Brummel
4cbb7795ef
Fourth walking-skeleton cycle: the reactive-semantics layer — both firing
policies (C6), the k-way ingestion merge (C3), the monotonic cycle_id clock
(C4), and freshness-gated recompute / sample-and-hold (C5). This is the first
point where the engine departs from RustAst rather than sharpening it.
Both rails ship together (user directive: "must sit right from the start"):
- A = fire-on-any-fresh + hold (as-of join);
- B = all-fresh barrier (synchronizing join), accumulating across cycles.
Per-input-group, mixable on one node. Encoded as Firing::{Any, Barrier(u8)} on
InputSpec (where C8 places firing); default Any keeps Sma/Sub unchanged.
Key design resolution (studied against RustAst src/ast/rtl/streams/): the
barrier token is the data *timestamp*, not cycle_id. RustAst's
last_cycle_per_input.all(== cycle_id) synchronizes one source's fan-out but
cannot synchronize independent sources — under C4 four same-timestamp sources
are four different cycle_ids, so the cycle_id barrier never fires for C6's own
OHLC example. Substituting timestamp is the minimal faithful generalization
(fires both the diamond rejoin and the multi-source bar). Mode A and the k-way
merge are both new (RustAst had neither).
Two read clocks, both load-bearing (resolves the 0003 audit's "0004 owns
cycle_id" with no write-only field): cycle_id is the freshness epoch (C5 reads
it via per-slot fresh_at == cycle_id); timestamp is the barrier token (C6 reads
it via last_ts == T). Sample-and-hold falls out of the existing push model — a
non-firing node pushes nothing, so consumers see the held value via window[0].
Scope (user-chosen): reactive semantics only — in-memory (timestamp, value)
sources; the merge is the permanent ingestion core, the Source trait (C11) +
data-server IO are a later orthogonal cycle. bootstrap/run/InputSpec signatures
change (the 0003 tests re-express on the multi-source API).
Headline test pair (identical sources, firing-only difference): A emits
[None,None,120,130,140,240] (holds); B emits [None,None,120,None,None,240]
(waits for timestamp coincidence). Plus determinism (C1), mixed A+B, the 0003
fan-out/join compat baseline, and the bootstrap rejections.
Grounding-check PASS: 10 load-bearing substrate assumptions ratified by green
tests; the spec's "before" shapes match disk exactly.
refs walking-skeleton
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>