TASK-72 step 2. AgentMessage consumes the typed segment list and dispatches
to owned primitives; ThinkingCard draws reasoning as a segment kind rather
than as <think> punctuation inside a flattened string, which removes the
think-fence collision class by construction.
MessageTextBlock and MessageCodeBlock are deliberately reused from the vendor
snapshot: they are markdown renderers, not agent vocabulary.
Composed by MANIFEST, imported by nothing. The activating edit is queued as
patch 0008. Qt6 qmllint: zero syntax findings; remaining warnings are the
widget-resolution class the vendor AiMessage also produces (38 vs 46).
Not verified: nothing has loaded this. No real tool round has rendered here.
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