Serve webhook inbound for multiple profiles off the one shared listener via a
URL prefix, with no second port bound.
- SessionSource gains a 'profile' field (round-trips through to_dict/from_dict;
omitted when unset so existing serialization is unchanged). It carries which
profile an inbound message was routed to.
- WebhookAdapter registers /p/{profile}/webhooks/{route_name} alongside the
existing /webhooks/{route_name}. _resolve_request_profile validates the
prefix against profiles_to_serve(): None when absent or multiplexing is off
(ignored, handled as default — no spurious 404), the profile name when valid,
_PROFILE_REJECTED (→ 404) when the profile isn't served. The resolved profile
is stamped onto the SessionSource.
- session-key namespacing and the per-turn home/credential scope now prefer
source.profile: SessionStore._resolve_profile_for_key(source),
_session_key_for_source fallback, and _resolve_profile_home_for_source all
honor it (→ the agent turn resolves that profile's config/skills/credentials
via the Phase 2 _profile_runtime_scope).
Constraint: routing inbound needs no per-profile platform credential, but the
agent still needs the routed profile's provider key — delivered by Phase 2's
secret scope. api_server (OpenAI-compatible surface) profile routing is a
focused follow-on; its source-construction path differs from webhook's.
Tests: SessionSource.profile round-trip + namespace drive; _resolve_request_
profile accept/reject/ignore matrix.
