feat(polish): add context safeguards, layered prompts, and output validation

Use redacted cursor neighborhood and pause-aware chunks for more natural polish,
validate protected terms with retry/local fallback, and structure bilingual prompts
for consistency and provider prefix caching.

OSGKeyboardShared/Models/PolishContext.swift

@@ -9,6 +9,34 @@
 
 import Foundation
 
+public struct FieldHints: Sendable, Equatable {
+    public let keyboardType: String?
+    public let returnKeyType: String?
+    public let isEmptyField: Bool
+    public let isContextAvailable: Bool
+
+    public init(
+        keyboardType: String? = nil,
+        returnKeyType: String? = nil,
+        isEmptyField: Bool = false,
+        isContextAvailable: Bool = false
+    ) {
+        self.keyboardType = keyboardType
+        self.returnKeyType = returnKeyType
+        self.isEmptyField = isEmptyField
+        self.isContextAvailable = isContextAvailable
+    }
+
+    public init(from context: FlowFieldContext) {
+        self.init(
+            keyboardType: context.keyboardType,
+            returnKeyType: context.returnKeyType,
+            isEmptyField: context.isEmptyField,
+            isContextAvailable: context.isContextAvailable
+        )
+    }
+}
+
 public struct PolishContext: Sendable {
     /// Coarse classification of the input field. When `.unknown` the
     /// LLM is told to pick a neutral tone on its own.
@@ -24,6 +52,12 @@ public struct PolishContext: Sendable {
     /// bias terminology choices.
     public let precedingText: String?
 
+    /// Optional text immediately after the insertion point.
+    public let followingText: String?
+
+    /// Input-field signals captured by the keyboard extension.
+    public let fieldHints: FieldHints?
+
     /// Extra dictionary block appended after `PersonalDictionary.promptFragment()`
     /// (e.g. builtin `phrases.tsv` terms on macOS local ASR).
     public let dictionarySupplement: String?
@@ -32,19 +66,26 @@ public struct PolishContext: Sendable {
     /// include in the prompt. The full preceding text is often
     /// hundreds of KB in a long note — we only need the tail.
     public let maxPrecedingChars: Int
+    public let maxFollowingChars: Int
 
     public init(
         appContext: AppContext = .unknown,
         intensity: PolishIntensity = .default,
         precedingText: String? = nil,
+        followingText: String? = nil,
+        fieldHints: FieldHints? = nil,
         dictionarySupplement: String? = nil,
-        maxPrecedingChars: Int = 500
+        maxPrecedingChars: Int = 600,
+        maxFollowingChars: Int = 200
     ) {
         self.appContext = appContext
         self.intensity = intensity
         self.precedingText = precedingText
+        self.followingText = followingText
+        self.fieldHints = fieldHints
         self.dictionarySupplement = dictionarySupplement
         self.maxPrecedingChars = maxPrecedingChars
+        self.maxFollowingChars = maxFollowingChars
     }
 
     /// Truncated view of `precedingText` ready for prompt injection.
@@ -54,4 +95,10 @@ public struct PolishContext: Sendable {
         if raw.count <= maxPrecedingChars { return raw }
         return String(raw.suffix(maxPrecedingChars))
     }
+
+    public var followingForPrompt: String? {
+        guard let raw = followingText, !raw.isEmpty else { return nil }
+        if raw.count <= maxFollowingChars { return raw }
+        return String(raw.prefix(maxFollowingChars))
+    }
 }