diff --git a/docs/architecture/legacy-engine.md b/docs/architecture/legacy-engine.md
index 2f1a3bc..0f60b44 100644
--- a/docs/architecture/legacy-engine.md
+++ b/docs/architecture/legacy-engine.md
@@ -42,3 +42,4 @@ organization rather than endpoint-first routing.
 - Battle and war resolution: `docs/architecture/legacy-engine-war.md`
 - Command catalog: `docs/architecture/legacy-commands.md`
 - Scenario system and rule sets: `docs/architecture/legacy-scenarios.md`
+- Inheritance points (유산 포인트): `docs/architecture/legacy-inherit-points.md`
diff --git a/docs/architecture/legacy-inherit-points.md b/docs/architecture/legacy-inherit-points.md
new file mode 100644
index 0000000..2c5c79c
--- /dev/null
+++ b/docs/architecture/legacy-inherit-points.md
@@ -0,0 +1,161 @@
+# Legacy Inheritance Points (유산 포인트)
+
+This document describes the cross-season inheritance point system, how points
+are accumulated, merged, and spent, and which gameplay effects they unlock.
+References include `legacy/hwe/sammo/InheritancePointManager.php`,
+`legacy/hwe/sammo/API/InheritAction/*`, `legacy/hwe/sammo/TriggerInheritBuff.php`,
+`legacy/hwe/sammo/API/General/Join.php`, and `legacy/hwe/sql/schema.sql`.
+
+## Overview
+
+- Inheritance points are **user-level, cross-game currency**.
+- Points are stored in KV storage under `inheritance_{userID}` and are **not
+  cleared on season reset** (`legacy/hwe/sql/reset.sql` does not drop
+  `storage`).
+- The current spendable balance is stored in the `previous` key.
+
+## Storage and Persistence
+
+- KV storage: `storage` table with `namespace = inheritance_{userID}`.
+- Snapshot table: `inheritance_result` records per-season snapshots
+  `{server_id, owner, general_id, year, month, value}`.
+- Logs: `user_record` with `log_type = inheritPoint`.
+
+`InheritancePointManager::applyInheritanceUser()` merges all stored point
+entries into a single total and writes it back to `previous`.
+
+## Point Types and Sources
+
+The key list is defined in `InheritanceKey` and configured in
+`InheritancePointManager`. Each key has a source and a coefficient.
+
+Directly stored keys (`storeType = true`):
+
+- `previous` (기존 보유): current spendable balance.
+- `lived_month`: +1 per executed turn (`TurnExecutionHelper::executeGeneralCommandUntil`).
+- `max_domestic_critical`: updated via `updateMaxDomesticCritical()` in
+  `legacy/hwe/func_gamerule.php`.
+- `active_action`: incremented by many commands (e.g. `che_출병`, `che_거병`,
+  `che_건국`, various nation commands). Coefficient = 3.
+- `unifier`: points from unification events (e.g. `che_건국` +250,
+  `check_united()` awards +2000 for high officers).<br>
+- `tournament`: awarded in tournament routines (`legacy/hwe/func_tournament.php`).
+
+Computed keys (`storeType = false` or derived):
+
+- `combat`: from `rank_data.warnum` (war engagements) * 5.
+- `sabotage`: from `rank_data.firenum` (strategy success) * 20.
+- `dex`: sum of arm-type dex, with overflow reduction, * 0.001.
+- `betting`: `betwin * 10 * (betwingold / betgold)^2`.
+- `max_belong`: max of `general.belong` and aux `max_belong`, * 10.
+
+Notes:
+
+- NPCs (`npc >= 2`) do not earn points.
+- If `game_env.isunited != 0`, only `previous` remains available; other keys
+  are suppressed for calculation/spending.
+
+## Merge and Apply Lifecycle
+
+The system uses a two-step merge:
+
+1. **Merge** (`mergeTotalInheritancePoint`)
+   - Computes derived keys and stores them into `inheritance_{userID}`.
+   - Records a snapshot into `inheritance_result`.
+2. **Apply** (`applyInheritanceUser`)
+   - Sums all keys into a total, logs to `user_record`, resets storage to only
+     `previous` (plus any rebirth-kept keys).
+
+This merge/apply is triggered in these places:
+
+- **End of season**: `check_united()` calls merge/apply for all player
+  generals when the game is unified.
+- **Death**: `General::kill()` merges and applies for the owner and refunds
+  pending inherit actions (random unique, reserved special war).
+- **Rebirth**: `General::rebirth()` merges and applies with reduced retention
+  (`rebirthStoreCoeff`).
+
+## Spending and Effects
+
+### Join-time bonuses (`API/General/Join.php`)
+
+Players can spend points during character creation:
+
+- Choose a war special (`inheritSpecial`)
+- Select a starting city (`inheritCity`)
+- Set a turn-time zone (`inheritTurntimeZone`)
+- Add bonus stats (`inheritBonusStat`)
+
+Costs are defined in `GameConst`:
+
+- `inheritBornSpecialPoint`
+- `inheritBornCityPoint`
+- `inheritBornTurntimePoint`
+- `inheritBornStatPoint`
+
+### InheritAction APIs (`API/InheritAction/*`)
+
+- `BuyHiddenBuff`: buys a hidden buff level (1..5) stored in aux
+  `inheritBuff` (cost curve `inheritBuffPoints`).
+- `SetNextSpecialWar`: reserves the next war special (`inheritSpecificSpecialWar`).
+- `ResetSpecialWar`: clears current war special (cost grows by
+  `inheritResetAttrPointBase`, Fibonacci-extended).
+- `ResetTurnTime`: randomizes turn time offset for future turns
+  (`nextTurnTimeBase`).
+- `ResetStat`: reassigns base stats; optional bonus stats cost
+  `inheritBornStatPoint`.
+- `BuyRandomUnique`: flags `inheritRandomUnique` to guarantee a unique drop
+  once unique items become available (see below).
+- `CheckOwner`: reveals another general's owner name (cost
+  `inheritCheckOwnerPoint`).
+
+All of these are disabled once `game_env.isunited` is set.
+
+### Unique items and auctions
+
+- **Random unique**: `inheritRandomUnique` is consumed in
+  `tryUniqueItemLottery()` when unique items are available. If no items are
+  available, points are refunded.
+- **Unique auctions**: `AuctionUniqueItem` uses `inheritPoint` as the bid
+  currency. Opening an auction requires `inheritItemUniqueMinPoint`.
+
+### Betting rewards
+
+When betting is configured with `reqInheritancePoint`, rewards are paid
+directly into `previous` (`Betting::giveReward()`), and logged to
+`user_record`.
+
+## Hidden Buff System (inheritBuff)
+
+The `inheritBuff` aux value is injected into `General` as a `TriggerInheritBuff`
+action. It modifies:
+
+- Combat chances: avoid/critical/strategy trial ratios
+- Domestic success/fail probabilities
+- Opponent combat chances (negative modifiers)
+
+Buff levels are 0..5 and multiply coefficients by 0.01 per level.
+
+## Rank Tracking
+
+`MergeInheritPointRank` event aggregates all keys (except `previous`) into
+`rank_data.inherit_earned_dyn`, and then updates:
+
+- `inherit_earned` (sum of earned)
+- `inherit_spent` (from `inherit_spent_dyn`)
+
+This is used for leaderboard-style tracking.
+
+## Related Constants
+
+Key cost and limits (from `GameConstBase` / scenario overrides):
+
+- `inheritBuffPoints` (level costs)
+- `inheritSpecificSpecialPoint`
+- `inheritResetAttrPointBase`
+- `inheritCheckOwnerPoint`
+- `inheritItemRandomPoint`
+- `inheritItemUniqueMinPoint`
+- `minMonthToAllowInheritItem`
+
+Scenario files can override these via `const` in `scenario_*.json`.