fix(engine): unattach a departing permanent's attachments symmetrically (CR 704.5n) - #8917
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`sever_battlefield_attachment_graph_on_exit` severed the attachment graph
one-sidedly: it cleared the departing host's `attachments` list but left every
attachment's `attached_to` back-pointer naming that host, relying on the
CR 704.5m/704.5n unattach SBA to clean the other side.
That SBA never runs for an effect that removes and returns a host inside a
single resolution. CR 704.3 checks state-based actions only when a player would
receive priority, and CR 704.4 states that they "pay no attention to what
happens during the resolution of a spell or ability". `ObjectId` is storage
identity in this engine, so the stale back-pointer silently re-validated
against the *returned* permanent — which CR 400.7 makes a new object with no
memory of, or relation to, the one that left.
Reported on Heart-Shaped Herb ("You may sacrifice a creature. If you do, return
that card to the battlefield ..."), which sacrifices and returns in one
resolution. Both symptoms follow from the dangling edge: the Equipment rendered
nowhere (the client drops an attachment whose `attached_to` is set from the
battlefield rows, expecting the host surface to render it, but the host no
longer listed it), and the returned creature kept the Equipment's continuous
bonus. Same shape as the Ephemerate + Skullclamp report in phase-rs#6465.
The sever now clears both directions, which is the direct implementation of
CR 301.5c: "An Equipment that equips an illegal or nonexistent permanent
becomes unattached from that permanent but remains on the battlefield."
- Clears `attached_to` only when it still names the departing host, so an
attachment re-pointed elsewhere by a concurrent effect keeps its live edge.
- CR 702.26b: phased-out attachments are skipped, matching the existing
`sba::check_unattached_equipment` guard — a phased-out permanent cannot be
affected by the host's exit.
- CR 701.3d: becoming unattached is a real game event ("this includes if ...
the object leaves the zone it was in"), so the sever returns the severed ids
and both call sites emit `GameEvent::Unattached` beside the existing
attachment-side emit. Without it, `trigger_matchers::match_unattach` loses
these triggers entirely: its `ZoneChanged` fallback arm re-derives "my host
left" from the attachment's live `attached_to`, and the attachment did not
itself move, so `TriggerSourceContext::source_read` resolves to `ExactLive`
and observes the freshly cleared `None`. That same condition is why the new
event cannot double-fire with the fallback arm.
CR 704.5m is still honored: `sba::check_unattached_auras` treats
`attached_to == None` as unattached, so a non-bestow Aura still goes to its
owner's graveyard and a bestow Aura still reverts in place per CR 702.103f.
Tests: an inline `zones.rs` pair covering the host-exit sever, the emitted
event, the no-re-attach-on-return case, and the re-pointed-attachment guard;
plus an integration test driving Heart-Shaped Herb's real activated-ability
pipeline with a Bonesplitter-equipped creature. Reverting the fix turns both
red — the integration test reports `attached_to == Some(Object(..))` naming the
returned creature, and a 7/5 instead of 5/5.
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Included review availability: Your plan provides up to 2 included reviews per hour; 1 remains after this review. 📝 WalkthroughWalkthroughThe attachment exit logic now synchronizes live and replayed zone changes, clears phased-out attachment back-pointers, and emits ChangesAttachment exit handling
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Bug fix Suggested reviewers: Sequence Diagram(s)sequenceDiagram
participant ZoneTransition
participant SeverAuthority
participant AttachmentState
participant GameEvent_Unattached
participant ZoneChanged
ZoneTransition->>SeverAuthority: sever departing host attachment edges
SeverAuthority->>AttachmentState: clear matching attachment pointers
SeverAuthority-->>ZoneTransition: return eligible attachment IDs
ZoneTransition->>GameEvent_Unattached: emit unattach events
ZoneTransition->>ZoneChanged: emit zone change
Merge Risk: ⚪ Minimal · up to The attachment-exit changes include live/replay parity and phased attachment coverage, with no remaining concrete merge risk identified. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@crates/engine/src/game/zones.rs`:
- Around line 1443-1444: Ensure resolved zone-change replay preserves the
attachment graph cleanup performed by move_to_zone: update
ResolvedZoneChangeCommand and apply_resolved_zone_change to carry and apply the
severed attachment IDs, or centralize the mutation in a shared live/replay
boundary. Keep the equivalent sever_battlefield_attachment_graph_on_exit cleanup
in move_to_library_at_index, which bypasses the resolved-command path.
- Around line 2099-2102: Update sever_battlefield_attachment_graph_on_exit so
every attachment whose attached_to resolves to object_id has that pointer
cleared regardless of is_phased_in(); only phased-in attachments should be added
to severed_attachments and emit GameEvent::Unattached. Add a regression test
covering host exit, same-ID host return, and subsequent attachment phase-in.
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crates/engine/src/game/zones.rscrates/engine/tests/integration/issue_8077_heart_shaped_herb_return_target.rs
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Changes requested — reviewed at 88f1953194e5543a1f0e907ff98d4690c7f18b11.
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High — attachment severing is not replayed.
zones.rs:1443-1444clears the live attachment graph beforeresolve_and_apply_zone_change, butResolvedZoneChangeCommandhas no attachment payload (types/resolved_commands.rs:876-888) andapply_resolved_zone_changeonly moves/resets the host (zones.rs:1121-1161). The repository replay test atzones.rs:4861-4916exercises this exact pre-cleanup clone shape. Make symmetric severing a shared live/replay transition or carry affected IDs in the command; add a pre-transition replay regression. -
High — phased-out attachments can reconnect to a new host incarnation.
zones.rs:2099-2107clears only phased-in attachments while always emptying the departing host’s attachment list (:2079-2083); direct phase-in scans can then reconnect without checking incarnation (effects/phase_out.rs:185-224,phasing.rs:145-152). CR 702.26i requires a directly phased attachment to phase in unattached if its former object left that zone. Clear all matchingattached_tovalues regardless of phase state, while emitting Unattached only for phased-in ones; add host-exit/return then attachment-phase-in coverage. -
Medium — required current-head parse-diff artifact is absent despite engine source changes. Regenerate exact-head evidence before re-requesting review.
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Generated for head Parse changes introduced by this PR✓ No card-parse changes detected. |
Review feedback on phase-rs#8917. **1. Attachment severing is now replayed (HIGH).** The live transition severs the attachment graph before delegating to `resolve_and_apply_zone_change`, but `ResolvedZoneChangeCommand` carries no attachment payload and `apply_resolved_zone_change` only moved and reset the host — so a state rebuilt from the journal still held the edges the live transition cut. `sever_battlefield_attachment_graph_on_exit` becomes a shared live/replay authority, the same arrangement `prune_object_bound_effects_on_exit` already uses. It now derives the departing object's own attachment edge from live state instead of taking `unattached_from` as a parameter, so the two paths cannot drift, and `apply_resolved_zone_change` calls it as well. The function is idempotent — a second call finds an empty `attachments` list and a `None` `attached_to` and returns early — which is what makes the live path safe, since it severs and then delegates, and the Command/Stack routes bypass the resolved-command path entirely. **2. Phased-out attachments no longer re-adopt a returned host (HIGH).** The previous revision skipped phased-out attachments entirely, citing CR 702.26b. That left the stale pointer in place, and CR 702.26i is the more specific rule: a directly phased-out attachment phases in attached to its old host only "if that object is still in the same zone. If not, ... phases in unattached." `phasing::phase_in_object` re-validates only that the named host is on the battlefield, not that it is the same incarnation, so a host that left and returned to the same `ObjectId` slot would be re-adopted on phase-in. The pointer is therefore cleared for every attachment naming the departing host, regardless of phase status. CR 702.26j ("abilities that trigger when a permanent becomes attached or unattached don't trigger when that permanent phases in or out") means that severing must be silent, so only phased-in attachments are returned for `GameEvent::Unattached` emission. `sba_phased_out_fortification_with_illegal_host_is_skipped` drove its illegal-host condition by moving the host to the graveyard and asserted the pointer survived, which is exactly the behavior CR 702.26i forbids. It is re-based onto an illegal host TYPE instead — a creature rather than a land, per CR 301.6 — with both permanents staying put, so it still tests the SBA's phased-out skip without depending on host exit. `sba_phased_in_fortification_with_illegal_host_is_unattached` is added as its reach guard: the two differ only in phase status, proving the SBA genuinely reaches that shape. Tests: `host_exit_severing_is_reproduced_by_resolved_command_replay` (modelled on `battlefield_exit_replay_ceases_the_linked_prepared_copy_like_live`) and `phased_out_attachment_does_not_readopt_a_returned_host`, covering host exit, same-`ObjectId` host return, and subsequent attachment phase-in. Both verified revert-to-red: neutering the replay sever call yields `Some(Object(..))` where `None` is expected, and restoring the phased-out skip fails the CR 702.26i assertion.
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Thanks — both HIGH findings were real. Pushed 1. Attachment severing is not replayed — fixed. You were right that the command carries no attachment payload. I took the "shared live/replay transition" option rather than adding a payload, since
Regression: 2. Phased-out attachments can reconnect to a new host incarnation — fixed. I had this wrong. I originally skipped phased-out attachments on CR 702.26b grounds ("treated as though it does not exist"), and declined this finding when my own pre-push review raised it, because So the pointer is now cleared for every attachment naming the departing host regardless of phase status, and only phased-in attachments are returned for That made the old guard test wrong rather than inconvenient — it was asserting exactly the behavior CR 702.26i forbids. Rather than delete it, I re-based it onto an illegal host type (a creature rather than a land, CR 301.6) with both permanents staying put, so it still tests the SBA's phased-out skip without routing through a host exit. Added Regression: 3. Parse-diff artifact. I think this one was a timing artifact: the Verification on One unrelated thing I hit: workspace-wide clippy fails on |
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matthewevans
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Approved at a7f4f6fb1578fa96aa7c781c6a6d62fa1896ccff.
The shared zone-exit severing authority now preserves live/replay parity, clears phased-out attachment back-pointers without emitting a phasing event, and keeps host-exit unattach events observable for phased-in attachments. The exact-head parse receipt reports no card-parse changes, and required CI is terminal green.
Manual quality gate: PASS — no parse-impact claim drift, the change extends the existing zone-transition authority, and the runtime Heart-Shaped Herb regression plus replay/phase-in regressions discriminate against the prior behavior.
2 participants
The bug
Reported on Discord: a creature with an Equipment attached was sacrificed and returned by Heart-Shaped Herb. The Equipment appeared to vanish from the battlefield instead of reverting to an unattached artifact, and the returned creature still had the Equipment's bonus applied.
Same shape as #6465 (Ephemerate + Skullclamp — "afterwards skullclamp is not visible on my battlefield"), which is filed
status:needs-repro. This should close that one out.Root cause
zones::sever_battlefield_attachment_graph_on_exitsevered the attachment graph one-sidedly. When a permanent left the battlefield it cleared the departing host'sattachmentslist, but left every attachment'sattached_toback-pointer still naming that host, relying on the CR 704.5m / CR 704.5n unattach SBA to clean the other side.That SBA never runs for this card:
Heart-Shaped Herb sacrifices and returns the creature inside a single resolution (
You may sacrifice a creature. If you do, return that card to the battlefield ...), so the SBA never observes the host as absent.ObjectIdis storage identity in this engine — the same slot is reused across a zone change. So the stale back-pointer silently re-validated against the returned permanent, which CR 400.7 makes a new object with no memory of, or relation to, the one that left.sba::is_valid_attachment_targetonly checkstarget.zone == Battlefieldplus the host core type, both of which the returned creature satisfies.Both reported symptoms follow from that one dangling edge:
client/src/viewmodel/battlefieldProps.tsdrops an attachment whoseattached_tois set from the battlefield rows, on the expectation that the host surface renders it — but the host no longer listed it.The fix
Make the severing symmetric. This is the direct implementation of CR 301.5c: "An Equipment that equips an illegal or nonexistent permanent becomes unattached from that permanent but remains on the battlefield."
sever_battlefield_attachment_graph_on_exitnow clears theattached_toback-pointer of every attachment naming the departing host, and is a shared live/replay authority — called frommove_to_zone,move_to_library_at_index, andapply_resolved_zone_change. That mirrorsprune_object_bound_effects_on_exit, which already had exactly this arrangement in the same function.It derives the departing object's own attachment edge from live state rather than taking it as a parameter, so the live and replay paths cannot drift, and it is idempotent: a second call finds an empty
attachmentslist and aNoneattached_toand returns without touching anything. That matters because the live path severs before delegating toresolve_and_apply_zone_change, and because the Command/Stack routes bypass the resolved-command path entirely.Two constraints on which edges are cut:
phasing::phase_in_objectre-validates only that the named host is on the battlefield, not that it is the same incarnation, so a phased-out attachment's pointer must be cleared too or a host that left and returned to the sameObjectIdslot would be re-adopted on phase-in. Per CR 702.26j that severing is silent — phased-out attachments are severed but emit no event.CR 704.5m is still honored.
sba::check_unattached_aurastreatsattached_to == Noneas unattached, so a non-bestow Aura still goes to its owner's graveyard and a bestow Aura still reverts in place per CR 702.103f on the next SBA pass.The part that is easy to miss
Clearing the back-pointer alone silently kills every host-exit unattach trigger (Stitcher's Graft, Captain's Hook, Grafted Wargear).
trigger_matchers::match_unattachhas aGameEvent::ZoneChangedfallback arm that re-derives "my host left" by reading the attachment's liveattached_to. The attachment itself never moved, soTriggerSourceContext::source_readresolves toExactLiveand reads the freshly clearedNone— no match, no trigger.Rather than teach the matcher to consult a snapshot, this extends an authority that already existed.
move_to_zoneandmove_to_library_at_indexalready emitGameEvent::Unattachedfor the attachment-leaves direction (unattached_from); that is the same relationship viewed from the other end. So the sever returns the severed ids and both call sites emit the host-leaves direction beside the existing emit.CR 701.3d is explicit that this is a real event: "If an Aura, Equipment, or Fortification that was attached to an object or player ceases to be attached to it, that counts as 'becoming unattached' ... this includes if ... the object leaves the zone it was in."
The
Unattachedarm ofmatch_unattachthen fires. It cannot double-fire with theZoneChangedfallback arm, for exactly the same reason the arm broke: that arm requiresattached_toto still name the departing host, and the sever has cleared it.Tests
Inline in
zones.rs:host_leaving_battlefield_clears_attachment_back_pointers— the sever, the emittedUnattachedevent with the rightattachment_id/old_target, the Equipment remaining on the battlefield (CR 704.5n), and no re-attach when the host returns.host_exit_leaves_reattached_equipment_edge_intact— over-clearing guard: an attachment pointing at a different host keeps its live edge and emits nothing.host_exit_severing_is_reproduced_by_resolved_command_replay— live/replay parity, modelled onbattlefield_exit_replay_ceases_the_linked_prepared_copy_like_liveso it uses the same pre-cleanup clone shape.phased_out_attachment_does_not_readopt_a_returned_host— host exit → same-ObjectIdreturn →phase_in_object, asserting the attachment phases in unattached and that the severing was silent.In
sba.rs,sba_phased_out_fortification_with_illegal_host_is_skippedpreviously drove its illegal-host condition by moving the host to the graveyard and asserted the pointer survived — which is the behavior CR 702.26i forbids. It is re-based onto an illegal host type (a creature rather than a land, CR 301.6) with both permanents staying put, so it still tests the SBA's phased-out skip without routing through a host exit.sba_phased_in_fortification_with_illegal_host_is_unattachedis added as its reach guard: the two differ only in phase status.Integration, in
issue_8077_heart_shaped_herb_return_target.rs— drives the realActivateAbility→DecideOptionalEffect→SelectCardspipeline with a real Bonesplitter (Equipped creature gets +2/+0) on the sacrificed creature. Reach-guards both graph directions and an effective4/2before activation to prove the bonus is live, then asserts the Equipment is still on the battlefield withattached_to == None, the returned creature does not list it, and the creature is5/5— base 2/2 plus three +1/+1 counters, with no Equipment bonus.Revert-to-red, measured on every regression test here:
attached_to = None→host_leaving_battlefield_clears_attachment_back_pointersfails on "equipment must be unattached when its host leaves the battlefield"; the integration test fails withleft: Some(Object(ObjectId(2)))— the stale pointer naming the returned creature — and a7/5instead of5/5.host_exit_severing_is_reproduced_by_resolved_command_replayfails withleft: Some(Object(ObjectId(1))) / right: Noneon "replay must reproduce the severed back-pointer".phased_out_attachment_does_not_readopt_a_returned_hostfails the CR 702.26i assertion identically.Note the two pre-existing guards in
zones.rs(aura_leaving_battlefield_clears_attached_to,sba_pipeline_graveyard_clears_attached_to) stay green while the bug is live: both move the attachment, and this defect requires the host to move.Verification
cargo test-all: 32836/32838 pass. The two failures areprobe-pin'spath_keys_cannot_escape_the_scratch_dirandproj_missing, which fail on Windows for environmental reasons (POSIX/root assumption and exec of a.shfixture).cargo clippy --all-targets -- -D warnings: clean../scripts/build-wasm.shandpnpm build: both succeed.The branch was rebased across 50 upstream commits that touched
zones.rs,sba.rs,trigger_matchers.rs,attach.rsandgame_state.rs, so the seams this change rests on were checked specifically:sever_battlefield_attachment_graph_on_exit,match_unattach,check_unattached_equipment,should_emit_sba_unattached_event,is_valid_attachment_targetandsource_readare untouched by those commits.Sibling paths considered
Host-exit paths that could leave a dangling back-pointer were swept:
zone_pipeline.rsultimately delivers throughmove_to_zone_with_entry_flagsormove_to_library_at_index;sba::check_token_cease_to_existceases tokens only after their earlier zone move already passed through severing;phasing.rsdoes not change zones; player elimination routes throughZoneMoveRequest::player_left_game;engine_debug.rshas its own explicit symmetric teardown.One path deliberately left alone:
zones::route_componentbumps a merge-absorbed component's incarnation (CR 730.3 + CR 400.7) and, as its own comment states, no sever runs there. Per CR 730.2 an absorbed component is not an independent battlefield permanent, so an Aura/Equipment would be attached to the merged survivor rather than to the component. It is untouched by this PR and a different failure mode; flagging it rather than expanding scope, and happy to file it separately if you think it is reachable.