vue-tui/.agents/docs/ink-divergences.md

vue-tui - Intentional Divergences from Ink

vue-tui started as a Vue 3 port of Ink, and it still tracks Ink closely: the aim is behavioral parity except where a difference is deliberate. It is no longer only a port, though. It has its own design decisions, additive features, and Vue-native choices.

This document records the places vue-tui intentionally differs from Ink by design. A difference that is not listed here is treated as a bug, or simply unverified behavior, not a design choice.

Reference baseline: Ink v7.0.4 (commit 40b3a7578811fd616341ca4e31cc7748aeeff12f). When bumping the target Ink version, re-validate every entry below against the new source.

How to Classify a Divergence

Classify each divergence by the first rule that applies. The order matters: earlier sections are narrower, while later sections are broader fallbacks.

1. If Ink's supported subset still behaves the same and vue-tui only accepts more inputs, supports more contexts, or exposes an extra capability, put it in Additive Supersets.
2. If the primary reason is alignment with Vue's API shape, framework model, mental model, or user expectations, put it in Vue API and Mental Model Divergences.
   • Use Model-Implied Differences when the difference comes from the React/Vue framework-model boundary. Matching Ink would require React-shaped machinery inside Vue, changing a core Vue-facing contract, or dealing with a React-only concept that has no Vue equivalent.
   • Use Vue-Idiomatic Choices when Ink could be copied, but vue-tui chooses the behavior or public surface that better fits Vue's reactivity, lifecycle, component boundaries, current-props model, or API conventions.
3. If the divergence is intentional but is not additive and is not primarily Vue-aligned, put it in Intentional Divergence Choices.
4. If the note is not a divergence, put it in Non-Behavioral Notes.

Each divergence entry states what Ink does, what vue-tui does, and why the difference is deliberate. Some entries also record consequences, costs, tests, or maintainer decisions where those details are needed to understand the decision.

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Additive Supersets

vue-tui supports more than Ink in these cases. Ink-supported inputs and common use cases remain compatible; vue-tui only adds accepted inputs, contexts, or capabilities.

Multiple <Static> regions

• Ink: keeps a single staticNode; only one <Static> is honored.
• vue-tui: findStatics(root) renders every <Static> in the tree.
• Why: a tree with two <Static> regions renders both. Maintainer decision (2026-05-30): KEEP.

Ctrl+C exits under the kitty protocol too

• Ink: exits only on the legacy \x03 byte (in App), so a kitty-protocol Ctrl+C (\x1b[99;5u) parses fine but never exits. Its guard is byte-specific, not Ctrl+C-specific.
• vue-tui: one encoding-agnostic exit in the always-on stdin controller (emitInput), via parseKeypress. It matches Ctrl+C in both the legacy and kitty forms (but not Ctrl+Shift+C), so it fires no matter which composable holds raw mode (useInput / useFocus / usePaste, or none).
• Why: exitOnCtrlC is defined in terms of Ctrl+C, not one byte encoding. Keeping the exit at the single always-on layer avoids splitting the behavior across two places. Opt out with exitOnCtrlC: false. Maintainer decision (2026-05-30): KEEP. Tests: usePaste-only app exits on {legacy,kitty} Ctrl+C in input-kitty.test.ts.

parseKeypress filters kitty query-responses

• Ink: filters kitty keyboard-protocol query-responses (ESC[?Nu) in exactly one place: the auto-detection lifecycle in ink.tsx (stripKittyQueryResponsesAndTrailingPartial on a private onData buffer). Its parse-keypress.ts has no query-response branch.
• vue-tui: mirrors that detection layer (in kitty-keyboard.ts) and adds a parser-level filter: parseKeypress returns { ignore: true } for ESC[?Nu, which useInput then drops.
• Why: the detection layer does not cover the runtime input pipeline (stdin 'data' -> inputParser -> emitInput -> useInput -> parseKeypress). In enabled mode it never runs; in auto mode its onData listener and the stdin controller's handleData both subscribe to the same 'data' event, so stripping its private buffer cannot stop the chunk reaching handleData; and after detection settles the listener is gone. Empirically (Layer 2 removed, rebuilt) a stray query-response reaches a useInput handler as spurious "[?1u" input in all of those cases, including a response split across two reads, which inputParser reassembles before dispatch. The parser-level filter is therefore intentional, not redundant. Introduced 2026-05-31. Tests: "kitty query-response - end-to-end filtering" in kitty-lifecycle.test.ts (RED without it).

useAnimation() outside a render tree drives a standalone animation

• Ink: the default AnimationContext.subscribe() is a no-op subscription with startTime: 0, so a useAnimation rendered outside an Ink tree never ticks.
• vue-tui: useAnimation falls back to a freshly created standalone scheduler (inject(AnimationSchedulerKey, null) ?? createAnimationScheduler()), so frame/time/ delta advance even with no surrounding app.
• Why: the composable still does useful work in isolation, such as a unit test or a non-rendered driver. Additive; inside a tree the injected scheduler is used exactly as Ink's. Contrast with the terminal-bound composables in the outside-render-tree entry, which throw because they have no meaningful standalone mode.

measureElement / useBoxMetrics also accept a Vue component-instance ref

• Ink: measureElement(node: DOMElement) and useBoxMetrics(...) read node.yogaNode directly: a host DOMElement only.
• vue-tui: the ref is resolved through $el as well: a ref bound to a Vue component (whose root host node is on $el), not just a host-node ref, resolves to the underlying yoga node.
• Why: in Vue a template ref on a component yields the component instance, and its host node is reached via $el. Because <Box> is a defineComponent, the $el path is in fact the primary path a normal ref on <Box> takes — the bare host-node ref is the rarer raw-host case. Supporting both is a strict superset that matches how Vue refs behave; a bare host-node ref still works identically to Ink.

renderToString supports screen-reader mode

• Ink: renderToString has only a columns option; it always renders the non-SR (ANSI) frame. Ink's live render() does expose isScreenReaderEnabled (plus a full accessibility stack), so this is Ink choosing not to surface SR in the string API, not a missing SR capability.
• vue-tui: renderToString accepts isScreenReaderEnabled?: boolean. In SR mode it returns the linearized accessibility text (renderScreenReaderOutput) and prepends the linearized <Static> output, just as the non-SR path prepends the painted static frame.
• Why: vue-tui already has a parity SR renderer for the live path. Surfacing it through the string API is a strict superset (default false is byte-identical to Ink) and keeps <Static> content in generated SR snapshots. Additive.

Two apps sharing one stdin both receive input

• Ink: raw-mode count and the input listener are per-App (useRef), and Ink reads via the 'readable' event + stdin.read() (pull, App.tsx:278-313). Two render()s to different stdout but one stdin each attach a readable listener, but the first-registered listener's read() loop drains the buffer every tick, so the second app receives no input until the first unmounts. And because counts are per-App, the first app's unmount calls stdin.setRawMode(false), dropping raw mode while the second still needs it.
• vue-tui: the terminal raw-mode toggle is refcounted per-stdin (a shared WeakMap), so one app's unmount cannot drop raw mode while another holds it; and the 'data' input listener is per-controller. Each app attaches its own handleData -> own parser -> own emitter. Since 'data' (push) broadcasts to every listener, both apps receive every keystroke, and the second keeps receiving after the first unmounts.
• Why: this covers a combination vue-tui already allows: two createApps to different stdout. The same-stdout no-op is keyed on stdout, not stdin. The push model has no drain race, and a shared raw-mode refcount matches the ownership model when several renderers share one input. The common one-app-to-terminal flow is unchanged: one controller's localRefs equals the shared refs. Test: raw-mode-lifecycle.test.tsx ("two apps sharing one stdin both receive input..."). Maintainer decision (2026-06-07): KEEP.

Vue API and Mental Model Divergences

These divergences come from choosing Vue's API shape, framework model, mental model, and user expectations as the source of truth while tracking Ink. Some are model-implied: matching Ink would require React-shaped machinery inside Vue, changing a core Vue-facing contract, or handling a React-only concept that has no Vue equivalent. Others are idiomatic choices: Ink could be copied, but vue-tui chooses the behavior or public surface that better fits Vue's reactivity, lifecycle, component boundaries, current-props model, or API conventions.

Model-Implied Differences

Reactive composable state is a shallowRef, not a plain snapshot

• Ink/React: a hook re-runs on every render of its component, so it can return a plain value and the caller always reads the latest one. useFocusManager().activeId, for instance, is a bare string | undefined, re-read fresh each render.
• vue-tui: a composable's setup() runs once, so reactive state cannot be a plain snapshot: it would freeze at setup time. vue-tui returns a shallowRef whose .value updates and re-renders the template; read these as .value. Every stateful composable follows this — useFocusManager().activeId is a single ref read as .value, while a composable may instead return an object of refs (useTerminalSize() returns { columns, rows }, read as .columns.value / .rows.value). An empty single-ref state holds null (Vue's convention for an empty ref: a template ref is ref<T | null>(null)), where Ink's plain value is undefined.
• Why: the two frameworks track a changing value differently. React reads the newest value by re-running the hook; Vue wraps it in a ref the template subscribes to. This is the general rule, not a per-API choice. useFocusManager().activeId is just one instance. This follows Vue's philosophy: changing state is exposed as a reactive source, not as a one-time snapshot. Maintainer decision (2026-06-07): KEEP.

useCursor() re-assertion follows fine-grained reactivity, not React's render cascade

• Ink: useCursor's no-deps useInsertionEffect (use-cursor.ts:27-32) re-runs on every render of the cursor component, re-marking the cursor dirty (ink.tsx:494-497); log-update resets cursorDirty each commit. React re-renders a whole subtree when an ancestor commits, so if the cursor component is in that subtree it re-renders and the cursor is re-asserted, even when only an ancestor's unrelated state changed. If an unrelated sibling owns the changing state, the cursor component does not re-render, so Ink does not re-assert and the cursor is dropped that commit.
• vue-tui: useCursor propagates via watch(positionRef, ..., {flush:'sync'}). It re-asserts when the position reference changes (or the owning component re-renders and re-sets it). Vue's fine-grained reactivity re-runs only components whose own deps changed, so an ancestor-driven commit does not re-run a cursor child that did not depend on the changed value, and a set-once cursor is dropped that commit.
• Why: they agree whenever the cursor child itself re-renders (its own deps change) and in the unrelated-sibling case (both drop). They differ whenever a commit happens without the cursor child's own deps changing — most commonly an ancestor-driven commit: React's render cascade re-renders the child and re-asserts the cursor; Vue's fine-grained reactivity does not re-run the child, so the cursor is dropped that commit. Setting the position reactively in the render body does not by itself close this gap (verified by running: an ancestor-only commit drops a render-body-set cursor in vue-tui while Ink re-asserts) — it helps only when that ancestor change also flows into a ref the child reads. This is a consequence of React's cascade vs Vue's fine-grained re-render model. A global per-commit re-assert would make vue-tui diverge from Ink in the opposite (unrelated-sibling) direction, where Ink drops the cursor. Keep the reactivity-tied behavior. Maintainer decision (2026-06-01): KEEP.

A setup()-throwing component emits a dev-only [Vue warn] on stderr

• Ink: a component that throws during render surfaces only through the error overview / exit path; React emits no extra framework warning on stderr (verified: stderr stays empty).
• vue-tui: in a development build, a component whose setup() throws additionally produces Vue's own [Vue warn] lines on stderr (for example, the missing-render-function warning) that Ink has no analog for. While console patching is active (the default; disabled by patchConsole: false or debug, independent of interactive mode), vue-tui treats the [Vue warn] prefix as Vue's framework-diagnostics channel and drops those stderr lines. The patch is installed before the first mount (matching Ink, which patches before the first render), so a setup() throw during the initial mount is filtered too. With patching off, every [Vue warn] surfaces.
• Why: these warnings come from Vue itself and are dev-only (stripped in production builds); they never enter the stdout frame and do not change the exit path. Documented so the stray warn is not mistaken for vue-tui behavior: it is Vue's framework diagnostics. The prefix filter may also drop user-authored stderr logs that intentionally reuse the reserved [Vue warn] prefix; use a different application prefix when that output must be preserved. Maintainer decision (2026-06-06): KEEP.

React concurrent mode

• Ink: built on React; useTransition and interruptible concurrent rendering are React features.
• vue-tui: no equivalent.
• Why: this is a React-only concept with no Vue equivalent, so it is N/A rather than a parity gap.

<Transform> treats all-comment children as no children

• Ink: Transform returns null only for undefined / null children. React's false child and a literal [] child are not nullish, so each creates an empty ink-text node that consumes a flex-gap slot, and in screen-reader mode that node still announces accessibilityLabel (a false or [] child with a label reads the label).
• vue-tui: after slot resolution, null / false / undefined / v-if="false" / a false-yielding && all materialize as the same Comment vnode — React's false !== null edge has no Vue equivalent. <Transform> treats an absent slot, an all-comment slot, or an empty slot array (() => []) as no renderable children and returns null: the node is omitted, no gap slot is consumed, and a <Transform accessibilityLabel> whose children all resolve this way announces nothing in screen-reader mode (the guard runs before label substitution, as in Ink). Boundary parity: '' and 0 children are text vnodes, not comments — both engines render a node ('' takes a gap slot; 0 prints 0) — and a Vue JSX {[]} child is a Fragment vnode that still renders a node, matching Ink; only the bare () => [] slot collapses.
• Why: a child set that renders nothing equals omitting the child — letting framework anchors occupy layout slots would be worse than matching Ink's React-only false !== null edge, which Vue cannot see. The same forcing covers the screen-reader case: Ink announces the label for false but not null children; vue-tui sees identical comments, cannot honor both, and consistently takes the null side. The () => [] collapse alone is not model-forced (Vue can see the empty array); it is a deliberate consistency rider — in each engine () => [] and () => [false] behave alike (Ink renders a node for both, vue-tui omits both), and aligning only [] would create an asymmetry that exists in neither engine without reaching parity. Maintainer decision (2026-06-07): KEEP. Test: transform.test.tsx.

Vue-Idiomatic Choices

Entry point - createApp() instead of render()

• Ink: render(<App/>, options?): options is RenderOptions; returns an Instance.
• vue-tui: createApp(App) returns a TuiApp; app.mount(options?) takes MountOptions.
• Why: mirrors Vue's own createApp mental model. A Vue developer expects an app object (TuiApp) they mount, not a one-shot render call. The mount-options bag and the app handle are therefore Vue-shaped (MountOptions / TuiApp), not render()-shaped (RenderOptions / Instance). Do not add Ink-compatible aliases here: aliases would make the public API look render-shaped while the actual runtime contract is app-shaped. Maintainer decision (2026-06-07): KEEP.

Removing display resets to the default (visible)

• Ink: applyDisplayStyles (styles.ts) calls setDisplay(DISPLAY_NONE) whenever the prop diff carries a display that is not 'flex', and Ink's reconciler diff emits a withdrawn key as display: undefined. So clearing a previously-set display ('none' or 'flex' → removed) hides the box: Ink treats the withdrawn prop as none, neither keeping the prior value nor restoring the default. (A box that simply omits display stays visible — 'display' in style is false, so no setDisplay runs; but an explicit display={undefined} is itself applied as DISPLAY_NONE and hides, like any non-'flex' value.) In the common toggle display={hidden ? 'none' : undefined}, Ink stays hidden on the undefined branch; you must set display="flex" to show it again.
• vue-tui: a removed/undefined display resets to the Box default DISPLAY_FLEX (visible): the same state as if the prop had never been set.
• Why: render = f(current props): no display set means the default (visible). Persisting a withdrawn prop, or flipping it to hidden, does not match that model. Maintainer decision (2026-05-31): KEEP.

Public composable naming follows Vue conventions

• Ink/React: public APIs are hooks (useFocus, useInput, ...), but return-type naming is mixed: the stream/app hooks return exported context types named XProps (useStdin → StdinProps, useStdout → StdoutProps, useApp → AppProps), newer hooks return exported non-XProps types — result-named (useBoxMetrics → UseBoxMetricsResult, useAnimation → AnimationResult) or a bare data name (useWindowSize → WindowSize) — and the rest fit neither: useInput/usePaste return void, useFocus/useFocusManager return an unexported type, useCursor an inline shape, useIsScreenReaderEnabled a bare boolean.
• vue-tui: public APIs are Vue composables (useFocus, useInput, ...). Where a composable's return type is exported under a name, the name always follows VueUse's UseXReturn convention (UseAppReturn, UseStdinReturn, UseStdoutReturn, UseStderrReturn, UseAnimationReturn, UseBoxMetricsReturn); the remaining composables return void, plain boolean, or small unexported inline shapes — never an XProps type. XProps is reserved for component props (BoxProps/TextProps, derived via ExtractPublicPropTypes).
• Why: the public surface should read like Vue code: named composable return types get a single convention (UseXReturn) instead of Ink's mix of XProps, result names, and bare names, and XProps keeps its Vue meaning (component props). Return shapes still mirror Ink field-for-field where the same public state exists; reactive state is represented as refs for the model-implied reason documented above. Do not export Ink-compatible alias names for these types: Vue-first naming is more important than making type imports look portable across React and Vue. Maintainer decision (2026-06-07): KEEP.

Function-valued composable inputs use MaybeRef, not getters

• Ink/React: useInput and usePaste use React's current-props model: a hook can keep a stable event listener and still call the latest handler after a re-render.
• vue-tui: setup() runs once, so passing a function prop's current value directly (useInput(props.onInput)) captures a one-time snapshot. When a composable should follow a function-valued prop, pass a live prop ref instead: useInput(toRef(props, "onInput")) / usePaste(toRef(props, "onPaste")). A wrapper closure that reads props.onInput(...) at event time is also correct.
• Why: this is Vue's standard reactive-source boundary: pass the source, not a value read from it in setup. The handler parameter accepts MaybeRef<Handler> and resolves it with unref() when input/paste occurs. It deliberately does not accept MaybeRefOrGetter<Handler> because a handler is itself a function: useInput(() => {}) must remain an input handler, not be reinterpreted as a getter that returns one. Maintainer decision (2026-06-06): KEEP.

<Static> uses a scoped slot object instead of positional render arguments

• Ink/React: <Static> receives a function-as-children render callback and calls it as render(item, absoluteIndex).
• vue-tui: <Static> exposes a Vue scoped slot with { item, index }, so template users write v-slot="{ item, index }" and TSX users pass a slot function that receives one props object.
• Why: this is the framework-native match for React render children. Vue scoped slots pass one props object, not multiple positional arguments, and that object form is what Vue users expect for slot payloads. The rendered item/index values remain equivalent. Maintainer decision (2026-06-06): KEEP.

Intentional Divergence Choices

These divergences are deliberate, but they are not strict supersets and are not primarily driven by Vue's framework model or API conventions. vue-tui intentionally chooses a different runtime behavior, ownership rule, or out-of-contract handling.

Non-Error thrown values keep their message in the error overview

• Ink: Ink accepts the throw — a thrown non-Error (throw 'boom') is caught by its ErrorBoundary and rendered through ErrorOverview (verified by running real Ink: an ERROR overview with a blank message, exit 0, no crash) because error.message is undefined for a string throw.
• vue-tui: the error boundary keeps the raw thrown value and ErrorOverview shows String(value) as the message, so throw 'boom' renders ERROR boom, not a blank ERROR. Like Ink, no stack block is rendered when the value carries no stack.
• Why: same input, different output — not an additive superset (both accept the non-Error throw; vue-tui takes no extra input), so this is an intentional choice. Showing String(value) gives a useful message for the (lint-discouraged) non-Error throw and keeps the message vue-tui surfaced before it stopped wrapping such throws in new Error(String(value)) (which produced a misleading synthetic stack pointing at framework internals; that stack is now gone). Introduced 2026-05-31.

Second mount() on a live stdout is an inert no-op

• Ink: render() keeps one instance per stdout (WeakMap<WriteStream, Ink>); a second render(node, {stdout}) on a stream that already has a live instance warns on stderr but reuses that instance and rerenders the new tree into it.
• vue-tui: a second mount() on a still-live stdout warns on stderr, wires no second renderer, renders nothing, and returns an empty placeholder object (the real controls — unmount(), waitUntilExit() — live on the app, not on mount()'s return value). The first app's tree stays on screen. The skip is scoped to that one guarded call — derived from what the app actually wired, never sticky: a guarded different app's unmount() settles only its own exit promise and never touches the owner's stream or registry entry; the owner double-firing mount() on its own stdout keeps a fully working unmount() (the warning's recovery path); an app that once hit the guard can later mount — and cleanly unmount — on a free stdout; and a live app that merely targeted another app's busy stream stays fully killable.
• Why: a second mount() on a live stdout is a misuse (forgot to unmount(), a re-render glitch fired mount() twice, or expecting mount() to re-render — it doesn't; update reactive state for that). Ink treats it as unsupported and warns too. vue-tui fails safe: it ignores the second mount, keeps the live app rendering, and warns with the two recovery paths. It deliberately doesn't copy Ink's reuse-and-rerender: there's no clean public path to it (createApp binds the tree to the app, so an Ink-style rerender would mean reaching into the live app's container or tearing it down first), and on a misuse path keeping the running app stable beats auto-tearing it down (which would churn on a re-render glitch). Maintainer decision (2026-06-04): KEEP. Test: instance-reuse-guard.test.tsx.

Raw mode is owned for the interactive lifetime by default (rawMode option)

• Ink: raw mode is lazy / reference-counted to input hooks. useInput / useFocus / usePaste enable it on mount and release it when the last one unmounts, so a screen with no input handler falls back to cooked mode. There is no option to hold it.
• vue-tui: the rawMode mount option defaults to 'always'. Raw mode is enabled at mount and held for the whole interactive run (when interactive and stdin is a TTY), regardless of which input composables are mounted. rawMode: 'auto' opts back into Ink's exact lazy behavior.
• Why: for a long-running interactive app (a full-screen TUI, a coding agent), Ink's lazy model makes raw mode toggle as the user moves between input and no-input screens. The main consequence is echo: on a no-input / streaming screen the terminal is back in cooked mode, so typed keys echo into the half-drawn frame (and line-buffer). Ctrl+C also changes path: on a no-input screen it is a kernel SIGINT rather than the app's own \x03 intercept. Note exitOnCtrlC defaults to true in both Ink and vue-tui, so by default Ctrl+C exits either way; the divergence is only the exit path/code (a clean exit 0 vs a re-raised SIGINT 130). It matters for an app that sets exitOnCtrlC: false to handle Ctrl+C itself: under the lazy model its opt-out is bypassed on a no-input screen (the SIGINT still exits). Holding raw for the lifetime keeps echo and Ctrl+C handling identical on every screen. This matches the cross-framework norm: Bubble Tea, Textual, Ratatui, and prompt_toolkit all own the terminal for the program lifetime. Ink's hook-driven model differs: its "cooked on a no-input screen" behavior follows from refcounting input hooks rather than from an explicit no-input-screen contract.
• Consequence: owning raw mode ref()s stdin, so an 'always' app stays alive until you explicitly unmount() / exit(). It does not auto-exit when idle (the same way an Ink app holding a useInput already does not). The "render and auto-exit" pattern (Ink's inline-output use) is rawMode: 'auto'. Tests: raw-mode-lifecycle.test.tsx ('always' holds raw with no input hook; 'auto' stays cooked; no mid-session oscillation).

Resize unconditionally cancels the pending trailing commit

• Ink: resized() paints synchronously via onRender() but does not cancel a pending throttled onRender; when that trailing commit re-runs and shouldClearTerminalForFrame clears (because the previous frame overflowed), Ink emits a second clearTerminal.
• vue-tui: onResize calls scheduler.cancel() as its first, unconditional step on every resize (not only narrowing ones), dropping any pending throttled commit before its synchronous commit, so the redundant trailing clear never fires.
• Why: the synchronous resize commit already reflects the current tree, so the pending commit would repeat the same clear. The dedup is triggered by an overflowing frame plus a pending commit — not by narrowing specifically; a widening resize cancels the pending commit too. Emitting one clear instead of two has no visible behavior difference (issue #26). The separate narrowing-only writer.clear() frame reset is a distinct mechanism.

Degenerate boxes do not lay out or paint children when the content area is gone

• Ink: its size model is border-box-like: width/height are handed to Yoga as the element's outer size, while border and padding consume space inside that size. Ink has no boxSizing / content-box prop. During paint, though, Ink only clips children when overflow is hidden. With default visible overflow, children can leak into border rows or outside the box when border/padding squeeze the content area to zero, and a bare width={0} Box can still let zero-width text wrapping create extra visible rows (B\nA beside a sibling). Examples in Ink v7.0.4 include: width={3} height={2} borderStyle="single" painting the child on the bottom border row; width={2} height={3} leaking the child past the right border; width={4} height={3} paddingX={1} borderStyle="single" leaking into the bottom border; and bare width={0} text reserving rows through wrap-ansi's width-0 layout.
• vue-tui: layout computes each Box's inner content size by subtracting computed border and padding from the outer box size, clamps it to {width >= 0, height >= 0}, and temporarily removes that Box's in-flow yoga children from the layout when either dimension is zero. Paint applies the same inner-content gate, so the in-flow child subtree neither reserves invisible rows nor writes glyphs outside a nonexistent content area. Border and background are still painted as far as the outer area permits. Absolutely-positioned children are exempt — their containing block is the padding box (inside the borders), not the content rect, so they still lay out and paint (clipped only by overflow:hidden), matching Ink. Positive-size content areas keep the existing overflow behavior; this is not a blanket overflow:hidden.
• Layout model guidance: primitive Box should preserve the Yoga/flexbox model rather than paper over it with ad-hoc layout corrections. Defaults such as flexShrink: 1 are part of that model, and a child resolving to zero width or height can be a valid layout result. Higher-level components are where stronger user intent belongs: scroll, list, and viewport abstractions should keep their content at natural size (flexShrink: 0, or an equivalent encapsulated default) and let a bounded viewport clip or offset what is visible. Paint containment is the renderer invariant underneath both cases: whatever Yoga resolves, in-flow children may only paint inside their owning Box's content rectangle; if that rectangle has no positive width or height, the in-flow child subtree does not paint. Absolutely-positioned children are the exception — they paint against the containing block and are suppressed only by overflow:hidden, matching Ink.
• Why: children need a real content rectangle to lay out and paint into. If the resolved content width or height is zero, rendering child text or nested borders on top of the frame, outside the box, or on later rows is an implementation artifact, not useful output. This follows the common TUI box model: Ratatui renders child widgets into an inner Rect, Textual reduces content space from the assigned box, and Rich panels render children with child width/height after subtracting the border. Bubble Tea's viewport follows the same separation at the component level: content keeps its natural size while the viewport exposes a bounded visible window and offsets. The behavior also prevents negative repeat/count math and paint crashes in tiny legal boxes. Maintainer decision (2026-06-07): KEEP. Tests: text-wrap-width.test.tsx, flex.test.tsx, text.test.tsx, absolute-in-degenerate-box.test.tsx.
• Future content-box: this does not block adding an explicit content-box option later. That option would change how a requested size is expanded into an outer box size before layout. Once an outer box exists, the paint invariant remains the same: a child subtree only lays out and paints when the resolved inner content rectangle has positive width and height. The default remains border-box-like, matching Ink's current public sizing model.

Out-of-type style values are forwarded, not defensively coerced

• Ink: several flex/align setters coerce an invalid runtime value to a default: flexShrink non-number -> 1; alignItems/alignSelf/alignContent/ justifyContent falsy ("") -> their default (STRETCH / AUTO / FLEX_START); and an out-of-set value matches none of Ink's if-chain branches, so no setter runs and the previous/default value persists.
• vue-tui: these setters trust the typed prop surface and forward the raw value to yoga: a non-number flexShrink is passed through; toAlign("")/toJustify("") look up "" and pass undefined to the setter; and out-of-set values that yoga happens to accept (space-*/auto on alignItems) reach yoga rather than being ignored.
• Why: every one of these is reachable only via a TS-bypass. The public prop types forbid them. Within the typed contract Ink and vue-tui are identical. Ink's per-value coercion is defensive code for runtime values vue-tui's types already exclude. Duplicating those typeof/falsy guards would add checks for inputs the public types reject. (flexGrow is not in this set: both only coerce null/undefined -> 0.) If a reviewer shows any case is reachable in-type, it becomes a bug to fix, not a divergence.

Removing flexDirection / flexWrap is parity through the public <Box>

• Ink: applyFlexStyles has no reset branch for these two props (every other flex prop does), so at the raw ink-box host layer an explicit flexDirection={undefined} leaves the previous value in place. But the public <Box> re-injects flexDirection:'row' / flexWrap:'nowrap' on every render (Box.tsx:84-85, before spreading user style), so a user who removes the prop still gets the default — Ink resets through the component.
• vue-tui: resets to the Box default (row / nowrap) explicitly (G19). Through the public <Box> this is identical to Ink (verified by running: a column → removed goes "A\nB" → "AB" in both engines).
• Why: this is not a user-observable divergence — both reset through the public component; only the raw-host-layer behavior differs (vue-tui resets, Ink persists). Kept as the explicit contrast to display, which has no Box default and so genuinely diverges. Maintainer decision (2026-05-30): KEEP.

Composables throw outside a render tree

• Ink: the hooks read a React context whose default value is a no-op object, so calling e.g. useStdin() outside an Ink tree returns inert defaults without an error.
• vue-tui: useApp, useStdout, useStderr, useStdin, useTerminalSize, useFocus, useFocusManager, useInput, usePaste, useCursor, and useIsScreenReaderEnabled throw when their context is absent ("... must be called inside a vue-tui render tree"). useBoxMetrics and useAnimation do not throw: they fall back. useBoxMetrics reports zero metrics, and useAnimation drives a standalone scheduler. See the additive entry.
• Why: a composable used in the wrong place is a bug, and a thrown error names it at the call site instead of returning a context that quietly does nothing. The two exceptions fall back because they have a meaningful standalone behavior (zero metrics / a working animation), so throwing would remove a useful capability. Required app, terminal, focus, and input context should fail fast when absent; no-op defaults hide bugs. Maintainer decision (2026-06-07): KEEP.

Invalid input is validated at the component layer, not the paint layer

• Principle: vue-tui validates invalid render input (a chalk-modifier backgroundColor like "bold", an unknown borderStyle) at the component-render layer (box.ts / text.ts), not down at the paint layer. A bad value therefore throws where the error boundary catches it -> ErrorOverview -> a clean reject of waitUntilExit(), exactly like any other component error. The app reports the error instead of crashing.
• Ink: validates the same inputs lazily at paint (colorize / render-border, run from the reconciler's commit hook): outside React's ErrorBoundary, so a bad value is an uncaught crash, not a recoverable error.
• Why: the key constraint is where paint runs. vue-tui's paint runs in a Vue post-flush callback (queuePostFlushCb, decoupled from render), so a throw there escapes onErrorCaptured and wedges the scheduler. Unlike a component error, it cannot be made recoverable. The escape itself is symmetric, not a Vue weakness: a component error boundary (React ErrorBoundary; vue-tui's onErrorCaptured wrapper) covers framework-managed component work, never the renderer's paint callbacks, so a paint-layer throw is uncatchable in both engines. Validating in Box / Text keeps a bad value on that boundary-driven recoverable path; Ink's paint-time check can only crash. This is a deliberately chosen fail-safe given a constraint that is symmetric across React and Vue (recover-vs-crash), not a Vue-model-forced difference — hence an intentional choice rather than a model-implied one.
• Cost: the component-layer check is eager (no paint-time layout/squash info), so it over-throws in a few degenerate, invalid-input-only cases Ink never reaches. Realistic inputs match Ink; both error on bad input. Only the channel (recoverable reject vs crash) differs. Maintainer decision (2026-06-07): KEEP. vue-tui makes the more reliable library choice here: reject the same invalid input with a recoverable, prop-specific error instead of preserving Ink's lower-level paint crash and chalk implementation message. Tests: background-color.test.tsx, plus the borderStyle validation tests.

Non-Behavioral Notes

These notes are not divergence entries. They document Vue-facing conventions or internal mechanics so they are not mistaken for parity gaps.

• The exported host-node type is TuiNode (TuiContainer | TuiTextLeaf | TuiComment, from @vue-tui/runtime/internal), not Ink's DOM-emulation DOMElement (nodeName / attributes / childNodes). vue-tui keeps a native host tree, so the exported type names that tree; measureElement and template refs accept it. The type rename itself does not imply a runtime behavior difference from Ink's DOM-emulation node.
• null / false / undefined / v-if="false" children are materialized by Vue as comment vnodes, which vue-tui's host renderer turns into an inert TuiComment: no yoga node, paints nothing, never shifts a sibling, and skipped when counting child positions (the child.type !== "comment" guards in paint.ts, text-measure.ts, and screen-reader.ts; G52). This is renderer mechanics, not a divergence entry by itself. The observable <Transform> literal-false edge is documented above as a model-implied divergence.
• Commit timing is deliberately Ink-aligned: leading+trailing throttle at Math.max(1, Math.ceil(1000/maxFps)) ms behind a maxFps > 0 guard (34ms at the default maxFps=30 — both engines compute exactly this), synchronous resize. The scheduler mirrors the observable timing of Ink's es-toolkit throttle (run-verified vs v7.0.4): the trailing timer re-arms on every deferred call, so the trailing commit fires at lastCall+wait (not windowStart+wait), and a call arriving a full window after the first deferral commits synchronously (es-toolkit's maxWait), keeping a ~wait cadence under sustained updates. This remains true even though re-renders come from Vue's fine-grained reactivity, not a React subtree re-render. One deliberate exception: resize cancels the pending trailing commit — see the divergence entry "Resize unconditionally cancels the pending trailing commit".