fix: hand off older query graphs to live subscriptions

[patrickleet]

Why

A live query could remain empty after successful SSR hydration even while the server delivered new rows. If one of those rows referenced a relationship already seeded by another query (for example, a layout), the replica rejected the entire incoming graph as incomparable. The subscription stayed active and reported no query error, leaving the page stuck until reload.

What changes

Record a local subscription-start fence. Snapshot delivery may take over relationships owned by queries that preceded that subscription. It still cannot overwrite an independently active live stream or query ownership acquired after it started. Server causal vectors, record clocks, authorization fences, and disposal fencing remain unchanged.

For example, a page can start with an empty list, then receive a newly created item referencing an owner already loaded by its layout. The item now appears through the existing subscription without polling or reloading.

Validation

• Reproduced the empty-list failure in an isolated protocol test before the fix.
• JavaScript build passes.
• All 377 JavaScript tests pass, including 46 protocol tests.
• Regression coverage includes initial insertion, relationship change, removal, rejection of later query ownership, and the existing incomparable-live-stream protections.

No user-facing UI copy is added. Documentation describes the handoff and its limits.

Stacked on #240 so it uses the same tested v5 runtime baseline; this PR contains only the subscription handoff fix.

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