fix(transport-webtransport): abort connection when session dies

[paschal533]

Problem

When a WebTransport session becomes invalid after a network interruption or laptop sleep/resume, connection.newStream() calls createBidirectionalStream() on the dead WebTransport object which throws:

DOMException: Failed to execute 'createBidirectionalStream' on 'WebTransport': No connection.

Three independent gaps caused the stale connection to remain in the connection manager indefinitely:

1. muxer.ts onCreateStream() — the DOMException from createBidirectionalStream() propagated unhandled; neither the muxer nor the connection were cleaned up.
2. muxer.ts incoming stream reader — errors from the incomingBidirectionalStreams reader were only logged; no cleanup triggered.
3. index.ts wt.closed rejection — cleanUpWTSession() only set maConn.timeline.close = Date.now(). This never dispatches a close event on maConn, so the connection manager was never notified even when wt.closed eventually fired.

Changes

src/muxer.ts

onCreateStream() — wrap createBidirectionalStream() in try/catch. On error, call this.abort(err) (all open streams) and this.maConn.abort(err) before rethrowing. maConn.abort() triggers: sendReset() → cleanUpWTSession() → wt.close(), then dispatches a StreamAbortEvent ('close' event) on maConn. This propagates through Connection → upgrader → connection:close event bus → connection manager removes the entry.

Incoming stream reader — add this.abort(err) and this.maConn.abort(err) to the .catch() handler (same cleanup for the inbound path).

src/index.ts

Split .catch().finally() into .then()/.catch(). In the .catch(), call cleanUpWTSession('remote_close') first (sets closed = true to prevent a double wt.close() call via sendReset()), then maConn?.abort(err) to fire the full close event chain.

test/muxer.spec.ts (new)

Two unit tests using sinon-ts stubs:

• onCreateStream catches DOMException and aborts maConn
• Incoming stream reader failure aborts maConn

Closes #1982

Test plan

• cd packages/transport-webtransport && npx aegir test -t node — both new muxer tests pass
• npx aegir build — no TypeScript errors
• Browser integration test (requires go-libp2p server): intentionally idle a connection and confirm that newStream() rejects cleanly and the connection is removed from the connection manager after resume