Document ttl and the drain window for Kafka splitting

[dmzmk]

No description provided.

[linear-code]

INT-498

[greptile-apps]

Greptile Summary

This PR updates the Kafka queue-splitting docs to document a new two-window lifecycle — an idle window (spec.ttl) that keeps the split warm for instant reconnects, followed by a drain window (spec.drainTimeout) that lets the workload finish consuming the backlog before teardown. It also clarifies that there is no cluster-wide equivalent for MirrordSplitConfig and removes the operator.kafkaSplittingDrainTimeout Helm row accordingly.

• spec.ttl is introduced as a new MirrordSplitConfig field; the hint correctly gates both spec.ttl and the new drain semantics behind operator version x.y.z.
• The semantics of spec.drainTimeout: unset changed: on earlier operators it meant "unpatch immediately" (same as 0), but on x.y.z+ it means "wait indefinitely." This breaking change is not called out explicitly enough in the hint, which only says spec.drainTimeout "alone controls" the stay-patched window on earlier operators.

Important Files Changed

Filename	Overview
docs/sharing-the-cluster/queue-splitting/kafka.md	Documents new two-window lifecycle (idle TTL + drain window) for Kafka splitting sessions; the drainTimeout unset semantics changed silently compared to pre-x.y.z operators, which the hint does not make explicit.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Last splitting session ends] --> B{spec.ttl set and > 0?}
    B -- Yes --> C[Idle window\noperator keeps forwarding\nup to spec.ttl seconds]
    B -- No --> D[Skip idle window]
    C -- New session reconnects --> E[Reuse split instantly\nno restart needed]
    C -- ttl elapses, no reconnect --> F[Stop forwarding new messages]
    D --> F
    F --> G{spec.drainTimeout value?}
    G -- "0" --> H[Unpatch immediately\nmessages in temp topic lost]
    G -- "N seconds" --> I[Drain window\nwait up to N seconds\nends early if topic empty]
    G -- "Unset x.y.z+: no cap" --> J[Wait indefinitely\nuntil backlog consumed]
    G -- "Unset pre-x.y.z: same as 0" --> H
    I -- New session reconnects --> K[Reuse split\nresume forwarding]
    J -- New session reconnects --> K
    I -- drained or timeout --> L[Delete temp queues\nUnpatch workload\nrestart onto original topic]
    J -- Fully drained --> L
    H --> L

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_{Reviews (3): Last reviewed commit: "Rename idelTimeout to ttl" | Re-trigger Greptile}