[idea] Support agent status detection when inside a PID-namespace sandbox (bubblewrap/fence)

[flexiondotorg]

idea / problem

herdr does not detect a coding agent inside a PID-namespace sandbox (bubblewrap, or fence = bubblewrap + Landlock). The pane shows no agent and no status. Claude Code and Codex fail; Pi and OpenCode work via their socket hooks.

Reproduce

Run fence -- claude (or codex) in a herdr pane.

Expected vs actual

• Expected: the pane identifies the agent and shows working/idle state, as it does unsandboxed.
• Actual: the pane stays blank.

Root cause

herdr identifies the agent by matching the pane's foreground process name from host /proc (src/platform/linux.rs, src/detect/mod.rs). The sandbox runs the agent in its own PID namespace behind a wrapper chain, so the foreground process is bwrap, not the agent. The match returns None, so detected_agent is unset and state scraping never runs. The agent's OSC and screen signals still reach the pane; only identification breaks.

requested change

Read an env hint, e.g. HERDR_AGENT=claude, from the foreground leader's /proc/<pid>/environ in probe_foreground_process (src/pane.rs) and use it as the agent, skipping the name match. An absent or unknown value falls through. This reuses the existing /proc access and needs no new IPC; env passes through the sandbox unchanged.

I have a branch with the proposed fix here:

• https://github.com/flexiondotorg/herdr/tree/herdr-agent-hint

why you want this

I want to use herdr, its ace! But, I run all my coding agents inside fence, and that breaks the status updates.

[flexiondotorg]

@ogulcancelik I'm keen to work on this if you agree with the approach 🙂

[flexiondotorg]

Aha! 😃

• ef0b4bc