[Bug]: usage.cost / commands.list / sessions.create fail with "session key 'main' has no explicit owner" on multi-agent gateways

Bug type: Behavior bug
Beta release blocker: No

Summary
Windows Companion v2026.7.1-4 paired to a multi-agent gateway (core 2026.9.x,
agents.ownership: "explicit") sends bare session key "main" (no agent
prefix) on several RPCs. Since the Aug-2026 multi-agent ownership change in
core, the gateway fail-closes ownerless requests with "no explicit owner".

Steps to reproduce

1. Configure a gateway with multiple agents and agents.ownership: "explicit".
2. Pair Windows Companion v2026.7.1-4 (stable, build 2026-09-03).
3. Open Usage, Command Center, or create a new session (triggers
   usage.cost, commands.list, sessions.create).

Expected behavior
RPCs resolve the current agent from context and send an agent-prefixed session
key (agent:<id>:...), or expose an agent picker when ambiguous.

Actual behavior
usage.cost, commands.list, and sessions.create all fail with
INVALID_REQUEST / "session key "main" has no explicit owner". sessions.list,
models.list, health succeed; chatting in an existing agent-prefixed session
from the list works.

Environment

• OpenClaw version: Companion v2026.7.1-4 (stable) / core 2026.9.x
• Operating system: Windows 10.0.26200.0 (x64)
• Install method: Windows Companion stable (unpackaged)
• Provider/routing chain: local gateway via wss:// (nginx TLS termination)

Logs

⇄ res ✗ usage.cost 40ms errorCode=INVALID_REQUEST
  errorMessage=Multiple agents are configured, but session key "main" has no explicit owner. Pass agentId or use an agent-prefixed session key.
⇄ res ✗ sessions.create 12ms errorCode=INVALID_REQUEST
  errorMessage=Multiple agents are configured, but session key "main" has no explicit owner. Pass agentId or use an agent-prefixed session key.
⇄ res ✗ commands.list 6ms errorCode=INVALID_REQUEST
  errorMessage=Multiple agents are configured, but this Gateway request has no explicit owner. Set agentId to one of the configured agents.

Likely cause (source, v2026.7.1-4)

• Windows/HubWindow.xaml.cs:37 — _currentAgentId = "main"
• A2UI/Actions/GatewayActionTransport.cs:100-102 — bare "main" session-key fallback
• Services/NodeService.cs:1768-1773 — _sessionKey = "main" default
• Chat/ChatSnapshotProjector.cs:39, Services/AppState.cs:243 — "main" fallbacks
• New-session path sends only ParentSessionKey, no AgentId

Impact and severity

• Affected: Windows Companion users with multi-agent gateways
• Severity: Medium (blocks Usage / Command Center / New Session; chat unaffected)
• Frequency: always
• Consequence: those surfaces are unusable on multi-agent gateways

Additional information

• Same ownerless-request class is being fixed in core: openclaw/openclaw #138369, #138341, #139222
• Adjacent: openclaw/openclaw-windows-node #1271 (no "New Session"/agent picker)
• The Control UI GitHub-connections page shows the same class of error ("this operation has no explicit owner") on this gateway

Start with Windows/HubWindow.xaml.cs, A2UI/Actions/GatewayActionTransport.cs, Services/NodeService.cs, Chat/ChatSnapshotProjector.cs, and Services/AppState.cs to trace how the current agent and session key are selected. Reproduce the Usage, Command Center, and New Session RPCs against a multi-agent gateway, then verify each request carries an explicit owner or presents an agent choice and no longer returns the reported INVALID_REQUEST errors.