Memoize the reload parse and short-circuit value-equal snapshots

The loader gains a ParseMemo — the previous walk's parsed documents keyed
by root-relative path, trusted on the git-index heuristic (mtime + size,
no hashing) and passed as an input so the loader stays stateless. A hit
skips exactly one file read; schema, order, coercions, dedupe, and every
directory listing run fresh, so memoized and cold walks are output-
identical (golden-corpus equivalence suite). Entries record only past the
schema gate, so a defect can never be answered from the memo.

The store skips the snapshot assignment wholesale when the fresh model is
value-equal — no @Observable churn, no render pass, no snapshotGeneration
bump — and a new landedReloads counter carries walk-completion for the
three consumers whose subject is the walk, not the snapshot: the card
window's comment thread, the comment search index, and the auto-committer's
covering gate (which now counts a completed walk as covering even when
nothing changed). Warnings and defects move on their own equality; failed
reloads bump neither counter. An injectable ParseCounter makes the
single-file-echo claim a test.

Claude-Session: https://claude.ai/code/session_01CqjXB7ASoWtbyoGod68k97

Kanban/App/AppModel.swift

@@ -889,8 +889,13 @@ public final class AppModel {
                 // await are reads of the store the composer is already diffing, which is why they are
                 // wired here rather than reached for: the engine holds the *policy* (when to wait, how
                 // long), the session supplies the two facts (`GitAutoCommitter.awaitCoveringSnapshot`).
+                //
+                // The generation the gate counts is `landedReloads` — completed *walks* rather than
+                // applied snapshots — because a value-equal reload skips the assignment and its
+                // counter since 2026-07-31, and a walk covers a flush's paths whether or not it found
+                // anything to change (`BoardStore.landedReloads`).
                 committer.awaitReloadQuiescence = { [weak store] in await store?.awaitQuiescence() }
-                committer.snapshotGeneration = { [weak store] in store?.snapshotGeneration }
+                committer.landedReloads = { [weak store] in store?.landedReloads }
                 // 02-architecture.md ▸ Write-failure surfacing, through the strip the board window
                 // already renders: a genuine commit failure means "your edits are saved, history has
                 // stopped advancing", which is exactly what the standing suspension row says. Lock

Kanban/App/CardWindowHost.swift

@@ -484,13 +484,19 @@ struct CardWindowHost: View {
                 attachments.isEditable = !locked
                 session.comments.isEditable = !locked
             }
-            // **The thread re-reads on every applied snapshot** (05 ▸ The comments column: "the pane
+            // **The thread re-reads on every landed reload** (05 ▸ The comments column: "the pane
             // reloads its thread from the same FSEvents stream").
             //
             // *Any* reload, not a filtered one, and that is a deliberate choice worth stating: the
-            // store's observable surface publishes `snapshotGeneration` and a `BoardModel` — it does
+            // store's observable surface publishes counters and a `BoardModel` — it does not vend the
-            // not vend the changed paths, and comments are outside the snapshot entirely
+            // changed paths, and comments are outside the snapshot entirely (01-storage-format.md
-            // (01-storage-format.md § Enhanced schema), so there is nothing to filter *on* here.
+            // § Enhanced schema), so there is nothing to filter *on* here.
+            //
+            // **`landedReloads`, not `snapshotGeneration`**, and for that same sentence's reason: a
+            // comment arriving changes the tree and leaves the model value-equal, and a value-equal
+            // landing skips the snapshot assignment (blessed 2026-07-31). Watching the applied counter
+            // would mean the one kind of change this pane exists to notice is the one kind it would
+            // sleep through.
             // Re-reading one card's thread is a handful of small files and happens only while a card
             // window is open; filtering would mean either widening the store's surface to carry paths,
             // or the pane keeping its own watcher — a second stream over the same tree, which the
@@ -499,7 +505,7 @@ struct CardWindowHost: View {
             // ledger's comment receipts through `CommentPath.classify` to tell a foreign arrival from
             // its own echo (`CardComments.reload`). `initial:` is deliberately absent: `start()`
             // already did the opening read, after the residue sweep that has to precede it.
-            .onChange(of: store.snapshotGeneration) { _, _ in
+            .onChange(of: store.landedReloads) { _, _ in
                 session.comments.reload()
             }
         } else {

Kanban/Git/GitAutoCommitter.swift

@@ -142,14 +142,21 @@ public final class GitAutoCommitter {
     @ObservationIgnored
     public var awaitReloadQuiescence: (@MainActor () async -> Void)?
 
-    /// **Which generation the board `currentSnapshot` answers with is at** —
+    /// **How many tree walks the board has landed** — `BoardStore.landedReloads`, incremented by
-    /// `BoardStore.snapshotGeneration`, incremented by every landed reload.
+    /// every reload that completed with a snapshot in hand.
+    ///
+    /// **The walk, not the applied snapshot**, and the distinction is load-bearing since 2026-07-31:
+    /// a reload whose tree turned out to be value-equal skips the snapshot assignment and its counter
+    /// (02-architecture.md § Live-reload resilience), and a gate watching *that* counter would sit out
+    /// its whole deadline on a flush whose covering walk had already landed. What covers a flush is a
+    /// walk that started after its writes reached disk, and a
+    /// completed walk covers them whether or not it found anything different to show.
     ///
     /// `nil` — the closure absent, or answering `nil` because the store has gone — means there is no
     /// snapshot to be outrun by, and the covering await becomes the no-op it is on every storeless
     /// committer.
     @ObservationIgnored
-    public var snapshotGeneration: (@MainActor () -> Int?)?
+    public var landedReloads: (@MainActor () -> Int?)?
 
     /// **How long an explicit flush waits for its covering reload** before composing from the snapshot
     /// it already has.
@@ -563,7 +570,7 @@ public final class GitAutoCommitter {
     /// after the later of them — 06's own "practical cushion", doing the job it is enough for — and
     /// `noteWillWrite()` cannot await at all, being the synchronous flush-before-overwrite.
     private func awaitCoveringSnapshot() async {
-        guard holdsUncoveredWrites, let read = snapshotGeneration else { return }
+        guard holdsUncoveredWrites, let read = landedReloads else { return }
         await awaitReloadQuiescence?()
         // Re-read the gate: the quiescence may itself have been the covering landing.
         guard holdsUncoveredWrites, let base = read() else { return }

Kanban/LiveStore/BoardStore.swift

@@ -230,15 +230,47 @@ public final class BoardStore: HealHost {
     /// path — see the type's doc comment for why. A failed reload leaves it exactly as it was.
     public private(set) var snapshot: BoardModel
 
-    /// How many snapshots this store has applied, ever — a counter, not a version.
+    /// How many snapshots this store has **applied**, ever — a counter, not a version.
     ///
     /// It exists for **the committed-overlay hold** (DRAG-REORDER.md § The committed-overlay hold):
-    /// a drop's overlay stands until "the next snapshot application on that store", and *application*
+    /// a drop's overlay stands until the next snapshot application on that store, and the whole point
-    /// is the event, not change. A reload that produced an identical model still ends the round trip
+    /// of the counter is that it is an *event* the overlay can watch rather than a value it would have
-    /// the overlay was covering — comparing `snapshot` values would leave the overlay standing
+    /// to diff.
-    /// exactly when the write turned out to be a no-op.
+    ///
+    /// **A value-equal reload does not bump it** (02-architecture.md § Live-reload resilience,
+    /// blessed 2026-07-31): "the store skips the assignment entirely when the fresh snapshot equals
+    /// the current one … so 'costs nothing visible' becomes *costs nothing*". Bumping
+    /// an observed counter is itself a render pass, so the skip has to cover this line too or it
+    /// covers nothing.
+    ///
+    /// The hold tolerates that, and provably: a hold is only ever armed by a drop whose write actually
+    /// rearranged something — `moveCards`/`moveLane` refuse a no-op arrangement *before* they open a
+    /// bracket, so a drop that would land value-equal never writes, never reloads, and its hold is
+    /// already the watchdog's to retire (`CommittedHold.timeout`) exactly as it was before the skip
+    /// existed. Anything whose subject is the *walk* rather than the snapshot reads `landedReloads`
+    /// instead.
     public private(set) var snapshotGeneration: Int = 0
 
+    /// How many tree walks this store has **landed with a snapshot in hand**, ever — bumped by every
+    /// successful reload, whether or not the snapshot it produced was different enough to assign.
+    ///
+    /// The counter for everything whose subject is the *walk*, which is everything that lives outside
+    /// the snapshot and therefore cannot be inferred from it:
+    ///
+    /// - **Comments.** They are not in `BoardModel` at all (01-storage-format.md § Enhanced schema),
+    ///   so a foreign comment arriving changes the tree, changes nothing in the snapshot, and must
+    ///   still refresh the card window's thread and board search's comment index. Keying either on
+    ///   `snapshotGeneration` would make the value-equal skip a freshness bug rather than an
+    ///   optimization.
+    /// - **The auto-committer's covering gate** (`GitAutoCommitter.awaitCoveringSnapshot`): what
+    ///   covers a flush is a *walk* that started after its writes hit disk, and a completed walk
+    ///   covers them whether or not the tree turned out to differ. A gate waiting on the applied
+    ///   counter would spin out its whole deadline on any value-equal landing.
+    ///
+    /// A failed reload bumps neither counter: it produced no snapshot, so it covers nothing and
+    /// refreshes nothing — the pre-skip behaviour of `snapshotGeneration` exactly, kept exactly.
+    public private(set) var landedReloads: Int = 0
+
     /// Tolerated anomalies from the load that produced `snapshot` (stray folders, an indexless
     /// UUID-shaped folder, a board-level `deleted:`). Replaced with the snapshot, so they always
     /// describe the tree currently on screen.
@@ -488,6 +520,41 @@ public final class BoardStore: HealHost {
     @ObservationIgnored
     private var reloadInFlight = false
 
+    /// **The last walk's parsed documents** (`BoardLoader.ParseMemo`, blessed 2026-07-31 —
+    /// 02-architecture.md § Live-reload resilience): what the next reload hands the loader so an
+    /// unchanged `index.md` is not re-read and re-parsed for the hundredth time.
+    ///
+    /// **The store is where it lives because the store is what has a *previous* walk.** The loader is
+    /// stateless statics and the memo is an argument to `load`, never hidden state inside it; the
+    /// first load of a board has no memo and walks cold, and every reload after it carries the one
+    /// the walk before produced.
+    ///
+    /// **Bookkeeping, not observable state** — `@ObservationIgnored`, and updated by every successful
+    /// landing whether or not the snapshot was assigned. A value-equal reload skips the assignment
+    /// precisely *because* nothing moved, and the memo it produced is the freshest set of stamps
+    /// there is; dropping it there would make every second reload cold.
+    ///
+    /// A failed reload leaves it alone: there is no `LoadResult` to take one from, and a memo keyed by
+    /// path plus mtime plus size is safe to hold indefinitely — every entry it can no longer answer
+    /// for simply misses.
+    ///
+    /// Internal rather than `private` for `reloadGeneration`'s reason: what the memo holds is the
+    /// claim, and a suite that could not read it would be asserting the effect of something it had to
+    /// take on faith.
+    @ObservationIgnored
+    private(set) var parseMemo = BoardLoader.ParseMemo()
+
+    /// **What each reload's walk actually read** (`BoardLoader.ParseCounter`) — the seam that makes
+    /// "an unchanged tree re-parses nothing" a test rather than an intention.
+    ///
+    /// `nil` in production, and the walk pays nothing for it there; a suite hangs a counter here and
+    /// reads it after `awaitQuiescence()`. The third seam this type keeps, on `loadBarrier`'s and
+    /// `announce`'s terms exactly: the *rules* are pure functions elsewhere, and what only a seam can
+    /// make assertable is the wiring — here, that the store hands the previous walk's memo to the
+    /// next walk at all.
+    @ObservationIgnored
+    var parseCounter: BoardLoader.ParseCounter?
+
     /// A reload owed but not started, because one was already running when the signal arrived — a
     /// **flag, not a queue**: any number of signals during one walk coalesce into exactly one
     /// follow-up, because the follow-up is a full tree walk that covers all of them. The origin is
@@ -646,6 +713,8 @@ public final class BoardStore: HealHost {
         self.snapshot = result.model
         self.loadWarnings = result.warnings
         self.defects = result.defects
+        // The opening walk was cold by definition; what it parsed is the first reload's memo.
+        self.parseMemo = result.memo
         self.skippedPaths = skipping
         self.reloadFailure = nil
         self.readOnlyLock = nil
@@ -720,6 +789,12 @@ public final class BoardStore: HealHost {
         // **This session's consented skips, on every walk it runs** (`skippedPaths`): the open's
         // decision stands for the session, so a reload sees the board the user chose to open.
         let skipping = skippedPaths
+        // **The previous walk's parse, offered to this one** (`parseMemo`). Read on the main actor
+        // and carried into the walk as a value, exactly like `skipping` and the ranker: the loader
+        // stays stateless statics and this reload's memo is a fact about a walk that already
+        // finished, not a channel back into one that has not.
+        let memo = parseMemo
+        let counter = parseCounter
         reloadInFlight = true
         Self.logger.debug("reload \(generation, privacy: .public) started (\(origin.rawValue, privacy: .public))")
 
@@ -729,7 +804,12 @@ public final class BoardStore: HealHost {
             let outcome: Result<LoadResult, BoardLoadFailure>
             do throws(BoardLoadFailure) {
                 outcome = .success(try BoardLoader.load(
-                    boardRoot: root, skipping: skipping, historyRanker: historyRanker))
+                    boardRoot: root,
+                    skipping: skipping,
+                    historyRanker: historyRanker,
+                    memo: memo,
+                    counter: counter
+                ))
             } catch {
                 outcome = .failure(error)
             }
@@ -841,53 +921,92 @@ public final class BoardStore: HealHost {
             }
             facts.vanishedFocus = focus.vanished
 
-            // **The motion language's one decision point** (03-board-ui.md § Motion, via `Motion`).
+            // **The memo rides the reload, not the snapshot** (`parseMemo`): bookkeeping, so it is
-            // "User-initiated structural changes animate; foreign changes snap" cannot live at the
+            // taken from every landing — the value-equal ones most of all, since those are exactly
-            // call sites here the way it did in the pathfinder — the one-way flow means the user's
+            // the walks whose stamps are freshest and whose successor would otherwise go cold.
-            // own delete arrives back through the watcher exactly like an agent's edit — so it lives
+            parseMemo = result.memo
-            // at the *reload*, whose origin is already classified. `Motion` owns which origins
+
-            // perform and in which voice; this store owns only the assignment they wrap.
+            // **The value-equal reconcile skips the assignment entirely** (02-architecture.md
+            // § Live-reload resilience, blessed 2026-07-31): "assigning an equal tree into an
+            // `@Observable` property still costs a render pass, so 'costs nothing visible' becomes
+            // *costs nothing*".
             //
-            // A `nil` animation is not a special case: `withAnimation(nil)` is the bare assignment,
+            // It is a skip of the **observable assignment and nothing else**. Everything a landing
-            // which is what the snapping origins and the Reduce Motion variant both want.
+            // owes — the memo above, the landing count, the warnings and defects (which describe the
-            withAnimation(Motion.reloadAnimation(
+            // *tree*, not the model, and can move while the model does not: a new stray folder, a
-                origin: origin,
+            // loose file appearing beside an untouched `index.md`), the breakage clearing, the
-                endsBracketedOperation: endsWholesaleOperation,
+            // comment index, the lock reconciliation, the display write-through, the heals, the
-                reduced: Motion.prefersReducedMotion
+            // announcement and the commit seam — happens below on every landing, equal or not.
-            )) {
+            //
-                snapshot = result.model
+            // What the guard covers is precisely what an equal model makes vacuous: `transient
-                snapshotGeneration += 1
+            // .resolve(against:)` re-grounds state against a tree that did not move, and
-                loadWarnings = result.warnings
+            // `recoverFocus` is handed a `.survived` outcome by construction (`focusOutcome` over two
-                // The one place transient state is re-grounded. It goes last, after `snapshot` is
+            // equal models can find nothing vanished), so skipping them changes no state a caller
-                // the new one, because a view woken by the snapshot's change must never observe a
+            // could observe — only the render pass they would have cost.
-                // selection still pointing at the old tree.
+            if result.model != snapshot {
+                // **The motion language's one decision point** (03-board-ui.md § Motion, via
+                // `Motion`). "User-initiated structural changes animate; foreign changes snap" cannot
+                // live at the call sites here the way it did in the pathfinder — the one-way flow
+                // means the user's own delete arrives back through the watcher exactly like an
+                // agent's edit — so it lives at the *reload*, whose origin is already classified.
+                // `Motion` owns which origins perform and in which voice; this store owns only the
+                // assignment they wrap.
                 //
-                // Inside the transaction deliberately: 03 § Motion has the selection highlight
+                // A `nil` animation is not a special case: `withAnimation(nil)` is the bare
-                // "ride whatever transaction is active rather than easing on its own", and a
+                // assignment, which is what the snapping origins and the Reduce Motion variant both
-                // re-grounding that landed outside this one would be exactly the independent ease
+                // want.
-                // that rules out.
+                withAnimation(Motion.reloadAnimation(
-                //
+                    origin: origin,
-                // The comment index' current answer rides along, because the filter half of the
+                    endsBracketedOperation: endsWholesaleOperation,
-                // re-grounding is the *whole* filter (04 ▸ Search, re-ruled 2026-07-29) — a card
+                    reduced: Motion.prefersReducedMotion
-                // matching only through its comments must not be evicted from the selection by a
+                )) {
-                // reload that asked a narrower question. The index is re-swept just below, outside
+                    snapshot = result.model
-                // the transaction, and its landing re-runs this constraint through `onRefine`.
+                    snapshotGeneration += 1
-                transient.resolve(against: result.model, commentMatches: commentIndex.matchingCards)
+                    // The one place transient state is re-grounded. It goes last, after `snapshot` is
-                // And *then* the recovery, on top of the set rule rather than instead of it: the
+                    // the new one, because a view woken by the snapshot's change must never observe a
-                // resolution leaves an emptied selection wherever the focused item used to be, and
+                    // selection still pointing at the old tree.
-                // this is 10-accessibility.md's answer to the hole ("focus recovers to the card's
+                    //
-                // lane … walks up then sideways"). Inside the same transaction for the highlight's
+                    // Inside the transaction deliberately: 03 § Motion has the selection highlight
-                // sake, exactly like the resolution it follows.
+                    // "ride whatever transaction is active rather than easing on its own", and a
-                recoverFocus(focus.recovery)
+                    // re-grounding that landed outside this one would be exactly the independent ease
+                    // that rules out.
+                    //
+                    // The comment index' current answer rides along, because the filter half of the
+                    // re-grounding is the *whole* filter (04 ▸ Search, re-ruled 2026-07-29) — a card
+                    // matching only through its comments must not be evicted from the selection by a
+                    // reload that asked a narrower question. The index is re-swept just below,
+                    // outside the transaction, and its landing re-runs this constraint through
+                    // `onRefine`.
+                    transient.resolve(against: result.model, commentMatches: commentIndex.matchingCards)
+                    // And *then* the recovery, on top of the set rule rather than instead of it: the
+                    // resolution leaves an emptied selection wherever the focused item used to be,
+                    // and this is 10-accessibility.md's answer to the hole ("focus recovers to the
+                    // card's lane … walks up then sideways"). Inside the same transaction for the
+                    // highlight's sake, exactly like the resolution it follows.
+                    recoverFocus(focus.recovery)
+                }
             }
-            // Outside it, equally deliberately — 03 keys transactions narrowly, and the banner
+
+            // **The walk landed, assignment or not** — the counter everything outside the snapshot
+            // watches (`landedReloads`). Bumped here rather than beside `snapshotGeneration` above
+            // precisely because it is not about the snapshot.
+            landedReloads += 1
+
+            // Outside the transaction, deliberately — 03 keys transactions narrowly, and the banner
             // conditions are not board structure. A lock clearing is not a thing the strip should
             // slide out on the back of a card being deleted.
             //
+            // Each guarded by its own equality rather than by the snapshot's, because each answers a
+            // different question about the tree: a stray folder appearing changes `loadWarnings` with
+            // the model untouched, and a loose file appearing beside an unedited `index.md` changes
+            // `defects` the same way. An unguarded assignment of an equal array is the render pass
+            // the skip above exists to avoid, one property further down.
+            //
             // Breakage always heals on a success — it *is* the claim "the last reload failed", and
             // this one did not.
-            reloadFailure = nil
+            if loadWarnings != result.warnings { loadWarnings = result.warnings }
-            defects = result.defects
+            if reloadFailure != nil { reloadFailure = nil }
+            if defects != result.defects { defects = result.defects }
             // **The comment index' freshness signal, and its stated interim** (04-interactions.md ▸
             // Search: "kept fresh by the same FSEvents stream while a query is active"). The store has
             // no changed-path channel — the watcher reports only *that* the tree changed
@@ -4268,9 +4387,14 @@ public final class BoardStore: HealHost {
             guard let self else { return }
             transient.constrainToSearch(in: snapshot, commentMatches: commentIndex.matchingCards)
         }
+        // **`landedReloads`, not `snapshotGeneration`**: comments are outside the snapshot entirely
+        // (01-storage-format.md § Enhanced schema), so a comment arriving changes the tree and leaves
+        // the model value-equal — and a value-equal landing skips the snapshot assignment. The
+        // freshness signal an index of window-scoped content can use is therefore the *walk*, which
+        // is what this counter is.
         commentIndex.update(
             query: transient.searchQuery,
-            generation: snapshotGeneration,
+            generation: landedReloads,
             targets: CommentSearchIndex.targets(in: snapshot)
         )
     }

Kanban/LiveStore/CommentSearchIndex.swift

@@ -61,9 +61,14 @@ public struct CommentSearchTarget: Sendable, Equatable {
 /// 04 says "kept fresh by the same FSEvents stream while a query is active". The store has no
 /// changed-path channel — `FolderWatcher` reports only *that* the tree changed (02-architecture.md),
 /// and the reload seam turns that into two snapshots rather than a path list — so the freshness signal
-/// available today is `BoardStore.snapshotGeneration`: **while a query is active, a landed reload
+/// available today is `BoardStore.landedReloads`: **while a query is active, a landed reload
 /// re-sweeps**. That is coarser than the ruling asks for (it re-reads threads a reload may not have
 /// touched) and it is bounded by the same thing that bounds the reload itself, the watcher's debounce.
+///
+/// The counter is the *walk's*, not the applied snapshot's, and it has to be: comments are outside the
+/// snapshot, so a comment arriving leaves the model value-equal and a value-equal reload skips its
+/// assignment (blessed 2026-07-31). Keyed on the applied counter, the index would sleep through the
+/// one kind of change it exists to notice.
 /// A changed-path channel would narrow it to the cards whose `comments/` actually moved; until one
 /// exists, this is the accepted interim and is written down here rather than discovered later.
 ///

Kanban/Storage/BoardLoader.swift

@@ -1,4 +1,5 @@
 import Foundation
+import Synchronization
 import os
 
 /// Walks a board's folder tree and produces an immutable `BoardModel` snapshot — a pure
@@ -193,6 +194,150 @@ public enum BoardLoader: Sendable {
         return GitignoreRules(parsing: text)
     }
 
+    // MARK: - The parse memo
+
+    /// **One `index.md`'s git-index heuristic record** (02-architecture.md § Live-reload resilience,
+    /// blessed 2026-07-31: "The walk memoizes its parse, never its result").
+    ///
+    /// Modification date and byte count, and deliberately nothing else: "The mtime+size trust is the
+    /// git-index heuristic; a writer that defeats it — content changed, mtime and size both
+    /// preserved — is outside the app's care." No content hashing, because a hash is a read of the
+    /// whole file and reading the whole file is the cost the memo exists to avoid.
+    ///
+    /// Stat'd through `FileManager.attributesOfItem`, **never** `URL.resourceValues`, which caches
+    /// its answers on the `URL` instance: a cached mtime would let the memo answer from a stamp taken
+    /// a reload ago, which is exactly the staleness the heuristic exists to detect.
+    public struct FileStamp: Sendable, Equatable {
+        public let modified: Date
+        public let size: Int
+
+        /// `nil` where the file cannot be stat'd at all — read as "cannot tell", and therefore as a
+        /// memo miss: the walk parses, exactly as it did before the memo existed.
+        init?(of url: URL) {
+            guard let attributes = try? FileManager.default.attributesOfItem(atPath: url.path),
+                  let modified = attributes[.modificationDate] as? Date,
+                  let size = attributes[.size] as? NSNumber
+            else {
+                return nil
+            }
+            self.modified = modified
+            self.size = size.intValue
+        }
+    }
+
+    /// **The previous walk's parsed documents, indexed by root-relative path** — the memo
+    /// (02-architecture.md § Live-reload resilience, blessed 2026-07-31: "the loader may reuse the
+    /// previous snapshot's parsed item for any `index.md` whose path, mtime, and size are unchanged
+    /// — the previous snapshot *is* the memo").
+    ///
+    /// **An input to `load`, never hidden state.** The loader is stateless statics and stays that
+    /// way: a caller that holds no memo gets a cold walk, and one that holds the last walk's memo
+    /// gets the same answer faster. That is the contract stated exactly — "result-purity with cost
+    /// unspecified: same tree in, same snapshot out, and the memo can only change how fast".
+    ///
+    /// ### Scope: the parse, and nothing else
+    ///
+    /// A hit skips one thing — opening and parsing one file. Everything *derived* from the document
+    /// (`schema`, `order`, the coercion trace, the identity dedupe, the trash's `kind`) is recomputed
+    /// from it on every walk, unchanged, which is what makes memoized and cold walks indistinguishable
+    /// in output rather than merely intended to be.
+    ///
+    /// **Directory enumeration is never memoized**: folder discovery, attachment listings, loose-file
+    /// detection, the trash's entries and the noise gate are read fresh every walk, "because
+    /// attachment changes never touch `index.md`" — a memo that covered them would go blind to
+    /// precisely the changes the snapshot is supposed to show.
+    ///
+    /// ### A defect can never be answered from it
+    ///
+    /// An entry is recorded only where the file parsed **and** its `schema` reading succeeded — the
+    /// two steps that can produce a `BoardLoadError` at all. So a defective `index.md` is never in the
+    /// memo, which settles both halves of the collect-all walk's question: a file that is broken and
+    /// stays broken has nothing to hit and is re-read and re-collected every walk, and a file whose
+    /// defect was repaired moved its mtime and size and would miss anyway. The skip channel inherits
+    /// this by construction — a skipped path *is* a defect path — so a skip is recomputed from a fresh
+    /// parse every walk and can never be decided from a memo.
+    ///
+    /// Withheld duplicate occurrences *are* recorded, and correctly so: their files parsed cleanly and
+    /// only the board-wide dedupe kept them out of the model, and that dedupe runs over the fresh walk
+    /// either way.
+    public struct ParseMemo: Sendable {
+        fileprivate struct Entry: Sendable {
+            let stamp: FileStamp
+            let document: FrontmatterDocument
+        }
+
+        fileprivate var entries: [String: Entry] = [:]
+
+        /// The empty memo — a cold walk. The only one a caller ever constructs; every other comes
+        /// out of a `LoadResult`.
+        public init() {}
+
+        /// How many documents this memo can answer for. The walk never asks; the suites do.
+        public var count: Int { entries.count }
+
+        fileprivate func document(at path: String, stamp: FileStamp) -> FrontmatterDocument? {
+            guard let entry = entries[path], entry.stamp == stamp else { return nil }
+            return entry.document
+        }
+
+        fileprivate mutating func record(_ document: FrontmatterDocument, at path: String, stamp: FileStamp?) {
+            guard let stamp else { return }
+            entries[path] = Entry(stamp: stamp, document: document)
+        }
+    }
+
+    /// **What one walk actually read** — the memo's whole claim, made assertable.
+    ///
+    /// The loader's contract is result-purity with *cost unspecified*, and a cost nothing can observe
+    /// is a cost nothing can regress: this is the observation handle, so "a single-file echo re-parses
+    /// one file, not the tree" is a test rather than a hope.
+    ///
+    /// Injected rather than a static tally, for `IdentityHistoryRanker`'s reason: `load` is stateless
+    /// statics called from several tasks at once, and a shared counter would be one mutable answer to
+    /// a per-walk question. `nil` — every production call — costs nothing at all.
+    public final class ParseCounter: Sendable {
+
+        /// One walk's tally: files opened and parsed, and documents answered from the memo.
+        public struct Counts: Sendable, Equatable {
+            public var parsed = 0
+            public var reused = 0
+        }
+
+        private let state = Mutex(Counts())
+
+        public init() {}
+
+        public var counts: Counts { state.withLock { $0 } }
+
+        fileprivate func noteParse() { state.withLock { $0.parsed += 1 } }
+        fileprivate func noteReuse() { state.withLock { $0.reused += 1 } }
+    }
+
+    /// One `index.md`, read through the memo — the memo's only point of contact with the walk.
+    ///
+    /// A hit is a document the previous walk parsed out of a file whose path, mtime and size have not
+    /// moved since; a miss is the ordinary `readDocument(at:path:)`, byte for byte the same call the
+    /// loader has always made. The stamp travels back out so the caller can record the document into
+    /// *this* walk's memo once its `schema` reading has succeeded — `ParseMemo` states why that, and
+    /// not the read, is the recording point.
+    ///
+    /// A file whose stamp cannot be read (`nil`) is always parsed and never recorded: "cannot tell"
+    /// reads as "not memoizable", which is the direction that costs a parse rather than correctness.
+    private static func memoizedDocument(
+        at url: URL,
+        path: String,
+        memo: ParseMemo?,
+        counter: ParseCounter?
+    ) throws(BoardLoadError) -> (document: FrontmatterDocument, stamp: FileStamp?) {
+        let stamp = FileStamp(of: url)
+        if let stamp, let hit = memo?.document(at: path, stamp: stamp) {
+            counter?.noteReuse()
+            return (hit, stamp)
+        }
+        counter?.noteParse()
+        return (try readDocument(at: url, path: path), stamp)
+    }
+
     // MARK: - Entry point
 
     /// Walks the board and answers a snapshot — or **every fail-fast defect the walk found**, as one
@@ -231,10 +376,20 @@ public enum BoardLoader: Sendable {
     ///
     ///   **Root paths are unskippable** (`unskippablePaths`) — an entry naming the root's own
     ///   `index.md` is ignored and the defect collected anyway.
+    ///
+    /// - Parameter memo: **the previous walk's parsed documents** (`ParseMemo`, blessed 2026-07-31).
+    ///   `nil` — a first load, a template read, a HEAD snapshot — is a cold walk. Passing the last
+    ///   walk's memo cannot change a single thing about the result, only how many files this one
+    ///   opens; see `ParseMemo` for the scope and for why a defect can never be answered from it.
+    ///
+    /// - Parameter counter: where this walk tallies what it read (`ParseCounter`). `nil` everywhere
+    ///   but the suites.
     public static func load(
         boardRoot: URL,
         skipping: Set<String> = [],
-        historyRanker: IdentityHistoryRanker? = nil
+        historyRanker: IdentityHistoryRanker? = nil,
+        memo: ParseMemo? = nil,
+        counter: ParseCounter? = nil
     ) throws(BoardLoadFailure) -> LoadResult {
         // Environmental, so immediate: a root that cannot be listed has no walk to collect from.
         do throws(BoardLoadError) {
@@ -253,6 +408,11 @@ public enum BoardLoader: Sendable {
         // what `BoardLoadFailure` carries when it does not.
         var failures: [BoardLoadError] = []
 
+        // **This walk's own memo, for the next one** (`ParseMemo`). Built as the walk goes and
+        // handed out on the `LoadResult`, so the loader keeps no state between calls: what the store
+        // passes back in is what came out of the walk before it.
+        var freshMemo = ParseMemo()
+
         /// Records one fail-fast defect — unless this open's user already consented to skipping that
         /// exact path.
         ///
@@ -277,12 +437,16 @@ public enum BoardLoader: Sendable {
         let boardIndexURL = boardRoot.appendingPathComponent(indexFileName)
         if FileManager.default.fileExists(atPath: boardIndexURL.path) {
             do throws(BoardLoadError) {
-                let document = try readDocument(at: boardIndexURL, path: indexFileName)
+                let read = try memoizedDocument(
+                    at: boardIndexURL, path: indexFileName, memo: memo, counter: counter)
                 // **The root's own `schema` stays required** (01-storage-format.md § Malformed input,
                 // re-ruled 2026-07-31): it is the this-really-is-a-board gate, and the one `schema` on
                 // the board that does not read as 1 when absent.
-                boardSchema = try validatedRootSchema(in: document, path: indexFileName)
+                boardSchema = try validatedRootSchema(in: read.document, path: indexFileName)
-                boardDocument = document
+                boardDocument = read.document
+                // Recorded past the schema gate, never before it — `ParseMemo`'s "a defect can never
+                // be answered from it".
+                freshMemo.record(read.document, at: indexFileName, stamp: read.stamp)
             } catch {
                 record(error)
             }
@@ -386,12 +550,19 @@ public enum BoardLoader: Sendable {
             let lanePath = laneName + "/" + indexFileName
             let laneDocument: FrontmatterDocument
             let laneSchema: (schema: Int, coerced: CoercedField?)
+            let laneStamp: FileStamp?
             // **A broken lane takes its subtree with it** (the collect-and-skip rule above): the
             // defect is recorded, the lane's cards are not enumerated, and the repair's re-check is
             // what surfaces whatever they were hiding.
             do throws(BoardLoadError) {
-                laneDocument = try readDocument(
+                let read = try memoizedDocument(
-                    at: laneURL.appendingPathComponent(indexFileName), path: lanePath)
+                    at: laneURL.appendingPathComponent(indexFileName),
+                    path: lanePath,
+                    memo: memo,
+                    counter: counter
+                )
+                laneDocument = read.document
+                laneStamp = read.stamp
                 // Below the root both keys are optional (re-ruled 2026-07-31): a missing `schema`
                 // reads as 1, a missing or unusable `order` as append-at-end. Both readings are
                 // coerce-tier — recorded here, logged, and acted on by nothing until the file's next
@@ -401,6 +572,7 @@ public enum BoardLoader: Sendable {
                 record(error)
                 continue
             }
+            freshMemo.record(laneDocument, at: lanePath, stamp: laneStamp)
             let laneOrder = IntegrityRules.resolvedOrder(in: laneDocument)
             noteCoercions(
                 in: laneDocument,
@@ -423,11 +595,14 @@ public enum BoardLoader: Sendable {
 
                 let card: WalkedCard
                 do throws(BoardLoadError) {
-                    card = try parseCard(at: cardURL, path: cardRelPath)
+                    card = try parseCard(at: cardURL, path: cardRelPath, memo: memo, counter: counter)
                 } catch {
                     record(error)
                     continue
                 }
+                // `parseCard` returning at all means the parse and the `schema` reading both
+                // succeeded, which is the recording point one level up spells out longhand.
+                freshMemo.record(card.document, at: cardRelPath + "/" + indexFileName, stamp: card.stamp)
                 noteCoercions(in: card.document, at: cardRelPath + "/" + indexFileName, plus: card.coercions)
 
                 // **The card-level claimed name** (01-storage-format.md § Fractal layout ▸ Rules,
@@ -539,17 +714,25 @@ public enum BoardLoader: Sendable {
             let entryPath = entryRelPath + "/" + indexFileName
             let document: FrontmatterDocument
             let schema: (schema: Int, coerced: CoercedField?)
+            let stamp: FileStamp?
             // Collected and skipped, the lane arm's rule one container over: a trash entry that will
             // not parse leaves the trash rather than refusing the board, and its own subtree was
             // never walked to begin with (the entry is opaque by design).
             do throws(BoardLoadError) {
-                document = try readDocument(
+                let read = try memoizedDocument(
-                    at: entryURL.appendingPathComponent(indexFileName), path: entryPath)
+                    at: entryURL.appendingPathComponent(indexFileName),
+                    path: entryPath,
+                    memo: memo,
+                    counter: counter
+                )
+                document = read.document
+                stamp = read.stamp
                 schema = try resolvedSchema(in: document, path: entryPath)
             } catch {
                 record(error)
                 continue
             }
+            freshMemo.record(document, at: entryPath, stamp: stamp)
             let order = IntegrityRules.resolvedOrder(in: document)
             noteCoercions(
                 in: document,
@@ -727,6 +910,7 @@ public enum BoardLoader: Sendable {
         return LoadResult(
             model: model,
             warnings: warnings,
+            memo: freshMemo,
             defects: defects,
             // Keyed by identity, so a withheld entry's reading has to go with it: two folders sharing
             // an id would otherwise leave a `kind` answer standing for the *other* one — the exact
@@ -929,6 +1113,9 @@ public enum BoardLoader: Sendable {
         /// This card's coerce-tier records for the strict fields, which only the rulebook can make
         /// (a missing key leaves no trace in `document.coercedFields`).
         let coercions: [CoercedField]
+        /// What this card's `index.md` looked like to `stat(2)` as the walk read it — the key the
+        /// next walk's memo hit is decided by, `nil` where the file could not be stat'd at all.
+        let stamp: FileStamp?
 
         var title: FieldValue<String> { document.title }
         var isDeleted: Bool { !document.deleted.isMissing }
@@ -961,9 +1148,25 @@ public enum BoardLoader: Sendable {
     ///
     /// `path` is root-relative and names the *folder*; the errors this throws name its `index.md`.
     /// Callers guard `isUUIDShaped` and `hasIndex` first, exactly as the lane walk always has.
-    private static func parseCard(at cardURL: URL, path: String) throws(BoardLoadError) -> WalkedCard {
+    ///
+    /// The **attachment listing stays fresh** here, memo or no memo (`ParseMemo` ▸ Scope): a hit
+    /// spares this card's `index.md` read and nothing else, because an attachment arriving in
+    /// `attachments/` never touches `index.md` and a card whose paperclip went stale would be the
+    /// memo lying about the tree.
+    private static func parseCard(
+        at cardURL: URL,
+        path: String,
+        memo: ParseMemo?,
+        counter: ParseCounter?
+    ) throws(BoardLoadError) -> WalkedCard {
         let cardPath = path + "/" + indexFileName
-        let document = try readDocument(at: cardURL.appendingPathComponent(indexFileName), path: cardPath)
+        let read = try memoizedDocument(
+            at: cardURL.appendingPathComponent(indexFileName),
+            path: cardPath,
+            memo: memo,
+            counter: counter
+        )
+        let document = read.document
         let schema = try resolvedSchema(in: document, path: cardPath)
         let order = IntegrityRules.resolvedOrder(in: document)
 
@@ -973,7 +1176,8 @@ public enum BoardLoader: Sendable {
             storedOrder: order.order,
             attachments: attachmentNames(in: cardURL),
             document: document,
-            coercions: [schema.coerced, order.coerced].compactMap { $0 }
+            coercions: [schema.coerced, order.coerced].compactMap { $0 },
+            stamp: read.stamp
         )
     }
 
@@ -1331,6 +1535,19 @@ public struct LoadResult: Sendable {
     public var model: BoardModel
     public var warnings: [LoadWarning]
 
+    /// **What this walk parsed, ready to be the next walk's memo** (`BoardLoader.ParseMemo`, blessed
+    /// 2026-07-31).
+    ///
+    /// It rides out here rather than being derived from `model` for two reasons. The stamps are not
+    /// in the snapshot and never will be — mtime and size are facts about files, not about a board —
+    /// and the documents that *are* in the snapshot would have to be re-indexed by path to be usable,
+    /// which is the walk's own knowledge being thrown away and re-derived. Carrying both together
+    /// keeps the loader a pure function whose caller holds the whole of what the next call may reuse.
+    ///
+    /// A caller that ignores it gets a cold walk every time, which is exactly what
+    /// `TemplateEngine`, `GitHeadSnapshot` and every first load do.
+    public var memo: BoardLoader.ParseMemo = BoardLoader.ParseMemo()
+
     /// **The typed defect stream** — everything this walk found that is pending *work*
     /// (02-architecture.md ▸ Components ▸ IntegrityRules, settled 2026-07-29). One channel, not
     /// three: loose card files, legacy `deleted:` keys, and a claimed board-root name held by the

Kanban/UI/Board/DragSession.swift

@@ -162,6 +162,13 @@ struct FileDropTarget: Equatable, Sendable {
 /// app-mediated echo is normally next, and a foreign one that lands first re-grounds everything
 /// anyway.
 ///
+/// It watches `BoardStore.snapshotGeneration`, which since 2026-07-31 does not move for a reload whose
+/// tree came back value-equal, and that is the right counter rather than a hazard: a hold is only ever
+/// armed by a drop whose write actually rearranged something — every drop path refuses a no-op
+/// arrangement *before* it opens a write bracket (`BoardStore.moveCards`, `moveLanes`, `moveLane`) —
+/// so a drop that would land value-equal never writes and never reloads, and its hold is the
+/// watchdog's to retire exactly as it was before the skip existed.
+///
 /// The `timeout` is the same guarantee the drag session's watchdog gives the drag itself: a write
 /// that was refused outright (a read-only board) produces no reload at all, and an overlay with no
 /// hand-off coming must still dissolve and let the snapshot be the authority again.

KanbanTests/AutoCommitTests.swift

@@ -1245,7 +1245,7 @@ struct AutoCommitMessageTests {
             var generation = 0
             var reads = 0
             committer.awaitReloadQuiescence = {}
-            committer.snapshotGeneration = {
+            committer.landedReloads = {
                 reads += 1
                 if reads == landsAfterReads {
                     current = (try? fixture.snapshot()) ?? current

KanbanTests/BoardLoaderTests.swift

@@ -1233,3 +1233,312 @@ struct BoardLoaderCoercionTraceTests {
         ])
     }
 }
+
+// MARK: - The parse memo
+
+private extension BoardFixture {
+
+    /// A file's modification date, forced. Used wherever a test rewrites bytes without changing the
+    /// byte *count*: the stamp rule is the subject there, and leaving it to the filesystem clock
+    /// would make the assertion a race against timestamp resolution rather than a statement about
+    /// mtime.
+    func setModified(_ relativePath: String, to date: Date) throws {
+        let folder = relativePath.isEmpty ? root : root.appendingPathComponent(relativePath, isDirectory: true)
+        try FileManager.default.setAttributes(
+            [.modificationDate: date],
+            ofItemAtPath: folder.appendingPathComponent("index.md").path
+        )
+    }
+}
+
+/// A board with every container the walk has: a root, two lanes, two cards in the first, one
+/// attachment, and one trashed card — so "the whole tree came out of the memo" is a claim about all
+/// four levels rather than about lanes.
+private func memoBoard() throws -> (fixture: BoardFixture, lane: String, card: String) {
+    let fixture = try BoardFixture()
+    let lane = "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa"
+    let card = "bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb"
+
+    try fixture.index("", "schema: 1\ntitle: Board\n")
+    try fixture.index(lane, "schema: 1\norder: 1024\ntitle: Todo\n")
+    try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ntitle: First\n")
+    try fixture.index("\(lane)/cccccccc-cccc-4ccc-8ccc-cccccccccccc", "schema: 1\norder: 2048\ntitle: Second\n")
+    try fixture.index(".trash/dddddddd-dddd-4ddd-8ddd-dddddddddddd", "schema: 1\norder: 1024\ntitle: Gone\n")
+    try fixture.strayFile("\(lane)/\(card)/attachments/shot.png", contents: "png")
+    return (fixture, lane, card)
+}
+
+/// Every `index.md` the board above holds — the number a warm walk must answer for without opening
+/// one of them.
+private let memoBoardIndexCount = 5
+
+/// A whole-second modification date, forced onto a file wherever a test needs two stamps to compare
+/// *exactly*. A date read back off the filesystem does not necessarily round-trip through
+/// `setAttributes` bit for bit (`Date` is a `Double` and the syscall's is a `timespec`), and a test
+/// about mtime equality must not turn into a test about that conversion.
+private let pinnedMtime = Date(timeIntervalSince1970: 1_750_000_000)
+
+/// **The walk memoizes its parse, never its result** (02-architecture.md § Live-reload resilience,
+/// blessed 2026-07-31 — `BoardLoader.ParseMemo`).
+///
+/// Two claims that pull in opposite directions, which is why they are pinned side by side. The memo
+/// has to actually save the reads: a walk over an untouched tree opens no `index.md` at all. And it
+/// has to be undetectable in the answer, for the files it saved and — harder — for everything it
+/// deliberately does not cover, which is every directory listing the walk makes. The equivalence half
+/// is stated again over the golden fixture boards (`FixtureMemoEquivalenceTests`); this suite pins the
+/// mechanism file by file, where a synthetic tree can be edited between two walks.
+@Suite("BoardLoader ▸ the parse memo")
+struct BoardLoaderParseMemoTests {
+
+    @Test("A cold walk parses every index.md and reuses nothing")
+    func aColdWalkParsesEverything() throws {
+        let (fixture, _, _) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let counter = BoardLoader.ParseCounter()
+        let result = try BoardLoader.load(boardRoot: fixture.root, counter: counter)
+
+        #expect(counter.counts == .init(parsed: memoBoardIndexCount, reused: 0))
+        #expect(result.memo.count == memoBoardIndexCount)
+    }
+
+    @Test("A walk over an untouched tree opens no index.md at all")
+    func anUntouchedTreeIsAnsweredEntirelyFromTheMemo() throws {
+        let (fixture, _, _) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 0, reused: memoBoardIndexCount))
+        // The whole of the claim's other half: the cheap walk and the cold one are the same walk.
+        #expect(warm.model == cold.model)
+        #expect(warm.warnings == cold.warnings)
+        #expect(warm.defects == cold.defects)
+        #expect(warm.trashKinds == cold.trashKinds)
+        #expect(warm.memo.count == cold.memo.count)
+    }
+
+    @Test("A single-file echo re-parses exactly that file")
+    func oneEditedFileIsTheOnlyOneReParsed() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ntitle: Renamed\n")
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 1, reused: memoBoardIndexCount - 1))
+        #expect(warm.model.lanes.first?.cards.first?.title.value == "Renamed")
+        // And the cold answer is still the answer: the memo changed the cost, nothing else.
+        #expect(warm.model == (try BoardLoader.load(boardRoot: fixture.root).model))
+    }
+
+    @Test("A same-size rewrite still re-parses, because the mtime moved")
+    func aSameSizeRewriteReParses() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        try fixture.setModified("\(lane)/\(card)", to: pinnedMtime)
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+
+        // "First" → "Third": identical byte count, so `size` alone would call this unchanged.
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ntitle: Third\n")
+        try fixture.setModified("\(lane)/\(card)", to: pinnedMtime.addingTimeInterval(1))
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 1, reused: memoBoardIndexCount - 1))
+        #expect(warm.model.lanes.first?.cards.first?.title.value == "Third")
+    }
+
+    /// **The heuristic's stated blind spot, pinned rather than discovered** (02-architecture.md: "The
+    /// mtime+size trust is the git-index heuristic; a writer that defeats it — content changed, mtime
+    /// and size both preserved — is outside the app's care").
+    ///
+    /// It is here so the boundary is a decision with a test on it: this is the one shape in which a
+    /// memoized walk and a cold walk disagree, and the design says so out loud.
+    @Test("A rewrite that preserves both mtime and size is trusted — the git-index heuristic's edge")
+    func aRewritePreservingTheStampIsTrusted() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        try fixture.setModified("\(lane)/\(card)", to: pinnedMtime)
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ntitle: Third\n")
+        try fixture.setModified("\(lane)/\(card)", to: pinnedMtime)
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 0, reused: memoBoardIndexCount))
+        #expect(warm.model.lanes.first?.cards.first?.title.value == "First")
+        // And the very next walk that *does* see a moved stamp catches up — the window is one write,
+        // not a standing state.
+        try fixture.setModified("\(lane)/\(card)", to: pinnedMtime.addingTimeInterval(1))
+        let next = try BoardLoader.load(boardRoot: fixture.root, memo: warm.memo)
+        #expect(next.model.lanes.first?.cards.first?.title.value == "Third")
+    }
+
+    // MARK: Directory enumeration is never memoized
+
+    @Test("An attachment arriving is seen by a walk that parsed nothing")
+    func attachmentListingsStayFresh() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        // An attachment never touches `index.md`, which is exactly why the memo must not cover the
+        // listing that finds it.
+        try fixture.strayFile("\(lane)/\(card)/attachments/second.png", contents: "png")
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 0, reused: memoBoardIndexCount))
+        #expect(warm.model.lanes.first?.cards.first?.attachments == ["second.png", "shot.png"])
+    }
+
+    @Test("A loose file arriving beside an untouched index.md is still a defect")
+    func looseFileDetectionStaysFresh() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        #expect(cold.looseCardFiles.isEmpty)
+        try fixture.strayFile("\(lane)/\(card)/notes.txt", contents: "loose")
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 0, reused: memoBoardIndexCount))
+        #expect(warm.looseCardFiles.map(\.fileNames) == [["notes.txt"]])
+    }
+
+    @Test("A new card folder is discovered, and it is the only file the walk opens")
+    func folderDiscoveryStaysFresh() throws {
+        let (fixture, lane, _) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        let arrival = "eeeeeeee-eeee-4eee-8eee-eeeeeeeeeeee"
+        try fixture.index("\(lane)/\(arrival)", "schema: 1\norder: 4096\ntitle: Arrived\n")
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo, counter: counter)
+
+        #expect(counter.counts == .init(parsed: 1, reused: memoBoardIndexCount))
+        #expect(warm.model.lanes.first?.cards.map(\.title.value) == ["First", "Second", "Arrived"])
+    }
+
+    @Test("A vanished card leaves the model, and its memo entry goes with it")
+    func aVanishedItemLeavesTheMemo() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let cold = try BoardLoader.load(boardRoot: fixture.root)
+        try FileManager.default.removeItem(at: fixture.root.appendingPathComponent("\(lane)/\(card)"))
+
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: cold.memo)
+
+        #expect(warm.model.lanes.first?.cards.map(\.title.value) == ["Second"])
+        #expect(warm.memo.count == memoBoardIndexCount - 1)
+    }
+
+    // MARK: Defects can never be answered from it
+
+    @Test("A defective index.md is never memoized, so a still-broken file is re-read every walk")
+    func aDefectIsNeverMemoized() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let healthy = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\nlabels: [a, b\n")
+
+        // The file does not change between these two walks, and neither of them can go quiet about
+        // it: a defective `index.md` is never recorded, so there is nothing for a later walk to hit.
+        // The healthy memo still spares the four files that *did* load, which is the point — the
+        // defect costs one read, not a cold walk.
+        for _ in 0..<2 {
+            let counter = BoardLoader.ParseCounter()
+            do throws(BoardLoadFailure) {
+                _ = try BoardLoader.load(boardRoot: fixture.root, memo: healthy.memo, counter: counter)
+                Issue.record("expected the broken card to fail the walk")
+            } catch {
+                #expect(error.defects.map(\.path) == ["\(lane)/\(card)/index.md"])
+            }
+            #expect(counter.counts == .init(parsed: 1, reused: memoBoardIndexCount - 1))
+        }
+
+        // And the aggregate is the cold aggregate, defect for defect.
+        do throws(BoardLoadFailure) {
+            _ = try BoardLoader.load(boardRoot: fixture.root, memo: healthy.memo)
+            Issue.record("expected the broken card to fail the walk")
+        } catch let warm {
+            do throws(BoardLoadFailure) {
+                _ = try BoardLoader.load(boardRoot: fixture.root)
+                Issue.record("expected the broken card to fail the walk")
+            } catch let cold {
+                #expect(warm.defects == cold.defects)
+            }
+        }
+    }
+
+    @Test("A repaired file re-parses and rejoins the board")
+    func aRepairedFileReParses() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let healthy = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\nlabels: [a, b\n")
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ntitle: Repaired\n")
+
+        let warm = try BoardLoader.load(boardRoot: fixture.root, memo: healthy.memo)
+        #expect(warm.model.lanes.first?.cards.first?.title.value == "Repaired")
+    }
+
+    @Test("A skip is recomputed from a fresh parse, memo or no memo")
+    func aSkipComposesWithTheMemo() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let healthy = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\nlabels: [a, b\n")
+        let skips: Set<String> = ["\(lane)/\(card)/index.md"]
+
+        let counter = BoardLoader.ParseCounter()
+        let warm = try BoardLoader.load(
+            boardRoot: fixture.root, skipping: skips, memo: healthy.memo, counter: counter)
+        let cold = try BoardLoader.load(boardRoot: fixture.root, skipping: skips)
+
+        // A skipped path is a defect path, so it was never in the memo and is read on every walk.
+        #expect(counter.counts.parsed == 1)
+        #expect(warm.model == cold.model)
+        #expect(warm.warnings == cold.warnings)
+        #expect(warm.warnings.contains(.userSkipped(path: "\(lane)/\(card)/index.md")))
+        // The skipped item is out of the board and out of the memo, both walks alike.
+        #expect(warm.memo.count == memoBoardIndexCount - 1)
+    }
+
+    @Test("A skipped path stays skipped across a memoized reload")
+    func aSkipHoldsAcrossReloads() throws {
+        let (fixture, lane, card) = try memoBoard()
+        defer { fixture.tearDown() }
+
+        let healthy = try BoardLoader.load(boardRoot: fixture.root)
+        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\nlabels: [a, b\n")
+        let skips: Set<String> = ["\(lane)/\(card)/index.md"]
+
+        let first = try BoardLoader.load(boardRoot: fixture.root, skipping: skips, memo: healthy.memo)
+        let second = try BoardLoader.load(boardRoot: fixture.root, skipping: skips, memo: first.memo)
+
+        #expect(second.model == first.model)
+        #expect(second.warnings == first.warnings)
+        #expect(second.model.lanes.first?.cards.map(\.title.value) == ["Second"])
+    }
+}

KanbanTests/BoardStoreTests.swift

@@ -602,3 +602,233 @@ struct BoardStoreTests {
         #expect(store.reloadGeneration == 0)
     }
 }
+
+// MARK: - The parse memo and the value-equal skip
+
+/// **"The walk memoizes its parse, never its result"** and **"the store skips the assignment entirely
+/// when the fresh snapshot equals the current one"** (02-architecture.md § Live-reload resilience,
+/// both blessed 2026-07-31).
+///
+/// The loader's half is pinned in `BoardLoaderParseMemoTests` and over the golden corpus in
+/// `FixtureMemoEquivalenceTests`; what only this suite can state is the *wiring* — that the store
+/// hands each walk the one before it (`BoardStore.parseCounter` is the seam that makes "re-parsed
+/// nothing" observable at all), and that the skip is a skip of the observable assignment and of
+/// nothing else the landing owes.
+@MainActor
+@Suite("BoardStore ▸ the parse memo and the value-equal skip")
+struct BoardStoreReloadMemoTests {
+
+    /// Every `index.md` `makeBoard()` puts in the walk's way: the root, two lanes, two cards. The
+    /// stray `notes/` folder holds one too and is deliberately not counted — a non-UUID-shaped folder
+    /// is never descended into, so the loader never opens it, memo or no memo.
+    static let indexCount = 5
+
+    /// One reload through the store's one inbound door, with a counter attached.
+    private func reload(_ store: BoardStore, _ origin: WatchOrigin = .foreign) async -> BoardLoader.ParseCounter.Counts {
+        let counter = BoardLoader.ParseCounter()
+        store.parseCounter = counter
+        store.handleWatcherEvent(.treeChanged(origin))
+        await store.awaitQuiescence()
+        store.parseCounter = nil
+        return counter.counts
+    }
+
+    @Test("A reload of an untouched tree opens no index.md and assigns no snapshot")
+    func anUnchangedTreeCostsNothing() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+        let before = store.snapshot
+
+        let counts = await reload(store)
+
+        #expect(counts == .init(parsed: 0, reused: Self.indexCount))
+        // The skip proper: no assignment, so no `@Observable` churn and no render pass.
+        #expect(store.snapshotGeneration == 0)
+        #expect(store.snapshot == before)
+        // And the landing still happened — the bookkeeping the skip must never cover.
+        #expect(store.landedReloads == 1)
+        #expect(store.reloadFailure == nil)
+    }
+
+    @Test("A single-file echo re-parses exactly that file, and does assign")
+    func oneEditedFileIsTheOnlyOneReParsed() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        try fixture.item("\(Ident.lane1)/\(Ident.card1)", Item.rich(order: "1024", title: "Renamed"))
+        let counts = await reload(store)
+
+        #expect(counts == .init(parsed: 1, reused: Self.indexCount - 1))
+        #expect(cardTitles(inLane: Ident.lane1, of: store.snapshot) == ["Renamed", "Second"])
+        #expect(store.snapshotGeneration == 1)
+        #expect(store.landedReloads == 1)
+    }
+
+    @Test("The memo carries from reload to reload rather than going cold every other walk")
+    func theMemoChains() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        // Three landings: one value-equal (which skips the assignment), one that changes a file, and
+        // one value-equal again. If the skipped landing dropped its memo, the walk after it would go
+        // cold — which is exactly the bug this pins.
+        #expect(await reload(store) == .init(parsed: 0, reused: Self.indexCount))
+        try fixture.item("\(Ident.lane1)/\(Ident.card2)", Item.rich(order: "2048", title: "Edited"))
+        #expect(await reload(store) == .init(parsed: 1, reused: Self.indexCount - 1))
+        #expect(await reload(store) == .init(parsed: 0, reused: Self.indexCount))
+
+        #expect(cardTitles(inLane: Ident.lane1, of: store.snapshot) == ["First", "Edited"])
+        #expect(store.snapshotGeneration == 1, "only the middle reload had anything to assign")
+        #expect(store.landedReloads == 3)
+        #expect(store.parseMemo.count == Self.indexCount)
+    }
+
+    @Test("A failed reload keeps the snapshot and bumps neither counter")
+    func aFailedReloadBumpsNothing() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+        let before = store.snapshot
+
+        try fixture.item(Ident.lane1, brokenIndex)
+        _ = await reload(store)
+
+        #expect(store.snapshot == before, "a failed reload never replaces a good snapshot")
+        #expect(store.snapshotGeneration == 0)
+        #expect(store.landedReloads == 0, "there is no snapshot in hand, so nothing was covered")
+        #expect(store.reloadFailure?.primary.path == indexPath(Ident.lane1))
+    }
+
+    @Test("A failed reload's breakage clears on the next success, which is value-equal")
+    func breakageClearsOnAValueEqualSuccess() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        try fixture.item(Ident.lane1, brokenIndex)
+        _ = await reload(store)
+        #expect(store.reloadFailure != nil)
+
+        // Repaired to exactly what it was: the model comes back value-equal, the assignment is
+        // skipped — and the standing breakage condition must still heal, because it is not board
+        // structure and is not what the skip covers.
+        try fixture.item(Ident.lane1, Item.rich(order: "1024", title: "Todo"))
+        _ = await reload(store)
+
+        #expect(store.reloadFailure == nil)
+        #expect(store.snapshotGeneration == 0, "the repaired tree is the tree that was already on screen")
+        #expect(store.landedReloads == 1)
+    }
+
+    // MARK: What the skip must never cover
+
+    @Test("Warnings follow the tree even when the model does not move")
+    func warningsFollowTheTree() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        // A second non-UUID-shaped folder: a stray is not in the model, so this changes `loadWarnings`
+        // and nothing else. It is also never descended into, so the walk still opens no file.
+        try fixture.item("scratch", "not a board item at all\n")
+        let counts = await reload(store)
+
+        #expect(counts == .init(parsed: 0, reused: Self.indexCount))
+        #expect(store.snapshotGeneration == 0)
+        #expect(store.landedReloads == 1)
+        #expect(store.loadWarnings.contains(.nonUUIDFolderIgnored(path: "scratch")))
+        #expect(store.loadWarnings.contains(.nonUUIDFolderIgnored(path: "notes")))
+    }
+
+    @Test("Defects follow the tree even when the model does not move")
+    func defectsFollowTheTree() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+        #expect(store.looseCardFiles.isEmpty)
+
+        // A loose file beside an untouched `index.md`: pending work the walk found, with the snapshot
+        // value-equal on either side of it. Defects are what `runScheduledHeals` reads, so a skip
+        // that swallowed them would silently retire the heal engine on quiet boards.
+        try "loose".write(
+            to: fixture.url("\(Ident.lane1)/\(Ident.card1)").appendingPathComponent("notes.txt"),
+            atomically: true,
+            encoding: .utf8
+        )
+        _ = await reload(store)
+
+        #expect(store.snapshotGeneration == 0)
+        #expect(store.landedReloads == 1)
+        #expect(store.looseCardFiles.map(\.fileNames) == [["notes.txt"]])
+    }
+
+    @Test("An attachment arriving moves the snapshot, because the snapshot carries the listing")
+    func attachmentsAreNotMemoized() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        let attachments = fixture.url("\(Ident.lane1)/\(Ident.card1)")
+            .appendingPathComponent("attachments", isDirectory: true)
+        try FileManager.default.createDirectory(at: attachments, withIntermediateDirectories: true)
+        try "png".write(to: attachments.appendingPathComponent("shot.png"), atomically: true, encoding: .utf8)
+
+        let counts = await reload(store)
+
+        // Not one file opened, and the card's paperclip is still current: directory enumeration is
+        // outside the memo's scope by design, because an attachment never touches `index.md`.
+        #expect(counts == .init(parsed: 0, reused: Self.indexCount))
+        #expect(lane(Ident.lane1, in: store.snapshot)?.cards.first?.attachments == ["shot.png"])
+        #expect(store.snapshotGeneration == 1)
+        #expect(store.landedReloads == 1)
+    }
+
+    @Test("A no-change reload announces nothing and leaves no state behind")
+    func aNoChangeReloadIsSilent() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        var spoken: [String?] = []
+        store.announce = { spoken.append($0) }
+        _ = await reload(store)
+        _ = await reload(store, .reconciling)
+
+        #expect(spoken == [nil, nil])
+        #expect(store.readOnlyLock == nil)
+        #expect(store.snapshotGeneration == 0)
+        #expect(store.landedReloads == 2)
+    }
+
+    @Test("A value-equal reload still lands for the auto-commit seam and the covering gate")
+    func aValueEqualReloadStillLands() async throws {
+        let fixture = try makeBoard()
+        defer { fixture.tearDown() }
+        let store = try BoardStore(rootURL: fixture.root)
+
+        let landings = LandingCount()
+        store.commitSeam = HistoryCommitSeam(
+            willWrite: {},
+            writeBracketDidClose: {},
+            reloadDidLand: { _ in landings.value += 1 }
+        )
+        _ = await reload(store)
+
+        // The covering gate counts landings, not assignments (`GitAutoCommitter.landedReloads`), and
+        // the commit seam is armed by every landing whether or not the snapshot moved — "a landing
+        // that finds nothing to commit is the silent no-op, not a wasted trip".
+        #expect(landings.value == 1)
+        #expect(store.landedReloads == 1)
+        #expect(store.snapshotGeneration == 0)
+    }
+}
+
+/// What the reload path told the history seam — a box, because `HistoryCommitSeam` is a struct of
+/// closures and a captured `var` cannot be read back after the reload has landed.
+@MainActor
+private final class LandingCount {
+    var value = 0
+}

KanbanTests/FixtureBoardTests.swift

@@ -784,3 +784,108 @@ struct FixtureSkippableDefectsTests {
         #expect(text.contains("labels: [red, green"), "the skipped file was rewritten")
     }
 }
+
+// MARK: - Memo-vs-cold equivalence, over every golden board
+
+/// **Result-purity with cost unspecified** (02-architecture.md § Live-reload resilience, blessed
+/// 2026-07-31: "The loader's contract is result-purity with cost unspecified: same tree in, same
+/// snapshot out, and the memo can only change how fast").
+///
+/// The memo is the one thing in the loader that could make two walks of the same tree disagree, so
+/// the claim is stated where the trees are real and hand-authored: every golden board is walked cold,
+/// then walked again with the first walk's memo, and the two results are compared whole. Nothing here
+/// edits a tree — the mechanism's per-file behaviour is `BoardLoaderParseMemoTests`' subject; this is
+/// the equivalence, across every shape the fixture corpus holds.
+///
+/// The malformed boards are included on purpose. A refusal is a result too, and a memo that changed
+/// which defects a walk collected — or their order — would be the worst possible way for this to be
+/// wrong, since the decision surface is written directly against that list.
+struct FixtureMemoEquivalenceTests {
+
+    /// Every board under `Fixtures/Valid`, by relative path.
+    static let validBoards = [
+        "Valid/rich-board.kanban",
+        "Valid/interrupted-create.kanban",
+        "Valid/non-uuid-strays.kanban",
+        "Valid/stray-files.kanban",
+        "Valid/tombstones.kanban",
+        "Valid/duplicate-order-tie-break.kanban",
+        "Valid/unknown-key-order.kanban",
+        "Valid/coercion.kanban",
+        "Valid/duplicate-top-level-keys.kanban",
+        "Valid/board-level-deleted.kanban",
+        "Valid/optional-keys.kanban",
+    ]
+
+    /// Every board under `Fixtures/Malformed`, by relative path.
+    static let malformedBoards = [
+        "Malformed/board-root-missing-index.kanban",
+        "Malformed/missing-schema.kanban",
+        "Malformed/unparseable-yaml.kanban",
+        "Malformed/schema-newer-than-app.kanban",
+        "Malformed/many-defects.kanban",
+        "Malformed/skippable-defects.kanban",
+    ]
+
+    @Test("A memoized walk of a valid board is the cold walk, whole", arguments: validBoards)
+    func aMemoizedWalkMatchesTheColdWalk(board: String) throws {
+        let cold = try loadFixture(board)
+        let warm = try BoardLoader.load(boardRoot: fixtureBoard(board), memo: cold.memo)
+
+        #expect(warm.model == cold.model)
+        #expect(warm.warnings == cold.warnings)
+        #expect(warm.defects == cold.defects)
+        #expect(warm.trashKinds == cold.trashKinds)
+        // The memo the second walk produced can stand in for the first's, which is what makes the
+        // store's chain of reloads self-sustaining rather than degrading walk by walk.
+        #expect(warm.memo.count == cold.memo.count)
+    }
+
+    @Test("A memoized walk of a valid board opens no index.md at all", arguments: validBoards)
+    func aMemoizedWalkReadsNothing(board: String) throws {
+        let cold = try loadFixture(board)
+
+        let counter = BoardLoader.ParseCounter()
+        _ = try BoardLoader.load(boardRoot: fixtureBoard(board), memo: cold.memo, counter: counter)
+
+        #expect(counter.counts.parsed == 0)
+        #expect(counter.counts.reused == cold.memo.count)
+        #expect(counter.counts.reused > 0, "a fixture with nothing to memoize proves nothing")
+    }
+
+    @Test("A memoized walk of a malformed board refuses identically", arguments: malformedBoards)
+    func aMemoizedWalkRefusesIdentically(board: String) {
+        // A refusing walk hands back no memo — that is the design, not an omission: a defective file
+        // is never recorded, and a walk that threw produced no `LoadResult` to carry one on. So the
+        // memo under test is the empty one a first walk would offer, and what is pinned is that the
+        // memo parameter never moves the aggregate a refusal reports.
+        let defects = refusal(board, memo: nil)
+        #expect(defects == refusal(board, memo: BoardLoader.ParseMemo()))
+        #expect(!defects.isEmpty, "\(board) is in the malformed corpus but loaded")
+    }
+
+    /// One malformed board's aggregate, or `[]` where it unexpectedly loaded.
+    private func refusal(_ board: String, memo: BoardLoader.ParseMemo?) -> [BoardLoadError] {
+        do throws(BoardLoadFailure) {
+            _ = try BoardLoader.load(boardRoot: fixtureBoard(board), memo: memo)
+            return []
+        } catch {
+            return error.defects
+        }
+    }
+
+    /// The malformed corpus' real memo case: a board that refuses is repaired-by-skip into one that
+    /// loads, and the memo that produced carries into the next walk without moving the answer.
+    @Test("A skipped-open board reloads through its own memo unchanged")
+    func aSkippedOpenReloadsUnchanged() throws {
+        let skips: Set<String> = [SkippableDefects.newerCardPath, SkippableDefects.brokenLanePath]
+        let root = fixtureBoard(SkippableDefects.board)
+
+        let cold = try BoardLoader.load(boardRoot: root, skipping: skips)
+        let warm = try BoardLoader.load(boardRoot: root, skipping: skips, memo: cold.memo)
+
+        #expect(warm.model == cold.model)
+        #expect(warm.warnings == cold.warnings)
+        #expect(warm.defects == cold.defects)
+    }
+}