What does this PR do?

On macOS, hermes update left running gateways on stale launchd service definitions and only restarted the current profile's LaunchAgent, leaving named-profile gateways pinned to the old code.

Two root causes:

1. Stale definitions are never reloaded. launchd does not hot-reload a plist — a changed definition is only applied by bootout/bootstrap. The update postflight called launchd_restart(), which kickstarts the cached definition, so a service whose plist changed across the update came back running the old one. launchd_start() self-heals via refresh_launchd_plist_if_needed(); the update path did not, forcing users to manually run hermes gateway start.
2. Only the current profile was restarted. The macOS branch inspected a single get_launchd_label() / get_launchd_plist_path(). The Linux/systemd branch right above it already enumerates all hermes-gateway* units; launchd was the outlier.

Fix

New restart_launchd_gateways_for_update() in hermes_cli/gateway.py:

• Discovers every ~/Library/LaunchAgents/ai.hermes.gateway*.plist (the launchd analogue of systemctl list-units hermes-gateway* — all profiles share one LaunchAgents dir).
• Reads each plist's own recorded HERMES_HOME and re-enters that profile's context via the existing _HERMES_HOME_OVERRIDE ContextVar, so each plist is regenerated for the correct profile.
• For each loaded service: graceful-restarts a current definition, or (for a stale one) drains in-flight agent runs with SIGUSR1 first, then refresh_launchd_plist_if_needed() does the bootout/bootstrap reload.

The macOS update postflight now delegates to it. launchd_restart() is unchanged, so its existing graceful-restart contract (and tests) are preserved.

Related Issue

Fixes #38053

This is distinct from the other open macOS launchd-restart PRs: it specifically addresses multi-profile enumeration and stale-plist refresh in the hermes update postflight, rather than KeepAlive/missing-plist/throttle behaviour in launchd_restart() itself (which is left untouched).

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✅ Tests (adding or improving test coverage)

Changes Made

• hermes_cli/gateway.py: add _launchd_agents_dir, _iter_hermes_launchd_plists, _hermes_home_from_launchd_plist, _launchd_service_is_loaded, and restart_launchd_gateways_for_update(). No existing function is modified (only import plistlib is added).
• hermes_cli/main.py: replace the single-profile macOS restart branch in _cmd_update_impl with a delegation to a small helper _restart_macos_launchd_gateways().
• tests/hermes_cli/test_gateway_service.py: TestLaunchdUpdatePostflight (11 tests).
• tests/hermes_cli/test_cmd_update.py: TestRestartMacosLaunchdGatewaysPostflight (2 tests).

How to Test

All side effects (launchctl, signals, subprocess) are mocked — no live gateway commands run.

pytest tests/hermes_cli/test_gateway_service.py::TestLaunchdUpdatePostflight \
       tests/hermes_cli/test_cmd_update.py::TestRestartMacosLaunchdGatewaysPostflight -q

Coverage includes: stale plist rewritten + bootout/bootstrap reload; a named profile regenerated in its own context (keeps its --profile arg); unloaded agents skipped; unreadable plists skipped; one profile failing does not abort the rest; and an assertion that every subprocess invocation is launchctl (proving no live hermes commands are needed).

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(update): ...)
• I searched for existing PRs to make sure this isn't a duplicate (this targets the unclaimed [Bug]: macOS launchd: hermes update does not restart profile gateways #38053; see Related Issue)
• My PR contains only changes related to this fix
• I've run the gateway + update test suites and they pass — note: a full pytest tests/ -q on macOS has pre-existing systemd/seed_supervise env failures unrelated to this change (CI runs the full suite on Linux)
• I've added tests for my changes (13)
• I've tested on my platform: macOS (Darwin 25.5)

Documentation & Housekeeping

• Docstrings added; README/docs/ — N/A
• No config keys added/changed — cli-config.yaml.example N/A
• No architecture/workflow change — CONTRIBUTING.md/AGENTS.md N/A
• Cross-platform impact considered — the launchd path is macOS-only; systemd/Windows untouched
• No tool behaviour/schema change — N/A

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