Duplicated normative call-sequence sketches across sibling artifacts drift independently under partial fixes

## Summary
An ADR's gap-inventory sketch and a story's acceptance-criterion sequence sketch are often parallel copies of the same call sequence. A partial fix that corrects one copy does not propagate to its twin. Convergence can then pass on the swept artifact while the unswept twin still carries a stale signature — caught only by a later fresh pass that happens to read both copies.

## Observed instance (generic)
A shared call-sequence appeared in both an ADR facet-inventory block and a story AC sketch. A sweep corrected the ADR copy (and even caught two extra stale lines the reviewer had not flagged), but the story copy retained a stale associated-function/no-await rendering of the same call. A subsequent fresh pass corroborated against shipped code and reset the convergence counter.

## Proposed remediation (either)
1. Engine flags cross-artifact duplicated normative sketches — a traceability/lint check for repeated call-form blocks that appear in more than one artifact kind (ADR + story), so a fix to one prompts a check of the others.
2. Fix-propagation guidance explicitly mandates sweeping ALL sibling copies of a shared sketch whenever any one is corrected.

## Impact
Partial fixes silently survive convergence; the twin drift only surfaces if a later fresh pass reads both artifacts, wasting a convergence cycle.