feat(typing): improve key hit accuracy and bump to 1.6.1

Add gap-filling hit regions, release-to-commit with slide-to-reselect,
touch intent offset, and full-pinyin next-key bias; cut release 1.6.1 (build 45).

OSGKeyboardExtTests/PinyinNextKeyResolverTests.swift

@@ -0,0 +1,181 @@
+// PinyinNextKeyResolverTests.swift
+// OSGKeyboard · Ext unit tests
+//
+// Phase 4: legal next-key sets and weighted ambiguous hit resolution.
+
+import XCTest
+@testable import OSGKeyboardShared
+
+final class PinyinNextKeyResolverTests: XCTestCase {
+    func testZhongPrefixAllowsG() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "zhon",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertEqual(keys, ["g"])
+    }
+
+    func testCompleteZhongAllowsNewSyllableInitials() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "zhong",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertNotNil(keys)
+        XCTAssertTrue(keys?.contains("g") == true) // zhongguo
+        XCTAssertTrue(keys?.contains("w") == true)
+    }
+
+    func testMultiSyllableTrailingGAllowsU() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "zhongg",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertTrue(keys?.contains("u") == true) // gu / guo
+    }
+
+    func testNiAllowsExtensionAndNewInitial() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "ni",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertTrue(keys?.contains("a") == true) // nia…
+        XCTAssertTrue(keys?.contains("h") == true) // nihao
+    }
+
+    func testEmptyRawDisablesBias() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertNil(keys)
+    }
+
+    func testEnglishDisablesBias() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "ni",
+            schema: .fullPinyin,
+            language: .english,
+            page: .letters
+        )
+        XCTAssertNil(keys)
+    }
+
+    func testDoublePinyinDisablesBias() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "nihk",
+            schema: .microsoftDoublePinyin,
+            language: .chinese,
+            page: .letters
+        )
+        XCTAssertNil(keys)
+    }
+
+    func testNumbersPageDisablesBias() {
+        let keys = PinyinNextKeyResolver.validNextKeys(
+            rawInput: "ni",
+            schema: .fullPinyin,
+            language: .chinese,
+            page: .numbers
+        )
+        XCTAssertNil(keys)
+    }
+
+    func testHitWeightsBoostLegalLetters() {
+        let keys = [
+            TypingKeyHitTarget(
+                id: "grid.0.0",
+                label: "G",
+                visualFrame: .zero,
+                behavior: .commitOnRelease
+            ),
+            TypingKeyHitTarget(
+                id: "grid.0.1",
+                label: "H",
+                visualFrame: .zero,
+                behavior: .commitOnRelease
+            ),
+            TypingKeyHitTarget(
+                id: "grid.0.2",
+                label: "⌫",
+                visualFrame: .zero,
+                behavior: .deleteRepeat
+            )
+        ]
+        let weights = PinyinNextKeyResolver.hitWeights(for: keys, validNext: ["g"])
+        XCTAssertEqual(weights["grid.0.0"], KeyHitBiasMetrics.legalBoost)
+        XCTAssertEqual(weights["grid.0.1"], KeyHitBiasMetrics.illegalShrink)
+        XCTAssertNil(weights["grid.0.2"])
+    }
+
+    func testWeightedNearestPrefersLegalKeyInGap() {
+        let left = TypingKeyHitTarget(
+            id: "L",
+            label: "F",
+            visualFrame: CGRect(x: 0, y: 0, width: 40, height: 50),
+            behavior: .commitOnRelease
+        )
+        let right = TypingKeyHitTarget(
+            id: "R",
+            label: "G",
+            visualFrame: CGRect(x: 46, y: 0, width: 40, height: 50),
+            behavior: .commitOnRelease
+        )
+        let plane = left.visualFrame.union(right.visualFrame)
+        // Shared expanded edge (half of 6pt gap) — both frames contain x=43.
+        let point = CGPoint(x: 43, y: 25)
+        let weighted = KeyHitTesting.hitTarget(
+            at: point,
+            targets: [left, right],
+            keyPlaneBounds: plane,
+            horizontalGap: 6,
+            verticalGap: 7,
+            edgeExpansion: 0,
+            hitWeights: [
+                "L": KeyHitBiasMetrics.illegalShrink,
+                "R": KeyHitBiasMetrics.legalBoost
+            ]
+        )
+        XCTAssertEqual(weighted?.id, "R")
+    }
+
+    func testClearSingleHitIgnoresBias() {
+        // Point clearly inside F — must not jump to boosted G.
+        let left = TypingKeyHitTarget(
+            id: "L",
+            label: "F",
+            visualFrame: CGRect(x: 0, y: 0, width: 40, height: 50),
+            behavior: .commitOnRelease
+        )
+        let right = TypingKeyHitTarget(
+            id: "R",
+            label: "G",
+            visualFrame: CGRect(x: 46, y: 0, width: 40, height: 50),
+            behavior: .commitOnRelease
+        )
+        let plane = left.visualFrame.union(right.visualFrame)
+        let point = CGPoint(x: 20, y: 25)
+        let hit = KeyHitTesting.hitTarget(
+            at: point,
+            targets: [left, right],
+            keyPlaneBounds: plane,
+            horizontalGap: 6,
+            verticalGap: 7,
+            edgeExpansion: 0,
+            hitWeights: [
+                "L": KeyHitBiasMetrics.illegalShrink,
+                "R": KeyHitBiasMetrics.legalBoost
+            ]
+        )
+        XCTAssertEqual(hit?.id, "L")
+    }
+}