fix: disconnect() tears down locally after sending the Leave instead of waiting for the server echo

[hiroshihorie]

Problem

engine.disconnect() sent the Leave and relied on the server's echo to run cleanup and emit EngineDisconnectedEvent, and Room.disconnect() waited up to 10 s for that event. Media nodes drop queued leave messages when they close the signal sink (pkg/routing/signal.go, signalMessageSink.Close, comment in place), so the echo can be lost. Every lost echo was a 10 s stall, a TimeoutException out of disconnect(), and a room left half torn down because Room.disconnect() never reached its own cleanup.

Found by the e2e-flutter suite (livekit/e2e-flutter#7): one agent per run against a local livekit-server 1.13.6, SignalClient did disconnect with no Leave received before it while the server logged sendLeave: true.

This design dates from the Dec 2023 engine rewrite (v1.5.5). #559 (v2.2.2, issue #553) made Room.disconnect() wait for the event, which turned a silently missing event into a visible stall. No other SDK waits on the server here: JS, Swift, Android and Rust all send the Leave and tear down locally.

Fix

Flutter now does the same.

• engine.disconnect() sends the Leave, runs cleanUp() and emits EngineDisconnectedEvent in one go. No dependency on the echo.
• A Leave that arrives after disconnect() started is the echo, or a server Leave racing ours, and is ignored.
• Room.disconnect() awaits the engine teardown and then its own cleanup, no wait on the server and no timeout. The engine event handler skips its cleanup while Room.disconnect() is running, so teardown has one owner and a connect() right after disconnect() returns cannot race a straggling handler. That is the case behind [bug] Actions stop working after second connect attempt to same room flutter livekit client #553, now covered by a test.

The first commit on this branch was a narrower fallback that completed the disconnect on socket close while keeping the echo dependency. The second commit replaces it with the alignment above.

Tests

test/core/disconnect_event_test.dart, four added:

• socket close without echo completes disconnect() with one clientInitiated event
• echo followed by socket close emits exactly one event
• disconnect() returns with engine and room torn down when the server sends nothing at all
• connect again to the same room right after disconnect() returns

The last two fail on main. Full suite 428 passing.

Not yet run

The e2e-flutter suite against this branch. The fallback version of the branch turned the suite's one warning into zero and cut the run by 9 s. Xcode is not available on my machine at the moment, so the final version has not had its real-server run yet. Will report here when it has.

🤖 Generated with Claude Code

[hiroshihorie]

e2e-flutter suite (livekit/e2e-flutter#7) against this branch, local livekit-server 1.13.6, macOS, three full runs on 2026-09-16:

• run 1: 8 pass, 10 skip, 0 warn, 0 fail
• run 2: 8 pass, 10 skip, 0 warn, 1 fail in ParticipantMetadataTest, a race in the test itself (un-awaited waitUntil), fixed in e2e-flutter 920b3b2
• run 3: 8 pass, 10 skip, 0 warn, 0 fail

ParticipantAttributesTest, the scenario whose agent hit the lost Leave echo on every run before, completed its teardown in about 0.5 s on all three runs with no warning. The 10 skips are camera scenarios, not runnable on this machine.