fix(model-library): remove artifact resolver unwrap

Replace the guarded unwrap in selected-artifact path resolution with direct iterator matching so production request handling stays panic-free while preserving zero, one, and many match behavior.

Record the Pantograph standards cleanup in the artifact load-target plan issue register.

Verification: cargo fmt --manifest-path rust/Cargo.toml --all; cargo test --manifest-path rust/Cargo.toml -p pumas-library read_only_library; cargo test --manifest-path rust/Cargo.toml -p pumas-library artifact_owner_fresh; cargo test --manifest-path rust/Cargo.toml -p pumas-library --test artifact_load_target_contract_fixtures; cargo check --manifest-path rust/Cargo.toml -p pumas-library; git diff --check

Author: MrScripty

docs/plans/pumas-artifact-load-target-resolution/plan.md

@@ -243,6 +243,9 @@ targets to workers.
   now rejects requests with no selected artifact identity, resolves a missing
   `selected_artifact_id` from a unique indexed `selected_artifact_path`, and
   reports typed diagnostics for missing or ambiguous path matches.
+- M2-003 closed: Pantograph review found a guarded production `unwrap()` in
+  selected-artifact path resolution. The resolver now expresses the zero,
+  one, and many match cases by matching iterator results directly.
 
 ## Risks And Mitigations
 | Risk | Mitigation |

rust/crates/pumas-core/src/model_library/artifact_load_target.rs

@@ -144,12 +144,13 @@ fn selected_artifact_id_from_path(
         index.list_model_package_facts_cache(model_id, ModelPackageFactsCacheScope::Detail)?,
     );
 
-    match matches.len() {
-        0 => Ok(SelectedArtifactIdentity::PathNotIndexed),
-        1 => Ok(SelectedArtifactIdentity::Resolved(
-            matches.into_iter().next().unwrap(),
-        )),
-        _ => Ok(SelectedArtifactIdentity::AmbiguousPath),
+    let mut matches = matches.into_iter();
+    match (matches.next(), matches.next()) {
+        (None, _) => Ok(SelectedArtifactIdentity::PathNotIndexed),
+        (Some(selected_artifact_id), None) => {
+            Ok(SelectedArtifactIdentity::Resolved(selected_artifact_id))
+        }
+        (Some(_), Some(_)) => Ok(SelectedArtifactIdentity::AmbiguousPath),
     }
 }