fix(delegate-task): align metadata with opencode core task tool

Match opencode core 'task' tool behavior for metadata consistency:

1. Model fallback: When categoryModel/task.model/resumeModel is undefined,

   fall back to parentContext.model so subagent metadata always includes

   model info. Thread parentContext into executeSyncContinuation for parity.

2. Task ID consistency: unstable-agent-task was missing taskId and

   backgroundTaskId in metadata. background_output used inconsistent

   snake_case 'task_id' vs camelCase 'taskId' elsewhere. Standardize on

   camelCase: taskId = sessionID (resume id), backgroundTaskId = bg task id.

Update text output blocks to use buildTaskMetadataBlock helper.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/sync-continuation.ts

@@ -1,5 +1,5 @@
 import type { DelegateTaskArgs, ToolContextWithMetadata } from "./types"
-import type { ExecutorContext, SessionMessage } from "./executor-types"
+import type { ExecutorContext, ParentContext, SessionMessage } from "./executor-types"
 import { isPlanFamily } from "./constants"
 import { publishToolMetadata } from "../../features/tool-metadata-store"
 import { getTaskToastManager } from "../../features/task-toast-manager"
@@ -14,11 +14,13 @@ import { normalizeSDKResponse } from "../../shared"
 import { buildTaskPrompt } from "./prompt-builder"
 import { buildTaskMetadataBlock } from "../../features/tool-metadata-store/task-metadata-contract"
 import { getTaskID } from "./task-id"
+import { resolveMetadataModel } from "./resolve-metadata-model"
 
 export async function executeSyncContinuation(
   args: DelegateTaskArgs,
   ctx: ToolContextWithMetadata,
   executorCtx: ExecutorContext,
+  parentContext: ParentContext,
   deps: SyncContinuationDeps = syncContinuationDeps
 ): Promise<string> {
   const { client, syncPollTimeoutMs, sisyphusAgentConfig } = executorCtx
@@ -81,7 +83,7 @@ export async function executeSyncContinuation(
         sessionId: continuationID,
         sync: true,
         command: args.command,
-        model: resumeModel,
+        model: resolveMetadataModel(resumeModel, parentContext.model),
       },
     }
     await publishToolMetadata(ctx, syncContMeta)