json_string_array took the first "Tags" array anywhere in the document,
justified by Self-before-Peer field order. An untagged Self omits the key
entirely (Go omitempty), so the match fell through into Peer and returned
a peer's tag — false-refusing every login join and false-verifying
untagged authkey joins on any tailnet with a tagged node. Extract Self by
brace counting (Location nests an object, so slicing to the next key
would truncate) and read the array inside it.
Refs #160
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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