light-client example broken?

[brenzi]

Reproduce

1. cargo build --release --examples --features "light-client"
2. RUST_LOG=info ./target/release/examples/light_client

Maybe related to elastic scaling? smol-dot/smoldot#2193

RUST_LOG=info ./target/release/examples/light_client
2026-01-31T13:56:06.568793Z  INFO smoldot: Chain initialization complete for polkadot. Name: "Polkadot". Genesis hash: 0x91b1…90c3. Chain specification starting at: 0xabf7…a9f1 (#29436543)
2026-01-31T13:56:06.568820Z  WARN smoldot: Chain specification of polkadot contains a `protocolId` field. This field is deprecated and its value is no longer used. It can be safely removed from the JSON document.
2026-01-31T13:56:06.568828Z  WARN smoldot: Chain specification of polkadot contains a non-empty `telemetryEndpoints` field. Smoldot doesn't support telemetry endpoints and as such this field is unused.
2026-01-31T13:56:06.569036Z  INFO smoldot: Parachain initialization complete for asset-hub-polkadot. Name: "Polkadot Asset Hub". Genesis hash: 0x68d5…de2f. Relay chain: polkadot (id: 1000)
2026-01-31T13:56:29.781894Z  INFO runtime-polkadot: Finalized block runtime ready. Spec version: 2000005. Size of `:code`: 1.7 MiB.
2026-01-31T13:56:38.142821Z  INFO runtime-asset-hub-polkadot: Successfully compiled runtime. Spec version: 2000005. Size of `:code`: 2.3 MiB.
Chain "AssetHub" height=11552872 hash=0xeae497490d87c0da3c8b0894fb3a538091d753205ef34f257f483c0c2d1ba188
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "Polkadot" height=29753328 hash=0x44fbea8abd4b8b93e862bf731c6c36bca85d6a79a4b0269fd1efaae7df802ef7
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753329 hash=0x96f5e8dcc64c2ea4c9a19dc9e522327825e6069df59c9a7cf1a7a7d37a2f080a
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753330 hash=0xa2a584ec688a8e8009a2492a0b9254d390c78ff14dac048dc4ec93667ee0a958
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753331 hash=0x543fb69b0b9fc1dd690c8eebef4da7de77fa689719cfd77c505192ba2be67f3d
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753332 hash=0x1383b03b5a2a0e91bfea8802462441f06c8582f38d8a1d6717b37c70d9b37b4f
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753333 hash=0xcd297afdb2ada87aa851be1c4c5e2330acd90b8d5d474bee09ddb3da93765273
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "Polkadot" height=29753334 hash=0xb923d5c1f15aa1cf784238938322af9607bd048d7499c4d9ea89c6c7d282d614
    #0: Timestamp.set
    #1: ParaInherent.enter
Chain "AssetHub" height=11552875 hash=0xe5ea054c65c2474807ec433a044850e9ceb20b91838565fc82c229cc57013e67
2026-01-31T13:58:39.236968Z  WARN subxt-light-client-background-task: Cannot send method response to id=45 chain=ChainId(0)
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552878 hash=0xcd9b4ab700414c5f908cb8718685d3d529710bb393a9fd10bf80fa9445f856bd
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552881 hash=0x653034013f4d9824201fcf122e22f28129c842dbbceceaa3987b83dbe050785b
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
    #2: Balances.transfer_keep_alive
Chain "AssetHub" height=11552884 hash=0xfea8eddf1567855bced4f0b07567fb9a958ebb5f3795a7f887c34f41d2e69980
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552887 hash=0xf157b48ad1e877ac044ebaa1a98dac26d10e1ad842cb13517d1b29de72c1713f
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552890 hash=0x449fdf0b94a5a273bd59c543b522e001c2f5314e5e80b987682ddccfd5f3415a
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552893 hash=0x705157b0b41f61d3c3ae88ff0453dc06989a6e15d869052087110393b6864fc8
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552896 hash=0xbdc7006205712832059026ec11aa8d871baf160297f40c6dfc982174eb0d3da8
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552899 hash=0xd9732253992ad9cca47899033349a297c66faa0e37ded4ebecce105d69aeda63
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552901 hash=0x165dd5d4fa0232db30a32344c25e77c336ad3b8637fbe0a367adf75ede0f2348
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552904 hash=0x04a04124495507606b676113d1728226b466447db1d447ac29d8685700594b0c
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
Chain "AssetHub" height=11552907 hash=0xe6db900e774e772e2e95127f8ef24698e94c184115b8391df6ff4578125e9c23
    #0: ParachainSystem.set_validation_data
    #1: Timestamp.set
    #2: Balances.transfer_keep_alive
Error: CannotGetBlockHeader(Rpc(ClientError(DisconnectedWillReconnect("Missed at least one block when the connection was lost"))))

[jsdw]

I think the effect of elastic scaling is that you see Smoldot missing out blocks, which is why the block height is not incrementing by one at a time. This might also mean that in the event of a network error, less time can elapse before Smoldot will not report the last finalized block that it gave to Subxt prior to disconneciton and thus missed at least one block, leading to that error!

I ran that example and as in your case I see AssetHub slipping 3 blocks at a time, but I also see blocks being announced from Polkadot as well as Asset Hub (which I would expect) and in yoru case blocks from Polkadot stopped being announced (I haven't been able to reproduce this yet).

My hope is that once Smoldot supports elastic scaling we might see this start to work better again, but in the event of network disconnections there would always be a limit to how long we can be disconnected for before such an error is handed back, and in that case it's up to the user to decide how to handle this case that blocks were missed.