diff --git a/CLAUDE.md b/CLAUDE.md
index d643081..8ff7af9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -69,8 +69,9 @@ All in `Shared/Model/`:
 
 ### Starter Data (deterministic seeds)
 - **Starter splits**: shipped as byte-canonical `SplitDocument` JSON in `Workouts/Resources/StarterSplits/*.split.json` with **fixed ULIDs** (shared `01DXF6DT00` prefix, frozen 2020 timestamp) and fixed content, regenerated only by `Scripts/generate_starter_splits.swift`. `SeedLibrary` (`Workouts/Seed/`) loads the catalog; **seeds are immutable** — `SyncEngine.save(split:)` transparently clones an edited seed to a fresh ULID and soft-deletes the seed, whose stub is exempt from pruning and vetoes resurrection forever (open views follow the identity swap via `sync.currentSplitID(for:)`).
-- **Auto-seed**: `SyncEngine.autoSeedIfEmpty()` writes the verbatim bundle bytes after connect, only into a verifiably empty container (no data files, no stubs) re-checked after a settle delay — wrong guesses are harmless because identical bytes make same-path conflicts empty and stubs reap resurrected seeds. The on-demand path (`SplitSeeder.seedDefaults`, "Add Starter Splits") restores deleted seeds (lifting the veto stub) or writes missing ones, skipping live names.
-- **Exercise library**: authored in `Exercise Library/` at the repo root (per-exercise `info.md`, SVG visuals, motion rigs, Python render pipeline); the app bundles the exported `Workouts/Resources/ExerciseMotions/*.motion.json` rigs, which double as the exercise picker's list (`ExerciseMotionLibrary.exerciseNames`).
+- **Auto-seed & reconcile**: after connect + reconcile, `SyncEngine.seedOrReconcile()` (deferred, settle-delayed) branches on container state so the two seeders can never both fire. An empty container → `autoSeedIfEmpty()` writes the verbatim bundle bytes (re-checked after the settle delay). A non-empty container → `reconcileSeeds()` diffs each bundled seed against its fixed-ULID file via the pure `SeedReconcilePlanner` (`Workouts/Sync/SeedReconcile.swift`): a stale revision is overwritten with current bundle bytes (a **semantic** compare with `schemaVersion` normalized — never a byte compare, since older files carry now-removed keys), a newly-shipped seed with no file and no stub is written (unless a live same-name split already exists, or a newer app version wrote the file), and a deleted seed (stub present) is left vetoed. Wrong guesses are harmless — identical bytes make same-path conflicts empty, stubs reap resurrected seeds, and the veto + name guards are re-checked right before each write. This is safe because a fixed-ULID file can never hold user content (every edit forks to a fresh ULID).
+- **Restore Starter Splits** (Settings) is the one deliberate veto lift: `SyncEngine.restoreSeeds()` removes a deleted seed's stub and rewrites the **current bundle bytes** (never the stub's old contents), still skipping seeds whose live file already exists (reconcile handles upgrades) or whose name collides with a live split; it returns the count for a brief in-Settings confirmation.
+- **Exercise library**: authored in `Exercise Library/` at the repo root (per-exercise `info.md`, SVG visuals, motion rigs, Python render pipeline); the app bundles the exported `Workouts/Resources/ExerciseMotions/*` resources — `*.motion.json` rigs, which double as the exercise picker's list (`ExerciseMotionLibrary.exerciseNames`), and `*.info.md` reference pages, parsed by `ExerciseInfo` and rendered in the Settings → Library → Exercises detail screen. Re-export both with `python3 render.py --export`.
 
 ## Guidelines
 
diff --git a/Workouts/HealthKit/WorkoutHealthWriter.swift b/Workouts/HealthKit/WorkoutHealthWriter.swift
index 3f1c3af..3f94aad 100644
--- a/Workouts/HealthKit/WorkoutHealthWriter.swift
+++ b/Workouts/HealthKit/WorkoutHealthWriter.swift
@@ -172,9 +172,15 @@ final class WorkoutHealthWriter {
         }
     }
 
+    /// The split's configured activity type, following the seed clone-on-edit
+    /// redirect (the estimate can run seconds to hours after the workout, so the
+    /// split may have forked in between). Generic strength when the split is gone.
     private func activityType(for doc: WorkoutDocument) -> WorkoutActivityType {
-        if let splitID = doc.splitID, let split = CacheMapper.fetchSplit(id: splitID, in: context) {
-            return split.activityTypeEnum
+        if let splitID = doc.splitID {
+            let resolved = syncEngine?.currentSplitID(for: splitID) ?? splitID
+            if let split = CacheMapper.fetchSplit(id: resolved, in: context) {
+                return split.activityTypeEnum
+            }
         }
         return .traditionalStrength
     }
diff --git a/Workouts/Seed/SplitSeeder.swift b/Workouts/Seed/SplitSeeder.swift
deleted file mode 100644
index 4462225..0000000
--- a/Workouts/Seed/SplitSeeder.swift
+++ /dev/null
@@ -1,32 +0,0 @@
-import Foundation
-import SwiftData
-
-/// The bundled immutable starter-split library, brought back on demand. The seeds
-/// themselves — fixed ULIDs, byte-canonical bundle JSON — live in `SeedLibrary`;
-/// editing one clones it and permanently tombstones the seed (see
-/// `SyncEngine.save(split:)`). The true first-run case is handled automatically by
-/// `SyncEngine.autoSeedIfEmpty`; this on-demand path (the "Add Starter Splits"
-/// button) is for a user who wants the starters back after removing some.
-enum SplitSeeder {
-    /// Add every starter split the user doesn't already have. For each seed:
-    ///   • skip if a live split with the same NAME exists — a user's edited clone of
-    ///     "Upper Body" must not be joined by a resurrected seed of the same name;
-    ///   • else if the seed was deleted (tombstoned), restore it (lifting the veto);
-    ///   • else write it fresh.
-    /// Seed `order` values are fixed (0–3); a collision with a user split's order is
-    /// an accepted cosmetic tie. Idempotent against double-taps and partial prior seeds.
-    @MainActor
-    static func seedDefaults(into context: ModelContext, using sync: SyncEngine) async {
-        let existing = (try? context.fetch(FetchDescriptor<Split>())) ?? []
-        let existingNames = Set(existing.map(\.name))
-
-        for seed in SeedLibrary.seeds {
-            if existingNames.contains(seed.doc.name) { continue }
-            if await sync.isTombstoned(id: seed.id) {
-                await sync.restoreSeed(seed)
-            } else {
-                await sync.writeSeed(seed)
-            }
-        }
-    }
-}
diff --git a/Workouts/Sync/DuplicateCleanup.swift b/Workouts/Sync/DuplicateCleanup.swift
new file mode 100644
index 0000000..8783ff0
--- /dev/null
+++ b/Workouts/Sync/DuplicateCleanup.swift
@@ -0,0 +1,235 @@
+import Foundation
+
+// Pure planning logic for the developer-facing "duplicate cleanup" tool. No I/O
+// and no `SyncEngine` dependency, so it's fully unit-testable in isolation:
+// `SyncEngine.scanForDuplicates()` gathers the already-decoded documents and the
+// referenced-split-id set, hands them to `DuplicateCleanupPlanner.plan(...)`, and
+// `SyncEngine.performCleanup(_:)` executes the resulting plan file by file.
+//
+// Duplicates are detected by a *content* fingerprint that deliberately ignores
+// identity (ids), timestamps, and cosmetic fields — two splits/workouts that were
+// created independently (e.g. by a sync hiccup, a restore, or manual testing) but
+// carry the same real content are duplicates even though every id differs.
+
+// MARK: - Plan
+
+struct DuplicateCleanupPlan: Sendable {
+    struct SplitGroup: Sendable, Identifiable {
+        /// Members that survive — always non-empty when the group is emitted.
+        var keep: [SplitDocument]
+        /// Members slated for deletion — always non-empty when the group is emitted.
+        var delete: [SplitDocument]
+
+        var id: String {
+            keep.isEmpty ? (delete.first?.id ?? "") : keep.map(\.id).joined(separator: ",")
+        }
+    }
+
+    struct WorkoutGroup: Sendable, Identifiable {
+        var keep: WorkoutDocument
+        var delete: [WorkoutDocument]
+
+        var id: String { keep.id }
+    }
+
+    var splitGroups: [SplitGroup]
+    var workoutGroups: [WorkoutGroup]
+
+    var isEmpty: Bool { splitGroups.isEmpty && workoutGroups.isEmpty }
+
+    /// Total number of documents this plan would delete across every group.
+    var deleteCount: Int {
+        splitGroups.reduce(0) { $0 + $1.delete.count } + workoutGroups.reduce(0) { $0 + $1.delete.count }
+    }
+}
+
+// MARK: - Planner
+
+enum DuplicateCleanupPlanner {
+    /// Builds a cleanup plan from already-decoded, already-`isReadable`-filtered
+    /// documents. `referencedSplitIDs` must include every split id any workout
+    /// (readable or quarantined) points at, plus any clone-redirect targets — the
+    /// caller (`SyncEngine.scanForDuplicates`) is responsible for assembling it.
+    static func plan(
+        splits: [SplitDocument],
+        workouts: [WorkoutDocument],
+        referencedSplitIDs: Set<String>,
+        isSeed: (String) -> Bool
+    ) -> DuplicateCleanupPlan {
+        DuplicateCleanupPlan(
+            splitGroups: planSplits(splits, referencedSplitIDs: referencedSplitIDs, isSeed: isSeed),
+            workoutGroups: planWorkouts(workouts)
+        )
+    }
+
+    // MARK: Splits
+
+    /// Hashable projection of a `MachineSetting`. The fingerprints keep the
+    /// nil / empty distinction (non-machine vs. machine-with-nothing-recorded)
+    /// and the user-defined order, both of which are real content.
+    private struct MachineSettingFingerprint: Hashable {
+        var name: String
+        var value: String
+    }
+
+    private static func fingerprint(_ settings: [MachineSetting]?) -> [MachineSettingFingerprint]? {
+        settings.map { $0.map { MachineSettingFingerprint(name: $0.name, value: $0.value) } }
+    }
+
+    /// Content-only projection of an exercise: ignores id and order (order is
+    /// captured by the parent's sort, not the element itself).
+    private struct ExerciseFingerprint: Hashable {
+        var name: String
+        var sets: Int
+        var reps: Int
+        var weight: Int
+        var loadType: Int
+        var durationSeconds: Int
+        var machineSettings: [MachineSettingFingerprint]?
+    }
+
+    /// Content-only projection of a split: ignores id, dates, color, systemImage,
+    /// order, and activityType.
+    private struct SplitFingerprint: Hashable {
+        var name: String
+        var exercises: [ExerciseFingerprint]
+    }
+
+    private static func fingerprint(_ doc: SplitDocument) -> SplitFingerprint {
+        SplitFingerprint(
+            name: doc.name.trimmingCharacters(in: .whitespacesAndNewlines),
+            exercises: doc.exercises.sorted { $0.order < $1.order }.map {
+                ExerciseFingerprint(
+                    name: $0.name, sets: $0.sets, reps: $0.reps, weight: $0.weight,
+                    loadType: $0.loadType, durationSeconds: $0.durationSeconds,
+                    machineSettings: fingerprint($0.machineSettings)
+                )
+            }
+        )
+    }
+
+    /// Survivor rules (safety-critical — see file header):
+    ///  1. A member referenced by any workout is always kept.
+    ///  2. A member that's a bundled seed is always kept.
+    ///  3. If neither rule protects anyone, the lexicographically smallest id
+    ///     (ULIDs sort chronologically) survives — deterministic across devices.
+    /// Everyone else in the group is deleted. A group with nothing to delete
+    /// (e.g. every member is protected) is dropped entirely.
+    private static func planSplits(
+        _ splits: [SplitDocument],
+        referencedSplitIDs: Set<String>,
+        isSeed: (String) -> Bool
+    ) -> [DuplicateCleanupPlan.SplitGroup] {
+        let grouped = Dictionary(grouping: splits, by: fingerprint)
+        var groups: [DuplicateCleanupPlan.SplitGroup] = []
+
+        for (_, members) in grouped where members.count > 1 {
+            var keep: [SplitDocument] = []
+            var candidates: [SplitDocument] = []
+            for member in members {
+                if referencedSplitIDs.contains(member.id) || isSeed(member.id) {
+                    keep.append(member)
+                } else {
+                    candidates.append(member)
+                }
+            }
+            if keep.isEmpty, let survivorID = candidates.map(\.id).min() {
+                keep = candidates.filter { $0.id == survivorID }
+                candidates.removeAll { $0.id == survivorID }
+            }
+            guard !candidates.isEmpty else { continue }
+            groups.append(DuplicateCleanupPlan.SplitGroup(
+                keep: keep.sorted { $0.id < $1.id },
+                delete: candidates.sorted { $0.id < $1.id }
+            ))
+        }
+
+        return groups.sorted { $0.id < $1.id }
+    }
+
+    // MARK: Workouts
+
+    /// Content-only projection of a log: ignores id and the started/completed
+    /// timestamps.
+    private struct WorkoutLogFingerprint: Hashable {
+        var exerciseName: String
+        var order: Int
+        var sets: Int
+        var reps: Int
+        var weight: Int
+        var loadType: Int
+        var durationSeconds: Int
+        var status: String
+        var currentStateIndex: Int
+        var notes: String
+        var machineSettings: [MachineSettingFingerprint]?
+    }
+
+    /// Content-only projection of a workout: ignores id, createdAt/updatedAt,
+    /// startedAt/completedAt, exact start/end time (only the calendar day of
+    /// `start` matters), and metrics.
+    private struct WorkoutFingerprint: Hashable {
+        var splitID: String
+        var splitName: String
+        var year: Int
+        var month: Int
+        var day: Int
+        var status: String
+        var logs: [WorkoutLogFingerprint]
+    }
+
+    private static func fingerprint(_ doc: WorkoutDocument) -> WorkoutFingerprint {
+        let comps = Calendar.current.dateComponents([.year, .month, .day], from: doc.start)
+        return WorkoutFingerprint(
+            splitID: doc.splitID ?? "",
+            splitName: doc.splitName ?? "",
+            year: comps.year ?? 0,
+            month: comps.month ?? 0,
+            day: comps.day ?? 0,
+            status: doc.status,
+            logs: doc.logs.sorted { $0.order < $1.order }.map {
+                WorkoutLogFingerprint(
+                    exerciseName: $0.exerciseName, order: $0.order, sets: $0.sets, reps: $0.reps,
+                    weight: $0.weight, loadType: $0.loadType, durationSeconds: $0.durationSeconds,
+                    status: $0.status, currentStateIndex: $0.currentStateIndex,
+                    notes: $0.notes ?? "",
+                    machineSettings: fingerprint($0.machineSettings)
+                )
+            }
+        )
+    }
+
+    /// Ranks a workout for survivorship — lower sorts first (wins): (1) holds the
+    /// HealthKit link (deleting that copy would cascade-delete the real Health
+    /// sample), (2) has metrics at all, (3) smallest id.
+    private static func survivorRank(_ doc: WorkoutDocument) -> (Int, Int, String) {
+        (doc.metrics?.healthKitWorkoutUUID != nil ? 0 : 1,
+         doc.metrics != nil ? 0 : 1,
+         doc.id)
+    }
+
+    /// If any member of a duplicate group is in progress, the whole group is
+    /// dropped — never touch an active workout, since the watch matches its live
+    /// run by workout id. Otherwise the survivor is picked by `survivorRank` and
+    /// everyone else is deleted.
+    private static func planWorkouts(_ workouts: [WorkoutDocument]) -> [DuplicateCleanupPlan.WorkoutGroup] {
+        let grouped = Dictionary(grouping: workouts, by: fingerprint)
+        var groups: [DuplicateCleanupPlan.WorkoutGroup] = []
+
+        for (_, members) in grouped where members.count > 1 {
+            if members.contains(where: { $0.status == WorkoutStatus.inProgress.rawValue }) { continue }
+
+            let ranked = members.sorted { a, b in
+                let ra = survivorRank(a), rb = survivorRank(b)
+                if ra.0 != rb.0 { return ra.0 < rb.0 }
+                if ra.1 != rb.1 { return ra.1 < rb.1 }
+                return ra.2 < rb.2
+            }
+            guard let survivor = ranked.first else { continue }
+            let toDelete = ranked.dropFirst().sorted { $0.id < $1.id }
+            groups.append(DuplicateCleanupPlan.WorkoutGroup(keep: survivor, delete: Array(toDelete)))
+        }
+
+        return groups.sorted { $0.id < $1.id }
+    }
+}
diff --git a/Workouts/Sync/SeedReconcile.swift b/Workouts/Sync/SeedReconcile.swift
new file mode 100644
index 0000000..2a416fd
--- /dev/null
+++ b/Workouts/Sync/SeedReconcile.swift
@@ -0,0 +1,114 @@
+import Foundation
+
+// Pure decision logic for bringing an install's on-disk starter-split library in
+// line with the current app bundle. No I/O and no `SyncEngine` dependency, so the
+// safety-critical part is fully unit-testable in isolation: `SyncEngine.reconcileSeeds()`
+// gathers the live seed-path files, stub set, and live split names, hands each seed to
+// `SeedReconcilePlanner.decision(...)`, and executes the returned skip / upgrade / write.
+//
+// Why this exists: starter seeds ship as byte-canonical `SplitDocument` JSON under
+// FIXED ULIDs (see `SeedLibrary`). `autoSeedIfEmpty` only ever writes them into a
+// verifiably empty container, so an existing install can never pick up an upgraded
+// seed revision or a newly-shipped seed. This planner decides, per seed, whether the
+// live fixed-ULID file is up to date, stale (needs the current bundle bytes), deleted
+// (vetoed), or missing (write it).
+//
+// Safety invariant this relies on: a live file at a seed's fixed ULID can NEVER hold
+// user-authored content — every user edit forks the seed to a fresh random ULID
+// (clone-on-edit), and fixed-ULID files only exist on app versions that have
+// clone-on-edit. So overwriting a seed-path file with current bundle bytes never
+// destroys user data; at worst it upgrades an older seed revision.
+
+// MARK: - Input
+
+/// Everything the planner needs to decide one seed, pre-gathered by the engine.
+struct SeedReconcileInput: Equatable {
+    /// The seed's fixed ULID.
+    let seedID: String
+    /// The bundle seed document (canonical current content).
+    let seedDoc: SplitDocument
+    /// The decoded live file currently sitting at the seed's fixed path, or `nil`
+    /// when no live file exists there (deleted, or never written).
+    let liveDoc: SplitDocument?
+    /// Whether a tombstone stub exists for this seed's id.
+    let hasStub: Bool
+}
+
+// MARK: - Decision
+
+enum SeedReconcileDecision: Equatable {
+    /// Do nothing — the reason is carried for logging and tests.
+    case skip(SeedSkipReason)
+    /// A live file exists at the seed path but differs from the bundle: overwrite it
+    /// with the verbatim bundle bytes (an older seed revision).
+    case upgrade
+    /// No live file, no veto, no name collision: write the verbatim bundle bytes (a
+    /// newly-shipped seed, or a pre-fixed-ULID install missing the file).
+    case write
+}
+
+enum SeedSkipReason: Equatable {
+    /// The live file already matches the bundle seed (schemaVersion-normalized).
+    case upToDate
+    /// The live file was written by a newer app version — never downgrade-rewrite it.
+    case quarantined
+    /// No live file, but a stub exists: the user deleted this seed. Respect the veto.
+    case vetoed
+    /// No live file and no stub, but a live split already uses this seed's name
+    /// (e.g. a legacy runtime-built or user-cloned "Upper Body"). Writing the seed
+    /// would duplicate it by name.
+    case nameCollision
+}
+
+// MARK: - Planner
+
+enum SeedReconcilePlanner {
+    /// The automatic on-connect decision for one seed (see the decision table in the
+    /// file header). `liveSplitNames` must be the names of every live split currently
+    /// in the container/cache after reconcile — the name-collision guard consults it.
+    static func decision(
+        for input: SeedReconcileInput,
+        liveSplitNames: Set<String>
+    ) -> SeedReconcileDecision {
+        if let live = input.liveDoc {
+            // A live file sits at the seed path. Never touch one a newer app version
+            // wrote (the forward-compat quarantine), otherwise compare content.
+            guard live.isReadable else { return .skip(.quarantined) }
+            return semanticallyEqual(live: live, seed: input.seedDoc)
+                ? .skip(.upToDate)
+                : .upgrade
+        }
+        // No live file at the seed path.
+        if input.hasStub { return .skip(.vetoed) }
+        if liveSplitNames.contains(input.seedDoc.name) { return .skip(.nameCollision) }
+        return .write
+    }
+
+    /// Semantic (not byte) equality of a live seed file against the bundle seed.
+    ///
+    /// A byte compare is wrong here: a container file may have been written by an
+    /// older app version, carrying extra now-removed keys and a lower `schemaVersion`.
+    /// Decoding both into the current `SplitDocument` already drops unknown keys, so
+    /// the only remaining artificial difference is the version stamp — normalize the
+    /// live doc's `schemaVersion` to the seed's before the `==` so an older wrapper of
+    /// identical content reads as up to date (no churn), while a genuine content
+    /// change reads as different (upgrade).
+    static func semanticallyEqual(live: SplitDocument, seed: SplitDocument) -> Bool {
+        var normalized = live
+        normalized.schemaVersion = seed.schemaVersion
+        return normalized == seed
+    }
+
+    /// Whether the deliberate "Restore Starter Splits" action should (re)write a seed:
+    /// only when no live file sits at its path and no live split already uses its name.
+    /// Unlike `decision(...)` a stub does NOT veto here — restore lifts the veto — but
+    /// the engine still removes the stub as a separate execution step. A seed whose
+    /// live file already exists is left for `decision(...)` to upgrade.
+    static func shouldRestore(
+        hasLiveFile: Bool,
+        seedName: String,
+        liveSplitNames: Set<String>
+    ) -> Bool {
+        !hasLiveFile && !liveSplitNames.contains(seedName)
+    }
+}
diff --git a/Workouts/Sync/SyncEngine.swift b/Workouts/Sync/SyncEngine.swift
index 5df2887..92469b7 100644
--- a/Workouts/Sync/SyncEngine.swift
+++ b/Workouts/Sync/SyncEngine.swift
@@ -11,8 +11,12 @@ enum ICloudStatus: Equatable {
 }
 
 /// Orchestrates the iCloud Drive file layer and the SwiftData cache. iCloud is
-/// the sole source of truth: every save/delete writes files only; the metadata
-/// observer (and the connect-time reconcile) is the sole mutator of the cache.
+/// the sole source of truth: every save/delete writes the file first, then
+/// mirrors the change into the cache immediately (a same-process write doesn't
+/// reliably wake the `NSMetadataQuery` observer — and never does in the
+/// simulator — so waiting on it leaves the UI blind to the user's own action).
+/// The observer and the connect-time reconcile re-apply idempotently and remain
+/// the sole channel for *remote* changes.
 @Observable
 @MainActor
 final class SyncEngine {
@@ -27,8 +31,9 @@ final class SyncEngine {
 
     /// Maps a seed's id to its clone's id after a clone-on-edit fork, so a view still
     /// holding the seed's id resolves to the live clone. In-memory only (@Observable
-    /// notifies on change); not persisted — a seed is edited at most once before it's
-    /// gone, so nothing needs to survive a relaunch.
+    /// notifies on change); not persisted — durability comes from `repointWorkouts`,
+    /// which rewrites `splitID` on the workout documents themselves at fork time.
+    /// This map only bridges views that captured the seed's id before the swap.
     private(set) var cloneRedirects: [String: String] = [:]
 
     /// Follow the redirect chain from `id` to the current live split id. A seed
@@ -154,7 +159,7 @@ final class SyncEngine {
         startMonitoring(documentsURL: store.rootURL)
         cleanupOldStubs()
         // Off the connect path so opening the gate isn't delayed by the settle wait.
-        Task { await self.autoSeedIfEmpty() }
+        Task { await self.seedOrReconcile() }
     }
 
     /// Invoked from the connecting screen when the user chooses not to keep
@@ -205,15 +210,8 @@ final class SyncEngine {
         onCacheChanged?()
     }
 
-    /// Apply a workout received from the watch. iCloud Drive stays the source of
-    /// truth (we write the file), but we also upsert the cache directly here.
-    ///
-    /// The phone's own edits drive a local view copy, so they don't need this — but a
-    /// watch-originated change has nothing else refreshing the phone UI, and a
-    /// same-process file overwrite doesn't reliably wake the `NSMetadataQuery`
-    /// observer. Upserting the doc we just wrote keeps cache and file consistent (the
-    /// observer re-applies idempotently if it does fire) and lets open phone screens
-    /// reflect watch progress live.
+    /// Apply a workout received from the watch — `save(workout:)` writes the file
+    /// and mirrors it into the cache, same as a local edit.
     func ingestFromWatch(_ doc: WorkoutDocument) async {
         // A workout deleted on the phone leaves a tombstone; a watch that missed the
         // delete may still push its stale copy. Honor the veto — never resurrect it —
@@ -224,9 +222,6 @@ final class SyncEngine {
             return
         }
         await save(workout: doc)
-        CacheMapper.upsertWorkout(doc, relativePath: doc.relativePath, into: context)
-        do { try context.save() } catch { report("Cache save failed", error) }
-        onCacheChanged?()
     }
 
     // MARK: - Public CRUD (write path: files only)
@@ -249,11 +244,12 @@ final class SyncEngine {
 
         do {
             try await store.write(doc, to: doc.relativePath)
+            CacheMapper.upsertSplit(doc, relativePath: doc.relativePath, into: context)
+            saveCacheAndNotify()
             lastSyncError = nil
         } catch {
             report("Failed to save split", error)
         }
-        // Cache updates reactively via the monitor.
         return doc.id
     }
 
@@ -279,6 +275,7 @@ final class SyncEngine {
             try context.save()
             cloneRedirects[doc.id] = clone.id
             lastSyncError = nil
+            await repointWorkouts(from: doc.id, to: clone.id)
             onCacheChanged?()
             return clone.id
         } catch {
@@ -287,10 +284,39 @@ final class SyncEngine {
         }
     }
 
+    /// Rewrite `splitID` on every workout that references `oldID`, so split lookups
+    /// (category grouping, add-exercise, plan mirroring, health estimates) keep
+    /// resolving after a seed fork — durably, across relaunches, and on the watch,
+    /// which the in-memory `cloneRedirects` map can't reach. `splitName` stays frozen
+    /// at what the workout was started as, matching rename semantics for regular
+    /// splits. Best effort per workout: a failed rewrite is reported and the redirect
+    /// map still covers it for this session.
+    private func repointWorkouts(from oldID: String, to newID: String) async {
+        guard let store else { return }
+        let referencing = (try? context.fetch(
+            FetchDescriptor<Workout>(predicate: #Predicate { $0.splitID == oldID })
+        )) ?? []
+        guard !referencing.isEmpty else { return }
+        for workout in referencing {
+            var wDoc = WorkoutDocument(from: workout)
+            wDoc.splitID = newID
+            wDoc.updatedAt = Date()
+            do {
+                try await store.write(wDoc, to: wDoc.relativePath)
+                CacheMapper.upsertWorkout(wDoc, relativePath: wDoc.relativePath, into: context)
+            } catch {
+                report("Failed to repoint workout \(wDoc.id) at edited split", error)
+            }
+        }
+        do { try context.save() } catch { report("Cache save failed", error) }
+    }
+
     func save(workout doc: WorkoutDocument) async {
         guard let store else { return }
         do {
             try await store.write(doc, to: doc.relativePath)
+            CacheMapper.upsertWorkout(doc, relativePath: doc.relativePath, into: context)
+            saveCacheAndNotify()
             lastSyncError = nil
         } catch {
             report("Failed to save workout", error)
@@ -302,11 +328,24 @@ final class SyncEngine {
     }
 
     func delete(split: Split) async {
-        await softDelete(id: split.id, kind: "split", livePath: split.jsonRelativePath)
+        let id = split.id, livePath = split.jsonRelativePath
+        await softDelete(id: id, kind: "split", livePath: livePath)
+        deleteCachedEntity(id: id)
+        saveCacheAndNotify()
     }
 
     func delete(workout: Workout) async {
-        await softDelete(id: workout.id, kind: "workout", livePath: workout.jsonRelativePath)
+        let id = workout.id, livePath = workout.jsonRelativePath
+        await softDelete(id: id, kind: "workout", livePath: livePath)
+        deleteCachedEntity(id: id)
+        saveCacheAndNotify()
+    }
+
+    /// Persist pending cache mutations and fan out the change notification — the
+    /// tail of every local write's immediate cache mirror.
+    private func saveCacheAndNotify() {
+        do { try context.save() } catch { report("Cache save failed", error) }
+        onCacheChanged?()
     }
 
     /// Writes a tombstone stub then removes the live file. Other devices learn of
@@ -502,47 +541,266 @@ final class SyncEngine {
         onCacheChanged?()
     }
 
-    /// Add one seed fresh: write its verbatim bundle bytes and upsert the cache. The
-    /// on-demand "Add Starter Splits" path uses this for a seed that's neither present
-    /// nor tombstoned.
-    func writeSeed(_ seed: SeedLibrary.Seed) async {
-        guard let store else { return }
-        do {
-            try await store.writeData(seed.data, to: seed.doc.relativePath)
-            CacheMapper.upsertSplit(seed.doc, relativePath: seed.doc.relativePath, into: context)
-            try context.save()
-            lastSyncError = nil
-        } catch {
-            report("Failed to add starter split \(seed.doc.name)", error)
+    /// Post-connect seed maintenance, deferred off the connect path. Settles first —
+    /// an empty or sparse listing right after connect can just mean the metadata index
+    /// / placeholder files haven't surfaced existing data yet — then branches so the
+    /// two seeders can never both fire: an empty container is first-run auto-seed's
+    /// alone; a non-empty one is reconciled against the current bundle.
+    private func seedOrReconcile() async {
+        // Give existing files a chance to surface before deciding empty-vs-reconcile
+        // (the same caution `autoSeedIfEmpty` also takes internally).
+        try? await Task.sleep(for: .seconds(5))
+        guard iCloudStatus == .available else { return }
+        if await containerEmpty() {
+            await autoSeedIfEmpty()
+        } else {
+            await reconcileSeeds()
         }
-        onCacheChanged?()
     }
 
-    /// Bring a previously-deleted seed back: lift its veto stub, then write its
-    /// verbatim bundle bytes. The bundle is the canonical restore source (seed content
-    /// is immutable), so this restores from the bundle rather than reconstructing from
-    /// the stub — the seed's stub is only ever a minimal veto marker. The stub is
-    /// removed first so neither a racing observer event nor a reconcile re-vetoes the
-    /// file we're about to write while the stub still exists.
-    func restoreSeed(_ seed: SeedLibrary.Seed) async {
+    /// Bring the on-disk seed set in line with the current bundle on a NON-empty
+    /// container (autoSeedIfEmpty owns the empty case). For each bundled seed, decide
+    /// via the pure `SeedReconcilePlanner`:
+    ///   • live file present, up to date          → skip
+    ///   • live file present, older revision       → overwrite with bundle bytes (upgrade)
+    ///   • live file present, newer app version     → skip (quarantine — never downgrade)
+    ///   • no live file, stub present              → skip (user deleted it; veto stands)
+    ///   • no live file, no stub, name in use       → skip (don't duplicate a same-name split)
+    ///   • no live file, no stub, name free         → write bundle bytes
+    ///
+    /// Safe even on a stale metadata index: writing bundle bytes another device also
+    /// wrote is a semantically empty conflict, and the stub + name guards are re-checked
+    /// right before each fresh write.
+    private func reconcileSeeds() async {
         guard let store, let tombstones else { return }
-        do {
-            try await tombstones.removeStub(at: "\(seed.id).json")
-            try await store.writeData(seed.data, to: seed.doc.relativePath)
-            CacheMapper.upsertSplit(seed.doc, relativePath: seed.doc.relativePath, into: context)
-            try context.save()
-            lastSyncError = nil
-        } catch {
-            report("Failed to restore starter split \(seed.doc.name)", error)
+
+        let livePaths = Set(await store.list().filter { !$0.hasPrefix("Stubs/") })
+        let stubIDs = await tombstones.listStubIDs()
+        let liveSplitNames = Set(((try? context.fetch(FetchDescriptor<Split>())) ?? []).map(\.name))
+
+        var didChange = false
+        for seed in SeedLibrary.seeds {
+            // Decode the live file at the seed's fixed path, if one exists. A file that
+            // exists but can't be read right now (evicted + download timed out) is left
+            // untouched — a later connect retries it.
+            var liveDoc: SplitDocument?
+            if livePaths.contains(seed.doc.relativePath) {
+                guard let data = try? await store.readData(from: seed.doc.relativePath),
+                      let decoded = try? DocumentCoder.decode(SplitDocument.self, from: data) else {
+                    continue
+                }
+                liveDoc = decoded
+            }
+
+            let input = SeedReconcileInput(
+                seedID: seed.id, seedDoc: seed.doc, liveDoc: liveDoc,
+                hasStub: stubIDs.contains(seed.id)
+            )
+
+            switch SeedReconcilePlanner.decision(for: input, liveSplitNames: liveSplitNames) {
+            case .skip:
+                continue
+            case .upgrade:
+                // Overwriting an existing seed-path file with canonical bundle bytes is
+                // always safe (the file can only ever be an older seed revision).
+                if await writeSeedBytes(seed) { didChange = true }
+            case .write:
+                // Re-check the veto and name guards against fresh state — the metadata
+                // index may have moved since the batch was gathered.
+                if await tombstones.stubExists(id: seed.id) { continue }
+                let names = Set(((try? context.fetch(FetchDescriptor<Split>())) ?? []).map(\.name))
+                if names.contains(seed.doc.name) { continue }
+                if await writeSeedBytes(seed) { didChange = true }
+            }
+        }
+
+        if didChange {
+            do { try context.save() } catch { report("Cache save failed", error) }
+            onCacheChanged?()
         }
-        onCacheChanged?()
     }
 
-    /// Whether a tombstone exists for `id` (placeholder-aware). The on-demand seed
-    /// path checks this to restore rather than re-create a deleted seed.
-    func isTombstoned(id: String) async -> Bool {
-        guard let tombstones else { return false }
-        return await tombstones.stubExists(id: id)
+    /// Force-restore the starter library on explicit user request ("Restore Starter
+    /// Splits"). For each seed with no live file and no live same-name split, lift its
+    /// veto stub if present — the ONE place the forever-veto is deliberately lifted —
+    /// and write the CURRENT bundle bytes (not the stub's old contents; the bundle is
+    /// the canonical restore source). Seeds whose live file already exists are left for
+    /// `reconcileSeeds` to upgrade. Returns how many seeds were (re)written.
+    @discardableResult
+    func restoreSeeds() async -> Int {
+        guard let store, let tombstones else { return 0 }
+
+        let livePaths = Set(await store.list().filter { !$0.hasPrefix("Stubs/") })
+
+        var restored = 0
+        for seed in SeedLibrary.seeds {
+            let liveNames = Set(((try? context.fetch(FetchDescriptor<Split>())) ?? []).map(\.name))
+            guard SeedReconcilePlanner.shouldRestore(
+                hasLiveFile: livePaths.contains(seed.doc.relativePath),
+                seedName: seed.doc.name,
+                liveSplitNames: liveNames
+            ) else { continue }
+
+            do {
+                // Lift the veto: drop the seed's tombstone stub if one exists, then
+                // write the verbatim bundle bytes.
+                if await tombstones.stubExists(id: seed.id) {
+                    try await tombstones.removeStub(at: "\(seed.id).json")
+                }
+                try await store.writeData(seed.data, to: seed.doc.relativePath)
+                CacheMapper.upsertSplit(seed.doc, relativePath: seed.doc.relativePath, into: context)
+                restored += 1
+                lastSyncError = nil
+            } catch {
+                report("Failed to restore starter split \(seed.doc.name)", error)
+            }
+        }
+
+        if restored > 0 {
+            do { try context.save() } catch { report("Cache save failed", error) }
+            onCacheChanged?()
+        }
+        return restored
+    }
+
+    /// Write a seed's verbatim bundle bytes and mirror it into the cache. Returns
+    /// whether the write succeeded (so the caller can flush + notify once at the end).
+    @discardableResult
+    private func writeSeedBytes(_ seed: SeedLibrary.Seed) async -> Bool {
+        guard let store else { return false }
+        do {
+            try await store.writeData(seed.data, to: seed.doc.relativePath)
+            CacheMapper.upsertSplit(seed.doc, relativePath: seed.doc.relativePath, into: context)
+            lastSyncError = nil
+            return true
+        } catch {
+            report("Failed to reconcile starter split \(seed.doc.name)", error)
+            return false
+        }
+    }
+
+    // MARK: - Duplicate cleanup (dev)
+
+    enum DuplicateScanError: Error, Sendable {
+        case notConnected
+        case unreadableFiles([String])
+    }
+
+    /// Scans every live (non-stub) document and builds a plan for exact-content
+    /// duplicate splits/workouts (see `DuplicateCleanupPlanner`). Read-only — no
+    /// files are touched. Fails closed: if ANY file can't be read or decoded, no
+    /// plan is produced, because an unreadable workout could reference any split
+    /// and silently proceeding could misjudge that split as unreferenced.
+    func scanForDuplicates() async throws -> DuplicateCleanupPlan {
+        guard let store else { throw DuplicateScanError.notConnected }
+
+        let paths = await store.list().filter { !$0.hasPrefix("Stubs/") }
+
+        var splits: [SplitDocument] = []
+        var workouts: [WorkoutDocument] = []
+        var referencedSplitIDs = Set<String>()
+        var failedPaths: [String] = []
+
+        for path in paths {
+            let data: Data
+            do {
+                data = try await store.readData(from: path)
+            } catch {
+                log.error("scanForDuplicates: read failed for \(path, privacy: .public): \(error)")
+                failedPaths.append(path)
+                continue
+            }
+
+            if path.hasPrefix("Splits/") {
+                do {
+                    let doc = try DocumentCoder.decode(SplitDocument.self, from: data)
+                    // Quarantined (written by a newer app version) splits are never
+                    // judged as duplicates or deleted.
+                    if doc.isReadable { splits.append(doc) }
+                } catch {
+                    log.error("scanForDuplicates: decode failed for \(path, privacy: .public): \(error)")
+                    failedPaths.append(path)
+                }
+            } else if path.hasPrefix("Workouts/") {
+                do {
+                    let doc = try DocumentCoder.decode(WorkoutDocument.self, from: data)
+                    // A quarantined workout's splitID still protects that split from
+                    // deletion even though the workout itself is excluded below.
+                    if let splitID = doc.splitID {
+                        referencedSplitIDs.insert(splitID)
+                        referencedSplitIDs.insert(currentSplitID(for: splitID))
+                    }
+                    if doc.isReadable { workouts.append(doc) }
+                } catch {
+                    log.error("scanForDuplicates: decode failed for \(path, privacy: .public): \(error)")
+                    failedPaths.append(path)
+                }
+            }
+        }
+
+        guard failedPaths.isEmpty else {
+            throw DuplicateScanError.unreadableFiles(failedPaths.sorted())
+        }
+
+        referencedSplitIDs.formUnion(cloneRedirects.values)
+
+        return DuplicateCleanupPlanner.plan(
+            splits: splits,
+            workouts: workouts,
+            referencedSplitIDs: referencedSplitIDs,
+            isSeed: SeedLibrary.isSeed(id:)
+        )
+    }
+
+    /// Executes a previously scanned plan. Every deletion is re-checked
+    /// immediately beforehand against the *current* cache state — a watch push or
+    /// another device's write can land between scan and delete — so nothing
+    /// referenced or active is ever removed even if the plan is a few seconds stale.
+    func performCleanup(_ plan: DuplicateCleanupPlan) async -> (splitsDeleted: Int, workoutsDeleted: Int, skipped: Int) {
+        var splitsDeleted = 0
+        var workoutsDeleted = 0
+        var skipped = 0
+
+        for group in plan.splitGroups {
+            for doc in group.delete {
+                let splitID = doc.id
+                if SeedLibrary.isSeed(id: splitID) {
+                    skipped += 1
+                    continue
+                }
+                let referencingWorkouts = (try? context.fetch(
+                    FetchDescriptor<Workout>(predicate: #Predicate { $0.splitID == splitID })
+                )) ?? []
+                guard referencingWorkouts.isEmpty else {
+                    skipped += 1
+                    continue
+                }
+                if let cached = CacheMapper.fetchSplit(id: splitID, in: context) {
+                    await softDelete(id: splitID, kind: "split", livePath: cached.jsonRelativePath)
+                } else {
+                    await softDelete(id: splitID, kind: "split", livePath: doc.relativePath)
+                }
+                deleteCachedEntity(id: splitID)
+                splitsDeleted += 1
+            }
+        }
+
+        for group in plan.workoutGroups {
+            for doc in group.delete {
+                let cached = CacheMapper.fetchWorkout(id: doc.id, in: context)
+                if cached?.status == .inProgress {
+                    skipped += 1
+                    continue
+                }
+                let livePath = cached?.jsonRelativePath ?? doc.relativePath
+                await softDelete(id: doc.id, kind: "workout", livePath: livePath)
+                deleteCachedEntity(id: doc.id)
+                workoutsDeleted += 1
+            }
+        }
+
+        saveCacheAndNotify()
+        return (splitsDeleted, workoutsDeleted, skipped)
     }
 
     // MARK: - Error Reporting
diff --git a/Workouts/Views/Settings/DuplicateCleanupView.swift b/Workouts/Views/Settings/DuplicateCleanupView.swift
new file mode 100644
index 0000000..1f13c43
--- /dev/null
+++ b/Workouts/Views/Settings/DuplicateCleanupView.swift
@@ -0,0 +1,281 @@
+//
+// DuplicateCleanupView.swift
+// Workouts
+//
+// Copyright 2025 Rouslan Zenetl. All Rights Reserved.
+//
+
+import SwiftUI
+
+/// Developer-facing tool: scans iCloud Drive for splits/workouts that are exact
+/// content duplicates (see `DuplicateCleanupPlanner`) — typically the residue of
+/// testing, a restore, or a sync hiccup — and offers to delete the extras. Never
+/// touches a split referenced by a workout, a bundled starter split, or an
+/// in-progress workout.
+struct DuplicateCleanupView: View {
+    @Environment(SyncEngine.self) private var sync
+
+    private enum ScanFailure {
+        case unreadableFiles([String])
+        case other(String)
+    }
+
+    private struct CleanupSummary {
+        var splitsDeleted: Int
+        var workoutsDeleted: Int
+        var skipped: Int
+    }
+
+    private enum Phase {
+        case idle
+        case scanning
+        case results(DuplicateCleanupPlan)
+        case failed(ScanFailure)
+        case deleting
+        case done(CleanupSummary)
+    }
+
+    @State private var phase: Phase = .idle
+    @State private var pendingPlan: DuplicateCleanupPlan?
+
+    var body: some View {
+        content
+            .navigationTitle("Clean Up Duplicates")
+            .confirmationDialog(
+                "Delete \(pendingPlan?.deleteCount ?? 0) Duplicate\((pendingPlan?.deleteCount ?? 0) == 1 ? "" : "s")?",
+                isPresented: Binding(
+                    get: { pendingPlan != nil },
+                    set: { if !$0 { pendingPlan = nil } }
+                ),
+                titleVisibility: .visible,
+                presenting: pendingPlan
+            ) { plan in
+                Button("Delete", role: .destructive) {
+                    pendingPlan = nil
+                    Task { await performDelete(plan) }
+                }
+                Button("Cancel", role: .cancel) {
+                    pendingPlan = nil
+                }
+            } message: { _ in
+                Text("This permanently deletes the duplicate copies shown below. Referenced splits, starter splits, and in-progress workouts are always kept.")
+            }
+    }
+
+    @ViewBuilder
+    private var content: some View {
+        switch phase {
+        case .idle:
+            idleView
+        case .scanning:
+            ProgressView("Scanning…")
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+        case .results(let plan):
+            resultsView(plan)
+        case .failed(let failure):
+            failureView(failure)
+        case .deleting:
+            ProgressView("Deleting…")
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+        case .done(let summary):
+            doneView(summary)
+        }
+    }
+
+    // MARK: - Idle
+
+    private var idleView: some View {
+        Form {
+            Section {
+                Button {
+                    Task { await scan() }
+                } label: {
+                    Label("Scan for Duplicates", systemImage: "magnifyingglass")
+                }
+            } footer: {
+                Text("Looks for splits and workouts that are exact content duplicates — for example, left over from testing or a sync hiccup — and offers to delete the extra copies. Splits referenced by a workout, starter splits, and in-progress workouts are never deleted.")
+            }
+        }
+    }
+
+    // MARK: - Results
+
+    @ViewBuilder
+    private func resultsView(_ plan: DuplicateCleanupPlan) -> some View {
+        if plan.isEmpty {
+            ContentUnavailableView(
+                "No Duplicates Found",
+                systemImage: "checkmark.circle",
+                description: Text("Everything in iCloud looks unique.")
+            )
+        } else {
+            List {
+                if !plan.splitGroups.isEmpty {
+                    Section("Duplicate Splits") {
+                        ForEach(plan.splitGroups) { group in
+                            splitGroupRow(group)
+                        }
+                    }
+                }
+                if !plan.workoutGroups.isEmpty {
+                    Section("Duplicate Workouts") {
+                        ForEach(plan.workoutGroups) { group in
+                            workoutGroupRow(group)
+                        }
+                    }
+                }
+                Section {
+                    Button(role: .destructive) {
+                        pendingPlan = plan
+                    } label: {
+                        HStack {
+                            Spacer()
+                            Text("Delete \(plan.deleteCount) Duplicate\(plan.deleteCount == 1 ? "" : "s")")
+                            Spacer()
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    private func splitGroupRow(_ group: DuplicateCleanupPlan.SplitGroup) -> some View {
+        VStack(alignment: .leading, spacing: 6) {
+            ForEach(group.keep) { doc in
+                memberRow(name: doc.name, detail: "\(doc.exercises.count) exercises", id: doc.id, isKeep: true)
+            }
+            ForEach(group.delete) { doc in
+                memberRow(name: doc.name, detail: "\(doc.exercises.count) exercises", id: doc.id, isKeep: false)
+            }
+        }
+        .padding(.vertical, 4)
+    }
+
+    private func workoutGroupRow(_ group: DuplicateCleanupPlan.WorkoutGroup) -> some View {
+        VStack(alignment: .leading, spacing: 6) {
+            memberRow(
+                name: group.keep.splitName ?? "(no split)",
+                detail: group.keep.start.formattedDate(),
+                id: group.keep.id,
+                isKeep: true
+            )
+            ForEach(group.delete) { doc in
+                memberRow(
+                    name: doc.splitName ?? "(no split)",
+                    detail: doc.start.formattedDate(),
+                    id: doc.id,
+                    isKeep: false
+                )
+            }
+        }
+        .padding(.vertical, 4)
+    }
+
+    private func memberRow(name: String, detail: String, id: String, isKeep: Bool) -> some View {
+        HStack {
+            VStack(alignment: .leading, spacing: 2) {
+                Text(name)
+                Text("\(detail) · id …\(id.suffix(6))")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+            }
+            Spacer()
+            if isKeep {
+                Label("Keep", systemImage: "checkmark.circle")
+                    .foregroundStyle(.secondary)
+            } else {
+                Label("Delete", systemImage: "trash")
+                    .foregroundStyle(.red)
+            }
+        }
+    }
+
+    // MARK: - Failure
+
+    @ViewBuilder
+    private func failureView(_ failure: ScanFailure) -> some View {
+        switch failure {
+        case .unreadableFiles(let paths):
+            List {
+                Section {
+                    Label(
+                        "Scan aborted: \(paths.count) file\(paths.count == 1 ? "" : "s") could not be read. Nothing was deleted.",
+                        systemImage: "exclamationmark.triangle.fill"
+                    )
+                    .foregroundStyle(.orange)
+                }
+                Section("Unreadable Files") {
+                    ForEach(paths, id: \.self) { path in
+                        Text(path)
+                            .font(.system(.footnote, design: .monospaced))
+                    }
+                }
+                Section {
+                    Button("Rescan") {
+                        Task { await scan() }
+                    }
+                }
+            }
+        case .other(let message):
+            List {
+                Section {
+                    Label(message, systemImage: "exclamationmark.triangle.fill")
+                        .foregroundStyle(.orange)
+                }
+                Section {
+                    Button("Try Again") {
+                        Task { await scan() }
+                    }
+                }
+            }
+        }
+    }
+
+    // MARK: - Done
+
+    private func doneView(_ summary: CleanupSummary) -> some View {
+        List {
+            Section {
+                Label(
+                    "Deleted \(summary.splitsDeleted) split\(summary.splitsDeleted == 1 ? "" : "s"), \(summary.workoutsDeleted) workout\(summary.workoutsDeleted == 1 ? "" : "s"). \(summary.skipped) skipped (referenced or active).",
+                    systemImage: "checkmark.circle.fill"
+                )
+                .foregroundStyle(.green)
+            }
+            Section {
+                Button("Scan Again") {
+                    Task { await scan() }
+                }
+            }
+        }
+    }
+
+    // MARK: - Actions
+
+    private func scan() async {
+        phase = .scanning
+        do {
+            let plan = try await sync.scanForDuplicates()
+            phase = .results(plan)
+        } catch let error as SyncEngine.DuplicateScanError {
+            switch error {
+            case .notConnected:
+                phase = .failed(.other("iCloud isn't connected yet. Try again in a moment."))
+            case .unreadableFiles(let paths):
+                phase = .failed(.unreadableFiles(paths))
+            }
+        } catch {
+            phase = .failed(.other(error.localizedDescription))
+        }
+    }
+
+    private func performDelete(_ plan: DuplicateCleanupPlan) async {
+        phase = .deleting
+        let result = await sync.performCleanup(plan)
+        phase = .done(CleanupSummary(
+            splitsDeleted: result.splitsDeleted,
+            workoutsDeleted: result.workoutsDeleted,
+            skipped: result.skipped
+        ))
+    }
+}
diff --git a/Workouts/Views/Settings/SettingsView.swift b/Workouts/Views/Settings/SettingsView.swift
index 721fdc1..3ab4714 100644
--- a/Workouts/Views/Settings/SettingsView.swift
+++ b/Workouts/Views/Settings/SettingsView.swift
@@ -6,20 +6,18 @@
 //
 
 import SwiftUI
-import SwiftData
 import IndieAbout
 
 struct SettingsView: View {
     @Environment(SyncEngine.self) private var sync
-    @Environment(\.modelContext) private var modelContext
     @Environment(AppServices.self) private var services
 
-    @Query(sort: \Split.order) private var splits: [Split]
-
     @AppStorage("restSeconds") private var restSeconds: Int = 45
     @AppStorage("doneCountdownSeconds") private var doneCountdownSeconds: Int = 5
     @AppStorage("weightUnit") private var weightUnit: WeightUnit = .lb
-    @State private var showingAddSplitSheet = false
+
+    @State private var isRestoringSeeds = false
+    @State private var restoreSeedsMessage: String?
 
     var body: some View {
         NavigationStack {
@@ -53,62 +51,50 @@ struct SettingsView: View {
                     Text("How long the watch waits on the finish screen before completing an exercise automatically.")
                 }
 
-                // MARK: - Splits Section
-                Section(header: Text("Splits")) {
-                    if splits.isEmpty {
-                        HStack {
-                            Spacer()
-                            VStack(spacing: 8) {
-                                Image(systemName: "dumbbell.fill")
-                                    .font(.largeTitle)
-                                    .foregroundColor(.secondary)
-                                Text("No Splits Yet")
-                                    .font(.headline)
-                                    .foregroundColor(.secondary)
-                                Text("Create a split to organize your workout routine.")
-                                    .font(.caption)
-                                    .foregroundColor(.secondary)
-                                    .multilineTextAlignment(.center)
-                            }
-                            .padding(.vertical)
-                            Spacer()
+                // MARK: - Library Section
+                Section(header: Text("Library")) {
+                    NavigationLink {
+                        SplitListView()
+                    } label: {
+                        Label("Splits", systemImage: "dumbbell.fill")
+                    }
+
+                    NavigationLink {
+                        ExerciseLibraryView()
+                    } label: {
+                        Label("Exercises", systemImage: "figure.strengthtraining.traditional")
+                    }
+                }
+
+                // MARK: - Starter Splits Section
+                Section {
+                    Button {
+                        Task {
+                            isRestoringSeeds = true
+                            restoreSeedsMessage = nil
+                            let n = await sync.restoreSeeds()
+                            isRestoringSeeds = false
+                            restoreSeedsMessage = n == 0
+                                ? "All starter splits are already present."
+                                : "Restored \(n) starter split\(n == 1 ? "" : "s")."
                         }
+                    } label: {
+                        HStack {
+                            Label("Restore Starter Splits", systemImage: "arrow.counterclockwise")
+                            if isRestoringSeeds {
+                                Spacer()
+                                ProgressView()
+                            }
+                        }
+                    }
+                    .disabled(isRestoringSeeds || sync.iCloudStatus != .available)
+                } header: {
+                    Text("Starter Splits")
+                } footer: {
+                    if let restoreSeedsMessage {
+                        Text(restoreSeedsMessage)
                     } else {
-                        ForEach(splits) { split in
-                            NavigationLink {
-                                SplitDetailView(split: split)
-                            } label: {
-                                HStack {
-                                    Image(systemName: split.systemImage)
-                                        .foregroundColor(Color.color(from: split.color))
-                                        .frame(width: 24)
-                                    Text(split.name)
-                                    Spacer()
-                                    Text("\(split.exercisesArray.count)")
-                                        .foregroundColor(.secondary)
-                                }
-                            }
-                        }
-                    }
-
-                    Button {
-                        showingAddSplitSheet = true
-                    } label: {
-                        HStack {
-                            Image(systemName: "plus.circle.fill")
-                                .foregroundColor(.accentColor)
-                            Text("Add Split")
-                        }
-                    }
-
-                    Button {
-                        Task { await SplitSeeder.seedDefaults(into: modelContext, using: sync) }
-                    } label: {
-                        HStack {
-                            Image(systemName: "wand.and.sparkles")
-                                .foregroundColor(.accentColor)
-                            Text("Add Starter Splits")
-                        }
+                        Text("Brings back the bundled starter splits you've deleted. Splits you've edited or created are never touched.")
                     }
                 }
 
@@ -133,6 +119,17 @@ struct SettingsView: View {
                     Text("iCloud Sync")
                 }
 
+                // MARK: - Developer Section
+                Section {
+                    NavigationLink {
+                        DuplicateCleanupView()
+                    } label: {
+                        Label("Clean Up Duplicates", systemImage: "wrench.and.screwdriver")
+                    }
+                } header: {
+                    Text("Developer")
+                }
+
                 // MARK: - About Section
                 Section {
                     IndieAbout(configuration: AppInfoConfiguration(
@@ -144,9 +141,6 @@ struct SettingsView: View {
                 }
             }
             .navigationTitle("Settings")
-            .sheet(isPresented: $showingAddSplitSheet) {
-                SplitAddEditView(split: nil)
-            }
             .onChange(of: restSeconds) { _, _ in services.watchBridge.pushAll() }
             .onChange(of: doneCountdownSeconds) { _, _ in services.watchBridge.pushAll() }
             .onChange(of: weightUnit) { _, _ in services.watchBridge.pushAll() }
diff --git a/WorkoutsTests/DuplicateCleanupPlannerTests.swift b/WorkoutsTests/DuplicateCleanupPlannerTests.swift
new file mode 100644
index 0000000..1007324
--- /dev/null
+++ b/WorkoutsTests/DuplicateCleanupPlannerTests.swift
@@ -0,0 +1,198 @@
+import Foundation
+import Testing
+@testable import Workouts
+
+/// Locks the survivor rules of `DuplicateCleanupPlanner` — the safety-critical
+/// part of the developer duplicate-cleanup tool. Referenced-split and seed
+/// protection must always beat "earliest ULID wins," an in-progress workout must
+/// never be touched, and the HealthKit-link holder must always survive (deleting
+/// it would cascade-delete the real Health sample). Fixed 26-char ULID-like ids
+/// keep every assertion deterministic.
+struct DuplicateCleanupPlannerTests {
+
+    // MARK: - Fixtures
+
+    private func id(_ n: Int) -> String {
+        "01TESTID" + String(repeating: "0", count: 16) + String(format: "%02d", n)
+    }
+
+    private func exercise(
+        name: String = "Bench Press", order: Int = 0, sets: Int = 3, reps: Int = 10,
+        weight: Int = 100, loadType: Int = LoadType.weight.rawValue, duration: Int = 0
+    ) -> ExerciseDocument {
+        ExerciseDocument(
+            id: "EX-\(name)-\(order)", name: name, order: order, sets: sets, reps: reps, weight: weight,
+            loadType: loadType, durationSeconds: duration
+        )
+    }
+
+    private func split(
+        id splitID: String, name: String = "Push Day", exercises: [ExerciseDocument]? = nil,
+        createdAt: Date = Date(timeIntervalSince1970: 0)
+    ) -> SplitDocument {
+        SplitDocument(
+            schemaVersion: SplitDocument.currentSchemaVersion, id: splitID, name: name, color: "indigo",
+            systemImage: "dumbbell.fill", order: 0, createdAt: createdAt, updatedAt: createdAt,
+            exercises: exercises ?? [exercise()], activityType: nil
+        )
+    }
+
+    private func log(name: String = "Bench Press", order: Int = 0, date: Date = Date(timeIntervalSince1970: 0)) -> WorkoutLogDocument {
+        WorkoutLogDocument(
+            id: "LOG-\(name)-\(order)", exerciseName: name, order: order, sets: 3, reps: 10, weight: 100,
+            loadType: LoadType.weight.rawValue, durationSeconds: 0, currentStateIndex: 0,
+            status: WorkoutStatus.completed.rawValue, notes: nil, date: date
+        )
+    }
+
+    private func workout(
+        id workoutID: String, splitID: String? = "SPLIT-1", splitName: String? = "Push Day",
+        start: Date, status: String = WorkoutStatus.completed.rawValue,
+        logs: [WorkoutLogDocument]? = nil, metrics: WorkoutMetrics? = nil
+    ) -> WorkoutDocument {
+        WorkoutDocument(
+            schemaVersion: WorkoutDocument.currentSchemaVersion, id: workoutID, splitID: splitID,
+            splitName: splitName, start: start, end: nil, status: status, createdAt: start, updatedAt: start,
+            logs: logs ?? [log(date: start)], metrics: metrics
+        )
+    }
+
+    /// A fixed calendar day/time built via `Calendar.current`, so it agrees with
+    /// the planner's own `Calendar.current`-based day bucketing regardless of the
+    /// test runner's time zone.
+    private func fixedDate(day: Int = 15, hour: Int = 9) -> Date {
+        var comps = DateComponents()
+        comps.year = 2024
+        comps.month = 3
+        comps.day = day
+        comps.hour = hour
+        return Calendar.current.date(from: comps)!
+    }
+
+    private func metrics(healthKitWorkoutUUID: String? = nil, recordedAt: Date = Date(timeIntervalSince1970: 0)) -> WorkoutMetrics {
+        WorkoutMetrics(
+            activeEnergyKcal: nil, avgHeartRate: nil, maxHeartRate: nil, minHeartRate: nil,
+            totalVolume: nil, hrZoneSeconds: nil, healthKitWorkoutUUID: healthKitWorkoutUUID,
+            source: .watch, recordedAt: recordedAt
+        )
+    }
+
+    // MARK: - Split survivor rules
+
+    @Test func identicalUnreferencedSplitsKeepEarliestULID() {
+        let earlier = split(id: id(1))
+        let later = split(id: id(2))
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [later, earlier], workouts: [], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.splitGroups.count == 1)
+        #expect(plan.splitGroups[0].keep.map(\.id) == [id(1)])
+        #expect(plan.splitGroups[0].delete.map(\.id) == [id(2)])
+    }
+
+    /// Referenced-protection must override "earliest ULID wins": a later,
+    /// referenced split survives and the earlier, unreferenced duplicate is the
+    /// one deleted — the opposite of the no-protection tiebreak.
+    @Test func referencedProtectionOverridesEarliestWins() {
+        let earlier = split(id: id(1)) // unreferenced, would win the earliest-id tiebreak alone
+        let later = split(id: id(2))   // referenced by a workout
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [earlier, later], workouts: [], referencedSplitIDs: [id(2)], isSeed: { _ in false }
+        )
+        #expect(plan.splitGroups.count == 1)
+        #expect(plan.splitGroups[0].keep.map(\.id) == [id(2)])
+        #expect(plan.splitGroups[0].delete.map(\.id) == [id(1)])
+    }
+
+    @Test func seedMemberNeverDeleted() throws {
+        let seedSplit = split(id: id(1))
+        let duplicate = split(id: id(2))
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [seedSplit, duplicate], workouts: [], referencedSplitIDs: [],
+            isSeed: { $0 == id(1) }
+        )
+        let group = try #require(plan.splitGroups.first)
+        #expect(group.keep.map(\.id) == [id(1)])
+        #expect(group.delete.map(\.id) == [id(2)])
+        #expect(!group.delete.contains { $0.id == id(1) })
+    }
+
+    @Test func differingExerciseContentNotGrouped() {
+        let a = split(id: id(1), exercises: [exercise(weight: 100)])
+        let b = split(id: id(2), exercises: [exercise(weight: 105)])
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [a, b], workouts: [], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.splitGroups.isEmpty)
+    }
+
+    /// Machine comfort settings are real content: splits identical except for a
+    /// setting value — or for the nil (non-machine) vs. empty (machine, nothing
+    /// recorded) distinction — must not be judged duplicates.
+    @Test func differingMachineSettingsNotGrouped() {
+        var lowSeat = exercise()
+        lowSeat.machineSettings = [MachineSetting(name: "Seat Height", value: "4")]
+        var highSeat = exercise()
+        highSeat.machineSettings = [MachineSetting(name: "Seat Height", value: "5")]
+        var machineNothingRecorded = exercise()
+        machineNothingRecorded.machineSettings = []
+
+        let a = split(id: id(1), exercises: [lowSeat])
+        let b = split(id: id(2), exercises: [highSeat])
+        let c = split(id: id(3), exercises: [machineNothingRecorded])
+        let d = split(id: id(4)) // machineSettings nil — not a machine exercise
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [a, b, c, d], workouts: [], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.splitGroups.isEmpty)
+    }
+
+    // MARK: - Workout grouping / survivor rules
+
+    @Test func sameDayWorkoutsDifferingOnlyInIDsAndTimestampsAreGrouped() {
+        let day = fixedDate(hour: 9)
+        let sameDayLater = fixedDate(hour: 20)
+        let w1 = workout(id: id(1), start: day)
+        let w2 = workout(id: id(2), start: sameDayLater)
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [], workouts: [w1, w2], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.workoutGroups.count == 1)
+        #expect(plan.workoutGroups[0].keep.id == id(1))
+        #expect(plan.workoutGroups[0].delete.map(\.id) == [id(2)])
+    }
+
+    @Test func differentDaysNotGrouped() {
+        let w1 = workout(id: id(1), start: fixedDate(day: 15))
+        let w2 = workout(id: id(2), start: fixedDate(day: 16))
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [], workouts: [w1, w2], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.workoutGroups.isEmpty)
+    }
+
+    @Test func inProgressMemberDropsEntireGroup() {
+        let start = fixedDate()
+        let w1 = workout(id: id(1), start: start, status: WorkoutStatus.inProgress.rawValue)
+        let w2 = workout(id: id(2), start: start, status: WorkoutStatus.inProgress.rawValue)
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [], workouts: [w1, w2], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        #expect(plan.workoutGroups.isEmpty)
+    }
+
+    /// The HealthKit-link holder must survive even though the other copy has the
+    /// lexicographically smaller (earlier) id — deleting the link holder would
+    /// cascade-delete the real Health sample.
+    @Test func healthKitLinkHolderSurvivesOverEarlierULID() throws {
+        let start = fixedDate()
+        let earlierNoLink = workout(id: id(1), start: start, metrics: nil)
+        let laterWithLink = workout(id: id(2), start: start, metrics: metrics(healthKitWorkoutUUID: "HK-UUID"))
+        let plan = DuplicateCleanupPlanner.plan(
+            splits: [], workouts: [earlierNoLink, laterWithLink], referencedSplitIDs: [], isSeed: { _ in false }
+        )
+        let group = try #require(plan.workoutGroups.first)
+        #expect(group.keep.id == id(2))
+        #expect(group.delete.map(\.id) == [id(1)])
+    }
+}
diff --git a/WorkoutsTests/SeedReconcilePlannerTests.swift b/WorkoutsTests/SeedReconcilePlannerTests.swift
new file mode 100644
index 0000000..f89456a
--- /dev/null
+++ b/WorkoutsTests/SeedReconcilePlannerTests.swift
@@ -0,0 +1,137 @@
+import Foundation
+import Testing
+import IndieSync
+@testable import Workouts
+
+/// Locks the decision table of `SeedReconcilePlanner` — the safety-critical logic that
+/// upgrades stale starter-seed revisions and adds newly-shipped seeds on an existing
+/// install without ever duplicating a user's split, resurrecting a deleted seed, or
+/// downgrade-rewriting a newer app version's file. All fixtures are plain structs so
+/// every assertion is a pure, deterministic function of the inputs.
+struct SeedReconcilePlannerTests {
+
+    // MARK: - Fixtures
+
+    private func exercise(
+        name: String, order: Int = 0, sets: Int = 3, reps: Int = 10, weight: Int = 100
+    ) -> ExerciseDocument {
+        ExerciseDocument(
+            id: "EX-\(name)-\(order)", name: name, order: order, sets: sets, reps: reps,
+            weight: weight, loadType: LoadType.weight.rawValue, durationSeconds: 0
+        )
+    }
+
+    /// A seed-shaped split at the current schema version, with a fixed frozen date so
+    /// two builds of "the same" content compare equal.
+    private func seed(
+        id: String = "01DXF6DT0038BDC2WC3EVX8ZJ5",
+        name: String = "Upper Body",
+        schemaVersion: Int = SplitDocument.currentSchemaVersion,
+        exercises: [ExerciseDocument]? = nil
+    ) -> SplitDocument {
+        SplitDocument(
+            schemaVersion: schemaVersion, id: id, name: name, color: "indigo",
+            systemImage: "dumbbell.fill", order: 0,
+            createdAt: Date(timeIntervalSince1970: 0), updatedAt: Date(timeIntervalSince1970: 0),
+            exercises: exercises ?? [exercise(name: "Bench Press")], activityType: nil
+        )
+    }
+
+    // MARK: - Live file present
+
+    /// An older app version wrote this seed at schemaVersion 1 (and, on disk, carried
+    /// extra now-removed keys — which decode into the current struct as simply absent).
+    /// The content is otherwise identical, so normalizing the version stamp must make it
+    /// read as up to date: no churn, no rewrite.
+    @Test func semanticEqualitySkipsAcrossSchemaVersions() {
+        let bundle = seed()                 // current schemaVersion
+        var live = bundle
+        live.schemaVersion = 1              // older wrapper, same content
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: live, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: []) == .skip(.upToDate))
+    }
+
+    /// The bundle seed gained an exercise since this install wrote its file — a real
+    /// content change must upgrade (overwrite with current bundle bytes), even though
+    /// the live file is a lower schema version.
+    @Test func contentChangeUpgrades() {
+        let bundle = seed(exercises: [exercise(name: "Bench Press"), exercise(name: "Overhead Press", order: 1)])
+        var live = seed(exercises: [exercise(name: "Bench Press")])   // one fewer exercise
+        live.schemaVersion = 1
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: live, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: []) == .upgrade)
+    }
+
+    /// A weight tweak alone is enough of a content change to upgrade.
+    @Test func exerciseWeightChangeUpgrades() {
+        let bundle = seed(exercises: [exercise(name: "Bench Press", weight: 135)])
+        let live = seed(exercises: [exercise(name: "Bench Press", weight: 115)])
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: live, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: []) == .upgrade)
+    }
+
+    /// A live file written by a NEWER app version (schemaVersion above current) is
+    /// quarantined — never downgrade-rewrite it, even though it differs.
+    @Test func newerSchemaFileIsQuarantined() {
+        let bundle = seed()
+        var live = seed(exercises: [exercise(name: "Something New")])
+        live.schemaVersion = SplitDocument.currentSchemaVersion + 1
+        #expect(!live.isReadable)   // guards the premise
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: live, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: []) == .skip(.quarantined))
+    }
+
+    // MARK: - No live file
+
+    /// No live file but a stub exists → the user deleted this seed. The veto stands.
+    @Test func stubVetoesResurrection() {
+        let bundle = seed()
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: nil, hasStub: true)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: []) == .skip(.vetoed))
+    }
+
+    /// No live file, no stub, but a live split (a legacy runtime-built or user-cloned
+    /// "Upper Body") already uses the seed's name → writing it would duplicate by name.
+    @Test func nameCollisionSkips() {
+        let bundle = seed(name: "Upper Body")
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: nil, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: ["Upper Body", "Core"]) == .skip(.nameCollision))
+    }
+
+    /// No live file, no stub, no same-name split → a genuinely missing seed (newly
+    /// shipped, or a pre-fixed-ULID install) gets written.
+    @Test func missingSeedIsWritten() {
+        let bundle = seed(name: "Bodyweight Core")
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: nil, hasStub: false)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: ["Upper Body", "Core"]) == .write)
+    }
+
+    /// A stub present but the same name also live: the veto is checked first, so it
+    /// still skips (as vetoed) rather than as a name collision — either way, no write.
+    @Test func stubTakesPrecedenceOverNameCollision() {
+        let bundle = seed(name: "Upper Body")
+        let input = SeedReconcileInput(seedID: bundle.id, seedDoc: bundle, liveDoc: nil, hasStub: true)
+
+        #expect(SeedReconcilePlanner.decision(for: input, liveSplitNames: ["Upper Body"]) == .skip(.vetoed))
+    }
+
+    // MARK: - Restore
+
+    /// Restore rewrites only a seed that is both absent and free of a name collision;
+    /// the presence of a veto stub is irrelevant (restore lifts it).
+    @Test func shouldRestoreOnlyWhenAbsentAndNameFree() {
+        // Absent, name free → restore (whether or not a stub exists).
+        #expect(SeedReconcilePlanner.shouldRestore(hasLiveFile: false, seedName: "Upper Body", liveSplitNames: []))
+        // Live file already present → reconcile handles any upgrade; restore leaves it.
+        #expect(!SeedReconcilePlanner.shouldRestore(hasLiveFile: true, seedName: "Upper Body", liveSplitNames: []))
+        // A live same-name split exists → don't duplicate it.
+        #expect(!SeedReconcilePlanner.shouldRestore(hasLiveFile: false, seedName: "Upper Body", liveSplitNames: ["Upper Body"]))
+    }
+}