feat: rebuild reactivity state from store after replay

Add `rebuildReactivityFromStore` to synchronize local reactivity
state with the hydrated variable store. This ensures tag activations
are correctly tracked following a reducer replay.

Also remove the unused `invalidateCompletions` function.

src/components/stores/journalStream.ts

@@ -14,6 +14,7 @@ import { createSignal } from "solid-js";
 import * as Comlink from "comlink";
 import type { StreamMessage } from "../journal/registry";
 import { getMessageType, validatePayload } from "../journal/registry";
+import { rebuildReactivityFromStore } from "../journal/var-reactivity";
 import type { WorkerState, WorkerPatch, SessionManifest } from "../../workers/journal.worker";
 import type { JournalWorkerAPI } from "../../workers/journal.worker";
 import {
@@ -162,6 +163,9 @@ function handlePatch(patch: WorkerPatch): void {
       saveRole(patch.state.myRole);
       // Rebuild derived state (revealedPaths, variables) by replaying reducers
       replayReducers();
+      // Rebuild local reactivity engine state so tag activations from
+      // hydrated variables are tracked for subsequent cascade computations.
+      rebuildReactivityFromStore(state.variables);
       break;
     }