FA-22953 / Autocomplete interactions / Member archive

Mention suggestion insertion: mention display doubles the trigger prefix · case 03

The trigger completion transition produces an incorrect observable state.

Member previewVariant 3 · 3 implementations · 22 checks per implementation

Case contract

A mention completion replaces only the active trigger span and stores a stable entity identifier separately from visible text. The trigger character is preserved exactly once, a trailing delimiter is added only when absent, and a stale mention query cannot replace a different trigger span. Offsets are code points.

Why this case matters

Autocomplete couples draft text, suggestion identity and asynchronous presentation; this bounded lifecycle model isolates one observable interaction defect.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
normal trigger	`"@@Alice"`	`"@Alice"`	Failed

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