fix(architecture): infer endpoint side from the dominant axis, not the bare dx sign - #379

Problem and value

Fixes #376.

On current main (1891105), an auto-routed connection whose source sits above a horizontally offset target is rejected by the Clean Flow Gate with clean-flow/endpoint-side-direction — deliver exits 1 for a diagram the router itself just laid out successfully.

Reproduction input (architecture, quality_profile: standard, viewBox [640, 360]):

{
  "schema_version": 1,
  "diagram_type": "architecture",
  "meta": { "title": "Hub above an offset spoke", "output": "hub-spoke.html",
            "quality_profile": "standard", "viewBox": [640, 360] },
  "components": [
    { "id": "hub",   "type": "cloud", "label": "Hub",   "pos": [200, 40],  "size": [176, 52] },
    { "id": "spoke", "type": "cloud", "label": "Spoke", "pos": [40, 240],  "size": [168, 52] }
  ],
  "connections": [{ "id": "hub-spoke", "from": "hub", "to": "spoke" }]
}

dx = -164, dy = +200. The router draws the vertical dogleg (data-composition-points="288,92;288,166;124,166;124,240" — out of the hub's bottom, into the spoke's top), but the old fallback selected left/right whenever center X differed, ignoring that the vertical delta was larger. The gate then failed the route it had just produced.

The fix compares center deltas and selects the horizontal side only when the horizontal delta is non-zero and at least as large as the vertical delta. Architecture rendering therefore agrees with its routed geometry.

Stability impact

• Affected mode and shared callers: architecture's inferred-side fallback in renderers/shared/geometry.mjs, consumed by cleanEndpointSideProblems and wired by render-architecture.mjs. The dx !== 0 && |dx| < |dy| class now infers vertical sides, matching the route.
• Compatibility: exact diagonals, horizontal-dominant inputs, pure vertical inputs, explicit sides, diagnostics, schemas, exit codes, and defaults remain unchanged. To avoid unrelated cross-mode regressions, workflow, dataflow, and lifecycle retain their established horizontal-first defaults through explicit legacy aliases; only architecture opts into the dominant-axis fallback.
• Failure behavior: the gate still fails closed for genuinely tangential routes; this removes the [Bug]: Auto-routing infers left/right for a hub above an offset spoke #376 false positive. No unrelated formatting or API changes are included.

Tests run

Comparison base 18911058008f17dc065af23a2cdc9bfeff6d3f7a; final candidate head f311e101083a12ad5874bfd726aa72b810028755 (97630b1 and f311e10, fork branch dajiaohuang:fix/376-dominant-axis-side-inference).

• node --test --test-concurrency=1 test/vertical-edge.test.mjs test/geometry.test.mjs test/layout-rules.test.mjs → 158 pass / 0 fail
• Extracted archify.zip package smoke (render, validate, and deliver for the reproduction) → passed
• npm run check:brand-marks, npm run check:validators, npm run check:release-identity, node test/golden.mjs → all passed
• Deterministic release archive regenerated with Node 22 (archify.zip, 79 files) and verified fresh

The full npm test sweep was attempted but hangs on this Windows host in update-notifier with idle node processes; it was interrupted after approximately 11 minutes. A broader node --test run excluding that test completed 997 tests (913 pass, 39 fail, 45 skipped); remaining failures are known Windows symlink/WSL/network/generated-gallery/star-history/evidence environment limitations. They are not introduced by this change. Remote CI remains the authoritative complete matrix.

Regression discipline: the two new tests fail against the unpatched source and pass with the fix (154 pass / 2 fail before, 158 pass / 0 fail in the focused final set).

New coverage:

• test/geometry.test.mjs — dominant-axis mirror pairs and preserved equal-delta, pure-vertical, and coincident-centre cases.
• test/layout-rules.test.mjs — the public [Bug]: Auto-routing infers left/right for a hub above an offset spoke #376 document through render, validate, and deliver, including route composition points.

Visual evidence

Not applicable — no styling or viewer change is intended. The user-visible difference is that this Class-A diagram now delivers successfully. Existing golden outputs remain unchanged.

Automated/browser and perceptual visual review: not applicable.

Generated artifacts

archify.zip was regenerated after the source changes using deterministic Node 22 packaging. The extracted package smoke test passed, and release identity/template freshness checks pass. No template, example HTML, golden, or Pages asset content was changed.

🤖 Generated with Claude Code