feat(funnel): add ObservationFunnel read-side listener mechanism

AGENTS.md

@@ -69,6 +69,8 @@ Commands (vehicle/commands.py) - protobuf-based signed command implementation (A
 
 `Router` (`router/base.py`) is an entity-agnostic composition wrapper (not part of the inheritance chain) that chains an ordered list of two-or-more backends sharing a common method surface and dispatches each method call down the chain with automatic per-command failover: it tries the first backend that has the method and, on any exception except `BluetoothUnconfirmedCommand`, retries the same call on the next backend that has it, returning the first success (raising the last error only if every applicable backend fails, `AttributeError` only if none has the method). Non-callable attributes resolve to the first backend that has them. Constructor: `Router(primary, secondary, *more_backends, health=None)`. The health check (`bool` | sync callable | async callable returning `bool`; omitted = attempt primary, fail over on exception with no probe) gates **only the primary**; the rest of the chain is reached purely through per-command failover — there is deliberately no per-backend health matrix. Double-execution caveat: a non-idempotent command that fails mid-flight can be re-run on the next backend, except for `BluetoothUnconfirmedCommand`, which propagates without replay.
 
+`ObservationFunnel` (`funnel.py`) is the **read** side, a separate mechanism from the command `Router` and not in its inheritance chain. It is a **funnel, not a selector**: every attached publisher feeds the same per-field listeners, so a field bound to one source survives that source dropping. There is deliberately no source health, availability, grace window, failback delay, priority, stickiness or per-field selection anywhere in it — **unavailability is a value a source reports** (a null/SNA reading), never something the funnel infers from a link dropping; inferring it would be the funnel asserting data it does not have. The only arbitration is `publish()` ignoring an observation older than the last one for that field and not re-dispatching an unchanged value; both are hard-coded, not configurable. It is **entirely synchronous and can never originate a request**: no `async def`/`await`, no polling loop, no request callable, no scheduling task — `tests/test_funnel.py::TestFunnelCannotOriginateWork` locks that in against the module's own AST, so keep the module synchronous rather than adding a fetch path. Polling belongs entirely to an external consumer, which may gate its own schedule on `listen_demand(paths, cb)` (a read-only observer over the activation counts) and feed results back through `VehicleDataResultPublisher.publish_result(dict)` — that publisher holds no client, session, or callable able to obtain one. Publishers push into the funnel (which is itself the `ObservationSink`) via `publish(Observation)`; `observed_at` values must come from one monotonic clock shared by every publisher on a funnel. `value(path)` returns the last observed value, its `None` meaning either never observed or reported unavailable. Fields are deliberately three (`Locked`, `ChargePortDoorOpen`, `DoorState.TrunkFront`); translations are positive allowlists, and an unmapped VCSEC enum or absent JSON leaf emits no observation rather than a guess, while an explicit JSON null emits an unavailable value. `BleBroadcastPublisher` reuses the existing `VehicleBluetooth` `listen_vehicle_lock_state`/`listen_charge_port`/`listen_front_trunk` seams and never connects, reads, or commands; because `VEHICLELOCKSTATE_UNLOCKED` is 0 with no proto3 presence, every VCSEC status broadcast reports a lock state and the funnel deduplicates the repeats. VCSEC `INTERNAL_LOCKED`/`SELECTIVE_UNLOCKED` and closure `UNKNOWN`/`FAILED_UNLATCH` are unmapped pending live-frame validation.
+
 `VehicleRouter` and `EnergySiteRouter` (`router/vehicle.py`, `router/energysite.py`) are thin entity-specific `Router` subclasses. `VehicleRouter(bluetooth_primary, teslemetry_secondary)` pairs a `VehicleBluetooth` primary with a cloud (`TeslemetryVehicle`) secondary; `EnergySiteRouter(local_energysite, teslemetry_energysite)` pairs a duck-typed local `EnergySite`-shaped object (e.g. aiopowerwall's `PowerwallEnergySite`, no dependency added) with a cloud `TeslemetryEnergySite` fallback. Both re-export from `router/__init__.py` (`tesla_fleet_api.router.Router` etc.) and from `tesla/__init__.py` (`tesla_fleet_api.tesla.Router`) for backward compatibility. They have no factory on the `Vehicles`/`EnergySites` collections. This repo owns the RSA keypair lifecycle and cloud registration (`Tesla.get_rsa_private_key`, `EnergySite.add_authorized_client`) that aiopowerwall's local signed transport depends on but does not implement itself; see `docs/energy_local_control.md` for the end-to-end pairing + `EnergySiteRouter` composition flow. The cloud-only `set_island_mode`/`go_off_grid`/`reconnect_grid` (`tesla/energysite.py`) can only send an unsigned `grpc_command`, which gateways can acknowledge without actuating the contactor — rather than ship that as a silent no-op, they unconditionally raise `SignedCommandRequired` (`exceptions.py`); only the signed local path via `add_authorized_client` + `EnergySiteRouter` actually actuates, and a success response from that transport still doesn't prove the contactor moved — verify state after the call.
 
 ### Vehicle Collections

tesla_fleet_api/__init__.py

@@ -4,6 +4,15 @@
 __version__ = "1.10.1"
 
 from tesla_fleet_api.const import Region, is_valid_region
+from tesla_fleet_api.funnel import (
+    BleBroadcastPublisher,
+    FieldPath,
+    Observation,
+    ObservationFunnel,
+    ObservationSink,
+    Publisher,
+    VehicleDataResultPublisher,
+)
 from tesla_fleet_api.tariff import (
     TariffPeriod,
     TariffRate,
@@ -23,6 +32,12 @@
 from tesla_fleet_api.util import firmware_at_least, firmware_compare
 
 __all__ = [
+    "BleBroadcastPublisher",
+    "FieldPath",
+    "Observation",
+    "ObservationFunnel",
+    "ObservationSink",
+    "Publisher",
     "Region",
     "TariffPeriod",
     "TariffRate",
@@ -33,6 +48,7 @@
     "Teslemetry",
     "TeslemetryClientRegistration",
     "Tessie",
+    "VehicleDataResultPublisher",
     "firmware_at_least",
     "firmware_compare",
     "get_tariff_periods",