fix(transport): guard liveness watchdog against long-running commands + tests

[dsarno]

Follow-up to #151 addressing the one correctness risk from review, plus unit tests.

Problem

ReceiveLoopAsync awaits HandleExecuteAsync inline, so while a command runs the loop stops calling ReceiveAsync and _lastInboundUtcTicks goes stale (server pings sent during execution sit unread in the buffer). A command that runs longer than _inboundLivenessTimeout (~37.5s) — play-mode test runs, large asset imports, batch/refresh ops with a server-assigned timeout above the liveness window — would make the watchdog Abort() the socket and cancel the in-flight command. Before #151 these survived (the separate keep-alive task kept sending pongs), so this was a regression introduced by the watchdog.

Fix

• Track an in-flight command counter (_commandsInFlight), incremented around dispatch in HandleExecuteAsync.
• The watchdog skips the abort while a command is in flight — that silence is expected (the receive loop is parked on dispatch, not on a dead socket).
• Refresh liveness in a finally before decrementing, so the gap until the next ReceiveAsync drains the buffered server pings can't race into a false trip.
• A genuinely dead socket still surfaces: the result-send fails or the next ReceiveAsync faults → existing HandleSocketClosureAsync path.

Refactor for testability

Extracted the two pure decisions into private static helpers so they can be unit-tested without sockets:

• ComputeInboundLivenessTimeout(TimeSpan) — max(30s, keepAlive × 2.5)
• ShouldTripLivenessWatchdog(sinceInbound, timeout, commandsInFlight)

Tests

Added to WebSocketTransportClientTests.cs (same reflection pattern as the existing tests in that file):

• Timeout derivation: 2.5× scaling, 30s floor (incl. zero cadence), large-cadence scaling.
• Trip decision: trips on real silence; does not trip with a command in flight; no trip within timeout or exactly at it.

Could not compile-check locally (no Unity/.NET toolchain in this environment); logic and conventions verified by inspection against the existing test file.

https://claude.ai/code/session_01HKue2hxNbVaNNYkpYABqjp

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