docs: bound params are overridable defaults — C12 amendment, glossary, guide

Task 7 of the bound-override cycle: the design ledger's C12 records the
bound-as-default semantics (axis 1 may name a bound param; identity reads
the authored document; the retired axes-bind-only-open-knobs restriction
was an implementation consequence, not a recorded decision), the glossary's
blueprint entry carries the same sentence, and the authoring-guide's
data-only starter section explains the one-file run+sweep quickstart.

closes #246

docs/authoring-guide.md

@@ -38,10 +38,11 @@ the same shape every node in `aura-std` already follows.
 - **The project's own signal doesn't need a crate by default.** `aura new`
   scaffolds a **data-only** project (`docs/project-layout.md`, "A project
   repo (two tiers)") — a strategy over the std vocabulary is a
-  blueprint/campaign document, not Rust: the scaffold ships a single closed
-  `signal.json` starter, runnable immediately with no build step, and also
-  the sweep target itself (a bound param is a default any `--axis` may
-  override, #246).
+  blueprint/campaign document, not Rust: the scaffold ships **one** closed
+  `signal.json` starter that serves both verbs — `aura run` uses its bound
+  values as-is, `aura sweep --axis <bp>.fast.length=2,4,8` overrides them
+  (bound = default, not fixed); `--list-axes` lists the open knobs and the
+  bound defaults alike, so every override target is discoverable.
 - **A project-specific *native* node type** — the moment §0's three-part
   pattern is actually needed — lives in an attached **node crate**:
   `aura nodes new <name>` scaffolds a sibling cdylib crate (`Cargo.toml` +

docs/design/INDEX.md

@@ -1132,6 +1132,16 @@ Seed-as-input reconciles Monte-Carlo with C1. The "frozen topology" of the
 atomic unit is one harness instance, selected by the harness's **structural
 axes** (C20); the structural experiment matrix is the outer orchestration over
 this dimension, the tuning sweep the inner (C19/C20).
+**Amendment (2026-07-12, #246).** A bound blueprint param is the param's
+**default**: axis 1 (param-sweep) may name a bound param — the family boundary
+re-opens it on the probe and on every member reload, and the axis binds it per
+cell. "Open" means *must be bound by an axis*; "bound" means *default,
+overridable by an axis*. `run`/`mc` still require every param resolved (a truly
+open param still refuses). Identity is untouched: `content_id_of` and
+`topology_hash` read the authored document, never a re-opened probe, and each
+member manifest records its per-cell bindings as before. The restriction this
+amends — axes bind only open knobs — was an implementation consequence of
+`bind()` shrinking the param surface, not a recorded decision.
 
 ### C13 — Hot-reload is authoring-only; deploy is frozen
 **Guarantee.** A node/strategy is authored as a native Rust `cdylib`,

docs/glossary.md

@@ -29,7 +29,7 @@ A strategy's primary, backtestable DAG output: one signed, bounded `f64 ∈ [-1,
 
 ### blueprint
 **Avoid:** —
-The param-generic, input-role-generic graph-as-data produced by running a Rust builder; it carries free numeric params and free input roles before bootstrap. Bootstrapped into a frozen instance by binding params + data + seed. Registered and inspected headless (`aura graph register`, `aura graph introspect --params` — the raw `param_space` namespace campaign axes bind against; cycle 0107/#196).
+The param-generic, input-role-generic graph-as-data produced by running a Rust builder; it carries free numeric params and free input roles before bootstrap. Bootstrapped into a frozen instance by binding params + data + seed. Registered and inspected headless (`aura graph register`, `aura graph introspect --params` — the raw `param_space` namespace campaign axes bind against; cycle 0107/#196); a *bound* param is an overridable **default** — a sweep axis naming it re-opens it per family (#246), while `run` uses it as-is.
 
 ### bootstrap
 **Avoid:** —