feat/pane-expansion : Add expansion anchors and enforce 250dp minimum…

[prateekbatra-g]

Improves the adaptive Master-Detail layout (CahierNavigationSuite) resizing behavior on large-screen devices. It adds snap-to anchors and guarantees that neither the list nor the detail pane is squished past legibility during resizing.
Key Changes

• Pane Expansion Anchors: Added snap positions in rememberPaneExpansionState at 0% (collapsed), 25% (minimum snap), 50% (half split), and 100% (expanded).
• 250dp Minimum Width: Enforced a 250.dp (MinPaneWidth) constraint using a custom .layout modifier on both listPane and detailPane.
• Refactoring: Extracted MinPaneWidth as a clean, file-level constant to prevent magic numbers and keep Composable signatures lightweight.

Before	After

[gemini-code-assist]

Code Review

This pull request configures pane expansion anchors for the list-detail scaffold, applies a custom layout modifier to enforce a minimum width on both the list and detail panes, and adjusts z-indices and elevations for proper layering. The reviewer suggests extracting the duplicated layout logic into a reusable Modifier extension function that handles clipping and collapsed states to prevent visual bleeding. Additionally, the reviewer highlights a discrepancy between the defined snapping anchors and the initial pane proportion of 0.3f, which could cause a jumpy user experience.

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[gemini-code-assist]

To avoid duplicating the complex .layout modifier logic in both listPane and detailPane, and to fix potential layout bugs, we should extract it into a reusable Modifier extension function.

Key Improvements:

1. Avoid Duplication: Keeps the code DRY and maintainable.
2. Prevent Overlap/Bleeding: When a pane's allocated width is smaller than MinPaneWidth (e.g., during resizing or when collapsing), the child would normally draw outside its bounds and overlap adjacent panes. Applying clipToBounds() prevents this visual bleeding.
3. Handle Collapsed State: If constraints.maxWidth == 0 (fully collapsed), we should avoid measuring and drawing the child at MinPaneWidth to prevent it from overlapping other visible content.

private val MinPaneWidth = 250.dp

private fun Modifier.minimumWidthLayout(minWidth: androidx.compose.ui.unit.Dp): Modifier = this
    .clipToBounds()
    .layout { measurable, constraints ->
        if (constraints.maxWidth == 0) {
            layout(0, 0) {}
        } else {
            val fixedWidth = minWidth.roundToPx()
            val placeable = measurable.measure(
                constraints.copy(
                    minWidth = fixedWidth,
                    maxWidth = maxOf(fixedWidth, constraints.maxWidth)
                )
            )
            val reportedWidth = constraints.maxWidth
            layout(reportedWidth, placeable.height) {
                placeable.placeRelative(0, 0)
            }
        }
    }

[gemini-code-assist]

Use the extracted minimumWidthLayout modifier to simplify the code and ensure correct clipping and collapsed state handling.

                                modifier = Modifier
                                    .fillMaxSize()
                                    .minimumWidthLayout(MinPaneWidth),

[gemini-code-assist]

Use the extracted minimumWidthLayout modifier here as well to keep the implementation consistent and clean.

                                        modifier = Modifier
                                            .fillMaxSize()
                                            .zIndex(1f)
                                            .minimumWidthLayout(MinPaneWidth),

[gemini-code-assist]

Add the import for clipToBounds to support the custom minimum width layout modifier.

Suggested change

	import androidx.compose.ui.layout.layout
	import androidx.compose.ui.draw.clipToBounds
	import androidx.compose.ui.layout.layout

[gemini-code-assist]

There is a discrepancy between the defined anchors (0f, 0.25f, 0.5f, 1f) and the initial pane proportion of 0.3f set in the LaunchedEffect (line 175).

Because 0.3f is not one of the snapping anchors, the pane might immediately snap to 0.25f or 0.5f as soon as the user starts dragging the handle, leading to a jumpy user experience. Consider aligning the initial proportion with one of the defined anchors (e.g., 0.25f or 0.5f), or adding 0.3f as an anchor if it is a desired snap point.

[cka-dev]

This is a nice update.

Only one thing: can you run the screenshot tests and make sure they are passing.
I think the change is affecting some of the existing screenshot tests.

[cka-dev]

lgtm