feat(gui): useProjection — the fifth framework hook seat through the standard kit

React half of the session-projection client base: the renderer contract gains
an open-key projections face on SessionMaybeProvideInfo (cellOf(key), distinct
from the static hooks roster), web-react mints projectionHook (per-bundle cache;
per-cell uSES binding via the shared observableHook cache; unresolved keys read
undefined through the absent source so hook order stays constant), standardKit
delivers kit.useProjection, and the runtime merges UseProjection into
SessionStandardProps/SessionMaybeStandardProps (overloads mirror useSession).
3 jsdom specs (kit delivery + live re-render, selector over undefined, faceless
bundle = all absent); existing direct-prop-feed specs gain the one-line stub the
new required seat mandates.

packages/client/ui-conversation/tests/chat-view.spec.tsx

@@ -105,6 +105,7 @@ function makeHarness(init?: Partial<ConversationSnapshot>) {
     useSession: bindSnapshotSelector(source),
     useSessions: emptySessions(),
     useWorkspaces: emptyWorkspaces(),
+    useProjection: (() => undefined),
     useInput: (() => { throw new Error('unused') }),
     inputActions: { setDraft: () => {}, submit: () => {} },
     useStore: bindSnapshotSelector(chat),

packages/client/ui-conversation/tests/gate-branch-tails.spec.tsx

@@ -76,6 +76,7 @@ describe('render branch tails', () => {
         useSession={bindSnapshotSelector({ getSnapshot: () => snap, subscribe: () => () => {} })}
         useSessions={bindSnapshotSelector(emptyList)}
         useWorkspaces={bindSnapshotSelector(emptyWorkspaces)}
+        useProjection={(() => undefined)}
         useInput={(() => { throw new Error('unused') })}
         inputActions={{ setDraft: () => {}, submit: () => {} }}
         useStore={bindSnapshotSelector(chat)}
@@ -111,6 +112,7 @@ describe('render branch tails', () => {
         useSession={bindSnapshotSelector({ getSnapshot: () => snap, subscribe: () => () => {} })}
         useSessions={bindSnapshotSelector(emptyList)}
         useWorkspaces={bindSnapshotSelector(emptyWorkspaces)}
+        useProjection={(() => undefined)}
         useInput={(() => { throw new Error('unused') })}
         inputActions={{ setDraft: () => {}, submit: () => {} }}
         useStore={bindSnapshotSelector(chat)}

packages/client/ui-conversation/tests/input-bar.spec.tsx

@@ -84,6 +84,7 @@ function bench(over?: BenchOptions) {
       items: [], state: 'idle', phase: 'ready', error: null,
       baselinesReady: true, recentWorkspaceId: undefined,
     })),
+    useProjection: (() => undefined),
     useInput: bindSnapshotSelector(shell.state),
     inputActions: shell.actions,
     keyboard: shell,

packages/client/ui-conversation/tests/input-matrix.spec.tsx

@@ -39,6 +39,7 @@ function mountBar(shell: SessionInputShell, over?: { running?: boolean; disabled
       items: [], state: 'idle', phase: 'ready', error: null,
       baselinesReady: true, recentWorkspaceId: undefined,
     })),
+    useProjection: (() => undefined),
     useInput: bindSnapshotSelector(shell.state),
     inputActions: shell.actions,
     keyboard: shell,

packages/client/ui-conversation/tests/input-scenarios.spec.tsx

@@ -125,6 +125,7 @@ async function scopedBench(register?: (slash: SlashService) => void) {
       items: [], state: 'idle', phase: 'ready', error: null,
       baselinesReady: true, recentWorkspaceId: undefined,
     })),
+    useProjection: (() => undefined),
     useInput: bindSnapshotSelector(shell.state),
     inputActions: shell.actions,
     keyboard: shell,

packages/client/ui-conversation/tests/queue-dock.spec.tsx

@@ -53,6 +53,7 @@ function kitFor(snapshot: ConversationSnapshot) {
     sessionId: SID,
     useSessions: (() => { throw new Error('unused') }) as unknown as SnapshotSelectorHook<SessionListState>,
     useWorkspaces: (() => { throw new Error('unused') }) as never,
+    useProjection: (() => undefined) as never,
     useInput: (() => { throw new Error('unused') }) as never,
     inputActions: { setDraft: () => {}, submit: () => {} } as never,
     session: snapshot,

packages/client/ui-conversation/tests/skeleton.spec.tsx

@@ -93,6 +93,7 @@ function mount(
           useSession={useSession}
           useSessions={props.useSessions}
           useWorkspaces={props.useWorkspaces}
+          useProjection={(() => undefined) as never}
           useInput={useInput}
           inputActions={inputActions}
           useStore={bindSnapshotSelector(chat)}
@@ -115,6 +116,7 @@ function mount(
           useSession={useSession}
           useSessions={props.useSessions}
           useWorkspaces={props.useWorkspaces}
+          useProjection={(() => undefined) as never}
           useInput={useInput}
           inputActions={inputActions}
           keyboard={wiring}
@@ -133,6 +135,7 @@ function mount(
     useSession,
     useSessions: bindSnapshotSelector(sessions),
     useWorkspaces: bindSnapshotSelector(workspaces),
+    useProjection: (() => undefined) as never,
     useInput,
     inputActions,
     renderSlot,