Make pred inspect report reductions for the exact input variant

[isPANN]

Background

Reduction availability is defined by a complete problem variant, not only by its model name. For example, MinimumDominatingSet<SimpleGraph, One> has a direct reduction to MinimumHittingSet, while MinimumDominatingSet<SimpleGraph, i32> does not.

pred inspect currently aggregates outgoing reductions at the model-name level. It can therefore advertise a reduction that cannot be executed for the inspected instance. The mismatch was reproduced in the PR #1105 agentic review report on the PR #1083 branch.

Objective

Make pred inspect compute reduces_to from the inspected instance's fully normalized variant. Every advertised target must be executable by pred reduce under the same default witness-capable path semantics.

Interface (Input → Output)

In: a serialized problem instance containing a canonical problem name and complete variant map.

Out: text and JSON pred inspect results whose reduces_to entries apply to that exact source variant. Edges registered only for sibling variants must not appear.

Technical recommendations

problemreductions-cli/src/commands/inspect.rs currently obtains outgoing reductions with a name-level graph query. Resolve the loaded instance to its exact reduction-graph node and derive targets from that node, using the same variant and witness-capability rules as pred reduce. Keep the implementation direct; do not add a parallel capability registry or compatibility layer.

Verification

Build the CLI and inspect the default weighted MinimumDominatingSet example. It is the SimpleGraph/i32 variant and must not advertise the unit-weight-only target:

cargo build -p problemreductions-cli --bin pred --locked
PRED_BIN=target/debug/pred

"$PRED_BIN" create --example MinimumDominatingSet -o /tmp/mds-i32.json
"$PRED_BIN" inspect /tmp/mds-i32.json --json \
  | jq -e '.variant.weight == "i32" and ((.reduces_to | index("MinimumHittingSet")) == null)'

if "$PRED_BIN" reduce /tmp/mds-i32.json --to MinimumHittingSet -o /tmp/mds-i32-bundle.json; then
  echo 'unexpected reduction success' >&2
  exit 1
fi

Both checks must exit 0: inspection omits the unavailable target, and direct reduction rejects it.

Negative control: the exact unit-weight rule example must retain the reduction in inspect, and the advertised operation must succeed:

"$PRED_BIN" create --example MinimumDominatingSet/SimpleGraph/One \
  --to MinimumHittingSet -o /tmp/mds-one.json
"$PRED_BIN" inspect /tmp/mds-one.json --json \
  | jq -e '.variant.weight == "One" and ((.reduces_to | index("MinimumHittingSet")) != null)'
"$PRED_BIN" reduce /tmp/mds-one.json --to MinimumHittingSet -o /tmp/mds-one-bundle.json

Add focused CLI regression coverage for both variants and run make check.

Out of scope

• Adding a weighted MinimumDominatingSet<i32> → MinimumHittingSet reduction.
• Changing model aliases or canonical-example selection.
• Redesigning solver capability reporting.