Ship a generic, spine-anchored join_on_ts helper + JoinedRow in the report
layer (sibling of summarize/f64_field), re-exported from lib.rs. It fuses N
recorded (Timestamp, Vec<Scalar>) tap streams on the recorded timestamp:
exactly one JoinedRow per spine entry, each side looked up by ts as
Some(row)/None where it did not fire. Option-per-side semantics keep the
engine honest — it reports presence; the consumer interprets absence (the
0.0/-1/false defaults are consumer truths, not engine ones). C8/C18 (post-run
reduction over recorded sink output), C3 (no in-graph join), C1 (one row per
ts, documented precondition).
Two unit tests pin the contract: cardinality-misalignment alignment (the #93
shape — a spine bar a side tap skipped resolves to None, not a zip-misalign)
and the spine-anchored drop of a side row at a non-spine ts. RED accepted on
the grounding-check record (both symbols were absent pre-cycle, so the tests
are RED-by-construction) and verified green here.
drain_trace's migration onto this helper + the Recorder doc note follow.
refs #93
Brummel
74324d178f