slice-3 §5.2 + §6: the binary's poll task now drains the brain's
function_call proposals from rx_function_call, dispatches through the
per-channel ToolRegistry (HangupTool wired at spawn_tap_engine time),
and writes function_call_output replies back through tx_function_call_output
which run_tap_client forwards as tap WS frames to the brain.
TapClient: handle_brain_frame now forwards function_call events to a
new tx_function_call mpsc side-channel instead of dropping them.
run_tap_client adds a select! arm draining rx_function_call_output +
sending each as a tap frame. Advisory events (speech_started/stopped,
tools.update) still log + count (slice-3 deferred-action posture).
TapEngine: spawn_tap_engine now takes AppState + constructs a per-channel
ToolRegistry (spec §6.2) with HangupTool pre-registered (§6.3). TapConn
gains rx_function_call, tx_function_call_output, tool_registry fields.
session_map: drive_all_sessions calls drain_function_calls in the same
cycle as the slice-2 §5.3 step 4 flush drain (one extra channel, same
cycle); the helper spawns each dispatch as its own task so the 750 ms
hangup teardown bound (AppState::close) can't stall the 10 ms poll
cadence.
files touched: crates/rutster-tap/src/{lib,tap_client}.rs,
crates/rutster/src/{session_map,tap_engine}.rs,
crates/rutster/tests/tap_integration.rs ( AppState arg ),
crates/rutster-brain-realtime/src/translator.rs (clippy needless_borrow ).
NOT touched: loop_driver.rs, rtc_session.rs (seam test §7.5 #6).
gates: cargo fmt --check OK. cargo clippy --all --tests -D warnings OK.
cargo test --all OK. cargo deny check has pre-existing environmental
failure (CVSS 4.0 unsupported in advisory-db; same on main).
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