Bug: Future hosted-agent workflow steps expand before they are actionable

[jaeyong8687]

Describe the bug
When Step 2 is expanded in the Foundry agent canvas, Step 3 is also expanded automatically. This makes a future task compete with the user’s active job and implies deployment is actionable before the build step is complete.

To Reproduce
Steps to reproduce the behavior:

1. Open the Foundry agent canvas.
2. Progress to the hosted-agent build workflow.
3. Expand Step 2.
4. Observe that Step 3 is also expanded.

Expected behavior
Only the active step is expanded by default. Future steps remain collapsed and unavailable until their prerequisites are satisfied, while completed steps remain available for deliberate back-navigation.

Evidence — C62

When step 2 is expanded, the step 3 is also auto expanded. Better to let users focuses on one job at a time, which should be the step2

Environment information (please complete the following information):

• Foundry Toolkit version: POC audit; version not recorded
• OS version: Not environment-specific

Additional context
Parent: #602

Priority: P2 — The defect creates workflow confusion but does not prevent task completion.
Size: S — Scoped disclosure and step-state behavior.
POC report: vscode/extension/ai-mlstudio/docs/experience-audit/agent-canvas-2026-07/report.md (not yet published upstream).

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