diff --git a/Sources/LocalData/Audit/StorageAuditReport.swift b/Sources/LocalData/Audit/StorageAuditReport.swift
index 1089b2e..8a831a3 100644
--- a/Sources/LocalData/Audit/StorageAuditReport.swift
+++ b/Sources/LocalData/Audit/StorageAuditReport.swift
@@ -1,9 +1,16 @@
 import Foundation
 
 /// Renders audit reports for storage key catalogs and registries.
+///
+/// Use this type to build human-readable snapshots of your storage surface area.
+/// Reports are useful for security reviews, compliance audits, and debugging
+/// catalog registration issues.
 public struct StorageAuditReport: Sendable {
     /// Returns descriptors for all keys in a catalog.
     ///
+    /// This applies the catalog name to each descriptor, so the output can be
+    /// grouped and traced back to its module.
+    ///
     /// - Parameter catalog: Catalog containing keys to describe.
     /// - Returns: An array of ``StorageKeyDescriptor`` values.
     public static func items(for catalog: some StorageKeyCatalog) -> [StorageKeyDescriptor] {
@@ -20,6 +27,9 @@ public struct StorageAuditReport: Sendable {
 
     /// Renders a text report for a list of type-erased keys.
     ///
+    /// Use this when you already have `AnyStorageKey` entries, such as from
+    /// `StorageRouter.allRegisteredEntries()`.
+    ///
     /// - Parameter entries: The keys to render.
     /// - Returns: A newline-delimited report string.
     public static func renderText(_ entries: [AnyStorageKey]) -> String {
@@ -36,6 +46,9 @@ public struct StorageAuditReport: Sendable {
 
     /// Renders a text report for the global registry grouped by catalog.
     ///
+    /// Each catalog section is prefixed with a header and followed by its
+    /// contained key descriptors.
+    ///
     /// - Returns: A report string grouped by catalog name.
     public static func renderGlobalRegistryGrouped() async -> String {
         let catalogs = await StorageRouter.shared.allRegisteredCatalogs()
@@ -78,6 +91,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats a storage domain for audit output.
+    ///
+    /// - Parameter domain: Domain to format.
+    /// - Returns: A concise, human-readable domain string.
     private static func string(for domain: StorageDomain) -> String {
         switch domain {
         case .userDefaults(let suite):
@@ -96,6 +112,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats a file directory for audit output.
+    ///
+    /// - Parameter directory: Directory to format.
+    /// - Returns: A concise directory string.
     private static func string(for directory: FileDirectory) -> String {
         switch directory {
         case .documents:
@@ -108,6 +127,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats platform availability for audit output.
+    ///
+    /// - Parameter availability: Availability to format.
+    /// - Returns: A concise availability string.
     private static func string(for availability: PlatformAvailability) -> String {
         switch availability {
         case .all:
@@ -122,6 +144,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats sync policy for audit output.
+    ///
+    /// - Parameter syncPolicy: Sync policy to format.
+    /// - Returns: A concise sync policy string.
     private static func string(for syncPolicy: SyncPolicy) -> String {
         switch syncPolicy {
         case .never:
@@ -134,6 +159,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats security policy for audit output.
+    ///
+    /// - Parameter security: Security policy to format.
+    /// - Returns: A concise security policy string.
     private static func string(for security: SecurityPolicy) -> String {
         switch security {
         case .none:
@@ -147,6 +175,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats encryption policy for audit output.
+    ///
+    /// - Parameter policy: Encryption policy to format.
+    /// - Returns: A concise encryption policy string.
     private static func string(for policy: SecurityPolicy.EncryptionPolicy) -> String {
         switch policy {
         case .aes256(let derivation):
@@ -159,6 +190,9 @@ public struct StorageAuditReport: Sendable {
     }
 
     /// Formats key derivation for audit output.
+    ///
+    /// - Parameter derivation: Derivation to format.
+    /// - Returns: A concise derivation string.
     private static func string(for derivation: SecurityPolicy.KeyDerivation) -> String {
         switch derivation {
         case .pbkdf2(let iterations, _):
diff --git a/Sources/LocalData/Helpers/EncryptionHelper.swift b/Sources/LocalData/Helpers/EncryptionHelper.swift
index 7abf42f..2529179 100644
--- a/Sources/LocalData/Helpers/EncryptionHelper.swift
+++ b/Sources/LocalData/Helpers/EncryptionHelper.swift
@@ -3,20 +3,29 @@ import CryptoKit
 
 /// Actor that handles all encryption and decryption operations.
 ///
-/// Uses AES-GCM or ChaChaPoly for symmetric encryption with derived keys, and
-/// stores a master key in Keychain for deterministic derivation.
+/// `EncryptionHelper` provides symmetric encryption using AES-GCM or
+/// ChaChaPoly. It derives per-key symmetric keys from a master key stored in
+/// Keychain (or from external key material when configured) so encrypted data
+/// is deterministic and recoverable across app launches.
 actor EncryptionHelper {
     
     /// Shared encryption helper instance.
     ///
-    /// Prefer this shared instance in production code. Tests can inject a custom instance.
+    /// Prefer this shared instance in production code. Tests can inject a custom instance
+    /// with isolated configuration and keychain dependencies.
     public static let shared = EncryptionHelper()
 
     /// Current encryption configuration.
+    ///
+    /// Controls key derivation defaults and master key settings.
     private var configuration: EncryptionConfiguration
     /// Keychain provider used for master key storage.
+    ///
+    /// Abstracted to allow test stubs and isolation.
     private var keychain: KeychainStoring
     /// External key material providers keyed by source identifier.
+    ///
+    /// Used for ``SecurityPolicy/EncryptionPolicy/external(source:keyDerivation:)``.
     private var keyMaterialProviders: [KeyMaterialSource: any KeyMaterialProviding] = [:]
     
     /// Creates an encryption helper with a configuration and keychain provider.
@@ -37,6 +46,8 @@ actor EncryptionHelper {
     /// Updates the configuration for the actor.
     ///
     /// - Parameter configuration: New encryption configuration.
+    /// - Warning: Changing these values after data is encrypted may make
+    ///   existing data unreadable unless migrated.
     public func updateConfiguration(_ configuration: EncryptionConfiguration) {
         self.configuration = configuration
     }
@@ -44,7 +55,7 @@ actor EncryptionHelper {
     /// Updates the keychain helper used for master key storage.
     ///
     /// - Parameter keychain: Keychain provider to use.
-    /// - Note: Internal for testing isolation.
+    /// - Note: Intended for testing isolation and dependency injection.
     public func updateKeychainHelper(_ keychain: KeychainStoring) {
         self.keychain = keychain
     }
@@ -56,6 +67,7 @@ actor EncryptionHelper {
     /// - Parameters:
     ///   - provider: The provider that supplies key material.
     ///   - source: Identifier used to look up the provider.
+    /// - Note: Required when using ``SecurityPolicy/EncryptionPolicy/external(source:keyDerivation:)``.
     public func registerKeyMaterialProvider(
         _ provider: any KeyMaterialProviding,
         for source: KeyMaterialSource
@@ -99,8 +111,13 @@ actor EncryptionHelper {
     
     // MARK: - Key Derivation
     
-    /// Derives an encryption key using the specified policy.
     /// Derives a symmetric key based on the encryption policy.
+    ///
+    /// - Parameters:
+    ///   - keyName: Logical key name used to seed derivation.
+    ///   - policy: Encryption policy describing algorithm and derivation.
+    /// - Returns: A symmetric key for encryption/decryption.
+    /// - Throws: ``StorageError/securityApplicationFailed`` when derivation fails or no provider exists.
     private func deriveKey(
         keyName: String,
         policy: SecurityPolicy.EncryptionPolicy
@@ -127,8 +144,14 @@ actor EncryptionHelper {
         }
     }
     
-    /// Derives key material based on the provided key derivation strategy.
     /// Derives key material using HKDF or PBKDF2.
+    ///
+    /// - Parameters:
+    ///   - keyName: Logical key name used to seed derivation.
+    ///   - derivation: Key derivation strategy.
+    ///   - baseKeyMaterial: Base key material (master key or external).
+    /// - Returns: A symmetric key derived from the inputs.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if derivation fails.
     private func deriveKeyMaterial(
         keyName: String,
         derivation: SecurityPolicy.KeyDerivation,
@@ -158,8 +181,10 @@ actor EncryptionHelper {
         }
     }
     
-    /// Gets or creates the master key stored in keychain.
     /// Retrieves or creates the master key stored in Keychain.
+    ///
+    /// - Returns: The master key data.
+    /// - Throws: ``StorageError/securityApplicationFailed`` or keychain errors.
     private func getMasterKey() async throws -> Data {
         if let existing = try await keychain.get(
             service: configuration.masterKeyService,
@@ -192,6 +217,13 @@ actor EncryptionHelper {
     // MARK: - AES-GCM Operations
     
     /// Encrypts data using the selected algorithm and key.
+    ///
+    /// - Parameters:
+    ///   - data: Plaintext data to encrypt.
+    ///   - key: Symmetric key to use.
+    ///   - policy: Encryption policy selecting the algorithm.
+    /// - Returns: Combined ciphertext for storage.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if encryption fails.
     private func encryptWithKey(
         _ data: Data,
         using key: SymmetricKey,
@@ -208,6 +240,12 @@ actor EncryptionHelper {
     }
     
     /// Encrypts data using AES-GCM.
+    ///
+    /// - Parameters:
+    ///   - data: Plaintext data to encrypt.
+    ///   - key: Symmetric key to use.
+    /// - Returns: Combined nonce + ciphertext + tag.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if encryption fails.
     private func encryptWithAESGCM(_ data: Data, using key: SymmetricKey) throws -> Data {
         do {
             let sealedBox = try AES.GCM.seal(data, using: key)
@@ -221,6 +259,13 @@ actor EncryptionHelper {
     }
     
     /// Decrypts data using the selected algorithm and key.
+    ///
+    /// - Parameters:
+    ///   - data: Combined nonce + ciphertext + tag.
+    ///   - key: Symmetric key to use.
+    ///   - policy: Encryption policy selecting the algorithm.
+    /// - Returns: Decrypted plaintext data.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if decryption fails.
     private func decryptWithKey(
         _ data: Data,
         using key: SymmetricKey,
@@ -237,6 +282,12 @@ actor EncryptionHelper {
     }
     
     /// Decrypts data using AES-GCM.
+    ///
+    /// - Parameters:
+    ///   - data: Combined nonce + ciphertext + tag.
+    ///   - key: Symmetric key to use.
+    /// - Returns: Decrypted plaintext data.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if decryption fails.
     private func decryptWithAESGCM(_ data: Data, using key: SymmetricKey) throws -> Data {
         do {
             let sealedBox = try AES.GCM.SealedBox(combined: data)
@@ -247,6 +298,12 @@ actor EncryptionHelper {
     }
     
     /// Encrypts data using ChaChaPoly.
+    ///
+    /// - Parameters:
+    ///   - data: Plaintext data to encrypt.
+    ///   - key: Symmetric key to use.
+    /// - Returns: Combined nonce + ciphertext + tag.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if encryption fails.
     private func encryptWithChaChaPoly(_ data: Data, using key: SymmetricKey) throws -> Data {
         do {
             let sealedBox = try ChaChaPoly.seal(data, using: key)
@@ -257,6 +314,12 @@ actor EncryptionHelper {
     }
     
     /// Decrypts data using ChaChaPoly.
+    ///
+    /// - Parameters:
+    ///   - data: Combined nonce + ciphertext + tag.
+    ///   - key: Symmetric key to use.
+    /// - Returns: Decrypted plaintext data.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if decryption fails.
     private func decryptWithChaChaPoly(_ data: Data, using key: SymmetricKey) throws -> Data {
         do {
             let sealedBox = try ChaChaPoly.SealedBox(combined: data)
@@ -269,6 +332,14 @@ actor EncryptionHelper {
     // MARK: - PBKDF2 Implementation
     
     /// Derives key data using PBKDF2-SHA256.
+    ///
+    /// - Parameters:
+    ///   - password: Base key material used as the PBKDF2 password.
+    ///   - salt: Salt value to strengthen derivation.
+    ///   - iterations: Number of PBKDF2 rounds.
+    ///   - keyLength: Desired output length in bytes.
+    /// - Returns: Derived key material.
+    /// - Throws: ``StorageError/securityApplicationFailed`` if iterations are invalid.
     private func pbkdf2SHA256(
         password: Data,
         salt: Data,
@@ -305,6 +376,11 @@ actor EncryptionHelper {
     }
     
     /// Computes HMAC-SHA256 for PBKDF2.
+    ///
+    /// - Parameters:
+    ///   - key: HMAC key.
+    ///   - data: Data to authenticate.
+    /// - Returns: HMAC output.
     private func hmacSHA256(key: Data, data: Data) -> Data {
         let symmetricKey = SymmetricKey(data: key)
         let mac = HMAC<SHA256>.authenticationCode(for: data, using: symmetricKey)
@@ -312,18 +388,29 @@ actor EncryptionHelper {
     }
     
     /// XORs two data buffers for PBKDF2 chaining.
+    ///
+    /// - Parameters:
+    ///   - left: First buffer.
+    ///   - right: Second buffer.
+    /// - Returns: XORed data.
     private func xor(_ left: Data, _ right: Data) -> Data {
         let xored = zip(left, right).map { $0 ^ $1 }
         return Data(xored)
     }
     
     /// Encodes a UInt32 as big-endian data.
+    ///
+    /// - Parameter value: Value to encode.
+    /// - Returns: Big-endian data representation.
     private func uint32BigEndian(_ value: UInt32) -> Data {
         var bigEndian = value.bigEndian
         return Data(bytes: &bigEndian, count: MemoryLayout<UInt32>.size)
     }
     
     /// Generates a deterministic salt from a key name.
+    ///
+    /// - Parameter keyName: Key name used to build the salt.
+    /// - Returns: Salt data used for key derivation.
     private func defaultSalt(for keyName: String) -> Data {
         Data(keyName.utf8)
     }
diff --git a/Sources/LocalData/Helpers/SyncHelper.swift b/Sources/LocalData/Helpers/SyncHelper.swift
index c05e26a..c6a820c 100644
--- a/Sources/LocalData/Helpers/SyncHelper.swift
+++ b/Sources/LocalData/Helpers/SyncHelper.swift
@@ -3,16 +3,20 @@ import WatchConnectivity
 
 /// Actor that handles WatchConnectivity sync operations.
 ///
-/// Manages data synchronization between iPhone and Apple Watch and provides
-/// size- and policy-based gating for outbound sync.
+/// `SyncHelper` manages data synchronization between iPhone and Apple Watch.
+/// It enforces LocalData's sync policies, validates payload size constraints,
+/// and delegates incoming application contexts to ``StorageRouter``.
 actor SyncHelper {
     
     /// Shared sync helper instance.
     ///
-    /// Prefer this shared instance in production code. Tests can inject a custom instance.
+    /// Prefer this shared instance in production code. Tests can inject a custom instance
+    /// with isolated configuration and `WCSession` behavior.
     public static let shared = SyncHelper()
     
     /// Current sync configuration.
+    ///
+    /// Controls size thresholds for automatic sync.
     private var configuration: SyncConfiguration
     
     /// Creates a helper with a specific configuration.
@@ -39,12 +43,18 @@ actor SyncHelper {
     // MARK: - Public Interface
     
     /// Syncs data to the paired device if appropriate.
+    ///
+    /// This method enforces LocalData's eligibility rules:
+    /// - availability must be `.all` or `.phoneWithWatchSync`
+    /// - sync policy must be `.manual` or `.automaticSmall`
+    /// - `.automaticSmall` must be under the configured size threshold
+    ///
     /// - Parameters:
     ///   - data: The data to sync.
     ///   - keyName: The key name for the application context.
     ///   - availability: The platform availability setting.
     ///   - syncPolicy: The sync policy setting.
-    /// - Throws: `StorageError.dataTooLargeForSync` if data exceeds size limit for automatic sync.
+    /// - Throws: ``StorageError/dataTooLargeForSync`` if data exceeds size limit for automatic sync.
     public func syncIfNeeded(
         data: Data,
         keyName: String,
@@ -72,6 +82,10 @@ actor SyncHelper {
     }
     
     /// Manually triggers a sync for the given data.
+    ///
+    /// This bypasses automatic size gating; callers should ensure payload size
+    /// is reasonable for application context updates.
+    ///
     /// - Parameters:
     ///   - data: The data to sync.
     ///   - keyName: The key name for the application context.
@@ -138,6 +152,9 @@ actor SyncHelper {
     }
 
     /// Lazily configures and activates WCSession.
+    ///
+    /// LocalData does not own session lifecycle beyond the minimal setup needed
+    /// to send updates; app-level services should activate WCSession explicitly.
     private func setupSession() {
         let session = WCSession.default
         session.delegate = SessionDelegateProxy.shared
@@ -165,11 +182,15 @@ actor SyncHelper {
     }
 }
 
-/// Internal proxy class that routes WCSessionDelegate callbacks to ``SyncHelper``.
+/// Internal proxy class that routes `WCSessionDelegate` callbacks to ``SyncHelper``.
+///
+/// The proxy bridges delegate callbacks into async code without exposing
+/// `WCSessionDelegate` conformance in the public API.
 internal final class SessionDelegateProxy: NSObject, WCSessionDelegate {
     /// Shared delegate proxy instance.
     static let shared = SessionDelegateProxy()
     
+    /// Handles WCSession activation completion.
     func session(_ session: WCSession, activationDidCompleteWith activationState: WCSessionActivationState, error: Error?) {
         if let error = error {
             Logger.error("WCSession activation failed: \(error.localizedDescription)")
@@ -178,6 +199,7 @@ internal final class SessionDelegateProxy: NSObject, WCSessionDelegate {
         }
     }
     
+    /// Receives an updated application context and forwards it to `SyncHelper`.
     func session(_ session: WCSession, didReceiveApplicationContext applicationContext: [String: Any]) {
         Task {
             await SyncHelper.shared.handleReceivedContext(applicationContext)
@@ -185,7 +207,9 @@ internal final class SessionDelegateProxy: NSObject, WCSessionDelegate {
     }
     
     #if os(iOS)
+    /// iOS-only callback when a session becomes inactive.
     func sessionDidBecomeInactive(_ session: WCSession) {}
+    /// iOS-only callback when a session deactivates.
     func sessionDidDeactivate(_ session: WCSession) {
         session.activate()
     }
diff --git a/Sources/LocalData/Migrations/AppVersionConditionalMigration.swift b/Sources/LocalData/Migrations/AppVersionConditionalMigration.swift
index e2de2ea..745256d 100644
--- a/Sources/LocalData/Migrations/AppVersionConditionalMigration.swift
+++ b/Sources/LocalData/Migrations/AppVersionConditionalMigration.swift
@@ -1,7 +1,10 @@
 import Foundation
 
 /// Conditional migration that runs only when the app version is below a threshold.
-public struct AppVersionConditionalMigration<Value: Codable & Sendable>: ConditionalMigration {
+///
+/// Use this wrapper to keep a legacy migration in place for older app versions
+/// while allowing newer versions to skip it.
+public struct AppVersionConditionalMigration<Value: Codable & Sendable>: StorageMigration {
     /// Destination key for the migration.
     public let destinationKey: StorageKey<Value>
     /// Minimum app version required to skip this migration.
@@ -10,6 +13,11 @@ public struct AppVersionConditionalMigration<Value: Codable & Sendable>: Conditi
     public let fallbackMigration: AnyStorageMigration
 
     /// Creates a version-gated migration.
+    ///
+    /// - Parameters:
+    ///   - destinationKey: The key that receives migrated data.
+    ///   - minAppVersion: The minimum app version that should *skip* the migration.
+    ///   - fallbackMigration: The migration to run when the version condition is met.
     public init(
         destinationKey: StorageKey<Value>,
         minAppVersion: String,
diff --git a/Sources/LocalData/Migrations/DefaultAggregatingMigration.swift b/Sources/LocalData/Migrations/DefaultAggregatingMigration.swift
index b8a393e..2a4c305 100644
--- a/Sources/LocalData/Migrations/DefaultAggregatingMigration.swift
+++ b/Sources/LocalData/Migrations/DefaultAggregatingMigration.swift
@@ -1,6 +1,10 @@
 import Foundation
 
 /// Default migration that aggregates multiple source values into one destination value.
+///
+/// Use this migration when you need to combine multiple legacy keys into a single
+/// destination value (for example, building a new composite model from several
+/// old preferences).
 public struct DefaultAggregatingMigration<Value: Codable & Sendable>: AggregatingMigration {
     /// Destination key for aggregated data.
     public let destinationKey: StorageKey<Value>
@@ -10,6 +14,11 @@ public struct DefaultAggregatingMigration<Value: Codable & Sendable>: Aggregatin
     public let aggregateAction: @Sendable ([AnyCodable]) async throws -> Value
 
     /// Creates an aggregating migration with a custom aggregation closure.
+    ///
+    /// - Parameters:
+    ///   - destinationKey: The key that receives the aggregated value.
+    ///   - sourceKeys: The legacy keys to read and aggregate.
+    ///   - aggregate: Closure that combines source values into a destination value.
     public init(
         destinationKey: StorageKey<Value>,
         sourceKeys: [AnyStorageKey],
@@ -30,6 +39,11 @@ public struct DefaultAggregatingMigration<Value: Codable & Sendable>: Aggregatin
 
     /// Determines whether the migration should run.
     ///
+    /// The migration runs when:
+    /// - the destination is allowed on the current platform
+    /// - the destination does not already exist
+    /// - at least one source key contains data
+    ///
     /// - Parameters:
     ///   - router: The storage router used to query state.
     ///   - context: Migration context for conditional checks.
@@ -53,6 +67,12 @@ public struct DefaultAggregatingMigration<Value: Codable & Sendable>: Aggregatin
 
     /// Executes the migration and returns a result.
     ///
+    /// The migration:
+    /// 1. Reads each source descriptor.
+    /// 2. Applies security to decode the raw data.
+    /// 3. Aggregates values into a destination value.
+    /// 4. Writes the destination value and deletes sources.
+    ///
     /// - Parameters:
     ///   - router: The storage router used to read and write values.
     ///   - context: Migration context for conditional checks.
diff --git a/Sources/LocalData/Migrations/DefaultTransformingMigration.swift b/Sources/LocalData/Migrations/DefaultTransformingMigration.swift
index eed3612..678d1a5 100644
--- a/Sources/LocalData/Migrations/DefaultTransformingMigration.swift
+++ b/Sources/LocalData/Migrations/DefaultTransformingMigration.swift
@@ -1,6 +1,9 @@
 import Foundation
 
 /// Default migration that transforms a single source value into a destination value.
+///
+/// Use this migration when the destination value type differs from the legacy
+/// type or when you need to normalize/clean legacy data before storage.
 public struct DefaultTransformingMigration<SourceValue: Codable & Sendable, DestinationValue: Codable & Sendable>: TransformingMigration {
     /// Destination key for the transformed value.
     public let destinationKey: StorageKey<DestinationValue>
@@ -10,6 +13,11 @@ public struct DefaultTransformingMigration<SourceValue: Codable & Sendable, Dest
     public let transformAction: @Sendable (SourceValue) async throws -> DestinationValue
 
     /// Creates a transforming migration with a custom transform closure.
+    ///
+    /// - Parameters:
+    ///   - destinationKey: The key that receives the transformed value.
+    ///   - sourceKey: The legacy key providing the source value.
+    ///   - transform: Closure that converts the source value into the destination type.
     public init(
         destinationKey: StorageKey<DestinationValue>,
         sourceKey: StorageKey<SourceValue>,
@@ -30,6 +38,11 @@ public struct DefaultTransformingMigration<SourceValue: Codable & Sendable, Dest
 
     /// Determines whether the migration should run.
     ///
+    /// The migration runs when:
+    /// - the destination is allowed on the current platform
+    /// - the destination does not already exist
+    /// - the source key contains data
+    ///
     /// - Parameters:
     ///   - router: The storage router used to query state.
     ///   - context: Migration context for conditional checks.
@@ -47,6 +60,12 @@ public struct DefaultTransformingMigration<SourceValue: Codable & Sendable, Dest
 
     /// Executes the migration and returns a result.
     ///
+    /// The migration:
+    /// 1. Reads the source value.
+    /// 2. Transforms it into the destination type.
+    /// 3. Writes the destination value.
+    /// 4. Deletes the source key.
+    ///
     /// - Parameters:
     ///   - router: The storage router used to read and write values.
     ///   - context: Migration context for conditional checks.
diff --git a/Sources/LocalData/Migrations/SimpleLegacyMigration.swift b/Sources/LocalData/Migrations/SimpleLegacyMigration.swift
index 6ac8185..b71eb0a 100644
--- a/Sources/LocalData/Migrations/SimpleLegacyMigration.swift
+++ b/Sources/LocalData/Migrations/SimpleLegacyMigration.swift
@@ -1,6 +1,9 @@
 import Foundation
 
 /// Simple 1:1 legacy migration from a single source key.
+///
+/// Use this migration when the source and destination value types are identical
+/// and no transformation is required.
 public struct SimpleLegacyMigration<Value: Codable & Sendable>: StorageMigration {
     /// Destination key for migrated data.
     public let destinationKey: StorageKey<Value>
@@ -8,6 +11,10 @@ public struct SimpleLegacyMigration<Value: Codable & Sendable>: StorageMigration
     public let sourceKey: AnyStorageKey
 
     /// Creates a migration from a legacy key to a destination key.
+    ///
+    /// - Parameters:
+    ///   - destinationKey: The key that receives migrated data.
+    ///   - sourceKey: The legacy key to read and remove.
     public init(destinationKey: StorageKey<Value>, sourceKey: AnyStorageKey) {
         self.destinationKey = destinationKey
         self.sourceKey = sourceKey
@@ -15,6 +22,11 @@ public struct SimpleLegacyMigration<Value: Codable & Sendable>: StorageMigration
 
     /// Determines whether the migration should run.
     ///
+    /// The migration runs when:
+    /// - the destination is allowed on the current platform
+    /// - the destination does not already exist
+    /// - the source key contains data
+    ///
     /// - Parameters:
     ///   - router: The storage router used to query state.
     ///   - context: Migration context for conditional checks.
@@ -32,6 +44,12 @@ public struct SimpleLegacyMigration<Value: Codable & Sendable>: StorageMigration
 
     /// Executes the migration and returns a result.
     ///
+    /// The migration:
+    /// 1. Reads raw source data.
+    /// 2. Removes legacy security (if needed).
+    /// 3. Decodes into the destination value type.
+    /// 4. Writes to the destination and deletes the source.
+    ///
     /// - Parameters:
     ///   - router: The storage router used to read and write values.
     ///   - context: Migration context for conditional checks.
diff --git a/Sources/LocalData/Models/AnyStorageKey.swift b/Sources/LocalData/Models/AnyStorageKey.swift
index def4262..13a6a42 100644
--- a/Sources/LocalData/Models/AnyStorageKey.swift
+++ b/Sources/LocalData/Models/AnyStorageKey.swift
@@ -1,9 +1,15 @@
 /// Type-erased wrapper around ``StorageKey`` for catalogs and audits.
+///
+/// `StorageKey` is generic over its `Value` type, so heterogeneous keys cannot
+/// be stored in a single array without type erasure. `AnyStorageKey` captures
+/// the descriptor and optional migration, enabling catalog registration and
+/// audit reporting.
 public struct AnyStorageKey: Sendable {
     /// Snapshot of key metadata for auditing and storage operations.
     public internal(set) var descriptor: StorageKeyDescriptor
     /// Optional migration associated with the key.
     public internal(set) var migration: AnyStorageMigration?
+    /// Migration executor captured from the original key.
     private let migrateAction: @Sendable (StorageRouter) async throws -> Void
 
     /// Creates a type-erased key from a typed ``StorageKey``.
@@ -17,6 +23,12 @@ public struct AnyStorageKey: Sendable {
         }
     }
 
+    /// Internal initializer for constructing modified wrappers.
+    ///
+    /// - Parameters:
+    ///   - descriptor: Descriptor describing the key.
+    ///   - migration: Optional migration.
+    ///   - migrateAction: Closure to execute migration for the key.
     private init(
         descriptor: StorageKeyDescriptor,
         migration: AnyStorageMigration?,
@@ -30,6 +42,7 @@ public struct AnyStorageKey: Sendable {
     /// Convenience factory for creating a type-erased key.
     ///
     /// - Parameter key: The concrete key to erase.
+    /// - Returns: A type-erased key wrapper.
     public static func key<Value>(_ key: StorageKey<Value>) -> AnyStorageKey {
         AnyStorageKey(key)
     }
diff --git a/Sources/LocalData/Models/AnyStorageMigration.swift b/Sources/LocalData/Models/AnyStorageMigration.swift
index f7415b6..2d979bb 100644
--- a/Sources/LocalData/Models/AnyStorageMigration.swift
+++ b/Sources/LocalData/Models/AnyStorageMigration.swift
@@ -1,11 +1,20 @@
 import Foundation
 
 /// Type-erased wrapper for ``StorageMigration`` for use in catalogs and registrations.
+///
+/// `StorageMigration` is a protocol with an associated type, which makes it
+/// difficult to store heterogeneous migrations in a single collection. This
+/// wrapper captures the migration's behavior and destination descriptor while
+/// preserving sendability.
 public struct AnyStorageMigration: Sendable {
     /// Descriptor for the migration destination key.
+    ///
+    /// Useful for auditing and for determining the target of the migration.
     public let destinationDescriptor: StorageKeyDescriptor
 
+    /// Captured closure that decides whether migration should run.
     private let shouldMigrateAction: @Sendable (StorageRouter, MigrationContext) async throws -> Bool
+    /// Captured closure that executes the migration.
     private let migrateAction: @Sendable (StorageRouter, MigrationContext) async throws -> MigrationResult
 
     /// Creates a type-erased migration from a concrete migration.
diff --git a/Sources/LocalData/Models/FileDirectory.swift b/Sources/LocalData/Models/FileDirectory.swift
index 01a089a..908f019 100644
--- a/Sources/LocalData/Models/FileDirectory.swift
+++ b/Sources/LocalData/Models/FileDirectory.swift
@@ -1,15 +1,26 @@
 import Foundation
 
 /// File system directory for file-based storage.
+///
+/// Use this enum to describe where a file should live within the app sandbox
+/// or a custom file URL.
 public enum FileDirectory: Sendable, Hashable {
     /// App documents directory.
+    ///
+    /// Best for user-facing or critical data that should be backed up.
     case documents
     /// App caches directory.
+    ///
+    /// Best for temporary or re-creatable data that may be purged by the system.
     case caches
     /// Custom directory URL.
+    ///
+    /// Use this to scope storage to a custom location (including App Group paths).
     case custom(URL)
 
     /// Resolves the directory to a concrete URL.
+    ///
+    /// - Returns: The resolved directory URL.
     public func url() -> URL {
         switch self {
         case .documents:
diff --git a/Sources/LocalData/Models/KeyMaterialSource.swift b/Sources/LocalData/Models/KeyMaterialSource.swift
index bf822cd..a093f61 100644
--- a/Sources/LocalData/Models/KeyMaterialSource.swift
+++ b/Sources/LocalData/Models/KeyMaterialSource.swift
@@ -1,11 +1,18 @@
 import Foundation
 
 /// Identifier for external key material providers.
+///
+/// Use this type to register and reference external key material when using
+/// ``SecurityPolicy/EncryptionPolicy/external(source:keyDerivation:)``.
 public struct KeyMaterialSource: Hashable, Sendable {
     /// Stable identifier for the provider or key source.
+    ///
+    /// This should be deterministic and consistent across app launches.
     public let id: String
 
     /// Creates a new key material source identifier.
+    ///
+    /// - Parameter id: Stable identifier for the external key provider.
     public init(id: String) {
         self.id = id
     }
diff --git a/Sources/LocalData/Models/MigrationContext.swift b/Sources/LocalData/Models/MigrationContext.swift
index 8e87ede..3580026 100644
--- a/Sources/LocalData/Models/MigrationContext.swift
+++ b/Sources/LocalData/Models/MigrationContext.swift
@@ -1,6 +1,9 @@
 import Foundation
 
 /// Context information available for conditional migrations.
+///
+/// Migrations use this context to decide whether they should run and to tailor
+/// behavior based on app version, device, system state, and historical data.
 public struct MigrationContext: Sendable {
     /// Current app version string.
     public let appVersion: String
@@ -14,6 +17,13 @@ public struct MigrationContext: Sendable {
     public let systemInfo: SystemInfo
 
     /// Creates a migration context with optional overrides.
+    ///
+    /// - Parameters:
+    ///   - appVersion: Current app version string. Defaults to the bundle version.
+    ///   - deviceInfo: Device metadata for platform checks.
+    ///   - migrationHistory: Historical migration timestamps by key name.
+    ///   - userPreferences: Optional preferences influencing migration behavior.
+    ///   - systemInfo: System information snapshot.
     public init(
         appVersion: String = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String ?? "Unknown",
         deviceInfo: DeviceInfo = .current,
diff --git a/Sources/LocalData/Models/MigrationError.swift b/Sources/LocalData/Models/MigrationError.swift
index af0bbdd..b5c5566 100644
--- a/Sources/LocalData/Models/MigrationError.swift
+++ b/Sources/LocalData/Models/MigrationError.swift
@@ -1,6 +1,9 @@
 import Foundation
 
 /// Migration-specific error types.
+///
+/// These errors describe why a migration failed or could not run, and are used
+/// in ``MigrationResult`` for reporting.
 public enum MigrationError: Error, Sendable, Equatable {
     /// Validation failed before migration could run.
     case validationFailed(String)
diff --git a/Sources/LocalData/Models/MigrationResult.swift b/Sources/LocalData/Models/MigrationResult.swift
index 3308aef..54060ca 100644
--- a/Sources/LocalData/Models/MigrationResult.swift
+++ b/Sources/LocalData/Models/MigrationResult.swift
@@ -1,19 +1,42 @@
 import Foundation
 
-/// Result of a migration operation with detailed information.
+/// Records the outcome of a migration along with counts, errors, and metadata.
+///
+/// `MigrationResult` is the canonical payload returned by migrations so callers can
+/// surface success/failure, auditing details, and performance data in a consistent way.
+/// It is intentionally lightweight and `Sendable` so it can cross concurrency boundaries.
 public struct MigrationResult: Sendable {
-    /// Whether the migration completed successfully.
+    /// Indicates whether the migration completed without fatal errors.
+    ///
+    /// A value of `false` does not always mean that no data moved; consult
+    /// `migratedCount` and `errors` for partial outcomes.
     public let success: Bool
-    /// Number of values migrated.
+    /// Number of items or records migrated during the operation.
+    ///
+    /// This count is used for audit logging and metrics. Its meaning depends on the
+    /// migration type (for example, key-by-key versus batch).
     public let migratedCount: Int
-    /// Errors captured during migration.
+    /// Errors captured while the migration executed.
+    ///
+    /// Consumers should surface these to developers and use them to decide on retries.
     public let errors: [MigrationError]
-    /// Additional metadata provided by the migration.
+    /// Additional metadata emitted by the migration for diagnostics or reporting.
+    ///
+    /// The dictionary must only contain `AnyCodable` values so results remain portable.
     public let metadata: [String: AnyCodable]
     /// Duration of the migration in seconds.
+    ///
+    /// Use this value for instrumentation and to flag unusually slow migrations.
     public let duration: TimeInterval
 
     /// Creates a migration result with optional details.
+    ///
+    /// - Parameters:
+    ///   - success: Whether the migration completed without fatal errors.
+    ///   - migratedCount: Number of items migrated. Defaults to `0`.
+    ///   - errors: Errors captured during the migration. Defaults to an empty array.
+    ///   - metadata: Metadata emitted by the migration. Defaults to an empty dictionary.
+    ///   - duration: Duration in seconds. Defaults to `0`.
     public init(
         success: Bool,
         migratedCount: Int = 0,
diff --git a/Sources/LocalData/Models/PlatformAvailability.swift b/Sources/LocalData/Models/PlatformAvailability.swift
index a3e10f3..646cd20 100644
--- a/Sources/LocalData/Models/PlatformAvailability.swift
+++ b/Sources/LocalData/Models/PlatformAvailability.swift
@@ -1,20 +1,35 @@
 import Foundation
 
-/// Specifies which platforms a storage key is allowed to run on.
+/// Declares which platforms a storage key can be used on.
+///
+/// `PlatformAvailability` guides the router when enforcing platform-specific usage.
+/// For example, watch-only keys prevent accidental reads on iOS, while sync-enabled
+/// keys signal that watch-to-phone data flows should be configured.
 public enum PlatformAvailability: Sendable {
     /// Available on iOS and watchOS (small data only on watch).
+    ///
+    /// Use this for data that is safe to exist on both devices without explicit sync.
     case all
     /// Available only on iOS (large or sensitive data).
+    ///
+    /// Prefer this for data that is too large or too sensitive for watch storage.
     case phoneOnly
     /// Available only on watchOS.
+    ///
+    /// Use this for watch-local data that should not be mirrored to iPhone.
     case watchOnly
     /// Available on iOS and watchOS with explicit sync behavior.
+    ///
+    /// Use this when your key participates in a defined sync strategy.
     case phoneWithWatchSync
 }
 
 /// Convenience helpers for platform checks.
 public extension PlatformAvailability {
-    /// Returns `true` if the key should be available on the given platform.
+    /// Returns `true` when the key is permitted on the supplied platform.
+    ///
+    /// - Parameter platform: The runtime platform to evaluate.
+    /// - Returns: `true` if the key can be used on the platform, otherwise `false`.
     func isAvailable(on platform: Platform) -> Bool {
         switch self {
         case .all:
diff --git a/Sources/LocalData/Models/SecurityPolicy.swift b/Sources/LocalData/Models/SecurityPolicy.swift
index f2db56b..6f6561a 100644
--- a/Sources/LocalData/Models/SecurityPolicy.swift
+++ b/Sources/LocalData/Models/SecurityPolicy.swift
@@ -2,40 +2,71 @@ import Foundation
 import CryptoKit
 import Security
 
-/// Security policy for a ``StorageKey``.
+/// Describes how a ``StorageKey`` secures its persisted data.
+///
+/// A `SecurityPolicy` is attached to each key so the storage layer can enforce
+/// encryption or Keychain placement consistently across the app.
 public enum SecurityPolicy: Equatable, Sendable {
     /// Stores data without additional security.
+    ///
+    /// Use this only for non-sensitive, non-personal data.
     case none
     /// Encrypts data before storage using the specified policy.
+    ///
+    /// The encryption policy describes the algorithm and key derivation strategy.
     case encrypted(EncryptionPolicy)
     /// Stores data directly in the Keychain with accessibility and access control options.
+    ///
+    /// Use this for credentials or secrets that must remain in Keychain storage.
     case keychain(accessibility: KeychainAccessibility, accessControl: KeychainAccessControl?)
 
     /// Recommended security policy for most sensitive data.
+    ///
+    /// This defaults to the recommended encryption policy to keep data encrypted at rest.
     public static let recommended: SecurityPolicy = .encrypted(.recommended)
 
     /// Encryption algorithm and key derivation settings.
+    ///
+    /// Use these options to align with organizational security requirements.
     public enum EncryptionPolicy: Equatable, Sendable {
         /// AES-256-GCM encryption.
+        ///
+        /// Choose when AES is preferred for compliance or interoperability reasons.
         case aes256(keyDerivation: KeyDerivation)
         /// ChaCha20-Poly1305 encryption.
+        ///
+        /// This is the recommended default for modern Apple platforms.
         case chacha20Poly1305(keyDerivation: KeyDerivation)
         /// External key material with key derivation.
+        ///
+        /// Use this when key material is provided by an HSM, secure enclave, or other source.
         case external(source: KeyMaterialSource, keyDerivation: KeyDerivation)
 
         /// Recommended encryption policy for most cases.
+        ///
+        /// Uses ChaCha20-Poly1305 with HKDF-derived keys.
         public static let recommended: EncryptionPolicy = .chacha20Poly1305(keyDerivation: .hkdf())
         /// Convenience for external key material with default HKDF.
+        ///
+        /// - Parameter source: The external key material provider.
+        /// - Returns: A policy configured with the default HKDF parameters.
         public static func external(source: KeyMaterialSource) -> EncryptionPolicy {
             .external(source: source, keyDerivation: .hkdf())
         }
     }
 
     /// Key derivation algorithms for encryption keys.
+    ///
+    /// These settings allow you to tune how raw key material is transformed into
+    /// encryption keys used by the selected algorithm.
     public enum KeyDerivation: Equatable, Sendable {
         /// PBKDF2 with optional iterations and salt.
+        ///
+        /// Provide `iterations` and `salt` when you need deterministic derivation.
         case pbkdf2(iterations: Int? = nil, salt: Data? = nil)
         /// HKDF with optional salt and info.
+        ///
+        /// Supply `info` to domain-separate keys for distinct purposes.
         case hkdf(salt: Data? = nil, info: Data? = nil)
     }
 }
diff --git a/Sources/LocalData/Models/Serializer.swift b/Sources/LocalData/Models/Serializer.swift
index 330dd6b..5561002 100644
--- a/Sources/LocalData/Models/Serializer.swift
+++ b/Sources/LocalData/Models/Serializer.swift
@@ -1,12 +1,21 @@
 import Foundation
 
 /// Encodes and decodes values for storage.
+///
+/// `Serializer` packages paired encode/decode closures with a human-readable name
+/// so storage services can serialize values consistently and report the format used.
 public struct Serializer<Value: Codable & Sendable>: Sendable, CustomStringConvertible {
     /// Encodes a value into `Data`.
+    ///
+    /// The closure must be `Sendable` so it can execute safely across concurrency contexts.
     public let encode: @Sendable (Value) throws -> Data
     /// Decodes a value from `Data`.
+    ///
+    /// The closure must be `Sendable` so it can execute safely across concurrency contexts.
     public let decode: @Sendable (Data) throws -> Value
     /// Human-readable serializer name used in audit reports.
+    ///
+    /// Keep names stable so audit output is predictable and searchable.
     public let name: String
 
     /// Creates a custom serializer.
@@ -26,6 +35,8 @@ public struct Serializer<Value: Codable & Sendable>: Sendable, CustomStringConve
     }
 
     /// Description used by `CustomStringConvertible`.
+    ///
+    /// Mirrors the `name` so logs and debug output show the configured serializer.
     public var description: String { name }
 
     /// JSON serializer using `JSONEncoder` and `JSONDecoder`.
@@ -70,6 +81,8 @@ public struct Serializer<Value: Codable & Sendable>: Sendable, CustomStringConve
 public extension Serializer where Value == Data {
     /// Serializer that passes through raw `Data`.
     ///
+    /// Use this when the caller already owns the encoding format.
+    ///
     /// - Returns: A serializer that returns `Data` unchanged.
     static var data: Serializer<Value> {
         Serializer<Value>(encode: { $0 }, decode: { $0 }, name: "data")
diff --git a/Sources/LocalData/Models/StorageDomain.swift b/Sources/LocalData/Models/StorageDomain.swift
index 8eb011b..d0f11fb 100644
--- a/Sources/LocalData/Models/StorageDomain.swift
+++ b/Sources/LocalData/Models/StorageDomain.swift
@@ -1,17 +1,32 @@
 import Foundation
 
 /// Storage location for a ``StorageKey``.
+///
+/// `StorageDomain` describes where values are stored and which storage backend is used.
+/// The router interprets these cases to route reads and writes to the correct helper.
 public enum StorageDomain: Sendable, Equatable {
     /// Standard `UserDefaults` using the provided suite name.
+    ///
+    /// Pass `nil` to target the default `UserDefaults` suite.
     case userDefaults(suite: String?)
     /// App group `UserDefaults` using the provided group identifier.
+    ///
+    /// Use this for data shared with extensions on the same device.
     case appGroupUserDefaults(identifier: String?)
     /// Keychain storage using the provided service identifier.
+    ///
+    /// Keychain storage is used for sensitive or credential-like data.
     case keychain(service: String?)
     /// File system storage in the specified directory.
+    ///
+    /// Suitable for larger values that should not live in defaults or Keychain.
     case fileSystem(directory: FileDirectory)
     /// Encrypted file system storage in the specified directory.
+    ///
+    /// Values are encrypted before being written to the file system.
     case encryptedFileSystem(directory: FileDirectory)
     /// App group file storage using the group identifier and directory.
+    ///
+    /// Use this for file-backed data that needs to be shared with app extensions.
     case appGroupFileSystem(identifier: String?, directory: FileDirectory)
 }
diff --git a/Sources/LocalData/Models/StorageError.swift b/Sources/LocalData/Models/StorageError.swift
index ffbd2dd..f5aed4d 100644
--- a/Sources/LocalData/Models/StorageError.swift
+++ b/Sources/LocalData/Models/StorageError.swift
@@ -1,37 +1,68 @@
 import Foundation
 
 /// Errors thrown by storage operations and migrations.
+///
+/// `StorageError` standardizes failures across storage helpers so callers can handle
+/// issues consistently, whether the underlying storage is defaults, files, or Keychain.
 public enum StorageError: Error, Equatable {
     /// Failed to encode a value.
+    ///
+    /// This indicates the serializer could not transform a value into `Data`.
     case serializationFailed
     /// Failed to decode stored data.
+    ///
+    /// This typically means the stored payload does not match the expected type.
     case deserializationFailed
     /// Failed to apply or remove security for stored data.
+    ///
+    /// This error is used when encryption or decryption fails.
     case securityApplicationFailed
     /// Underlying Keychain error.
+    ///
+    /// The associated `OSStatus` comes from Security framework APIs.
     case keychainError(OSStatus)
     /// File system error description.
+    ///
+    /// Uses a `String` to preserve a descriptive message while remaining `Equatable`.
     case fileError(String) // Changed from Error to String for easier Equatable conformance
     /// A phone-only key was accessed on watchOS.
+    ///
+    /// The associated value is the key name.
     case phoneOnlyKeyAccessedOnWatch(String)
     /// A watch-only key was accessed on iOS.
+    ///
+    /// The associated value is the key name.
     case watchOnlyKeyAccessedOnPhone(String)
     /// Invalid UserDefaults suite name.
+    ///
+    /// The associated value is the invalid suite identifier.
     case invalidUserDefaultsSuite(String)
     /// Invalid App Group identifier.
+    ///
+    /// The associated value is the invalid group identifier.
     case invalidAppGroupIdentifier(String)
     /// Sync payload exceeded the configured maximum size.
+    ///
+    /// The key cannot be synced because the payload is too large.
     case dataTooLargeForSync
     /// No value exists for the requested key.
     case notFound
     /// The key is not registered in any catalog.
+    ///
+    /// The associated value is the missing key name.
     case unregisteredKey(String)
     /// Duplicate key names detected during registration.
+    ///
+    /// The associated array lists the duplicate key names.
     case duplicateRegisteredKeys([String])
     /// Missing or empty key description.
+    ///
+    /// The associated value is the key name missing the description.
     case missingDescription(String)
 
     /// Compares two storage errors for equality.
+    ///
+    /// This custom equality handles associated values, including `OSStatus`.
     public static func == (lhs: StorageError, rhs: StorageError) -> Bool {
         switch (lhs, rhs) {
         case (.serializationFailed, .serializationFailed),
@@ -59,4 +90,8 @@ public enum StorageError: Error, Equatable {
     }
 }
 
+/// `StorageError` includes `OSStatus` values which are not `Sendable` by default.
+///
+/// The enum is effectively immutable, so we mark it `@unchecked Sendable` to allow
+/// it to cross concurrency boundaries.
 extension StorageError: @unchecked Sendable {}
diff --git a/Sources/LocalData/Models/StorageKeyDescriptor.swift b/Sources/LocalData/Models/StorageKeyDescriptor.swift
index f5af324..2db56ea 100644
--- a/Sources/LocalData/Models/StorageKeyDescriptor.swift
+++ b/Sources/LocalData/Models/StorageKeyDescriptor.swift
@@ -1,29 +1,54 @@
 import Foundation
 
 /// Snapshot of a ``StorageKey`` used for audit and registration.
+///
+/// `StorageKeyDescriptor` captures the immutable metadata needed for audits, duplicate
+/// detection, and catalog reporting without carrying the key's generic type.
 public struct StorageKeyDescriptor: Sendable, CustomStringConvertible {
     /// Key name within its domain.
+    ///
+    /// This is the primary identifier used for duplicate detection.
     public let name: String
     /// Storage domain for the key.
+    ///
+    /// The router uses this to determine which storage helper should be used.
     public let domain: StorageDomain
     /// Security policy applied to the key.
+    ///
+    /// Indicates whether encryption or Keychain placement is required.
     public let security: SecurityPolicy
     /// Serializer name used for encoding/decoding.
+    ///
+    /// This is recorded for audit output; the serializer itself remains on the key.
     public let serializer: String
     /// String representation of the value type.
+    ///
+    /// Useful for diagnostics when reviewing audit reports.
     public let valueType: String
     /// Owning module or feature name.
+    ///
+    /// Use this to identify the feature responsible for the stored data.
     public let owner: String
     /// Platform availability for the key.
+    ///
+    /// Governs which runtime platforms are allowed to access the key.
     public let availability: PlatformAvailability
     /// Sync policy for WatchConnectivity.
+    ///
+    /// Used when determining sync eligibility and constraints.
     public let syncPolicy: SyncPolicy
     /// Human-readable description for audit reports.
+    ///
+    /// Descriptions are required to keep audit results interpretable.
     public let description: String
     /// Optional catalog name the key belongs to.
+    ///
+    /// Catalog names aid in grouping keys by feature or module.
     public let catalog: String?
 
     /// Internal initializer used by factories and audits.
+    ///
+    /// Callers should prefer `from(_:)` unless building descriptors manually.
     init(
         name: String,
         domain: StorageDomain,
diff --git a/Sources/LocalData/Models/SyncPolicy.swift b/Sources/LocalData/Models/SyncPolicy.swift
index 2430c69..9d22926 100644
--- a/Sources/LocalData/Models/SyncPolicy.swift
+++ b/Sources/LocalData/Models/SyncPolicy.swift
@@ -1,11 +1,20 @@
 import Foundation
 
 /// Defines how a key participates in WatchConnectivity sync.
+///
+/// `SyncPolicy` is interpreted by sync helpers to decide if and when data should
+/// be pushed between iPhone and Apple Watch.
 public enum SyncPolicy: Sendable {
     /// No sync behavior.
+    ///
+    /// Use this for keys that should remain device-local.
     case never
     /// Sync only when the app explicitly requests it.
+    ///
+    /// Use this when you need full control over sync timing.
     case manual
     /// Automatically sync when data size is below the configured threshold.
+    ///
+    /// Use this for small payloads that should stay in sync without manual triggers.
     case automaticSmall
 }
diff --git a/Sources/LocalData/Protocols/AggregatingMigration.swift b/Sources/LocalData/Protocols/AggregatingMigration.swift
index 676577d..81a8d5d 100644
--- a/Sources/LocalData/Protocols/AggregatingMigration.swift
+++ b/Sources/LocalData/Protocols/AggregatingMigration.swift
@@ -1,3 +1,6 @@
+/// Defines migrations that aggregate multiple source keys into a single destination.
+///
+/// Use this protocol when a new storage key is derived from multiple legacy values.
 import Foundation
 
 /// Migration protocol that combines multiple sources into a single destination.
diff --git a/Sources/LocalData/Protocols/ConditionalMigration.swift b/Sources/LocalData/Protocols/ConditionalMigration.swift
deleted file mode 100644
index f0a35bc..0000000
--- a/Sources/LocalData/Protocols/ConditionalMigration.swift
+++ /dev/null
@@ -1,4 +0,0 @@
-import Foundation
-
-/// Marker protocol for migrations that primarily use conditional checks.
-public protocol ConditionalMigration: StorageMigration {}
diff --git a/Sources/LocalData/Protocols/KeyMaterialProviding.swift b/Sources/LocalData/Protocols/KeyMaterialProviding.swift
index c328f50..ab34a7d 100644
--- a/Sources/LocalData/Protocols/KeyMaterialProviding.swift
+++ b/Sources/LocalData/Protocols/KeyMaterialProviding.swift
@@ -1,3 +1,6 @@
+/// Supplies encryption key material to support external key sources.
+///
+/// Conformers provide raw bytes used by ``SecurityPolicy.EncryptionPolicy.external``.
 import Foundation
 
 /// Supplies external key material for encryption policies.
diff --git a/Sources/LocalData/Protocols/KeychainStoring.swift b/Sources/LocalData/Protocols/KeychainStoring.swift
index 2c10f37..f8c5f14 100644
--- a/Sources/LocalData/Protocols/KeychainStoring.swift
+++ b/Sources/LocalData/Protocols/KeychainStoring.swift
@@ -1,3 +1,6 @@
+/// Defines the Keychain operations required by the storage layer.
+///
+/// This protocol enables swapping concrete Keychain implementations for testing.
 import Foundation
 
 /// Protocol defining the interface for Keychain operations.
diff --git a/Sources/LocalData/Protocols/StorageKeyCatalog.swift b/Sources/LocalData/Protocols/StorageKeyCatalog.swift
index 3fa5d91..3e02d1d 100644
--- a/Sources/LocalData/Protocols/StorageKeyCatalog.swift
+++ b/Sources/LocalData/Protocols/StorageKeyCatalog.swift
@@ -1,3 +1,6 @@
+// Defines catalog types that group storage keys for registration and auditing.
+//
+// Catalogs are the mechanism used by the router to validate keys and detect duplicates.
 /// Collection of storage keys used for registration and auditing.
 public protocol StorageKeyCatalog: Sendable {
     /// Human-readable catalog name used in audit reports.
diff --git a/Sources/LocalData/Protocols/StorageMigration.swift b/Sources/LocalData/Protocols/StorageMigration.swift
index 96a4d3d..511193d 100644
--- a/Sources/LocalData/Protocols/StorageMigration.swift
+++ b/Sources/LocalData/Protocols/StorageMigration.swift
@@ -1,3 +1,6 @@
+/// Defines the core migration contract used by the storage router.
+///
+/// All migration types build on this protocol to move or transform stored data.
 import Foundation
 
 /// Core migration protocol for moving data into a destination ``StorageKey``.
diff --git a/Sources/LocalData/Protocols/StorageProviding.swift b/Sources/LocalData/Protocols/StorageProviding.swift
index ade3dac..33afb8d 100644
--- a/Sources/LocalData/Protocols/StorageProviding.swift
+++ b/Sources/LocalData/Protocols/StorageProviding.swift
@@ -1,3 +1,6 @@
+/// Defines the storage operations required by concrete backends.
+///
+/// Storage helpers conform to this protocol to provide a common API surface.
 import Foundation
 
 /// Abstraction for basic storage operations.
diff --git a/Sources/LocalData/Protocols/TransformingMigration.swift b/Sources/LocalData/Protocols/TransformingMigration.swift
index 92a4cdd..bd3db5b 100644
--- a/Sources/LocalData/Protocols/TransformingMigration.swift
+++ b/Sources/LocalData/Protocols/TransformingMigration.swift
@@ -1,3 +1,6 @@
+/// Defines migrations that transform a source value into a new destination value.
+///
+/// Use this protocol when a single legacy key can be mapped to a new schema.
 import Foundation
 
 /// Migration protocol that transforms a source value into a destination value.