The quest log never showed the `[n]` count of party members on a quest, because `IsUnitOnQuest` was a stub that always answered nil.
1.12.1 (`0x4dfe10`) checks both arguments first. It reads the row's quest id (`0x4df150`; a header or out-of-range row answers nil before the unit is resolved), resolves the token, and admits only you or one of the four party slots, by guid (`0x4e7f70`). It then needs the unit held as a player and scans the 20 `PLAYER_QUEST_LOG` ids for that quest. The answer is 1 or nil. The ids reach party members on the wire. `UNIT_QUEST_LOG_CHANGED` (`0x51bc63` → `0x51bd90`) fires once whenever any slot of a unit's window changes, so an open log recounts.
Unit snapshots now carry the window, the binding follows those steps, and the event fires. Tests cover each path and run the stock `QuestLogFrame.xml` to a `[2]` row; they fail against the stub.
Fixes#818
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
