`_hasSigil` short-circuits before any FFI hop and used to require a
`.`, `:`, `@`, or `+` in the text. A phone number with no leading `+`
and no separators (`0731098515`) or with parens-and-space-only
separation (`(0731) 098 515`) never crossed into NSDataDetector /
android.util.Patterns and silently rendered as plain body text.
Track a digit counter while walking the sigil scan and trip after the
fifth digit — enough to plausibly be a phone but cheap enough that
`I'm 30 today` still skips FFI. The native min-7-digit filter (added in
5512acd) still handles ZIPs / scores / version strings, so the looser
sigil doesn't cost us false positives on the rendered side.
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