Fix intermittent IllegalGeneration error in spk publish

[jrray]

Problem

spk publish sometimes fails with:

ERROR   × failed to commit new starting offsets for the kafka index updates
  │ consumer: Consumer commit error: IllegalGeneration (Broker: Specified
  │ group generation id is not valid)

Root cause

listen_to_index_status_updates() (run by spk publish to wait for the index to update) subscribe()d to the index-updates topic via Kafka consumer-group management, then immediately commit()ed the starting offsets — before the consumer had joined the group / finished rebalancing. The group join only happens on the first poll (stream.next()), so the commit was sent with no valid group generation, yielding IllegalGeneration. It's intermittent because it's a timing race against the join/rebalance.

The commit also served no purpose: this consumer uses a fresh, ephemeral Ulid group id every run, so the committed offsets are never read back.

Fix

Switch this read-only, ephemeral consumer from subscribe() + commit() to manual partition assign(), carrying the starting offsets in the TopicPartitionList. Manual assignment has no group generation, so the race cannot occur. The subscribe() call is removed (a consumer can't mix subscribe and assign).

The indexer's long-lived consumer (listen_to_package_events_and_run_index_updates) is untouched — it legitimately uses a stable group id and offset commits.

Testing

Verified by cargo check -p spk-storage. Not reproduced end-to-end against a live Kafka broker.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 15.08380% with 152 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spk-storage/src/storage/messaging/kafka.rs	15.08%	152 Missing ⚠️

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