Work card says "Steps could not be read right now" under its own live activity line when an agent has two runs #3357

Problem

A running Workspace Work card shows "Steps could not be read right now." directly under its own live activity line ("Running cd /home/developer; …"). The card says the agent is working and, in the same breath, that something failed. Nothing failed.

Cause

Reproduced on dev (b70a85a11) with two tasks on one agent:

• client_portal/work/service.py reads an agent's pipeline steps only when the agent has exactly ONE live run. With two or more (a Workspace chat turn plus a schedule or API run is enough), every card is set to steps.state = "unknown" without reading anything.
• portalWork.js::stepsLine renders unknown as "Steps could not be read right now."
• Most agents publish no pipeline at all. With one run they read none, which shows no sentence (Workspace Work card says "<agent> doesn't report steps" while its own live activity line shows the agent reporting #3001). So the failure sentence appears only because a second run started.

Fix

1. Principle, at the card: the "could not be read" sentence never renders while the card has a live activity line. A run that visibly reports progress is never described as unreadable, whatever the feed says.
2. At the source: an agent with several live runs gets one pipeline read. If it publishes nothing, every card reads none. Only stages that cannot be matched to one run stay unknown.

Acceptance criteria

• A card with a live activity line never shows "Steps could not be read right now."
• Two concurrent runs on an agent that publishes no pipeline: both cards read none, so no sentence.
• A single-run agent and a real read failure behave as today.
• Tests: a mounted card spec, a stepsLine unit test and a backend service test with two runs. Each fails on revert.

Related: #3001.