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/tools/background-task/create-background-output.ts

@@ -10,11 +10,13 @@ import { formatTaskResult } from "./task-result-format"
 import { formatTaskStatus } from "./task-status-format"
 
 import { getAgentDisplayName } from "../../shared/agent-display-names"
+import { recordBackgroundOutputConsumption } from "../../shared/background-output-consumption"
 
 const SISYPHUS_JUNIOR_AGENT = getAgentDisplayName("sisyphus-junior")
 
 type ToolContextWithMetadata = {
   sessionID: string
+  messageID?: string
   metadata?: (input: { title?: string; metadata?: Record<string, unknown> }) => void
   callID?: string
   callId?: string
@@ -139,6 +141,7 @@ export function createBackgroundOutput(manager: BackgroundOutputManager, client:
         }
 
         if (resolvedTask.status === "completed") {
+          recordBackgroundOutputConsumption(ctx.sessionID, ctx.messageID, resolvedTask.sessionID)
           return await formatTaskResult(resolvedTask, client)
         }