[Architecture Review][P1] Standardize Storage SPI capabilities + TCK

[qqeasonchen]

Execution meta — see plan: #5296

• Phase: 4 — boundary decoupling
• Severity: P1
• Depends on: [Architecture Review][P0] Single protocol path (HTTP + CloudEvents) and ingress/egress adapters #5299
• Blocks: (none)

Problem

MeshStoragePlugin unifies send/poll, which is the right direction, but Kafka, RocketMQ 4/5, and Lite Topic differ significantly in partitions, pull cursor, and broker ACK capabilities.

Proposed direction

Add a capability declaration and a TCK for storage plugins:

StorageCapabilities
- partitions
- seekByOffset
- delayedBrokerAck
- liteTopic
- topicManagement
- orderedDelivery
- durablePullCursor

Each plugin must pass:

• send → poll round-trip;
• restart / recovery;
• seek / offset;
• partition assignment;
• retry / DLQ;
• broker outage;
• configuration validation and security/auth;
• semantic compatibility.

Acceptance criteria

• StorageCapabilities exists and each plugin declares its capabilities.
• A shared TCK covers the scenarios above and is run per plugin.
• Plugins that cannot satisfy a capability are explicitly marked, not silently divergent.

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Part of the Architecture Review.