docs: caveat SVD spatial positions reflect voting patterns, not policy content

SVD axes capture agreement structure — centrists 'moving left' means
voting patterns diverged from right-wing, not that parties changed
ideology. 'Acceptance without conversion' is a behavioral claim.
Documented as best-practice learning.

reports/overton_window/overton_window_synthesis.md

@@ -46,6 +46,8 @@ This is spatial *divergence*, not convergence. Centrist parties did not become r
 
 The tension between greater voting support and greater ideological distance is the puzzle that the mechanism analysis resolves.
 
+**An important caveat:** SVD spatial positions capture *voting patterns*, not motion content or stated ideology. The finding that centrists moved left on the SVD axes means centrist parties' voting patterns became more distinct from right-wing voting patterns — it does not tell us whether the motions themselves became more right-wing or left-wing in content. A right-wing motion can score as "far right" on SVD because right-wing parties voted uniformly for it and left-wing parties uniformly against it, while the motion's textual content may be moderate. Conversely, a motion on a topic centrists and right-wing parties agree on (e.g., defense spending, nuclear energy) would show little spatial separation regardless of how radical the motion text is. SVD measures agreement structure, not policy positions. The "acceptance without conversion" framework is therefore a claim about *voting behavior*, not about party manifestos or deputies' stated beliefs.
+
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 ## Indicator 3: Content Extremity