FSV: 50-agent foreground-equivalent concurrency with human active

[ChrisRoyse]

Parent: #717. Supersedes the narrow background-only reading of #1001/#755.

Problem

The final acceptance gate must prove the actual operator target: many agents using foreground-equivalent capabilities at the same time while the human keeps using the computer. Background-only non-interference is insufficient and can mask capability loss.

Required FSV scenario

Use real Synapse MCP tools and primary agent sessions. No subagents as the proof surface.

Minimum acceptance:

• Launch or connect 50 agent sessions, or the maximum supported count plus a filed capacity issue if a real local hard limit is discovered after reversible setup work.
• Give each session an agent_logical_foreground / foreground lane or owned target.
• Run a mix of tasks requiring click, type, read, screenshot, browser navigation/eval, and shell work.
• Human actively uses the real OS foreground during the run.
• Read physical SoTs after each trigger: session registry, foreground-lane registry, target ownership, action log rows, target DOM/UIA/file/window state, and human OS foreground/cursor samples.

Edges:

• concurrent lane acquisition pressure;
• one crashed/disconnected agent;
• one attempted cross-target action;
• one task requiring real OS foreground lease;
• stale client/tool-profile refresh.

No GitHub Actions/CI gate. No automated FSV harness.