fix(react): stabilize streaming renders

[Railly]

Summary

Fixes #311.

Append-paced streaming rebuilt the complete spec for every patch. Because each ElementRenderer received the new spec reference, unchanged elements still executed on every patch. Fresh bindings and resolved-props wrappers could then turn consumer effects into a Maximum update depth exceeded loop.

This change:

• derives iterative bottom-up versions for elements and their structural descendants
• skips unchanged internal element renderers before their hooks execute
• memoizes catalog component execution across unchanged observable inputs
• stabilizes resolved props and bindings with key-aware shallow equality
• resets an element error boundary when a corrective streamed version arrives
• keeps the validation-functions default stable

Public spec, streaming, renderer, and binding contracts remain unchanged.

Evidence

On a 26-element workload with 200 separately committed patches touching one element:

• element/catalog executions: 5,226 before, 226 after
• untouched leaf executions: 5,025 before, 0 after
• binding-write reproduction: update-depth loop before, 26 bounded writes after

The regression matrix covers direct complete specs, later children, state updates, repeat callback freshness, functions and directives, shared-child DAGs, cyclic graphs, 12,000-node depth, watch cleanup after unmount, error recovery, cyclic runtime state, and BigInt values.

Verification

• pnpm test: 1,085/1,085
• pnpm type-check: 59/59
• pnpm lint: 14/14
• focused regression: 16/16, repeated five times
• force-red mutations for renderer bailout, key ownership, bindings, callbacks, DAG invalidation, deep traversal, watch cleanup, and recovery
• independent Gemini 3.7 Flash review: final PASS
• Review Gate on exact signed SHA 476e27a: pass

Remaining gap

Chrome heap retention and Fiber collection after forced GC were not measured locally. The tests directly prove removal of the repeated React work and update loop, but do not claim a browser heap profile.

[vercel]

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