fix: remove design-debt shims — falsy ID bug, selector normalization, concurrency, exception swallowing

pipeline.ts: || undefined → ?? undefined (9 occurrences)
- || converts valid subject ID 0 to undefined because 0 is falsy in JS.
  This broke clause witnesses and topology references for the first subject.

domain-index.ts: remove .toLowerCase() on CSS selectors
- CSS selectors are case-sensitive (IDs, class names, attribute values).
  Lowercasing on lookup but not on storage (selectorIndex) meant case-
  sensitive selectors never matched — returning empty arrays silently.

canonical.ts: add warning when visualBoxes falls back to layout boxes
- visualBoxes ?? boxes silently substituted layout coordinates for visual
  space, producing incorrect results for transform-dependent assertions.
  Now emits console.warn so silent data corruption is visible.

extraction.ts: serialize materializeSemanticSelector calls (3 sites)
- Changed Promise.all over page.evaluate() to sequential for..of. While
  Playwright serializes CDP calls internally, concurrent DOM-modifying
  evaluate() calls create undefined execution order. Sequential resolution
  eliminates theoretical race conditions for semantic selector injection.

engine.ts: include stack trace in evaluator exception diagnostics
- Catch-all converted ALL exceptions (including TypeError from programming
  bugs) to IMH_EVALUATOR_EXCEPTION with just err.message. Now includes
  stack trace and logs to console.warn for visibility. Distinguishes
  TypeError (programming bug) from other evaluation errors.

648 SDK tests + 57 E2E hard tests pass, zero regressions.

packages/imhotep-core/src/canonical.ts

@@ -778,7 +778,9 @@ export function adaptSolverWorldToCanonical(
     matrices: solverWorld.matrices ?? { values: [] },
     rects: solverWorld.rects,
     boxes: solverWorld.boxes,
-    visualBoxes: solverWorld.visualBoxes ?? solverWorld.boxes,
+    visualBoxes: solverWorld.visualBoxes && solverWorld.visualBoxes.boxId.length > 0
+      ? solverWorld.visualBoxes
+      : (console.warn('[imhotep-core] adaptSolverWorldToCanonical: visualBoxes missing, falling back to layout boxes. Visual-space assertions may produce incorrect results.'), solverWorld.boxes),
     fragments: {
       fragmentId: [],
       subjectId: [],

packages/imhotep-core/src/pipeline.ts

@@ -802,8 +802,8 @@ export function executionIrToClauseDescriptors(context: ExecutionContext): Claus
         clauseKind: 'unknown',
         version: 1,
         subjectRef: executionIr.clauseSubject[i],
-        referenceRef: executionIr.clauseReference[i] || undefined,
-        frameRef: executionIr.clauseFrame[i] || undefined,
+        referenceRef: executionIr.clauseReference[i] ?? undefined,
+        frameRef: executionIr.clauseFrame[i] ?? undefined,
         options: { unsupported: true, rawType: clauseType },
       })
       continue
@@ -837,13 +837,13 @@ export function executionIrToClauseDescriptors(context: ExecutionContext): Claus
       clauseId: `clause_${i}`,
       clauseKind,
       version: 1,
-      subjectRef: subjectRef || undefined,
-      referenceRef: referenceRef || undefined,
-      frameRef: executionIr.clauseFrame[i] || undefined,
-      stateRef: context.stateIds[executionIr.clauseState[i]] || undefined,
-      timelineRef: context.timelineIds[executionIr.clauseTimeline[i]] || undefined,
-      envGuardRef: context.envGuardIds[executionIr.clauseEnvGuard[i]] || undefined,
-      toleranceRef: context.toleranceIds[executionIr.clauseTolerance[i]] || undefined,
+      subjectRef: subjectRef ?? undefined,
+      referenceRef: referenceRef ?? undefined,
+      frameRef: executionIr.clauseFrame[i] ?? undefined,
+      stateRef: context.stateIds[executionIr.clauseState[i]] ?? undefined,
+      timelineRef: context.timelineIds[executionIr.clauseTimeline[i]] ?? undefined,
+      envGuardRef: context.envGuardIds[executionIr.clauseEnvGuard[i]] ?? undefined,
+      toleranceRef: context.toleranceIds[executionIr.clauseTolerance[i]] ?? undefined,
       bounds: Object.keys(bounds).length > 0 ? bounds : undefined,
       options: Object.keys(options).length > 0 ? options : undefined,
     })