refactor(engine): type the captured child-boundary stack depth

crates/engine/src/game/effects/change_zone.rs

@@ -1121,7 +1121,7 @@ pub fn resolve(
             per_obj_ctx.source_id,
         );
         let delivery_start = events.len();
-        let stack_depth_before_zone_move = state.resolution_stack.len();
+        let stack_depth_before_zone_move = state.resolution_stack.capture_child_boundary();
         match process_one_zone_move_with_terminal(state, &per_obj_ctx, *obj_id, events) {
             crate::game::zone_pipeline::ZoneMoveTerminalResult::Completed(completion) => {
                 logical_zone_change_group
@@ -1996,7 +1996,7 @@ pub fn resolve_all(
         let anticipated_pause =
             anticipated_zone_change_delivery(state, obj_id, dest_zone, ability.source_id);
         let delivery_start = events.len();
-        let stack_depth_before_zone_move = state.resolution_stack.len();
+        let stack_depth_before_zone_move = state.resolution_stack.capture_child_boundary();
         match crate::game::zone_pipeline::execute_zone_move_with_terminal_and_controller(
             state,
             obj_id,

crates/engine/src/game/effects/each_player_copy_chosen.rs

@@ -34,6 +34,7 @@ use crate::types::game_state::{
 };
 use crate::types::identifiers::ObjectId;
 use crate::types::player::PlayerId;
+use crate::types::resolution::ChildStackDepth;
 
 /// Effect parameters threaded through the whole APNAP walk. Bundled so the
 /// resolver, the `SelectTargets` continuation, and the replacement-resume drain
@@ -263,7 +264,7 @@ pub(crate) fn drive_from_copy(
     );
     // Depth 1: skip the depth-0 chain prelude so per-resolution ledgers
     // (`last_created_token_ids`) are not reset.
-    let stack_depth_before_copy = state.resolution_stack.len();
+    let stack_depth_before_copy = state.resolution_stack.capture_child_boundary();
     super::resolve_ability_chain(state, &copy_ability, events, 1)?;
 
     // CR 616.1: The copy parked a replacement-ordering choice. Do NOT read
@@ -326,7 +327,7 @@ pub(crate) fn perform_counter_step_then_advance(
                     params.source_id,
                     player,
                 );
-                let stack_depth_before_counter = state.resolution_stack.len();
+                let stack_depth_before_counter = state.resolution_stack.capture_child_boundary();
                 super::resolve_ability_chain(state, &counter_ability, events, 1)?;
                 // CR 616.1: the counter placement paused for a replacement
                 // ordering — park an `AwaitingCounters` continuation.
@@ -398,9 +399,13 @@ pub(crate) fn drain_pending(state: &mut GameState, events: &mut Vec<GameEvent>)
 fn park_each_player_copy_chosen_after_current_step(
     state: &mut GameState,
     pending: PendingEachPlayerCopyChosen,
-    stack_depth_before_step: usize,
+    stack_depth_before_step: ChildStackDepth,
 ) {
-    match state.resolution_stack.len().cmp(&stack_depth_before_step) {
+    match state
+        .resolution_stack
+        .capture_child_boundary()
+        .cmp(&stack_depth_before_step)
+    {
         std::cmp::Ordering::Less => {
             panic!("each-player-copy-chosen step removed a parent before it could be re-parked")
         }

crates/engine/src/game/effects/mod.rs

@@ -32,8 +32,8 @@ use crate::types::identifiers::{ObjectId, TrackedSetId};
 use crate::types::mana::ManaCost;
 use crate::types::player::{Player, PlayerId};
 use crate::types::resolution::{
-    AbilityContinuationFrame, FrameGate, OptionalEffectFrame, PendingRepeatedOptionalPayment,
-    RepeatedOptionalPaymentFrame, ResolutionFrame,
+    AbilityContinuationFrame, ChildStackDepth, FrameGate, OptionalEffectFrame,
+    PendingRepeatedOptionalPayment, RepeatedOptionalPaymentFrame, ResolutionFrame,
 };
 use crate::types::zones::Zone;
 
@@ -1184,11 +1184,11 @@ fn drain_active_repeat_until(state: &mut GameState) {
 fn park_repeat_until_after_inner_pause(
     state: &mut GameState,
     pending: crate::types::game_state::PendingRepeatUntil,
-    stack_depth_before_iteration: usize,
+    stack_depth_before_iteration: ChildStackDepth,
 ) {
     match state
         .resolution_stack
-        .len()
+        .capture_child_boundary()
         .cmp(&stack_depth_before_iteration)
     {
         std::cmp::Ordering::Less => {
@@ -1362,7 +1362,7 @@ fn drain_pending_change_zone_iteration(state: &mut GameState, events: &mut Vec<G
                 )
             });
             let delivery_start = events.len();
-            let stack_depth_before_zone_move = state.resolution_stack.len();
+            let stack_depth_before_zone_move = state.resolution_stack.capture_child_boundary();
             match crate::game::effects::change_zone::process_one_zone_move_with_terminal(
                 state, &ctx, *obj_id, events,
             ) {
@@ -1618,7 +1618,7 @@ fn drain_active_repeat_for(state: &mut GameState, events: &mut Vec<GameEvent>) {
             } else {
                 &ability
             };
-            let stack_depth_before_iteration = state.resolution_stack.len();
+            let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
             // CR 608.2c + CR 109.5: Drive the FULL chain (parent effect +
             // sub_ability + line-1660 continuation wiring) for each resumed
             // iteration, mirroring iteration 0's path. Calling `resolve_effect`
@@ -1680,11 +1680,11 @@ fn drain_active_repeat_for(state: &mut GameState, events: &mut Vec<GameEvent>) {
 fn park_repeat_for_after_current_iteration(
     state: &mut GameState,
     pending: crate::types::game_state::PendingRepeatIteration,
-    stack_depth_before_iteration: usize,
+    stack_depth_before_iteration: ChildStackDepth,
 ) {
     match state
         .resolution_stack
-        .len()
+        .capture_child_boundary()
         .cmp(&stack_depth_before_iteration)
     {
         std::cmp::Ordering::Less => {
@@ -7422,7 +7422,7 @@ fn drive_repeat_for_outermost(
     while iteration < base_iterations {
         let mut iter_ability = effective.clone();
         iter_ability.repeat_for = None;
-        let stack_depth_before_iteration = state.resolution_stack.len();
+        let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
         resolve_chain_body(state, &iter_ability, events, depth)?;
         if state.waiting_for != initial_waiting_for
             || (!initial_continuation_present && state.active_ability_continuation().is_some())
@@ -9520,7 +9520,7 @@ pub fn resolve_ability_chain(
         None => resolve_chain_body(state, ability, events, depth),
         Some(RepeatContinuation::ControllerChoice) => {
             let initial_waiting_for = state.waiting_for.clone();
-            let stack_depth_before_iteration = state.resolution_stack.len();
+            let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
             resolve_chain_body(state, ability, events, depth)?;
             if state.waiting_for != initial_waiting_for {
                 // Inner pause: stash so the drain re-sets the repeat prompt
@@ -9547,7 +9547,7 @@ pub fn resolve_ability_chain(
             stop_on_duplicate_exiled_names,
         }) => loop {
             let initial_waiting_for = state.waiting_for.clone();
-            let stack_depth_before_iteration = state.resolution_stack.len();
+            let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
             resolve_chain_body(state, ability, events, depth)?;
             if state.waiting_for != initial_waiting_for {
                 park_repeat_until_after_inner_pause(
@@ -9597,7 +9597,7 @@ pub fn resolve_ability_chain(
                 // iteration's stale result.
                 state.resolution_coin_flip = None;
                 let initial_waiting_for = state.waiting_for.clone();
-                let stack_depth_before_iteration = state.resolution_stack.len();
+                let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
                 resolve_chain_body(state, ability, events, depth)?;
                 if state.waiting_for != initial_waiting_for {
                     // Inner pause: stash the loop ability with its remaining cap
@@ -11193,7 +11193,7 @@ fn resolve_chain_body(
                     } else {
                         effective
                     };
-                let stack_depth_before_iteration = state.resolution_stack.len();
+                let stack_depth_before_iteration = state.resolution_stack.capture_child_boundary();
                 // CR 608.2d: A kind-driven or member-driven iteration whose action
                 // is optional fires its per-iteration "you may" gate through the
                 // full chain. All other iterations resolve the effect directly —

crates/engine/src/game/effects/token_copy.rs

@@ -21,6 +21,7 @@ use crate::types::identifiers::{CardId, ObjectId, ObjectIncarnationRef};
 use crate::types::proposed_event::{
     CopyTokenSpec, EtbTapState, ProposedEvent, TokenCharacteristics,
 };
+use crate::types::resolution::ChildStackDepth;
 use crate::types::resolved_commands::{
     ResolvedCopyBodyModifications, ResolvedTokenBody, ResolvedTokenCreationCommand,
 };
@@ -285,7 +286,7 @@ fn drain_copy_token_resolution(
         if batch.count == 0 {
             continue;
         }
-        let stack_depth_before_batch = state.resolution_stack.len();
+        let stack_depth_before_batch = state.resolution_stack.capture_child_boundary();
         let spec = super::token::copy_probe_spec_for(
             batch.copy.source_id,
             batch.copy.controller,
@@ -357,9 +358,13 @@ fn drain_copy_token_resolution(
 fn park_copy_token_after_current_batch(
     state: &mut GameState,
     pending: PendingCopyTokenResolution,
-    stack_depth_before_batch: usize,
+    stack_depth_before_batch: ChildStackDepth,
 ) {
-    match state.resolution_stack.len().cmp(&stack_depth_before_batch) {
+    match state
+        .resolution_stack
+        .capture_child_boundary()
+        .cmp(&stack_depth_before_batch)
+    {
         std::cmp::Ordering::Less => {
             panic!("copy-token batch removed a parent frame before it could be re-parked")
         }

crates/engine/src/game/effects/vote.rs

@@ -28,6 +28,7 @@ use crate::types::game_state::{
 };
 use crate::types::identifiers::ObjectId;
 use crate::types::player::PlayerId;
+use crate::types::resolution::ChildStackDepth;
 
 use super::resolve_ability_chain;
 use crate::game::ability_utils::build_resolved_from_def;
@@ -381,7 +382,7 @@ pub fn resolve_tally(
             // If a ballot parks an interactive choice (e.g. ChooseFromZoneChoice),
             // stash remaining voters and return early; the drain function resumes.
             let initial_waiting_for = state.waiting_for.clone();
-            let stack_depth_before_ballot = state.resolution_stack.len();
+            let stack_depth_before_ballot = state.resolution_stack.capture_child_boundary();
             let mut remaining_voters: Vec<PlayerId> = choice_ballots.clone();
 
             while let Some(voter) = remaining_voters.first().copied() {
@@ -654,7 +655,7 @@ pub(crate) fn drain_active_vote_ballot(state: &mut GameState, events: &mut Vec<G
     let source_id = pending.source_id;
     let controller = pending.controller;
     let template = pending.ability_template;
-    let stack_depth_before_ballot = state.resolution_stack.len();
+    let stack_depth_before_ballot = state.resolution_stack.capture_child_boundary();
 
     while let Some(voter) = remaining_voters.first().copied() {
         remaining_voters.remove(0);
@@ -694,9 +695,13 @@ pub(crate) fn drain_active_vote_ballot(state: &mut GameState, events: &mut Vec<G
 fn park_vote_ballot_after_current_ballot(
     state: &mut GameState,
     pending: PendingVoteBallotIteration,
-    stack_depth_before_ballot: usize,
+    stack_depth_before_ballot: ChildStackDepth,
 ) {
-    match state.resolution_stack.len().cmp(&stack_depth_before_ballot) {
+    match state
+        .resolution_stack
+        .capture_child_boundary()
+        .cmp(&stack_depth_before_ballot)
+    {
         std::cmp::Ordering::Less => {
             panic!("vote ballot removed a parent frame before it could be re-parked")
         }

crates/engine/src/game/engine_debug.rs

@@ -971,7 +971,7 @@ fn drain_debug_card_entries(
     events: &mut Vec<GameEvent>,
 ) {
     while pending.remaining > 0 && matches!(state.waiting_for, WaitingFor::Priority { .. }) {
-        let child_stack_start = state.resolution_stack.len();
+        let child_stack_start = state.resolution_stack.capture_child_boundary();
         let object_id = materialize_debug_card(
             state,
             &pending.source,
@@ -986,9 +986,9 @@ fn drain_debug_card_entries(
         state.waiting_for = entry.waiting_for;
 
         if !matches!(state.waiting_for, WaitingFor::Priority { .. })
-            || state.resolution_stack.len() > child_stack_start
+            || state.resolution_stack.capture_child_boundary() > child_stack_start
         {
-            if state.resolution_stack.len() > child_stack_start {
+            if state.resolution_stack.capture_child_boundary() > child_stack_start {
                 state
                     .insert_debug_card_entries_parent_at_child_boundary(pending, child_stack_start)
                     .expect("debug-card parent must sit below the entry child stack");

crates/engine/src/types/game_state.rs

@@ -48,9 +48,10 @@ use super::replacements::ReplacementEvent;
 #[cfg(debug_assertions)]
 use super::resolution::debug_assert_runtime_resolution_invariants;
 use super::resolution::{
-    AbilityContinuationFrame, ChangeZoneFrame, FrameGate, MultiDrawFrame, OptionalEffectFrame,
-    PendingCoinFlip, PendingMutateMerge, PendingProliferateActions, RepeatedOptionalPaymentFrame,
-    ResolutionFrame, ResolutionStack, ResolutionStackError, ResolutionStateWire,
+    AbilityContinuationFrame, ChangeZoneFrame, ChildStackDepth, FrameGate, MultiDrawFrame,
+    OptionalEffectFrame, PendingCoinFlip, PendingMutateMerge, PendingProliferateActions,
+    RepeatedOptionalPaymentFrame, ResolutionFrame, ResolutionStack, ResolutionStackError,
+    ResolutionStateWire,
 };
 use super::resolved_commands::{
     ManaPaymentRecipient, ResolvedContinuousEffectCommand,
@@ -18826,9 +18827,13 @@ impl GameState {
     pub fn push_change_zone_iteration_after_child(
         &mut self,
         pending: PendingChangeZoneIteration,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) {
-        match self.resolution_stack.len().cmp(&child_stack_start) {
+        match self
+            .resolution_stack
+            .capture_child_boundary()
+            .cmp(&child_stack_start)
+        {
             std::cmp::Ordering::Less => {
                 panic!("ChangeZone move removed a parent before it could be parked")
             }
@@ -18860,9 +18865,13 @@ impl GameState {
     pub fn replace_active_change_zone_iteration_after_child(
         &mut self,
         pending: PendingChangeZoneIteration,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) {
-        match self.resolution_stack.len().cmp(&child_stack_start) {
+        match self
+            .resolution_stack
+            .capture_child_boundary()
+            .cmp(&child_stack_start)
+        {
             std::cmp::Ordering::Less => {
                 panic!("ChangeZone move removed its active owner before it could be re-parked")
             }
@@ -19063,7 +19072,7 @@ impl GameState {
     pub fn insert_copy_token_parent_at_child_boundary(
         &mut self,
         pending: PendingCopyTokenResolution,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack
             .insert_copy_token_parent_at_child_boundary(pending, child_stack_start)
@@ -19093,7 +19102,7 @@ impl GameState {
     pub fn insert_debug_card_entries_parent_at_child_boundary(
         &mut self,
         pending: PendingDebugCardEntries,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack
             .insert_debug_card_entries_parent_at_child_boundary(pending, child_stack_start)
@@ -19141,7 +19150,7 @@ impl GameState {
     pub fn insert_each_player_copy_chosen_parent_at_child_boundary(
         &mut self,
         pending: PendingEachPlayerCopyChosen,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack
             .insert_each_player_copy_chosen_parent_at_child_boundary(pending, child_stack_start)
@@ -19184,7 +19193,7 @@ impl GameState {
     pub fn insert_repeat_for_parent_at_child_boundary(
         &mut self,
         pending: PendingRepeatIteration,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack.insert_parent_at_child_boundary(
             super::resolution::ResolutionFrame::RepeatFor(pending),
@@ -19227,7 +19236,7 @@ impl GameState {
     pub fn insert_repeat_until_parent_at_child_boundary(
         &mut self,
         pending: PendingRepeatUntil,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack.insert_parent_at_child_boundary(
             super::resolution::ResolutionFrame::RepeatUntil(pending),
@@ -19274,7 +19283,7 @@ impl GameState {
     pub fn insert_vote_ballot_parent_at_child_boundary(
         &mut self,
         pending: PendingVoteBallotIteration,
-        child_stack_start: usize,
+        child_stack_start: ChildStackDepth,
     ) -> Result<(), ResolutionStackError> {
         self.resolution_stack.insert_parent_at_child_boundary(
             super::resolution::ResolutionFrame::VoteBallot(pending),

crates/engine/src/types/mod.rs

@@ -81,10 +81,10 @@ pub use proposed_event::{AppliedReplacementKey, ProposedEvent, ReplacementId};
 pub use replacements::ReplacementEvent;
 pub use replay::{RecordedAction, ReplayHeader, ReplayLog, REPLAY_FORMAT_VERSION};
 pub use resolution::{
-    AbilityContinuationFrame, ChangeZoneFrame, DirectChoiceGate, FrameGate, FrameKind,
-    MultiDrawFrame, OptionalEffectFrame, PerCategoryZoneChoiceFrame, RepeatedOptionalPaymentFrame,
-    ResolutionFrame, ResolutionStack, ResolutionStackError, ResolutionStateWire,
-    RESOLUTION_STATE_WIRE_VERSION,
+    AbilityContinuationFrame, ChangeZoneFrame, ChildStackDepth, DirectChoiceGate, FrameGate,
+    FrameKind, MultiDrawFrame, OptionalEffectFrame, PerCategoryZoneChoiceFrame,
+    RepeatedOptionalPaymentFrame, ResolutionFrame, ResolutionStack, ResolutionStackError,
+    ResolutionStateWire, RESOLUTION_STATE_WIRE_VERSION,
 };
 pub use resolved_commands::{
     ManaPaymentRecipient, ProducedManaUnit, ResolvedCommandJournalEntry, ResolvedCommandOrdinal,