fix!: correct eight wrong # Errors sections and seal the error variants

Documentation (#78). Every item below was measured against the code
rather than read:

- `expected_information_gain` and `predict_ranking` had `# Errors`
  immediately followed by `# Preconditions`, with the error list stranded
  at the bottom of the latter — rustdoc rendered a BLANK Errors section on
  both. The heading now sits with its content.
- `predict_outcome`, `predict_ranking` and the free
  `expected_information_gain` all omitted `GridTooCoarse`.
- `predict_margin` claimed `JointUnavailable` "if the LATEST slice holds
  ranked events". Measured with an early ranked slice and a late scored
  one: it fails. The condition is *any* slice.
- `add_events` documented three errors and can return five more; it also
  claimed a weights `MismatchedShape` that is unreachable through it,
  since weights arrive one-per-`Member`. That check belongs to
  `EventBuilder::weights`, and the doc now says so.
- `converge` and `converge_partial` both omitted the drift-variance
  `InvalidParameter`.

`History` gains a hand-written `Debug` (#76). Summarising, not
exhaustive — a derived one would print every competitor's skill at every
slice. It exists because without it a consumer cannot `#[derive(Debug)]`
on any struct holding a `History`, which is how both known consumers
store one.

`#[non_exhaustive]` on all 17 `InferenceError` struct variants and on
`Outcome::Scored` (#74). The enum carried the attribute; no variant did,
so adding a field to any of them — and downstream construction of any of
them — were both in the public contract. This crate added two variants in
two days.

The options structs are deliberately NOT sealed. `ConvergenceOptions` and
`GameOptions` are constructed by struct literal at 65 sites of which only
8 use `..default()`, and specifying all three convergence fields is a
natural complete statement rather than a partial one. That is a real
trade-off rather than an oversight, and it is left as a decision on #74.

Also spells `UnknownKeys::Reject` explicitly at both sites that
wildcarded it. `#[non_exhaustive]` on your own enum gives no exhaustiveness
safety net if you then match `_`.

Sealing the variants pushed ten test sites from constructing errors to
`matches!`, which is the better assertion anyway — an `assert_eq!` against
a constructed error breaks whenever a field is added, which is the exact
fragility the attribute exists to prevent.

BREAKING CHANGE: `InferenceError`'s struct variants and `Outcome::Scored`
are `#[non_exhaustive]` — downstream patterns need `..` and downstream
construction is no longer possible.

Refs #78, #76, #74

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ

tests/convergence_strictness.rs

@@ -54,6 +54,7 @@ fn hitting_the_cap_is_an_error() {
             iterations,
             final_step,
             epsilon,
+            ..
         } => {
             assert_eq!(iterations, 1);
             assert!(

tests/degenerate_inputs.rs

@@ -160,6 +160,7 @@ fn event_builder_rejects_a_weights_length_mismatch() {
                 kind: "weights",
                 expected: 1,
                 got: 2,
+                ..
             }
         ),
         "expected a weights MismatchedShape, got {err:?}"

tests/drift_scale.rs

@@ -277,13 +277,11 @@ fn reject(scale: f64) -> InferenceError {
 
 #[test]
 fn negative_scale_is_rejected() {
-    assert_eq!(
+    assert!(matches!(
         reject(-1.0),
-        InferenceError::InvalidParameter {
-            name: "drift_scale",
-            value: -1.0
-        }
-    );
+        InferenceError::InvalidParameter { name: "drift_scale", value, .. }
+            if value == -1.0
+    ));
 }
 
 #[test]

tests/event_builder_members.rs

@@ -135,7 +135,8 @@ fn weights_still_guards_a_members_team() {
             InferenceError::MismatchedShape {
                 kind: "weights",
                 expected: 2,
-                got: 1
+                got: 1,
+                ..
             }
         ),
         "{err:?}"

tests/game.rs

@@ -155,7 +155,7 @@ mod malformed_games {
         let err = Game::<i64, _>::ranked(&[&[a]], Outcome::winner(0, 1), &GameOptions::default())
             .unwrap_err();
         assert!(
-            matches!(err, InferenceError::NotEnoughTeams { got: 1 }),
+            matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
             "{err:?}"
         );
     }
@@ -173,7 +173,7 @@ mod malformed_games {
         )
         .unwrap_err();
         assert!(
-            matches!(err, InferenceError::NotEnoughTeams { got: 1 }),
+            matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
             "{err:?}"
         );
     }
@@ -184,7 +184,7 @@ mod malformed_games {
             Game::<i64, ConstantDrift>::ranked(&[], Outcome::ranking([]), &GameOptions::default())
                 .unwrap_err();
         assert!(
-            matches!(err, InferenceError::NotEnoughTeams { got: 0 }),
+            matches!(err, InferenceError::NotEnoughTeams { got: 0, .. }),
             "{err:?}"
         );
     }
@@ -198,7 +198,7 @@ mod malformed_games {
             Game::<i64, _>::ranked(&[&[], &[a]], Outcome::winner(0, 2), &GameOptions::default())
                 .unwrap_err();
         assert!(
-            matches!(err, InferenceError::EmptyTeam { team: 0 }),
+            matches!(err, InferenceError::EmptyTeam { team: 0, .. }),
             "{err:?}"
         );
     }

tests/ingestion_shape.rs

@@ -40,7 +40,7 @@ fn a_one_team_event_is_an_error_not_a_panic() {
         }])
         .unwrap_err();
     assert!(
-        matches!(err, InferenceError::NotEnoughTeams { got: 1 }),
+        matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
         "{err:?}"
     );
 }
@@ -56,7 +56,7 @@ fn a_zero_team_event_is_an_error() {
         }])
         .unwrap_err();
     assert!(
-        matches!(err, InferenceError::NotEnoughTeams { got: 0 }),
+        matches!(err, InferenceError::NotEnoughTeams { got: 0, .. }),
         "{err:?}"
     );
 }
@@ -75,7 +75,7 @@ fn an_empty_team_is_an_error_rather_than_a_free_win() {
         }])
         .unwrap_err();
     assert!(
-        matches!(err, InferenceError::EmptyTeam { team: 0 }),
+        matches!(err, InferenceError::EmptyTeam { team: 0, .. }),
         "{err:?}"
     );
     // Nothing was recorded, so the history is still empty.
@@ -93,7 +93,7 @@ fn an_empty_team_is_reported_by_position() {
         }])
         .unwrap_err();
     assert!(
-        matches!(err, InferenceError::EmptyTeam { team: 1 }),
+        matches!(err, InferenceError::EmptyTeam { team: 1, .. }),
         "{err:?}"
     );
 }
@@ -170,7 +170,7 @@ fn the_event_builder_inherits_the_shape_checks() {
     let mut h = history();
     let err = h.event(1).team(["a"]).winner(0).commit().unwrap_err();
     assert!(
-        matches!(err, InferenceError::NotEnoughTeams { got: 1 }),
+        matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
         "{err:?}"
     );
 }

tests/non_finite_results.rs

@@ -56,7 +56,7 @@ fn overflow_during_inference_is_reported_not_hidden() {
 
     for (name, sigma, beta, score_sigma, scores) in cases {
         match scored_fit(sigma, beta, score_sigma, scores) {
-            Err(InferenceError::NonFiniteResult { context, step }) => {
+            Err(InferenceError::NonFiniteResult { context, step, .. }) => {
                 assert_eq!(context, "History::converge", "{name}");
                 assert!(
                     !step.0.is_finite() || !step.1.is_finite(),

tests/predict_margin.rs

@@ -148,6 +148,6 @@ fn shape_errors_are_reported() {
     let empty: [&&str; 0] = [];
     assert!(matches!(
         h.predict_margin(&[&[&"veteran"], &empty]),
-        Err(InferenceError::EmptyTeam { team: 1 })
+        Err(InferenceError::EmptyTeam { team: 1, .. })
     ));
 }

tests/prediction.rs

@@ -20,13 +20,13 @@ fn unknown_keys_are_reported_not_silently_dropped() {
     let err = h
         .predict_outcome(&[&[&"a"], &[&"ghost"]])
         .expect_err("an unknown key must not yield a confident prediction");
-    assert_eq!(
-        err,
-        InferenceError::UnknownKey {
-            team: 1,
-            member: 0,
-            key: "\"ghost\"".to_owned(),
-        }
+    assert!(
+        matches!(
+            &err,
+            InferenceError::UnknownKey { team: 1, member: 0, key, .. }
+                if key == "\"ghost\""
+        ),
+        "{err:?}"
     );
 
     // Every prediction entry point, not just one.
@@ -42,13 +42,13 @@ fn unknown_keys_are_reported_not_silently_dropped() {
 fn an_entirely_unknown_team_is_an_error() {
     let h = history_with(&["a", "b"], 0.0);
     let err = h.predict_outcome(&[&[&"a"], &[&"x", &"y"]]).unwrap_err();
-    assert_eq!(
-        err,
-        InferenceError::UnknownKey {
-            team: 1,
-            member: 0,
-            key: "\"x\"".to_owned(),
-        }
+    assert!(
+        matches!(
+            &err,
+            InferenceError::UnknownKey { team: 1, member: 0, key, .. }
+                if key == "\"x\""
+        ),
+        "{err:?}"
     );
 }
 
@@ -56,18 +56,18 @@ fn an_entirely_unknown_team_is_an_error() {
 fn degenerate_team_shapes_are_errors_rather_than_panics() {
     let h = history_with(&["a", "b"], 0.0);
 
-    assert_eq!(
+    assert!(matches!(
         h.predict_outcome(&[&[&"a"]]).unwrap_err(),
-        InferenceError::NotEnoughTeams { got: 1 }
-    );
-    assert_eq!(
+        InferenceError::NotEnoughTeams { got: 1, .. }
+    ),);
+    assert!(matches!(
         h.predict_outcome(&[]).unwrap_err(),
-        InferenceError::NotEnoughTeams { got: 0 }
-    );
-    assert_eq!(
+        InferenceError::NotEnoughTeams { got: 0, .. }
+    ),);
+    assert!(matches!(
         h.predict_outcome(&[&[&"a"], &[]]).unwrap_err(),
-        InferenceError::EmptyTeam { team: 1 }
-    );
+        InferenceError::EmptyTeam { team: 1, .. }
+    ));
 }
 
 #[test]
@@ -93,13 +93,10 @@ fn the_outcome_space_is_capped_rather_than_hanging() {
     let refs: Vec<&[&&str]> = too_many.iter().map(Vec::as_slice).collect();
 
     let err = h.predict_outcome(&refs).unwrap_err();
-    assert_eq!(
+    assert!(matches!(
         err,
-        InferenceError::TooManyTeams {
-            got: 8,
-            max: MAX_PREDICTED_TEAMS
-        }
-    );
+        InferenceError::TooManyTeams { got: 8, max, .. } if max == MAX_PREDICTED_TEAMS
+    ));
 
     // The cheap paths stay available at any size.
     let wins = h.predict_win_probabilities(&refs).unwrap();
@@ -282,15 +279,12 @@ fn information_gain_respects_the_entropy_ceiling() {
 #[test]
 fn information_gain_reports_unknown_keys() {
     let h = history_with(&["a", "b"], 0.0);
-    assert_eq!(
-        h.expected_information_gain(&[&[&"a"], &[&"ghost"]])
+    assert!(matches!(
+        &h.expected_information_gain(&[&[&"a"], &[&"ghost"]])
             .unwrap_err(),
-        InferenceError::UnknownKey {
-            team: 1,
-            member: 0,
-            key: "\"ghost\"".to_owned(),
-        }
-    );
+        InferenceError::UnknownKey { team: 1, member: 0, key, .. }
+            if key == "\"ghost\""
+    ));
 }
 
 /// A draw-enabled history has three outcomes to weigh rather than two, so the

tests/prediction_bounds.rs

@@ -154,7 +154,7 @@ fn the_known_ceiling_violation_no_longer_answers_wrongly() {
             gain <= 2.0_f64.ln() + 1e-9,
             "returned {gain}, over the ln 2 ceiling"
         ),
-        Err(InferenceError::GridTooCoarse { needed, max }) => {
+        Err(InferenceError::GridTooCoarse { needed, max, .. }) => {
             assert!(needed > max, "needed {needed} should exceed max {max}");
         }
         Err(e) => panic!("unexpected error {e:?}"),