fix: resolve 3 community-reported bugs (#2915, #2917, #2918)

- background_output: snapshot read cursor before consuming, restore on
  /undo message removal so re-reads return data (fixes #2915)
- MCP loader: preserve oauth field in transformMcpServer, add scope/
  projectPath filtering so local-scoped MCPs only load in matching
  directories (fixes #2917)
- runtime-fallback: add 'reached your usage limit' to retryable error
  patterns so quota exhaustion triggers model fallback (fixes #2918)

Verified: bun test (4606 pass / 0 fail), tsc --noEmit clean

src/plugin/event.ts

@@ -17,6 +17,11 @@ import {
   setPendingModelFallback,
 } from "../hooks/model-fallback/hook";
 import { getRawFallbackModels } from "../hooks/runtime-fallback/fallback-models";
+import {
+  clearBackgroundOutputConsumptionsForParentSession,
+  clearBackgroundOutputConsumptionsForTaskSession,
+  restoreBackgroundOutputConsumption,
+} from "../shared/background-output-consumption";
 import { resetMessageCursor } from "../shared";
 import { getAgentConfigKey } from "../shared/agent-display-names";
 import { readConnectedProvidersCache } from "../shared/connected-providers-cache";
@@ -366,6 +371,8 @@ export function createEventHandler(args: {
         clearPendingModelFallback(sessionInfo.id);
         clearSessionFallbackChain(sessionInfo.id);
         resetMessageCursor(sessionInfo.id);
+        clearBackgroundOutputConsumptionsForParentSession(sessionInfo.id);
+        clearBackgroundOutputConsumptionsForTaskSession(sessionInfo.id);
         firstMessageVariantGate.clear(sessionInfo.id);
         clearSessionModel(sessionInfo.id);
         clearSessionPromptParams(sessionInfo.id);
@@ -382,6 +389,12 @@ export function createEventHandler(args: {
       }
     }
 
+    if (event.type === "message.removed") {
+      const messageID = props?.messageID as string | undefined;
+      const sessionID = props?.sessionID as string | undefined;
+      restoreBackgroundOutputConsumption(sessionID, messageID);
+    }
+
     if (event.type === "message.updated") {
       const info = props?.info as Record<string, unknown> | undefined;
       const sessionID = info?.sessionID as string | undefined;