Vis.discover() is a wrapper, not a thin delegate — ADR-0002 Principle 2 drift

[gerchowl]

Tier 3 — design question flagged by adversarial review

`Vis.discover()` in `src/pymat/vis/_model.py` claims to be part of the
"thin delegate" set per ADR-0002,
but it actually does translation:

def discover(self, *, category=None, roughness=None, metallic=None,
             limit=5, auto_set=False):
    from mat_vis_client import search
    results = search(
        category=category,
        roughness=roughness,
        metalness=metallic,   # ← rename: metallic → metalness
        limit=limit,
    )
    if auto_set and results:
        top = results[0]
        self.source = top["source"]
        self.material_id = top["id"]
    return results

Three ways this violates Principle 2 ("client is exposed, not wrapped"):

1. Arg renaming: `metallic` → `metalness` (py-mat's internal name vs
   mat-vis-client's name).
2. `auto_set=True` side-effects the Vis — that's a mutation disguised
   as a search.
3. The underlying `mat_vis_client.search` already takes roughness +
   metalness as ranges (widened in `pymat.vis.search`). `Vis.discover`
   passes scalars through; they hit a different code path.

Decision

Option A — relocate: move `discover` to a module function
`pymat.vis.discover_for(material, ...)` that takes a material
explicitly, and delete the method. Leaves `Vis` as pure
identity + scalars + delegate sugar.

Option B — footnote the ADR: acknowledge `discover` as the one
exception where py-mat does translation, because it's a search layered
over the client and the tag-aware semantics are genuinely py-mat-side.

Recommendation

(B). `discover` has been in `Vis` since pre-3.0 and the
`auto_set=True` convenience is genuinely useful on a Material.
Moving it to a module function loses the dotted sugar
(`steel.vis.discover(...)`) without a clear win. Footnote in
ADR-0002 Principle 2 describing `.discover` as the "tag-aware
convenience wrapper" exception.

Labels

`question` — behavior stays the same either way; this is about
the documentation contract.