feat: per-session store + configurable host limits; fix divider drag runaway

- state: side-store per conversation, injected as a prop instead of a module singleton
- host: schemastery Config (read/media/list/terminal limits) resolved from cordis config
- shape: types/exports/peerDependencies for the web profile + plugin-shape spec
- fix: split divider emits incremental deltas so drags track the cursor 1:1
- docs: README refresh

src/invariant.ts

@@ -0,0 +1,32 @@
+/**
+ * Package-owned invariant companion for `dsh-better-sidebar`.
+ * @module dsh-better-sidebar/invariant
+ */
+
+/* jscpd:ignore-start */
+import type { Context } from './context-types.ts'
+
+const PACKAGE_NAME = 'dsh-better-sidebar'
+
+/** Cordis companion plugin name. */
+export const name = 'dsh-better-sidebar-invariant'
+/** Service required before the companion can reserve package ownership. */
+export const inject = ['invariants']
+
+/**
+ * No runtime invariant: the sidebar owns no service state or event protocol
+ * of its own — every route is mounted under the host's httpServer fence, the
+ * pty lifecycle is exercised by the smoke spec, and the panel's store is a
+ * plain snapshot registry asserted by the behavior specs. The route fence,
+ * pty quota, and store semantics are each observed through their seams.
+ */
+const install: () => void = () => {}
+
+/**
+ * Register this package's invariant companion.
+ * @param ctx - Cordis context carrying the invariant service.
+ * @returns the installed registration's disposer after setup succeeds.
+ */
+export const apply = (ctx: Context): Promise<() => void> =>
+  Promise.resolve(ctx.invariants.register(PACKAGE_NAME, install))
+/* jscpd:ignore-end */