Cycle 0009 (Walking skeleton milestone). A run's two C18 "from day one"
artefacts — a reproducible manifest and summary metrics — land as a new,
pure-additive `report` module in aura-engine:
- summarize(equity, exposure) -> RunMetrics: a post-run pure reduction over a
run's recorded pip-equity + exposure streams. total_pips (last cumulative
value), max_drawdown (worst running-peak-to-trough), exposure_sign_flips (a
turnover proxy: adjacent normalized-sign changes, flat distinct from
long/short via a three-way sign0). Total and pure: empty -> zeros, identical
inputs -> identical metrics (C1/C12).
- RunManifest: the reproducible descriptor (commit, params as name->value
pairs, data-window, seed, broker label). Caller-supplied — the engine cannot
introspect a git commit or seed. params is the honest precursor to the
deferred typed param-space (node.rs; 0008 audit).
- RunReport { manifest, metrics } + to_json(): canonical, hand-rolled JSON for
the structured C14 face.
- f64_field(rows, field): bridges a recording sink's Vec<Scalar> rows to
summarize; panics on a kind/width mismatch (a wiring bug), like the engine's
other "checked at wiring" violations.
Why post-run, not a node: a node emits one record per eval with no terminal
eval (C8), so an end-of-run reduction has no home as a node; the World drains
its cycle-0006 recording sinks after Harness::run and folds them here. Matches
C18's "store manifests + metrics, re-derive results on demand".
Why hand-rolled JSON, not serde: the workspace is deliberately zero-dependency
and the schema is tiny/closed/flat; serde is reconsidered when the run-registry
milestone grows the schema. (User-approved at spec review.)
Scope: the surface + a determinism end-to-end test reusing the cycle-0007
two-sink harness; the `aura run` subcommand that prints the report is #8. No
engine/Harness/node-contract change; workspace stays zero-dependency.
Verified: cargo test --workspace green (aura-engine 40, incl. 10 new report
tests); clippy --all-targets -D warnings clean; RUSTDOCFLAGS=-D warnings cargo
doc clean.
closes#6
Brummel
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