fix bottom-row flick previews in portrait mode

docs/testing/issue-930.tdd.md

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+# Issue #930 TDD Evidence
+
+## Source and user journey
+
+- Source: <https://github.com/KazumaProject/JapaneseKeyboard/issues/930>
+- As a user flicking a key on the bottom row in portrait mode, I want the
+  selected character to remain visible while flicking down, even though there
+  is no keyboard space below the key.
+- As a user holding that key, I want all five long-press guide values, including
+  the bottom-flick `0`, to remain visible without overlapping.
+
+## Execution report
+
+- RED: `PopupWindowExtensionTest` was added before the placement helper existed.
+  Running the focused test failed during test compilation with
+  `Unresolved reference: calculateFlickBottomPopupPlacement`.
+- GREEN: the bottom-flick placement now detects portrait bottom-row keys and
+  places their popup above the anchor with a downward-pointing arrow. The same
+  focused command passed all three placement cases.
+- RED: the long-press guide tests initially failed to compile because its
+  placement helper did not exist. A second RED showed that fixed-height spacing
+  overlapped when the popup size was increased.
+- GREEN: portrait bottom-row long-press guides now shift the top, left, center,
+  and right values inward while placing the bottom value over the anchor. The
+  spacing uses both popup and anchor height, so configured popup scaling remains
+  separated.
+- Regression: all 13 TenKey unit tests passed, and
+  `:app:assembleLiteStandardDebug` completed successfully.
+- Emulator: `:app:installLiteStandardDebug` installed the updated APK on
+  `Medium_Phone_API_36.1`, and the Lite IME was selected again.
+
+## Test specification
+
+| # | What is guaranteed | Test or command | Type | Result |
+|---|---|---|---|---|
+| 1 | A portrait bottom-row down-flick is shown above the key instead of being omitted below the keyboard | `PopupWindowExtensionTest.portraitBottomRowFlickBottomIsPlacedAboveTheAnchor` | Unit | PASS |
+| 2 | A portrait non-bottom-row down-flick keeps its normal directional placement | `PopupWindowExtensionTest.portraitNonBottomRowFlickBottomKeepsTheDirectionalPlacement` | Unit | PASS |
+| 3 | A landscape bottom-row down-flick keeps its existing directional placement | `PopupWindowExtensionTest.landscapeBottomRowFlickBottomKeepsTheDirectionalPlacement` | Unit | PASS |
+| 4 | A portrait bottom-row long press displays the complete five-way guide inside the keyboard edge | `PopupWindowExtensionTest.portraitBottomRowLongPressGuideIsShiftedAboveTheKeyboardEdge` | Unit | PASS |
+| 5 | Enlarged long-press popups use scaled spacing and do not collapse onto each other | `PopupWindowExtensionTest.portraitBottomRowLongPressGuideUsesTheScaledPopupSpacing` | Unit | PASS |
+| 6 | Non-bottom portrait and landscape guides retain their previous offsets | `PopupWindowExtensionTest.portraitNonBottomRowLongPressGuideKeepsItsExistingOffsets`, `landscapeBottomRowLongPressGuideKeepsItsExistingOffsets` | Unit | PASS |
+| 7 | Existing TenKey behavior remains valid | `:tenkey:testDebugUnitTest` | Unit, 13 tests | PASS |
+| 8 | The Lite Standard debug application packages successfully | `:app:assembleLiteStandardDebug` | Build | PASS |
+| 9 | The modified TenKey module satisfies Android Lint | `:tenkey:lintDebug` | Static analysis | PASS |
+
+## Coverage and known gaps
+
+No JaCoCo task is configured for this module, so no numeric coverage percentage
+is available. The placement helpers' bottom-row, non-bottom-row, portrait,
+landscape, default-size, and scaled-size branches are exercised directly.
+
+The complete Lite application unit suite executed 1,260 tests, with 1,253
+passing, 4 skipped, and 3 unrelated existing failures in SQLite migration and
+system n-gram tests. Application-wide lint also remains blocked by 15 existing
+errors, beginning with a `MissingPermission` error in
+`GemmaImeMediaPanelController.kt`; TenKey lint passes.
+
+RED and GREEN were recorded without checkpoint commits because repository
+instructions reserve commits and GPG authentication for the user.