Add `derive_position_events(record, instrument_id) -> Vec<PositionEvent>` to
aura-engine (report.rs), the broker-independent Stage-2 audit layer of C10: the
first difference of the executed book derived from a PositionManagement dense
record. A pure post-run reduction, sibling of summarize_r — same positional,
type-erased Scalar read of the 14-column record, no in-graph node (the hot path
stays domain-free, C14). A reversal emits Close then the opposite open at one
event_ts (close first); a window-end open position emits its open with no
synthetic Close (the table records actual executed events — unlike summarize_r,
which force-closes for the R metric). instrument_id is a caller-supplied scalar
(aura-engine depends only on aura-core; it cannot import InstrumentSpec).
Two r_col indices added (DIRECTION=4, SIZE=10), the lockstep guard in
stage1_r_e2e.rs extended to name-pin `direction`, and an agreement E2E folds both
summarize_r and derive_position_events over one recorded ledger (one Close per
closed round-trip; every open closed-or-open-at-end; referential integrity).
Scope: the derive only. Fixed-fractional / currency / equity-feedback sizing is
#116 (it owns the equity->Sizer z^-1 register per C10) — deferring it here avoids
a circular dependency. Supersedes the rolled-back 0064 exposure-integral derive
(abandoned per #117): this derives from the executed book, never exposure deltas.
Verified by the orchestrator: cargo build + clippy --all-targets -D warnings
clean; full workspace suite 0 failed; aura-engine lib 214 pass (incl. the 6
derive_* unit tests); stage1_r_e2e 11 pass (incl. the new E2E + extended guard).
Fork decisions recorded on #115.
closes#115
Brummel
7aaa3e5d5c