Adds the second lifecycle hook the #283 design revision pairs with
finalize: Node::initialize (default no-op) runs once per node, in
topological order, before the first source value — inside the
deterministic sequence, no within-sim concurrency (C1). Consumers
acquire run resources there (the record consumer opens its streaming
writer); the hook is infallible by signature, so an acquiring node
stores its error, degrades to inert, and surfaces the failure once,
terminally, at finalize.
Every existing node keeps the default. Pinned by the mirror test
run_initializes_every_node_once_before_the_stream (init0,init1
strictly before any eval, exactly once), the shape of the existing
finalize test. RED was observed by temporarily reverting the flush
(test fails with evals-before-inits), then re-applied.
Ledger note for cycle close: C8's lifecycle section gains initialize
as finalize's mirror.
refs #283
claude
b8ba324a41