Quests: escorts stay on the follower list, quest givers come back

Escorts lost their place on the hero's follower list after a load, so
quest checks like the one in "Furchtbares Verbrechen" failed; they are
added back once after loading (town NPCs that tag along briefly are left
out). Restarted quests stay available (flag 1), which their giver's dialog
and accepting them need. Quest givers are read from the quest scripts:
when a running quest's giver dies, the quest restarts and the giver is
spawned again at her start; an accepted quest without its giver is repaired
on load. Notes on the script format and opcodes in docs/quests.md.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/game/engine/orders.h

@@ -68,6 +68,47 @@ constexpr size_t kCreatureId = 0xc;
 constexpr size_t kCreatureX = 0x1c;
 constexpr size_t kCreatureY = 0x20;
 
+// Escorts (measured 2026-10-26, docs/quests.md): an NPC told to follow
+// (cCreature::ReceiveOrder 0x52e400, e.g. 0x52e64f) stores its leader id at
+// +0x251, sets bit 4 of +0x1f4 (escorts of quest scripts have 0x100 instead,
+// measured on "Jagd auf die Wilderer"; the leave order clears both) and is added to the leader's follower list
+// (+0x39c..+0x3a0, 9-byte entries {u32 id, u32, u8}) with AddFollower.
+// Quest scripts test "@npc" (0x498aa0 case 0x40) against that list.
+constexpr size_t kCreatureLeader = 0x251;
+constexpr size_t kCreatureStatus = 0x1f4;
+constexpr uint32_t kStatusFollowing = 0x104;
+constexpr size_t kCreatureFollowersBegin = 0x39c;
+constexpr size_t kCreatureFollowersEnd = 0x3a0;
+constexpr size_t kFollowerEntrySize = 9;
+
+#pragma pack(push, 1)
+struct FollowerEntry {
+    uint32_t id;
+    uint32_t value;  // 1 for escorts, as the follow order adds them
+    uint8_t flag;    // 1 for escorts
+};
+#pragma pack(pop)
+static_assert(sizeof(FollowerEntry) == kFollowerEntrySize);
+
+// cCreature::AddFollower (0x54b070, thiscall (const FollowerEntry*), ret 4):
+// adds the entry to the leader's list unless its id is in it.
+inline void AddFollower(void* leader, const FollowerEntry& entry) {
+    using Fn = void(__fastcall*)(void*, void*, const FollowerEntry*);
+    reinterpret_cast<Fn>(0x0054b070)(leader, nullptr, &entry);
+}
+
+inline bool HasFollower(const void* leader, uint32_t id) {
+    const auto* creature = static_cast<const uint8_t*>(leader);
+    const auto* begin = *reinterpret_cast<const uint8_t* const*>(creature + kCreatureFollowersBegin);
+    const auto* end = *reinterpret_cast<const uint8_t* const*>(creature + kCreatureFollowersEnd);
+    for (const uint8_t* entry = begin; entry && entry < end; entry += kFollowerEntrySize) {
+        if (*reinterpret_cast<const uint32_t*>(entry) == id) {
+            return true;
+        }
+    }
+    return false;
+}
+
 // The walk path (measured 2026-10-18): waypoints {x, y} at +0x2ed + i * 8,
 // the current segment's start index at +0x36d, the count at +0x371, and the
 // step's sub-unit remainder (x, y, 1/1024 units) at +0x37d / +0x381.