Preserve foreground paint order for content with decorative tails

[chubes4]

Problem

Sibling stacking heuristics can classify an entire text-bearing foreground component as a decorative underlay because one descendant protrudes from its box. In Fisiostetic, a speech bubble with a decorative tail is ranked below the hero image even though source order paints the bubble above it.

Fresh Fisiostetic trunk evidence:

• Hero image node 20:72 emits z-index:2.
• Bubble instance 20:64 emits z-index:1.
• The bubble appears after the image in source/emission order and contains visible text.
• LayoutIntentClassifier::siblingLayerRole() treats hasProtrudingDecorativeUnderlay() as evidence that the containing node itself is an underlay.

Owning contract

A content-bearing foreground node may own decorative protrusions without becoming a decorative underlay. Semantic role heuristics must not invert explicit/source paint order for overlapping foreground content.

Acceptance

• A text-bearing speech bubble with a protruding tail remains above an earlier overlapping image.
• The tail can still extend outside the bubble and participate in local isolation.
• True decorative plates/tracks remain underlays.
• Existing hero top-strip behavior remains covered without treating arbitrary foreground content as underlay.
• Add deterministic stacking contract coverage for both cases.

AI assistance

OpenAI GPT-5.6 Sol via OpenCode reproduced the defect on current trunk, traced the sibling-role ranking, and helped formulate the acceptance contract. Chris Huber remains responsible for the resulting change.

[chubes4]

Root-cause correction from the current trunk diagnostics: nodes 20:72 and 20:64 are both classified as content; the bubble is not being labeled as an underlay. The inversion comes from inferred reverse_child_order layer ranks (20:72 receives 2, 20:64 receives 1). The repair therefore preserves explicit source z-indexes and promotes overlapping text-bearing foreground above image-only media only when the competing rank is inferred. Existing protruding footer-underlay behavior remains unchanged.

AI assistance: OpenAI GPT-5.6 Sol via OpenCode ran the fixture and contract suite, found the contradictory diagnostics, and refined the root-cause analysis. Chris Huber remains responsible for the change.