fix(voyager): clear node border highlight residue on switch

[allmonday]

Problem

When a user double-clicked an entity in the ER diagram (banner highlight kicks in: outer frame + title background painted orange) and then clicked another entity, the previous node's title background cleared correctly but a faint orange stroke lingered on the outer frame — a visible "didn't clean up fully" smudge that compounded with every switch.

Root cause

Two independent original-color stores that don't talk to each other:

• graph-ui.js::highlightSchemaBanner writes stroke / stroke-width / fill via setAttribute and saves the originals to DOM attributes data-original-stroke / -stroke-width / -fill (via _saveOriginalAttributes).
• graphviz.svg.js::setupNodesEdges (init-time) snapshots fill+stroke only (no stroke-width) to jQuery .data("graphviz.svg.color").
• clearSchemaBanners was calling gv.highlight() (which routes through restoreElement → _restoreElementColors) and then just removeAttribute-ing the data-original-* — without ever writing the saved originals back to the SVG attributes.

restoreElement couldn't reliably restore because:

1. Its jQuery data store lacks stroke-width (it hardcodes 1 on restore — see graphviz.svg.js:479)
2. The two stores are blind to each other's writes — setAttribute changes don't propagate to jQuery .data(), and data-original-* is private to graph-ui.js

Fix

In clearSchemaBanners, between gv.highlight() and removeAttribute, write the saved data-original-* values back to their corresponding SVG attributes. graph-ui.js becomes the last writer and overrides any inconsistency left by graphviz.svg.js.

   clearSchemaBanners() {
     if (this.gv) { this.gv.highlight() }
     this._lastHighlight = null

     const allPolygons = document.querySelectorAll("polygon[data-original-stroke]")
     allPolygons.forEach((polygon) => {
+      const origStroke = polygon.getAttribute("data-original-stroke")
+      const origStrokeWidth = polygon.getAttribute("data-original-stroke-width")
+      const origFill = polygon.getAttribute("data-original-fill")
+      if (origStroke !== null) polygon.setAttribute("stroke", origStroke)
+      if (origStrokeWidth !== null) polygon.setAttribute("stroke-width", origStrokeWidth)
+      if (origFill !== null) polygon.setAttribute("fill", origFill)
       polygon.removeAttribute("data-original-stroke")
       polygon.removeAttribute("data-original-stroke-width")
       polygon.removeAttribute("data-original-fill")
     })
   }

~12 lines added, single file, no API change. highlightSchemaBanner and _saveOriginalAttributes are intentionally untouched (the write path is correct; the bug was in the clear path).

Scope boundaries (what this fix does NOT do)

• ❌ Doesn't touch graphviz.svg.js (vendored library; larger blast radius)
• ❌ Doesn't change HIGHLIGHT_COLOR / HIGHLIGHT_STROKE_WIDTH constants (no color tweak)
• ❌ Doesn't change which node gets highlighted or when (no trigger logic change)
• ❌ Doesn't touch spec 007's renderErDiagram subgraph refetch logic (independent visual fix)

Test plan

• pytest tests/ -k voyager → 41 passed, 0 regressions (this change is front-end only)
• Manual browser verification still pending (T003/T004 in tasks.md):
  • uv run uvicorn demo.enterprise_voyager.voyager_demo:app --port 8010
  • Follow specs/008-voyager-node-border-residue/quickstart.md §2.2–2.10
  • Key check (§2.2): double-click Employee → click Department → DevTools compare Employee outer-frame polygon stroke / stroke-width / fill with never-clicked Role node — must be identical
  • §2.8: 20+ rapid switches, no accumulating residue
  • §3: regression sweep (existing toggles, sidebar tabs, schema/mode switches all unchanged)

Spec kit artifacts

Full spec-kit trail under specs/008-voyager-node-border-residue/:

• spec.md (3 clarify Q&As)
• plan.md + research.md (4 implementation decisions, root cause analysis)
• data-model.md (DOM attribute data flow + 8 edge cases)
• contracts/clear-banners-restore.md (before/after code, invariants, scope boundaries)
• quickstart.md (10 manual verification procedures + DevTools snippets + failure triage)
• tasks.md (6 tasks, 3 auto-completed, 3 pending manual)

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