feat(celestia-node-fiber): Listen takes fromHeight for resume-from-height subscriptions

[walldiss]

Summary

Threads a `fromHeight uint64` parameter through the Fibre DA Listen path so a subscriber can rejoin the stream from a past block height without missing blobs. Consumes the matching celestia-node API change landed in celestiaorg/celestia-node#4962, which gave `Blob.Subscribe` a `fromHeight` argument backed by a `WaitForHeight` loop.

API change

```go
// block/internal/da/fiber

• Listen(ctx context.Context, namespace []byte) (<-chan BlobEvent, error)

• Listen(ctx context.Context, namespace []byte, fromHeight uint64) (<-chan BlobEvent, error)
  ```

• `fromHeight == 0` — preserve existing "follow from chain tip" semantics.
• `fromHeight > 0` — replay events from that block forward. Historical heights return immediately; future heights block until the chain advances.

Why

Followers restarting (crashes, rolling updates, lagging nodes) need to pick up blobs they missed while offline. Before this change, a restart either replayed nothing (missed blobs) or required a separate `GetAll`-per-height catchup pathway. Blob.Subscribe from celestia-node#4962 makes the resume path first-class; this PR surfaces it through ev-node's DA abstraction.

What ships

File	Change
`block/internal/da/fiber/types.go`	`DA.Listen` signature + doc
`block/internal/da/fibremock/mock.go`	Replay matching blobs with `height >= fromHeight` before attaching live subscriber
`block/internal/da/fiber_client.go`	Outer `fiberDAClient.Subscribe` passes `0` to `fiber.Listen` — `datypes.DA.Subscribe` doesn't plumb a starting height yet, so resume at the outer layer is a future change
`tools/celestia-node-fiber/listen.go`	Adapter's `Listen` propagates `fromHeight` to `client.Blob.Subscribe`
`tools/celestia-node-fiber/go.mod`	Bump celestia-node to the merged ref from #4962 (`v0.0.0-20260423143400-194cc74ce99c`)
`tools/celestia-node-fiber/adapter_test.go`	`fakeBlob.subscribeFn` gets `fromHeight`; assertion that `0` is forwarded
`tools/celestia-node-fiber/testing/showcase_test.go`	`TestShowcase` passes `fromHeight=0`; new `TestShowcaseResume` end-to-end test

Verified

• `go build -tags fibre ./...` clean
• `go vet -tags fibre ./...` clean
• `go test -count=1 ./...` — unit tests pass
• `go test -tags fibre -count=1 ./testing/...` — `TestShowcase` (single-val end-to-end) + `TestShowcaseResume` both pass in ~16s total

TestShowcaseResume sample output

```
phase1 upload[0] blob_id=00f005a3... height=111
phase1 upload[1] blob_id=002222b7... height=111
phase1 upload[2] blob_id=00d4ba53... height=112

resume fromHeight=111

phase2 listen[1/3] blob_id=00f005a3... height=111 data_size=13
phase2 listen[2/3] blob_id=002222b7... height=111 data_size=13
phase2 listen[3/3] blob_id=00d4ba53... height=112 data_size=13
```

All 3 historical blobs replayed from `fromHeight=111` with correct heights and DataSize.

Follow-up

Plumbing `fromHeight` through `datypes.DA.Subscribe` so the sequencer / follower layers can surface it end-to-end. That change is broader than the Fibre-specific plumbing here; keeping the scope tight.

🤖 Generated with Claude Code

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