Keep ghost text perfectly still through word accepts (TextEdit jitter)

Cotabby.xcodeproj/project.pbxproj

@@ -305,6 +305,7 @@
 		709F365A846B908D953FA92D /* FoundationModelPromptRenderer.swift in Sources */ = {isa = PBXBuildFile; fileRef = FE7BF162A12703249726F20A /* FoundationModelPromptRenderer.swift */; };
 		70D6F9480DA4104AD5669569 /* WelcomePermissionStepView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5D6C2318E405AA717D1C256 /* WelcomePermissionStepView.swift */; };
 		7179FB0EC6411166CCD79F6B /* CompositionInputModeClassifier.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4F283E5B403F9FEBFB4BA04A /* CompositionInputModeClassifier.swift */; };
+		7324B18578C646B1ADFF0C3F /* InsertedTextAdvanceTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7C46024A6D18B1AD9D04B3BD /* InsertedTextAdvanceTests.swift */; };
 		735C2E64CA51F58098B30A0D /* it.txt in Resources */ = {isa = PBXBuildFile; fileRef = 0397F1DACB094A0F6A66BC0E /* it.txt */; };
 		74422BB837D6A319D12BF981 /* BaseCompletionPromptRenderer.swift in Sources */ = {isa = PBXBuildFile; fileRef = 85EF79E6144D6C6AD062B569 /* BaseCompletionPromptRenderer.swift */; };
 		744B06C2488156B178675615 /* PermissionManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = 85BF316556FDA64CB8AD07B6 /* PermissionManager.swift */; };
@@ -523,6 +524,7 @@
 		CF2EADEEEF5AA63FB9B9EA8E /* SuggestionInserter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0A3D1125B962CBE0269EEDDB /* SuggestionInserter.swift */; };
 		CF39EB76C3ECF8F764C1B4FB /* DeviceInfo.swift in Sources */ = {isa = PBXBuildFile; fileRef = 29ED42C4BDD0C521101AF95E /* DeviceInfo.swift */; };
 		CF4205B85D881B8176590D25 /* FocusSnapshotResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 04E25414C307A20B6F9F20EC /* FocusSnapshotResolver.swift */; };
+		CFDB42AB7DC7F9663450BC7F /* InsertedTextAdvance.swift in Sources */ = {isa = PBXBuildFile; fileRef = A1267FF524A170ACC144E919 /* InsertedTextAdvance.swift */; };
 		D0D4C0E28F5CD99669A49414 /* FoundationModelAvailabilityService.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8724ECA8FABBC82B0A2B943B /* FoundationModelAvailabilityService.swift */; };
 		D1D7D50E5C620042CEA3A77E /* LaunchAtLogin in Frameworks */ = {isa = PBXBuildFile; productRef = E0AA9F90B83B823132880E6F /* LaunchAtLogin */; };
 		D21EBD25BCB37E69B633BC00 /* CotabbyDebugOptionsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93AF1246C1C2E296A1162E63 /* CotabbyDebugOptionsTests.swift */; };
@@ -549,6 +551,7 @@
 		DA23422A2CF77CFD3B1283C8 /* OnboardingTemplateFeatureListTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D814BBA41CF29E8DD9954651 /* OnboardingTemplateFeatureListTests.swift */; };
 		DAD77998F793468D4D64B705 /* DateMacroEvaluator.swift in Sources */ = {isa = PBXBuildFile; fileRef = F671FE53CDEAE9091EFBCE45 /* DateMacroEvaluator.swift */; };
 		DB1310FF3576ACA6472C4DB1 /* TrailingDuplicationFilterTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = E19A5B462891263BDFB56607 /* TrailingDuplicationFilterTests.swift */; };
+		DB7BE0A914BF75654D9EA6FF /* InsertedTextAdvance.swift in Sources */ = {isa = PBXBuildFile; fileRef = A1267FF524A170ACC144E919 /* InsertedTextAdvance.swift */; };
 		DC0394C83D334B92A512A775 /* NOTICE.md in Resources */ = {isa = PBXBuildFile; fileRef = 66CF2A70D4699421AC9BD849 /* NOTICE.md */; };
 		DC84D6A6A2F9A1060CD20ABB /* TokenCountEstimator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 1BA30E71C21C77BB6EA4C166 /* TokenCountEstimator.swift */; };
 		DCABB8D2B391C7820D6CA5FF /* InsertionSafetyGate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7D472F9F396672E57873303B /* InsertionSafetyGate.swift */; };
@@ -811,6 +814,7 @@
 		78E280F4F39A9D86840800D2 /* SuggestionCoordinator+Lifecycle.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "SuggestionCoordinator+Lifecycle.swift"; sourceTree = "<group>"; };
 		78E49BDA7F3A42455C4C5350 /* HuggingFaceModelBrowserView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HuggingFaceModelBrowserView.swift; sourceTree = "<group>"; };
 		7C0FCC5CCF6AE528E3C4DDA7 /* PerformanceMetricsStoreTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PerformanceMetricsStoreTests.swift; sourceTree = "<group>"; };
+		7C46024A6D18B1AD9D04B3BD /* InsertedTextAdvanceTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InsertedTextAdvanceTests.swift; sourceTree = "<group>"; };
 		7C9BB65FA5FC42B89766B037 /* he-100k.txt */ = {isa = PBXFileReference; lastKnownFileType = text; path = "he-100k.txt"; sourceTree = "<group>"; };
 		7D472F9F396672E57873303B /* InsertionSafetyGate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InsertionSafetyGate.swift; sourceTree = "<group>"; };
 		7E44E393DD58B978B1EAB6CF /* GhostTextColorPreset.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GhostTextColorPreset.swift; sourceTree = "<group>"; };
@@ -866,6 +870,7 @@
 		9E5F074ED7E340E9B9E4C5E0 /* EmojiPickerModels.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EmojiPickerModels.swift; sourceTree = "<group>"; };
 		9E6439213F2A273702A6E26B /* GhostFontMetrics.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GhostFontMetrics.swift; sourceTree = "<group>"; };
 		9E72A3972E15749337539C2D /* EmojiRecents.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EmojiRecents.swift; sourceTree = "<group>"; };
+		A1267FF524A170ACC144E919 /* InsertedTextAdvance.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InsertedTextAdvance.swift; sourceTree = "<group>"; };
 		A168A7B6A7AD11559B60C56B /* ApplicationBundleMetadataTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ApplicationBundleMetadataTests.swift; sourceTree = "<group>"; };
 		A28B4A4368DB33C25E3AB5F3 /* EmojiPaneView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EmojiPaneView.swift; sourceTree = "<group>"; };
 		A3E8E86A14090BC7BD13BA76 /* AppDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppDelegate.swift; sourceTree = "<group>"; };
@@ -1366,6 +1371,7 @@
 				D0AF9479EF020071CA64CCC1 /* HuggingFaceModelsTests.swift */,
 				BAC01317B0B68E3C4125E421 /* InputMonitorTests.swift */,
 				01F583E92B0A78212B330E6E /* InputSuppressionControllerTests.swift */,
+				7C46024A6D18B1AD9D04B3BD /* InsertedTextAdvanceTests.swift */,
 				43D627C4A55359EAF4676FF7 /* InsertionSafetyGateTests.swift */,
 				2960080A726E51198225147A /* InsertionStrategySelectorTests.swift */,
 				2930EC34057319130393696B /* KeyCodeLabelsTests.swift */,
@@ -1596,6 +1602,7 @@
 				043E8AA850F930222DD112C0 /* GhostSuggestionLayout.swift */,
 				7E44E393DD58B978B1EAB6CF /* GhostTextColorPreset.swift */,
 				41BBD5A4BA08CABE77860886 /* HardwareCapabilityProbe.swift */,
+				A1267FF524A170ACC144E919 /* InsertedTextAdvance.swift */,
 				7D472F9F396672E57873303B /* InsertionSafetyGate.swift */,
 				E0D2FEEA4304C86324BAADAB /* InsertionStrategySelector.swift */,
 				EAAE6B395FAB604DF059280A /* KeyCodeLabels.swift */,
@@ -1932,6 +1939,7 @@
 				266DB36F6BD7AD1038F13E39 /* InputModels.swift in Sources */,
 				5ADAA8600CE1A5ED570F889E /* InputMonitor.swift in Sources */,
 				3AC2F7F221F7C59242B06DFC /* InputSuppressionController.swift in Sources */,
+				CFDB42AB7DC7F9663450BC7F /* InsertedTextAdvance.swift in Sources */,
 				FC0C0C43EEC80325FE699B5A /* InsertionSafetyGate.swift in Sources */,
 				ADBCB725707ED11B19C7F08D /* InsertionStrategySelector.swift in Sources */,
 				1C267B67EA61527B74C9D051 /* KeyCodeLabels.swift in Sources */,
@@ -2156,6 +2164,7 @@
 				5F019E5A0679FFB52F129798 /* InputModels.swift in Sources */,
 				2DF5A3826AAB99C279EBB8DE /* InputMonitor.swift in Sources */,
 				6955C3A4D7AB3EEF7FA7C469 /* InputSuppressionController.swift in Sources */,
+				DB7BE0A914BF75654D9EA6FF /* InsertedTextAdvance.swift in Sources */,
 				DCABB8D2B391C7820D6CA5FF /* InsertionSafetyGate.swift in Sources */,
 				9D0F4829D11BCD4DB1290410 /* InsertionStrategySelector.swift in Sources */,
 				F78F594F77C26C233377E71F /* KeyCodeLabels.swift in Sources */,
@@ -2342,6 +2351,7 @@
 				663D37E35292F38666D807A7 /* HuggingFaceModelsTests.swift in Sources */,
 				07D046D406411ED85AC5758A /* InputMonitorTests.swift in Sources */,
 				0FCBF2250722780E46A92EE6 /* InputSuppressionControllerTests.swift in Sources */,
+				7324B18578C646B1ADFF0C3F /* InsertedTextAdvanceTests.swift in Sources */,
 				83EC3543DC45B1601F119BF9 /* InsertionSafetyGateTests.swift in Sources */,
 				FC255241A3B34A5717F09B36 /* InsertionStrategySelectorTests.swift in Sources */,
 				F66F0D982EBAF5A3E99C5342 /* KeyCodeLabelsTests.swift in Sources */,

Cotabby/App/Coordinators/SuggestionCoordinator+Acceptance.swift

@@ -240,7 +240,7 @@ extension SuggestionCoordinator {
         insertionChunk: String,
         liveContext: FocusedInputContext
     ) {
-        if overlayController.advanceInline(to: remainingText) {
+        if overlayController.advanceInline(to: remainingText, insertedText: insertionChunk) {
             return
         }
 
@@ -250,6 +250,7 @@ extension SuggestionCoordinator {
             oldCaretRect: liveContext.caretRect,
             caretQuality: liveContext.caretQuality,
             observedCharWidth: liveContext.observedCharWidth,
+            fieldStyle: liveContext.resolvedFieldStyle,
             isRightToLeft: isRTL
         )
         presentOverlay(
@@ -492,9 +493,9 @@ extension SuggestionCoordinator {
         }
 
         state = .ready(text: advancedSession.remainingText, latency: advancedSession.latency)
-        // Same exact-width slide as Tab acceptance; the user typed the next characters, so the tail
-        // shrank by them. Fall back to the (session-start) caret anchor only if the slide can't apply.
-        if !overlayController.advanceInline(to: advancedSession.remainingText) {
+        // Same slide as Tab acceptance; the user typed the next characters, so the caret traveled
+        // by exactly them. Fall back to the (session-start) caret anchor only if the slide can't apply.
+        if !overlayController.advanceInline(to: advancedSession.remainingText, insertedText: typedCharacters) {
             presentOverlay(
                 text: advancedSession.remainingText,
                 at: session.baseContext.caretRect,
@@ -578,17 +579,21 @@ extension SuggestionCoordinator {
     /// Estimates the caret rect after inserting a chunk by shifting the old caret in the text
     /// direction. LTR shifts right; RTL shifts left.
     /// When `observedCharWidth` is available (measured from real AX child frames), we use it
-    /// directly — this matches the target app's actual font. Falls back to NSFont measurement.
+    /// directly — this matches the target app's actual font. Otherwise the field's resolved font
+    /// measures the chunk (the host's true caret travel), and only a host with no usable style
+    /// falls back to a system-font approximation.
     static func predictedCaretRect(
         after insertedChunk: String,
         oldCaretRect: CGRect,
         caretQuality: CaretGeometryQuality,
         observedCharWidth: CGFloat?,
+        fieldStyle: ResolvedFieldStyle? = nil,
         isRightToLeft: Bool = false
     ) -> CGRect {
         let measuredWidth = predictedChunkWidth(
             insertedChunk: insertedChunk,
-            observedCharWidth: observedCharWidth
+            observedCharWidth: observedCharWidth,
+            fieldStyle: fieldStyle
         )
         let chunkWidth: CGFloat
 
@@ -628,20 +633,28 @@ extension SuggestionCoordinator {
 
     private static func predictedChunkWidth(
         insertedChunk: String,
-        observedCharWidth: CGFloat?
+        observedCharWidth: CGFloat?,
+        fieldStyle: ResolvedFieldStyle? = nil
     ) -> CGFloat {
         if let observed = observedCharWidth {
             return observed * CGFloat(insertedChunk.count)
         }
 
+        // The field's own font is the host's true caret travel; the system-14 fallback measured
+        // TextEdit's Helvetica 12 a quarter too wide, and the resulting overshoot surfaced as a
+        // corrective snap once AX published the real caret.
+        if let hostAdvance = InsertedTextAdvance.width(of: insertedChunk, style: fieldStyle) {
+            return hostAdvance
+        }
+
         let attrs: [NSAttributedString.Key: Any] = [
             .font: NSFont.systemFont(ofSize: 14)
         ]
         return (insertedChunk as NSString).size(withAttributes: attrs).width
     }
 
     /// Gives the host app ~30ms to process the synthetic keystroke, then forces an AX snapshot
-    /// so the overlay snaps to the real caret position without waiting for the 250ms poll.
+    /// so the overlay snaps to the real caret position without waiting for the 80ms poll.
     func schedulePostInsertionRefresh() {
         DispatchQueue.main.asyncAfter(deadline: .now() + 0.03) { [weak self] in
             guard let self else { return }

Cotabby/App/Coordinators/SuggestionCoordinator+Prediction.swift

@@ -698,7 +698,10 @@ extension SuggestionCoordinator {
             newText: reconciledSession.remainingText,
             newCaretRect: liveContext.caretRect,
             newInputFrameRect: liveContext.inputFrameRect,
-            newFocusChangeSequence: liveContext.focusChangeSequence
+            newFocusChangeSequence: liveContext.focusChangeSequence,
+            // While the host has not published our own synthetic insert, this snapshot's caret is
+            // the pre-insertion one; re-anchoring to it is the left-then-right accept jitter.
+            isAwaitingPostInsertionSync: interactionState.isAwaitingPostInsertionSync
         ) {
             presentOverlay(
                 text: reconciledSession.remainingText,

Cotabby/Models/SuggestionSubsystemContracts.swift

@@ -226,18 +226,19 @@ protocol SuggestionOverlayControlling: AnyObject {
     func showSuggestion(_ text: String, geometry: SuggestionOverlayGeometry)
     func hide(reason: String)
 
-    /// Advances a visible single-line inline ghost to `remainingText` by sliding the panel by the
-    /// exact rendered width of the text just handed off, keeping the remaining glyphs on the same
-    /// pixels (no caret re-read, no jitter). Returns `false` when the controller cannot safely slide
-    /// (hidden, mirror mode, RTL, multi-line, or nothing rendered to measure against); callers then
-    /// fall back to a caret-anchored present.
-    func advanceInline(to remainingText: String) -> Bool
+    /// Advances a visible single-line inline ghost to `remainingText` by sliding the panel right
+    /// by the caret's travel for `insertedText` (the text that just landed in the host, whether
+    /// Cotabby typed it or the user did). The slide reads the held overlay state, never a fresh AX
+    /// caret, so it cannot jitter against AX noise. Returns `false` when the controller cannot
+    /// safely slide (hidden, mirror mode, RTL, multi-line, or nothing rendered to measure
+    /// against); callers then fall back to a caret-anchored present.
+    func advanceInline(to remainingText: String, insertedText: String) -> Bool
 }
 
 extension SuggestionOverlayControlling {
     /// Default: not supported, so conformers that do not render an inline panel (e.g. test doubles)
     /// transparently fall back to the caret-anchored present path.
-    func advanceInline(to remainingText: String) -> Bool { false }
+    func advanceInline(to remainingText: String, insertedText: String) -> Bool { false }
 }
 
 @MainActor

Cotabby/Services/UI/OverlayController.swift

@@ -225,12 +225,12 @@ final class OverlayController: SuggestionOverlayControlling {
     }
 
     /// Advances a visible single-line inline ghost to `remainingText` by sliding the panel right by
-    /// the exact rendered width of the text just handed off, so the remaining glyphs stay on the same
-    /// pixels. This is the "perfectly still" path for word-by-word acceptance and type-through: it
-    /// reads the held overlay state (not a fresh AX caret), so it cannot jitter against AX noise.
+    /// the caret's travel for `insertedText`. This is the "perfectly still" path for word-by-word
+    /// acceptance and type-through: it reads the held overlay state (not a fresh AX caret), so it
+    /// cannot jitter against AX noise.
     /// Returns `false` when the held overlay is not a single-line, LTR, inline ghost this can safely
     /// slide; the caller then falls back to a caret-anchored present.
-    func advanceInline(to remainingText: String) -> Bool {
+    func advanceInline(to remainingText: String, insertedText: String) -> Bool {
         guard case let .visible(beforeText, geometry, mode) = state,
               case .inline = mode,
               !geometry.isRightToLeft,
@@ -242,8 +242,24 @@ final class OverlayController: SuggestionOverlayControlling {
         }
 
         let renderFont = lastInlineRenderFont ?? NSFont.systemFont(ofSize: fontSize)
-        let shift = GhostSuggestionLayout.renderedWidth(of: beforeText, font: renderFont)
-            - GhostSuggestionLayout.renderedWidth(of: remainingText, font: renderFont)
+        // Trusted-geometry hosts get the slide measured in the field's own font: that is the
+        // caret's true travel, so the anchor stays aligned with the post-publish AX caret and the
+        // stability gate never has to issue a delayed corrective nudge. The ghost render font is
+        // floored at 14pt for legibility, so its width of the same text overshoots a 12pt host by
+        // ~15% per accepted word; that error used to accumulate in the anchor until the gate
+        // snapped the tail sideways with no input in flight. The cost is a few points of tail
+        // shift at the accept keystroke itself (the ghost glyphs are wider than the host's), which
+        // lands exactly when the text visibly changes anyway. Untrusted/web geometry keeps the
+        // pixel-identical ghost-width slide: its anchors are approximate either way, and observed
+        // char-width hosts already correct through their own machinery.
+        let shift: CGFloat
+        if geometry.caretQuality == .exact,
+           let hostAdvance = InsertedTextAdvance.width(of: insertedText, style: geometry.resolvedFieldStyle) {
+            shift = hostAdvance
+        } else {
+            shift = GhostSuggestionLayout.renderedWidth(of: beforeText, font: renderFont)
+                - GhostSuggestionLayout.renderedWidth(of: remainingText, font: renderFont)
+        }
         // A non-positive or non-finite shift means the tail did not shrink as expected; re-anchor.
         guard shift.isFinite, shift > 0 else {
             return false