docs(ledger, glossary): ratify the fold summary-row timestamp semantics

Fieldtest spec_gap (#335): the timestamp a fold's one summary row
carries was undocumented. Ratified as-is (derived decision, minuted on
the issue): the row is emitted at finalize and stamped with the instant
of the last contributing (warm) value (TapFold::last_ts) — first alone
pins the first contributing instant, and min/max deliberately do not
carry the extremum's instant (a whole-window row privileges no interior
instant, and the extremum ts would cost extra state for no consumer).

The issue's initial finalize-ts reading (and the first draft of this
ratification) was refuted in review against tap_fold.rs: a tap that
goes cold before run end stamps the last WARM eval's instant, not the
run-end instant — observationally identical only while the tap stays
warm to the end, which is what the fieldtest fixtures did. Correction
minuted on the issue.

Recorded in C27's Current state and the glossary tap-plan paragraph;
the fold-registry roster doc lines state it on the surface itself
(sibling commit).

closes #335

docs/glossary.md

@@ -327,7 +327,7 @@ A named recorded stream produced by a recording `sink` — the addressable label
 
 Since C27 (#282) the word also names a second, author-facing sense: a **declared tap** — a `Composite.taps` entry `Tap { name, from: {node, field} }` a hand-authored blueprint declares on an interior output wire, the output-side twin of an `input_role`. It is a pure declaration (no channel endpoint); the harness binds it run-mode-aware (a single `aura run` constructs a recorder at each and persists the series through the trace store; a sweep leaves it unbound and inert). This is an OPEN, per-blueprint author-declared name — distinct from the CLOSED campaign `persist_taps` vocabulary above, which selects among fixed observables of the standard R-harness. Both senses land as `ColumnarTrace`s in the same trace store; the closed vocabulary is what a `campaign document` selects, the declared tap is what a blueprint author names.
 
-Since #283 what CONSUMES a declared tap is itself declared per run by a **tap plan**: a subscription is either `Named { label, params }` — resolved against a layered **fold registry** whose core vocabulary is `record | count | sum | mean | min | max | first | last`, each entry carrying a doc line (the help surface and the roster-enumerating refusal) and a scalar-typed param schema (all core entries param-less; growth is a new Rust entry per C25, and higher layers register entries without touching the core) — or `Live(closure)`, the single non-data variant (an in-process consumer with consumer-owned loss policy). `record` streams the full series to the trace store at constant memory (no buffer-then-drain); folds keep an O(1) accumulator and land one summary row at finalize. Both declared-tap entry points are arms of the single verb `aura run` (`aura measure` is the post-hoc IC analysis over already-persisted traces and constructs no tap plan); `aura run` subscribes every declared tap to `record` by default, and its repeatable `--tap TAP=FOLD` selector (#310) replaces that default with an explicit plan — only listed taps are bound, unlisted taps stay unbound/inert. A fold's one summary row is stamped with the source value's own timestamp for `first`/`last` (they pin a single source instant) and with the finalize timestamp for the accumulator folds (`count | sum | mean | min | max` summarise a range; `min`/`max` deliberately do not carry the extremum's instant — ratified #335).
+Since #283 what CONSUMES a declared tap is itself declared per run by a **tap plan**: a subscription is either `Named { label, params }` — resolved against a layered **fold registry** whose core vocabulary is `record | count | sum | mean | min | max | first | last`, each entry carrying a doc line (the help surface and the roster-enumerating refusal) and a scalar-typed param schema (all core entries param-less; growth is a new Rust entry per C25, and higher layers register entries without touching the core) — or `Live(closure)`, the single non-data variant (an in-process consumer with consumer-owned loss policy). `record` streams the full series to the trace store at constant memory (no buffer-then-drain); folds keep an O(1) accumulator and land one summary row at finalize. Both declared-tap entry points are arms of the single verb `aura run` (`aura measure` is the post-hoc IC analysis over already-persisted traces and constructs no tap plan); `aura run` subscribes every declared tap to `record` by default, and its repeatable `--tap TAP=FOLD` selector (#310) replaces that default with an explicit plan — only listed taps are bound, unlisted taps stay unbound/inert. A fold's one summary row is emitted at finalize and stamped with the instant of the last contributing (warm) value — `first` alone pins the first contributing instant, and `min`/`max` deliberately do not carry the extremum's instant (ratified #335).
 
 ### topology hash
 **Avoid:** —