herdr on Windows: pane run types the bare bash boot-script path into a PowerShell pane, so spawned agents never start

[NNK-github]

Environment

• OS: Windows 11 Pro
• Shell: Git for Windows bash (MSYS2)
• agmsg: 1.1.11 (main @ 7c6220e)
• herdr: 0.7.5-preview.2026-07-29-44b3adb12552 (Windows beta)
• agent CLI: codex 0.146.0

Repro

1. Run a shell inside a herdr pane on Windows (HERDR_ENV=1, HERDR_PANE_ID set, herdr on PATH).
2. spawn.sh codex some-name --window --boot-prompt "..."

What happens

launch_in_herdr creates the tab fine (all the JSON parsing works), then does herdr pane run "$new_id" "$BOOT" where $BOOT is the extension-less bash boot script (e.g. C:/Users/<me>/AppData/Local/Temp/agmsg-spawn/boot-XXXXXX). On Windows the herdr pane's default shell is PowerShell, so the path is just typed into PowerShell, which cannot execute an extension-less bash script — Windows pops the "How do you want to open this file?" picker (or silently returns to the prompt). The agent never boots; the tab sits at an idle PS prompt.

Everything else on the Windows path works: socket API from Git Bash, tab create/read/run, HERDR_ENV/HERDR_PANE_ID propagation into MSYS bash. I verified that running the same boot script wrapped in Git Bash inside that pane boots the agent normally.

Suggested fix

Wrap the boot invocation for Windows in launch_in_herdr, same pattern the project already uses for commandWindows in hooks.json:

   herdr pane rename "$new_id" "$NAME" >/dev/null 2>&1 || true
-  herdr pane run "$new_id" "$BOOT" 2>/dev/null \
-    || die "herdr pane run failed for pane $new_id"
+  case "$(uname -s)" in
+    MINGW*|MSYS*|CYGWIN*)
+      _gb="${GIT_BASH:-${AGMSG_BASH:-C:\\Program Files\\Git\\bin\\bash.exe}}"
+      herdr pane run "$new_id" "& '${_gb}' -lc '${BOOT}'" 2>/dev/null \
+        || die "herdr pane run failed for pane $new_id" ;;
+    *)
+      herdr pane run "$new_id" "$BOOT" 2>/dev/null \
+        || die "herdr pane run failed for pane $new_id" ;;
+  esac

Tested locally on the environment above: spawn → herdr tab → codex boots → agmsg message delivered back. Happy to PR if useful.