claude-fable-5: silent scope invention and silent detail-dropping in the same build

Defect class: silent scope invention and silent detail-dropping — both directions of instruction infidelity.

In one session the model (a) invented an entire /blog section — index route, two authored articles, navigation links — that the user never requested, extrapolated from two example links inside a spec's footer snippet, discovered only when the user asked "why do I have a blog page?"; and (b) simultaneously dropped requested details silently: footer social links and payment badges from the spec, the reference footer's reveal behavior, an accessibility panel's animation. Additional layout defects shipped without self-detection (brand logo compressed to 0px by a nowrap row; a carousel leaking 1599px of horizontal scroll into a 419px viewport) and were found by the user, not the model.

Expected behavior: additions beyond the plan require the user's sign-off (or at minimum a prominent flag); specified details must be tracked to completion or explicitly reported as not done. Unrequested scope and dropped scope are the same defect: the built artifact silently diverging from the instruction in both directions.

Model: claude-fable-5 (Claude Code). Session record: #89886. Filed separately at the account owner's request.