Brummel
a78a0557f4
Add `aura sweep <blueprint.json> --list-axes`: a read-only query sub-mode that lists a loaded blueprint's open sweepable knobs (one `<name>:<kind>` per line, param_space() order), then exits. Closes the discovery gap #169 surfaced — today the only way to learn the axis names is to guess one and read a MissingKnob/UnknownKnob error, and that error names only the rejected knob, never the valid set. Prerequisite for #173 (IS-refit walk-forward must know which axes to re-fit per in-sample window). Derived surface decision (recorded on #169): the query lands on the SWEEP verb, not `graph introspect`. The axis names `--axis` accepts are produced by the sweep's own harness-wrapping — the loaded signal (name "stage1_signal") is nested via wrap_stage1r as a BlueprintNode::Composite, so collect_params prefixes the names (stage1_signal.fast.length), NOT the raw param_space (fast.length; empirically: the bare name → UnknownKnob). Only the sweep verb, which owns the wrapping, can print the names the user will actually pass; a shared blueprint_axis_probe single-sources the probe for both the sweep terminal and --list-axes, so listed == swept by construction (and stays correct across #159's harness retirement). Boss-signed on grounding-check PASS (independent, fresh-context; one BLOCK raised + fixed: the malformed-sweep .expect panic-path is now pinned by a this-cycle E2E over unknown_node.json, not an untested current-behaviour claim). Engine/registry untouched (invariants 1/8/9). refs #169