captured } = harness()
   const denied = await dispatch(captured, {