Foundation commit for the browser-provider plugin migration (#25214).
Mirrors the architecture established by PR #25182 (web providers):
- agent/browser_provider.py — BrowserProvider ABC. Preserves the legacy
CloudBrowserProvider lifecycle contract bit-for-bit (create_session,
close_session, emergency_cleanup, session metadata shape) so the
dispatcher in tools/browser_tool.py becomes a pure registry lookup.
Renames is_configured() → is_available() for parity with WebSearchProvider.
- agent/browser_registry.py — selection registry with the same
three-rule resolution as web_search_registry:
1. Explicit config wins (returns even if is_available() == False so
the dispatcher surfaces a precise credentials error)
2. Single-eligible shortcut
3. Legacy preference walk: browser-use → browserbase, filtered by
availability. Firecrawl is intentionally NOT in the legacy walk
(matches pre-migration behaviour — Firecrawl was only reachable
via explicit browser.cloud_provider: firecrawl).
- hermes_cli/plugins.py — adds ctx.register_browser_provider() facade,
one-liner mirror of register_web_search_provider().
No plugins registered yet; no dispatcher cutover yet. The next commits
move browserbase/browser-use/firecrawl into plugins/browser/<vendor>/
and switch tools/browser_tool.py over to the registry.
