The command surface was already almost entirely platform machinery —
this card proves it and pins it. Headless probes established that
NSWindow.validateMenuItem answers enablement AND rewrites the row title
from the delegate-supplied manager, so 'Undo Move 3 Cards' flows step
phrase to Edit menu with no code of ours; under the lock the rows dim
and keep their names, the correct reading of the-stack-survives. The
toolbar twins validate through validateUserInterfaceItem, which never
touches labels — 03's static-label exception proven rather than
asserted — and their specs' enablement abstention is pinned so nobody
later adds a second, disagreeing answer. The one link a headless run
cannot close is the nil-target key-window resolution itself: standard
responder-chain behavior with none of our code in it, left as the
manual check. Base-edition 'disabled without undo' scaffolding is
reworded away — every base board has undo now. New suites cover the
trash's two doors (delete-then-undo byte-identical to Put Back's
effect), position-preserving restore of a middle card, and the
capstone: five gestures forward, five presses back to the origin
board, five forward again, the menu phrase asserted after every press.
Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY
Every crossing validates its expectations before writing: each step
carries per-item HistoryExpectations — folder, effective ancestor-walked
liveness, and exactly the fields the gesture set — and a mismatch pops
the step, posts the signpost ('Undo skipped — Fix login changed outside
Lanework'), and falls through to the next. Validation reads disk, not
the in-memory snapshot: the snapshot is by construction one reload
behind every app write, so a rapid second undo would false-skip against
the pre-state — disk is what current can honestly mean at press time.
Stale and failed part ways: a stale step is one the board moved past,
so dropping it loses nothing; a failed one is refused by a usually
momentary condition, so it stays put and the crossing stops with only
performWrite's own error row — which forced the provider off
NSUndoManager onto two plain arrays, since a popped group cannot be put
back. The read-only lock disables Undo/Redo through the adapter while
the stack survives to resume on clear. Delete and restore validate
presence alone — a machine timestamp is not a decision — and a
malformed field matches nothing, since it is a shape the app never
writes.
Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY
The provider seam 12 promised: HistoryProviding speaks 13's vocabulary
— register a HistoryStep (bare 06 phrase plus undo/redo closures
returning applied or skipped), canUndo/canRedo, action names, clear —
and no UndoManager type appears anywhere in it, proven by a fake that
satisfies the seam with counters. The base provider wraps a private
UndoManager with groupsByEvent off so coalescing stays the Writer call
site's decision; undo re-registers the reversed step from inside the
undo, which makes a stale-skipped step vanish for free and the
crossing loop fall through to the next. BoardUndoManager adapts the
protocol to the responder chain — a stackless UndoManager subclass
answering from the provider — so Pro's git provider inherits menu
enablement, dynamic titles, and the nil-target toolbar pair by binding
the protocol. One stack per board session, born in beginSession,
cleared in the close flush; every window over the board answers it
through windowWillReturnUndoManager. Headless probes shaped the
routing: a real NSTextView's own manager wins natively, but a field
editor's does not — BoardUndoRouting answers the per-window text
manager while any NSText is first responder, so a search-field typo
never crosses a board step.
Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY
rzen