fix: preserve sourceProposedPlan through incremental event path

The thread.turn-start-requested handler updated modelSelection, runtimeMode,
and interactionMode but never stored the event's sourceProposedPlan field.
Because buildLatestTurn only carries forward sourceProposedPlan from the
previous latestTurn when turnIds match, the field was permanently lost for
new turns created via the incremental event path.

Fix:
- Add pendingSourceProposedPlan field to Thread to bridge the gap between
  turn-start-requested (which has the plan reference but no turnId) and
  later events that call buildLatestTurn (which create the turn).
- Store event.payload.sourceProposedPlan in the turn-start-requested handler.
- Pass pendingSourceProposedPlan to buildLatestTurn as a fallback for new
  turns where the previous latestTurn turnId doesn't match.
- Seed pendingSourceProposedPlan in mapThread (snapshot path) for consistency.

Author: cursoragent

apps/web/src/store.ts

@@ -158,6 +158,7 @@ function mapThread(thread: OrchestrationThread): Thread {
     archivedAt: thread.archivedAt,
     updatedAt: thread.updatedAt,
     latestTurn: thread.latestTurn,
+    pendingSourceProposedPlan: thread.latestTurn?.sourceProposedPlan,
     branch: thread.branch,
     worktreePath: thread.worktreePath,
     turnDiffSummaries: thread.checkpoints.map(mapTurnDiffSummary),
@@ -214,17 +215,20 @@ function buildLatestTurn(params: {
   startedAt: string | null;
   completedAt: string | null;
   assistantMessageId: NonNullable<Thread["latestTurn"]>["assistantMessageId"];
+  sourceProposedPlan?: Thread["pendingSourceProposedPlan"];
 }): NonNullable<Thread["latestTurn"]> {
+  const resolvedPlan =
+    params.previous?.turnId === params.turnId
+      ? params.previous.sourceProposedPlan
+      : params.sourceProposedPlan;
   return {
     turnId: params.turnId,
     state: params.state,
     requestedAt: params.requestedAt,
     startedAt: params.startedAt,
     completedAt: params.completedAt,
     assistantMessageId: params.assistantMessageId,
-    ...(params.previous?.turnId === params.turnId && params.previous.sourceProposedPlan
-      ? { sourceProposedPlan: params.previous.sourceProposedPlan }
-      : {}),
+    ...(resolvedPlan ? { sourceProposedPlan: resolvedPlan } : {}),
   };
 }
 
@@ -534,6 +538,7 @@ export function applyOrchestrationEvent(state: AppState, event: OrchestrationEve
           : {}),
         runtimeMode: event.payload.runtimeMode,
         interactionMode: event.payload.interactionMode,
+        pendingSourceProposedPlan: event.payload.sourceProposedPlan,
         updatedAt: event.occurredAt,
       }));
       return threads === state.threads ? state : { ...state, threads };
@@ -629,6 +634,7 @@ export function applyOrchestrationEvent(state: AppState, event: OrchestrationEve
                   thread.latestTurn?.turnId === event.payload.turnId
                     ? (thread.latestTurn.startedAt ?? event.payload.createdAt)
                     : event.payload.createdAt,
+                sourceProposedPlan: thread.pendingSourceProposedPlan,
                 completedAt: event.payload.streaming
                   ? thread.latestTurn?.turnId === event.payload.turnId
                     ? (thread.latestTurn.completedAt ?? null)
@@ -671,6 +677,7 @@ export function applyOrchestrationEvent(state: AppState, event: OrchestrationEve
                   thread.latestTurn?.turnId === event.payload.session.activeTurnId
                     ? thread.latestTurn.assistantMessageId
                     : null,
+                sourceProposedPlan: thread.pendingSourceProposedPlan,
               })
             : thread.latestTurn,
         updatedAt: event.occurredAt,
@@ -755,6 +762,7 @@ export function applyOrchestrationEvent(state: AppState, event: OrchestrationEve
                 startedAt: thread.latestTurn?.startedAt ?? event.payload.completedAt,
                 completedAt: event.payload.completedAt,
                 assistantMessageId: event.payload.assistantMessageId,
+                sourceProposedPlan: thread.pendingSourceProposedPlan,
               })
             : thread.latestTurn;
         return {

apps/web/src/types.ts

@@ -104,6 +104,7 @@ export interface Thread {
   archivedAt: string | null;
   updatedAt?: string | undefined;
   latestTurn: OrchestrationLatestTurn | null;
+  pendingSourceProposedPlan?: OrchestrationLatestTurn["sourceProposedPlan"];
   branch: string | null;
   worktreePath: string | null;
   turnDiffSummaries: TurnDiffSummary[];