Create-agent harness dropdown shows every option unavailable when CLI is only on login-shell PATH, not GUI PATH #6662

Summary

Buzz Desktop's manual "Add agent > Create agent" form shows every preset harness (Claude Code, Codex, Buzz Agent, Goose, Amp, Cursor, Devin) as unavailable — even when the corresponding CLI is installed and already in active use by other managed agents on the same machine.

Reproduction

1. Install claude/codex/etc. CLIs to a directory that is only added to PATH via a login-shell rc file (e.g. ~/.zshrc: export PATH="$HOME/.local/bin:$PATH"), not present in the OS/launchd default PATH.
2. Launch Buzz Desktop normally (Dock/Finder/LaunchServices — not from a terminal that already has the augmented PATH).
3. Open "Add agent > Create agent" and look at the "Agent harness" dropdown.
4. Every harness option is marked unavailable/CLI-missing, including ones that are demonstrably installed and working.

Environment

• Buzz Desktop 0.5.18, macOS 26.6.2 (25G83), arm64
• claude and codex both resolve fine from an interactive shell (~/.local/bin), and both are actively running as managed-agent worker pools on this same machine at the time of the repro — so the binaries are not actually missing.
• launchctl getenv PATH returns empty on this machine, i.e. a GUI-launched process gets the OS's bare minimum default PATH, not the login-shell PATH that adds ~/.local/bin.

Root cause (best guess, unconfirmed against source)

Same class of bug as #4628: Desktop's harness-availability check for the create-agent UI appears to run against Electron's bare launchd environment rather than a login-shell-resolved PATH (or a PATH augmented the way the already-working agent-worker spawn path is). That worker-spawn path clearly can find these binaries — agents configured via agent_command_override (e.g. pointing at a wrapper script under ~/.local/bin-adjacent paths) start and run fine. Only the create-agent form's dropdown detection appears to miss them.

Unlike #4628 (which is a runtime setup-payload parse failure after an agent is already configured with a custom command), this blocks agent creation entirely at the picker stage — before any config is saved — for every preset harness, not just custom ones. Filing separately since the user-facing surface and failure point differ, but flagging as likely related/same-root-cause.

Impact

Blocks creating any new managed agent through the manual "Create agent" flow, and equally blocks buzz agents draft-create (owner-reviewed draft flow) — that command opens the same prefilled create-agent form, so the draft path does not route around the broken dropdown either. On a machine where CLIs are installed via a login-shell PATH addition (a very common setup, e.g. pipx, nvm, ~/.local/bin installs), this makes the "Create agent" UI unusable regardless of whether the harness is actually present.

Suggested fix

Have the create-agent harness-detection check resolve commands the same way the already-working managed-agent spawn path does (inherit/resolve login-shell PATH, or explicitly search common user-local bin dirs like ~/.local/bin) instead of relying on Electron's bare launchd PATH.