[sebxt]

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fix

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fix(ast): 查找空字符串 key 时不再匹配已 Unset 的槽位

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en: Unset zeroes the removed pair, and a zeroed Pair{} has the key "". linkedPairs.Get compared only the key, so on {"a":1,"":2} after Unset("a"), Get("") matched the removed slot and reported the key as missing, and Set("", v) appended a duplicate "" pair ({"":2,"":3}).

The linear search now skips zeroed slots. A slot is treated as removed only when its hash is 0, its key is empty and its value is V_NONE; pairs built by NewPair (parser, Set) always have a non zero hash, so a real "" key, and a key explicitly set to an empty Node{} (relied on by TestNodeAny), still match.

Added TestGetEmptyKeyAfterUnset in ast/node_test.go; it fails on main and passes with this change. go test ./ast (default and with SONIC_USE_OPTDEC=1 SONIC_USE_FASTMAP=1 SONIC_ENCODER_USE_VM=1), go test ./issue_test ./generic_test . pass.

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Fixes #1004