agentHost: enable subagent integration test for Claude real SDK

[TylerLeonhardt]

Now that subagent routing is wired up for Claude, enable the shared subagent integration test for the Claude real-SDK suite.

Changes

• Refactor IRealSdkProviderConfig.subagentToolName (string) to subagentToolNames (readonly string[]) so providers that expose multiple subagent-kind tools can list them all. The first entry is used in the test prompt; all entries are exempted from the parent must not contain inner tool calls assertion.
• Claude registers both Task and Agent as subagent-kind tools (see claudeToolDisplay.ts) and the model may pick either when asked to spawn a subagent. List both.
• Flip supportsSubagents: true for the Claude config.
• Copilot config updated to use the new array shape (['task']).

Verification

Both real-SDK suites pass end-to-end with AGENT_HOST_REAL_SDK=1:

Protocol WebSocket — Real Claude SDK
  ✔ subagent tool calls are routed to the subagent session, not flat in the parent (18s)
  ... 7 passing, 2 pending (worktree + plan mode still unsupported)

Protocol WebSocket — Real Copilot SDK
  ... 10 passing (no regression)

[Copilot]

Pull request overview

This PR enables the shared real-SDK subagent routing integration test for Claude by allowing provider configs to declare multiple subagent-spawning tool names.

Changes:

• Replaces the single subagentToolName config with subagentToolNames.
• Updates the shared subagent test to prompt with the first tool name and exempt all configured subagent tools from parent-session inner-tool assertions.
• Enables Claude subagent support with both Task and Agent, while updating Copilot to the new array shape.

Show a summary per file

File	Description
src/vs/platform/agentHost/test/node/protocol/realSdkTestHelpers.ts	Generalizes shared real-SDK subagent test configuration and assertions for multiple subagent tool names.
src/vs/platform/agentHost/test/node/protocol/copilotRealSdk.integrationTest.ts	Updates Copilot real-SDK config to use subagentToolNames.
src/vs/platform/agentHost/test/node/protocol/claudeRealSdk.integrationTest.ts	Enables Claude shared subagent testing and lists both Claude subagent tool names.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0