refactor(gui): slot system standard — single register, four props shares, framework store seat

The definitive slot model for the web client, replacing the first-generation
define/register two-step, ScopedSlots whitelist faces, and binding handles:

- 'root' is the only a-priori slot (SlotsService built-in); the shell renders
  exactly ctx.slots.renderSlot('root', {}).
- register is the single API: children = slot declaration + render
  authorization + runtime spec in one options object; misconfiguration fails
  loud at load (duplicate declaration, undeclared contribution, one store
  handle under two scopes).
- Component props arrive in four auto-derived shares: PropsRuntime<K>
  (owner params + session/global standard kits via declare-merge),
  PropsRenderSlots<S>, PropsStore<H>, and the inject business face.
  sessionId is framework-supplied; hooks are framework-made only.
- Framework store seat: defineStore factories declare schema/actions/persist;
  read = useStore, write = baked actions only; store scope derives from the
  mounting entry; per-session persist keys and clearPersisted lifecycle.
- inject factories read the apply closure's own ctx (binding handles retired;
  root-ctx back door closed); SessionProvider is self-wired render-prop.
- Rendering sits behind the SlotRenderer install seam; runtime stays
  React-free; ownership ledger keyed to the single entry axis closes the
  stale-authority window (StaleAuthorizationError probes).

Docs: the slot type-chain note is refreshed in place as the slot system
standard RFC (bilingual pair re-recorded); the web client architecture RFC
defers its slot sections there; packages/client/AGENTS.md gains the slot and
props discipline; gui-testing/web-styling notes drop missions/ references.

Tests: suites rewritten to the standard (props fed directly, real store
engines via createXXXStore().create(), no render machinery); load-time
negative samples for declaration/authorization/store conflicts; verified by
real-host playwright run (three columns, empty state, collapse, keyed session
remount, cross-slot selection sharing).

docs(ui-sidebar): point contract reference at the committed slot standard RFC

missions/ is workspace-local and never committed; the README must not cite it.

packages/client/ui-sidebar/tests/tree.spec.ts

@@ -32,12 +32,12 @@ function summary(init: SummaryInit): SessionSummary {
 function listOf(...summaries: SessionSummary[]): SessionListState {
   const byId: Record<SessionId, SessionSummary> = {}
   for (const s of summaries) byId[s.id] = s
-  return { ids: summaries.map(s => s.id), byId }
+  return { ids: summaries.map(s => s.id), byId, current: undefined }
 }
 
 const view = (partial: Partial<TreeView> = {}): TreeView => ({
-  expandedProjects: partial.expandedProjects ?? new Set(),
-  expandedSessions: partial.expandedSessions ?? new Set(),
+  expandedProjects: partial.expandedProjects ?? [],
+  expandedSessions: partial.expandedSessions ?? [],
   query: partial.query ?? '',
 })
 
@@ -94,7 +94,7 @@ describe('deriveRows grouping', () => {
       summary({ id: 'b', cwd: '/p', updatedAt: 2 }),
     )
     expect(deriveRows(list, view()).filter(r => r.type === 'session')).toHaveLength(0)
-    const rows = deriveRows(list, view({ expandedProjects: new Set(['/p']) }))
+    const rows = deriveRows(list, view({ expandedProjects: ['/p'] }))
     expect(rows.slice(1)).toEqual([
       expect.objectContaining({ type: 'session', id: 'b', depth: 0 }),
       expect.objectContaining({ type: 'session', id: 'a', depth: 0 }),
@@ -112,8 +112,8 @@ describe('deriveRows session tree', () => {
 
   it('nests children under expanded parents with increasing depth', () => {
     const rows = deriveRows(treeList, view({
-      expandedProjects: new Set(['/p']),
-      expandedSessions: new Set(['root', 'kid']),
+      expandedProjects: ['/p'],
+      expandedSessions: ['root', 'kid'],
     }))
     expect(rows.slice(1)).toEqual([
       expect.objectContaining({ id: 'other', depth: 0, hasChildren: false }),
@@ -124,7 +124,7 @@ describe('deriveRows session tree', () => {
   })
 
   it('collapses subtrees at unexpanded sessions', () => {
-    const rows = deriveRows(treeList, view({ expandedProjects: new Set(['/p']) }))
+    const rows = deriveRows(treeList, view({ expandedProjects: ['/p'] }))
     const ids = rows.filter((r): r is SessionRow => r.type === 'session').map(r => r.id)
     expect(ids).toEqual(['other', 'root'])
   })
@@ -133,7 +133,7 @@ describe('deriveRows session tree', () => {
     const rows = deriveRows(listOf(
       summary({ id: 'p1', cwd: '/a', updatedAt: 2 }),
       summary({ id: 'stray', cwd: '/b', parentId: sid('p1'), updatedAt: 1 }),
-    ), view({ expandedProjects: new Set(['/a', '/b']) }))
+    ), view({ expandedProjects: ['/a', '/b'] }))
     expect(rows).toEqual([
       expect.objectContaining({ type: 'project', key: '/a' }),
       expect.objectContaining({ id: 'p1', depth: 0 }),
@@ -147,7 +147,7 @@ describe('deriveRows session tree', () => {
       summary({ id: 'x', cwd: '/p', parentId: sid('y'), updatedAt: 2 }),
       summary({ id: 'y', cwd: '/p', parentId: sid('x'), updatedAt: 1 }),
       summary({ id: 'self', cwd: '/p', parentId: sid('self'), updatedAt: 3 }),
-    ), view({ expandedProjects: new Set(['/p']), expandedSessions: new Set(['x', 'y', 'self']) }))
+    ), view({ expandedProjects: ['/p'], expandedSessions: ['x', 'y', 'self'] }))
     const ids = rows.filter((r): r is SessionRow => r.type === 'session').map(r => r.id)
     expect(ids).toContain('self')
     expect(ids).toContain('x')
@@ -160,7 +160,7 @@ describe('deriveRows session tree', () => {
       summary({ id: 'b', cwd: '/p', updatedAt: 7 }),
       summary({ id: 'a', cwd: '/p', updatedAt: 7 }),
       summary({ id: 'c', cwd: '/p', updatedAt: 7 }),
-    ), view({ expandedProjects: new Set(['/p']) }))
+    ), view({ expandedProjects: ['/p'] }))
     const ids = rows.filter((r): r is SessionRow => r.type === 'session').map(r => r.id)
     expect(ids).toEqual(['a', 'b', 'c'])
   })
@@ -170,7 +170,7 @@ describe('deriveRows session tree', () => {
       summary({ id: 'p', cwd: '/p', updatedAt: 9 }),
       summary({ id: 'old', cwd: '/p', parentId: sid('p'), updatedAt: 1 }),
       summary({ id: 'new', cwd: '/p', parentId: sid('p'), updatedAt: 5 }),
-    ), view({ expandedProjects: new Set(['/p']), expandedSessions: new Set(['p']) }))
+    ), view({ expandedProjects: ['/p'], expandedSessions: ['p'] }))
     const ids = rows.filter((r): r is SessionRow => r.type === 'session').map(r => r.id)
     expect(ids).toEqual(['p', 'new', 'old'])
   })
@@ -178,7 +178,7 @@ describe('deriveRows session tree', () => {
   it('carries the running flag onto rows', () => {
     const rows = deriveRows(
       listOf(summary({ id: 'a', cwd: '/p', running: true })),
-      view({ expandedProjects: new Set(['/p']) }))
+      view({ expandedProjects: ['/p'] }))
     expect(rows[1]).toEqual(expect.objectContaining({ id: 'a', running: true }))
   })
 })