bug(workspace): an external client's agent page lists other people's runs of that agent (run ids and timings) #3139

What happens

An external Workspace client (a person the agent is shared with, no platform account) opening an agent's page receives other people's runs of that agent: the recent-work read returns every execution except loops, including other users' chat turns, with their run id, trigger, start and end times and duration.

Why

src/backend/client_portal/agent_page.py _recent_work (~L318-368) excludes only _CLIENT_HIDDEN_TRIGGERS = {"loop"} for a client and projects id, status, triggered_by, started_at, completed_at, duration_ms, schedule_name. The message, cost and model are already projected away, but the rows themselves are not scoped to the viewer, so a client learns when and how long other people used the agent.

Repro

1. Share an agent with two people; both chat with it.
2. As one of them, open the agent in the Workspace and read the agent-page response: the other person's turns are listed with their ids and timings.

(Found in the ent#610 PR A2 review round 2, client walk: 10 of 12 runs listed to the client belonged to another user.)

Fix direction

For a non-platform viewer, scope the rows in SQL to work the viewer can account for — their own turns (source_user_email / source_channel_client = viewer) plus schedule runs — and apply the same scope to the stats band's counts so the two cannot disagree. Keep the platform view unchanged.

Acceptance

• A client sees only their own chat turns and the agent's scheduled runs; no other person's run id or timing.
• Stats counts shown to a client match the rows they can see.
• Tests for two clients on one agent (each sees only their own turns) and for the platform view (unchanged).