fieldtest: bound-override cycle — 4 examples, 6 findings (4 working, 1 friction, 1 bug)

Per-cycle fieldtest over the #246 surface, consumer-perspective, public
interface only: the scaffold quickstart end to end (aura new -> run ->
--list-axes -> override sweep), --list-axes on a partially-open
blueprint, an override family reproduced bit-identically (3/3 members),
and the error surface (wrong axis name, kind-mismatched value — both
exit 2). Corpus under fieldtests/cycle-246-bound-override/.

Dispositions: the one bug (F6) is fixed in this commit — authoring-guide
§1 still asserted a bound param 'never shows up in --list-axes' and 'no
aura sweep --axis can reopen it', contradicting the shipped #246
semantics and the C12 amendment; the three-states paragraph now reads
open = must-bind, bound = overridable default. The friction finding (F5,
KindMismatch/MissingKnob printed as raw Debug structs beside polished
prose) is filed as #247.

refs #246

docs/authoring-guide.md

@@ -259,14 +259,16 @@ purpose — three open campaign axes, see §3. This is the milestone fieldtest
 corpus's own example, verified below; byte-identical to the on-disk
 `fieldtests/milestone-research-artifacts/mra_1_strategy_smacross.json`.)
 
-A `bind` in an `add` op pins that param to a fixed value and **removes it
-from the sweepable param space**: a bound param is closed — it never shows
-up in `--params`/`--list-axes`, and no campaign axis and no `aura sweep
---axis` can reopen it. `bind` is for a constant the strategy never varies;
-leave a param unbound, as all three are here, to keep it open for sweeping.
+A `bind` in an `add` op pins that param to a value and removes it from the
+**open** param space (`--params`): a bound param is a **default** (#246) — a
+run uses it as-is, while any campaign axis or `aura sweep --axis` naming it
+re-opens it for that family and binds it per cell. `--list-axes` lists it
+after the open knobs as `<name>:<KIND> default=<value>`. `bind` is for a
+value the strategy carries by default; leave a param unbound, as all three
+are here, to make binding it mandatory for every sweep.
 
-A param therefore has three states: **open** (a sweepable axis), **bound**
-(closed by a `bind` — gone from the axis namespace), and **ganged** (open, but
+A param therefore has three states: **open** (an axis every sweep MUST bind),
+**bound** (a default any axis MAY override, #246), and **ganged** (open, but
 fused with its siblings under ONE public knob declared by a `gang` op; the
 member addresses are unbindable and only the gang's own single-segment name —
 wrapped like any knob, e.g. `graph.channel_length` — appears in `--list-axes`).