[Critical] Subagents display as "System: [date]..." instead of their label parameter

[YoungVoney]

When spawning subagents via sessions_spawn(label="..."), the subagent session appears in the sidebar with a misleading display name that makes it look like a generic system message. The label parameter is completely ignored.

Reproduction Steps

1. Spawn a subagent: sessions_spawn(task="...", label="test-subagent-demo")
2. Check claw.so sidebar
3. Observe display name

Expected Behavior

Sidebar should show:

• Display name reflecting the label: "Subagent: test-subagent-demo"
• Clear indication it's a spawned task
• Session type prefix to distinguish from system messages

Actual Behavior

From HTML inspection (2026-02-17 05:39 UTC):

• Actual session key: agent~main~subagent~d9c91c16-4e0c-425c-ba00-e1073be9dbc5
• Display name shown: "System: [2026-02-16 07:10:54 UTC] Exec completed…"
• Label provided: test-subagent-demo (not shown anywhere)

What users see:
OpenClaw (expanded) ├─ telegram:g-agent-main-main ├─ System: [2026-02-16 07:10:54 UTC] Exec completed… ← this is actually a subagent! ├─ Cron: ClawRouter Wallet Monitor ├─ Cron: Daily Memory Curation └─ Cron: Anti-Todo Hourly Logger

Comparison with cron jobs (working correctly):

• Cron display: "Cron: ClawRouter Wallet Monitor" ✅ clear and descriptive
• Subagent display: "System: [date] Exec completed..." ❌ misleading and generic

Impact

• Subagents are effectively invisible - can't identify or monitor spawned tasks
• Cannot distinguish between:
  • Actual system events/notifications
  • Completed subagents
  • Active subagents
  • Failed subagents
• Defeats the primary use case of claw.so - monitoring background work
• Makes debugging impossible - can't find the relevant session

Proposed Solution

1. Use the label parameter from sessions_spawn() in the display name
2. Add session type prefix:
   • "Subagent: test-subagent-demo"
   • "Subagent: test-subagent-demo (from telegram:g-agent-main-main)" (with parent)
3. Match cron job pattern: Follow the same clear naming as cron jobs ("Cron: [name]")

Environment

• OpenClaw version: 2026.2.15
• Platform: Web UI (claw.so)
• Session format: agent:main:subagent:* (shown in sidebar as agent~main~subagent~*)

Additional Context

HTML session entries use ~ separator:

• Main: agent~main~main → displays as telegram:g-agent-main-main ✅
• Subagent: agent~main~subagent~d9c91c16... → displays as System: [date]... ❌
• Cron: agent~main~cron~45661fdb... → displays as Cron: ClawRouter Wallet Monitor ✅

Only subagents have this naming problem.