fix(insertion): IME-safe accept so Japanese/CJK suggestions land on Tab

[FuJacob]

Summary

With a composing input method active (Japanese kana, Chinese pinyin, Korean hangul), the synthetic Unicode keystroke that commits an accepted suggestion is re-absorbed into the IME's composition instead of landing as literal text, so Tab consumed the suggestion word by word while inserting nothing and the session reset on the next AX poll. This detects composing input sources via Text Input Sources and commits accepts through the pasteboard instead, triggered by an AXPress on the host's real Edit > Paste menu item (located language-independently by its Cmd-V key equivalent, cached per process), so no key event exists for the input method to swallow.

Validation

• On-device, dev build, macOS Japanese IME and ATOK in a Chrome contenteditable and a native field: ghost suggestions on committed Japanese now insert on Tab, word-by-word accepts advance correctly, and switching back to a Latin layout keeps using the unchanged keystroke path. Verified in the structured logs that the committed text grows by each accepted chunk (it previously stayed frozen while the session advanced).
• Two earlier approaches were verified broken on-device and are documented in code comments: an AX kAXSelectedTextAttribute write (Chromium reports .success but silently no-ops) and synthetic Cmd-V at the HID tap (the Command flag is merged away against the physically held Tab; 12/12 pastes traversed the tap chain with nothing landing).
• xcodebuild build-for-testing ... CODE_SIGNING_ALLOWED=NO then test-without-building for CompositionInputModeClassifierTests + SuggestionSessionReconcilerTests: ** TEST SUCCEEDED **, 80 tests, 0 failures.
• swiftlint lint --quiet on all changed files: exit 0, no findings.

Linked issues

None filed; reported by a Japanese user on Reddit against v0.5.1-beta (suggestions intermittent, Tab accepts vanish without inserting). Happy to link a tracking issue if we open one.

Risk / rollout notes

• Detection is deliberately conservative: any non-keyboard-layout input source other than the shared Roman/eisu mode (com.apple.inputmethod.Roman) is treated as composing, so unknown third-party IMEs route through the paste path rather than the swallowable keystroke path. Latin keyboard users see zero behavior change.
• The IME accept path touches the clipboard: it is snapshotted (all representations) and restored 300ms later, with overlapping accepts coalescing onto one restore and a changeCount guard so a user copy during the window is never clobbered. The menu press can also briefly highlight the host's Edit menu title.
• CI build heads-up, pre-existing and not introduced here: main already requires a cotabbyinference revision with setComputeLogprob (Cut inference and AX hot-path waste: P-core threads, gated logprob, halved KV, geometry cache #667) that is not yet pushed to the package's GitHub main, so the fresh -resolvePackageDependencies in CI fails on main and on this PR alike until the package commit is pushed.

Greptile Summary

Introduces an IME-safe suggestion acceptance path for Japanese, Chinese, Korean, and other composing input methods, fixing a bug where Tab-accepted completions were silently re-absorbed by the input method instead of landing as text.

• Detection: KeyboardInputSourceMonitor subscribes to kTISNotifySelectedKeyboardInputSourceChanged and caches the result of CompositionInputModeClassifier, which conservatively treats any non-keyboard-layout, non-Roman-eisu source as composing — so unknown third-party IMEs (ATOK, Sogou) default to the safe path rather than the broken keystroke path.
• Insertion: SuggestionInserter.insert now checks the provider and routes composing sessions through insertViaPaste, which prefers pressing the host's real Edit > Paste menu item via AXPress (language-independently located by Cmd-V key equivalent, cached per PID) over a synthetic Cmd-V, since no key event exists for the IME to intercept.
• Suppression fix: The observer tap's keyDown handler now also checks isSynthetic(event) as a backstop, preventing the synthetic Cmd-V from being misclassified as a shortcut mutation when a real keystroke races to consume the countdown token.

Confidence Score: 5/5

Safe to merge. Latin keyboard users follow the unchanged code path; the composing-IME path falls back gracefully through menu press → synthetic Cmd-V → keystroke, restoring the clipboard on every failure branch.

The classification rule is pure and fully unit-tested. The AX menu walk is bounded (depth-1 only, early exit on the first Cmd-V item) and every element handle receives a 50 ms messaging timeout before being queried, capping per-accept latency. Clipboard snapshot/restore is guarded against overlapping accepts and user copies. The suppression backstop in the observer tap correctly prevents the synthetic Cmd-V from being misidentified as a user shortcut. No correctness issues were found across all changed files.

No files require special attention.

Important Files Changed

Filename	Overview
Cotabby/Support/CompositionInputModeClassifier.swift	New pure classification enum; intentionally free of Carbon/TIS for testability. Conservative 'composing' default for unknown non-layout sources is correct and well-documented.
CotabbyTests/CompositionInputModeClassifierTests.swift	Thorough test suite covering layout, hiragana, katakana, Chinese, Korean, Roman direct mode, unknown IME, and nil-mode cases. Behavioral contract is fully specified.
Cotabby/Services/Input/KeyboardInputSourceMonitor.swift	New @mainactor monitor subscribes to kTISNotifySelectedKeyboardInputSourceChanged, caches result, and uses takeRetainedValue/takeUnretainedValue correctly per TIS ownership rules.
Cotabby/Services/Suggestion/SuggestionInserter.swift	IME-safe path gates on isComposingIMEActiveProvider, routes to pressPasteMenuItem then synthetic Cmd-V fallback; clipboard snapshot/restore logic is well-guarded against overlapping pastes.
Cotabby/Support/AXHelper.swift	pasteMenuItem walks menu bar to find Cmd-V item language-independently; every element handle gets pollMessagingTimeout before being messaged, preventing main-thread stalls on slow Chromium pages.
Cotabby/Services/Input/InputMonitor.swift	Adds isSynthetic identity check as backstop in the observer tap keyDown case; prevents synthetic Cmd-V from being classified as a shortcut mutation when a real key races to consume the suppression countdown token.
Cotabby/App/Core/CotabbyAppEnvironment.swift	Wires KeyboardInputSourceMonitor into SuggestionInserter via a weak-captured closure; monitor is stored on env to extend its lifetime for the session.
Cotabby.xcodeproj/project.pbxproj	Adds CompositionInputModeClassifier.swift, KeyboardInputSourceMonitor.swift, and CompositionInputModeClassifierTests.swift to all three relevant build targets (Cotabby, Cotabby Dev, CotabbyTests).

Sequence Diagram

sequenceDiagram
    participant User as User (Tab key)
    participant IM as InputMonitor (accept tap)
    participant SI as SuggestionInserter
    participant KIM as KeyboardInputSourceMonitor
    participant AX as AXHelper
    participant App as Host App

    User->>IM: Tab keyDown
    IM->>SI: insert(suggestion)
    SI->>KIM: isComposingIMEActiveProvider()
    KIM-->>SI: true (Japanese IME active)

    SI->>SI: insertViaPaste(text)
    SI->>SI: snapshotPasteboard()
    SI->>SI: pasteboard.setString(text)

    SI->>AX: pasteMenuItem(forApplicationPID:)
    Note over AX: Walk menuBar→topLevelItem→menu→item
    Note over AX: Match Cmd-V by key char+modifiers
    AX-->>SI: "AXUIElement (Edit > Paste)"

    SI->>App: AXUIElementPerformAction(kAXPressAction)
    App->>App: Execute paste command (no key event)
    App-->>SI: .success

    Note over SI: Cache menu item per pid
    SI->>SI: Schedule clipboard restore (300ms)
    SI-->>IM: true (inserted)

    Note over SI,App: 300ms later
    SI->>SI: restorePasteboard (if changeCount unchanged)

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Comments Outside Diff (1)

1. Cotabby/Services/Suggestion/SuggestionInserter.swift, line 252-261 (link)

   DispatchWorkItem restore closure weak-self bookkeeping

   The closure calls self?.clearPendingPasteboardRestore() via a weak capture. If self is released before the 300 ms fires, pendingPasteboardRestore and savedClipboardForRestore are never nilled, leaving stale in-flight bookkeeping. The clipboard itself is still restored correctly (saved is captured by value). In practice SuggestionInserter lives for the app's lifetime so this is currently harmless, but worth noting for maintenance.

   

_{Reviews (2): Last reviewed commit: "Address Greptile review on #668" | Re-trigger Greptile}

[FuJacob]

Addressed all three review findings in 2ec2fd9: refresh() is now private, the paste-menu walk applies the 50ms poll timeout to every element it messages (menu bar, top-level items, menus, and items), and the missing-modifiers case is an explicit guard. Local validation on the rebased branch: xcodegen no drift, swiftlint clean, build-for-testing succeeded, full unit bundle 982 tests / 0 failures.