GridQuantizer: opt-in grid snapping for flowchart layouts

[clintecker]

The transform the grid-alignment metric was built to guard — the "then snap" half of the lint-first plan. Flowchart first (highest value, hardest edges); other box families follow.

What

GridQuantizer.quantize(_ layout: FlowchartLayout, unit:), opt in with DiagramSpacing(gridSnap: 4).

• One seam — applied inside DiagramLayoutEngine.layout(_ chart: Flowchart, …), the single dispatch both render paths (CoreGraphics + RenderScene) and the lint IR call. All three inherit identical snapped geometry, so the draw-vs-scene conformance ratchet stays green with zero per-path work.
• Boxes grow, never clip — origin rounds down, far corner up; w/h become grid multiples.
• Edges stay attached — endpoints are re-anchored onto the snapped node borders (a grown box moves its right/bottom edge independently of the endpoint), interior waypoints snap to nearest (preserving orthogonal routing).
• Cache-safe — gridSnap is in DiagramSpacing.fingerprint, so snapped/unsnapped renders don't collide.

Verification

• Snapping drives node-coord alignment to 100% (through the metric).
• Snapped layout stays lint-clean — no edge-endpoint-detached / edge-occludes-node / nodes-overlap on the (subgraph-bearing) flowchart fixture.
• Boxes never shrink; gridSnap off is a strict identity.
• Rendered snapped vs plain: visually intact (containers, back-edges, arrows all correct), moves ≤4pt.
• 416 tests (+5). Off by default → no gallery/perf impact.

Scope

Flowchart only; block/C4/architecture/ER/class/state extend the same pattern next, then the metric floors get raised.

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.

[coderabbitai]

Warning

Review limit reached

You’ve reached a temporary PR review limit under our Fair Usage Limits Policy.

Your recent review volume is higher than typical usage, so adaptive limits are currently applied.

Next review available in: 1 minute

Enable usage-based reviews in Billing to review now. Otherwise, wait until the next included review is available.
You're only billed for reviews past your plan's rate limits ($0.25/file).

How can I continue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based reviews.

How do review limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan review availability.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, additional reviews become available more gradually as earlier reviews age out of the rolling window.

Please refer docs for additional details.

Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 38a3bf8e-3aa0-4b23-a1c0-d2c93f926b14

📥 Commits

Reviewing files that changed from the base of the PR and between 0150f2a and 116334a.

📒 Files selected for processing (5)

• Sources/MermaidLayout/DiagramLayoutFlowchart.swift
• Sources/MermaidLayout/DiagramSpacing.swift
• Sources/MermaidLayout/GridQuantizer.swift
• Sources/MermaidLayout/MermaidLayout.docc/SceneGeometryAndLinting.md
• Tests/MermaidLayoutTests/GridQuantizerTests.swift

---

_{Comment @coderabbitai help to get the list of available commands.}