refactor: explicit returns + void floating promises (T3.a typeaware sweep) (#756)

Cluster T3.a — mechanical fixes for consistent-return and no-floating-promises.

Files touched (15):
- server/shared/tool-call-display.ts — default throw in buildCanonicalDetailDisplay switch
- server/agent/prompt-attachments.ts — default throw in renderPromptAttachmentAsText switch
- server/workspace-directory.ts — default throw in getSortValue switch
- server/agent/mcp-server.ts — default throw in mcpCreateWorktreeInput switch
- server/terminal/terminal-session-controller.ts — default return in dispatch switch
- server/daemon-e2e/agent-configs.ts — default return false in isProviderAvailable switch
- server/agent/agent-manager.ts — void dispatchSessionEvent fire-and-forget call
- server/agent/mcp-shared.ts — void 4 notify() floating calls
- app/agent-status-bar.utils.ts — default throw in getStatusSelectorHint switch
- app/keyboard-shortcuts.ts — default throw in resolvePayload switch
- app/resolve-agent-form.ts — default throw in resolveAgentForm switch
- app/ui/dropdown-menu.tsx — void .then() + return undefined for promise/always-return
- app/use-agent-form-state.ts — void refreshSnapshot() floating call
- cli/worktree/create.ts — default throw in toDaemonCreateInput switch
- cli/onboard.ts — return process.exit(1) to satisfy consistent-return in catch

Deferred (outside 15-file cap or in EXCLUDE list):
- server/worktree-session.ts — getSortValue (same pattern, cap reached)
- Multiple files with other errors (unbound-method, unsafe-type-assertion) are separate clusters

packages/app/src/hooks/resolve-agent-form.ts

@@ -553,5 +553,7 @@ export function resolveAgentForm(
 
     case "RESET":
       return { ...state, userModified: INITIAL_USER_MODIFIED };
+    default:
+      throw new Error("unreachable");
   }
 }

packages/app/src/hooks/use-agent-form-state.ts

@@ -459,7 +459,7 @@ export function useAgentFormState(options: UseAgentFormStateOptions = {}): UseAg
   }, []);
 
   const refreshProviderModels = useCallback(() => {
-    refreshSnapshot();
+    void refreshSnapshot();
   }, [refreshSnapshot]);
 
   const refetchProviderModelsIfStale = useCallback(() => {