fix(web): orthogonal float epsilon — flat edges no longer dive past target

[naorsabag]

Summary

Reproduced on the orion-main flow at `/flow/eIxRYAM39kwT`: the `claude-router → mongodb` road entered the database from the top instead of the left, then dove out into empty space (the user-visible "dead end").

Root cause is sub-pixel float drift after `shiftRoutesAfterSnap`: two endpoints that should share `y` differed by ~1 ULP (3e-15). `orthogonalizeRoutePoints` used strict `!==`, declared the segment diagonal, and inserted a phantom vertical corner. `inferPortAssignmentsFromRoutes` then ran `targetHandleFromSegment(0, -3e-15)` and picked `bottom` (because `|dx|=0` is not `≥ |dy|=3e-15`), so `extendRouteToNodeCenters` shifted the endpoint upward away from the node — that's the dead-end.

Fix: 0.5px epsilon on the axis-equality test. Below that we treat the segment as already orthogonal, so float noise can't fabricate a corner.

Test plan

• `npm test` in `packages/web` — 41/41 pass, including the new regression in `flow-layout.test.ts` for the sub-pixel-y case
• Verified locally against the live `flow/eIxRYAM39kwT`: route now goes `claude-router:right → mongodb:left` as a single horizontal segment instead of detouring past mongodb's top edge
• Visually confirm in `npx openhop@beta demo` after merge

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed edge routing precision in flow layouts by handling sub-pixel floating-point variations to prevent phantom orthogonal corners and incorrect port assignments.
• Tests
  • Added a regression test covering orthogonal route handling with sub-pixel mismatches to prevent future regressions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 58bd8334-2282-4cee-a2eb-2378ee78b8de

📥 Commits

Reviewing files that changed from the base of the PR and between eb62f50 and cb9296f.

📒 Files selected for processing (2)

• packages/web/__tests__/flow-layout.test.ts
• packages/web/src/lib/flow-layout.ts

✅ Files skipped from review due to trivial changes (1)

• packages/web/tests/flow-layout.test.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/web/src/lib/flow-layout.ts

---

Walkthrough

This PR addresses floating-point precision issues in orthogonal route layout by introducing an epsilon-based tolerance check. A new ORTHOGONAL_EPSILON constant prevents tiny coordinate drift from creating phantom orthogonal corners, which could otherwise mis-infer port assignments. A regression test validates the fix.

Changes

Sub-pixel Epsilon Tolerance for Orthogonal Routes

Layer / File(s)	Summary
Epsilon Constant Definition packages/web/src/lib/flow-layout.ts	Introduces ORTHOGONAL_EPSILON constant to define tolerance threshold for orthogonality checks after snap/shift operations.
Orthogonalization Logic packages/web/src/lib/flow-layout.ts	Corner-insertion condition in orthogonalizeRoutePoints updated to use tolerance-based comparison, treating points as aligned when both x and y differences are within epsilon.
Regression Test packages/web/__tests__/flow-layout.test.ts	New test case validates inferPortAssignmentsFromRoutes correctly handles route points with sub-pixel y-coordinate noise, asserting flat alignment and expected port assignments.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• naorsabag/OpenHop#57: Both PRs modify orthogonalization logic—main PR adds ORTHOGONAL_EPSILON to prevent sub-pixel noise from creating phantom corners, while the retrieved PR also orthogonalizes routes before port inference.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main fix: addressing floating-point epsilon tolerance in orthogonal route handling to prevent edges from extending past their target nodes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/orthogonal-float-epsilon

---

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

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/web/__tests__/flow-layout.test.ts`:
- Around line 288-324: The test currently calls inferPortAssignmentsFromRoutes
with a 2-point straight route which already biases horizontal dominance and
won't reproduce the pre-fix failure; update the test to run the route through
the orthogonalization step that used to insert the phantom corner (e.g., call
shiftRoutesAfterSnap or orthogonalizeRoutes on the noisyRoute for the
topology/displayEdges before calling inferPortAssignmentsFromRoutes) so the tiny
dy drift can create the intermediate corner and the regression is exercised;
locate the test's topology, edge (topology.displayEdges[0]), noisyRoute, and
replace the direct call to inferPortAssignmentsFromRoutes with the sequence that
orthogonalizes the route first and then infers port assignments.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 352aa593-c66d-4812-84a9-3904099ab069

📥 Commits

Reviewing files that changed from the base of the PR and between 2cb0644 and eb62f50.

📒 Files selected for processing (2)

• packages/web/__tests__/flow-layout.test.ts
• packages/web/src/lib/flow-layout.ts