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+# **TextArena Game Design Document: “Runic Grid”**
+
+*(Design stage only – no code yet)*  
+This design invents an original game, **Runic Grid**, inspired structurally by turn-based spatial strategy but **completely distinct** in theme, background, and terminology from any tic-tac-toe or negotiation examples.
+
+---
+
+## 1. Concept Paragraph
+
+In **Runic Grid**, two rival mystics, the **Solar Scribe** and the **Lunar Scribe**, compete to inscribe magical runes onto a sacred 3×3 **Runic Tablet**. Each cell of the Tablet can bear only one rune, either a **Sun Rune (☼)** or a **Moon Rune (☽)**. The goal is to channel divine alignment by creating a continuous triad of your own rune horizontally, vertically, or diagonally before your opponent does. This design has no themes of trade, debate, or negotiation—it is a deterministic puzzle duel of pattern claiming. The core actions are **[Inscribe:x,y]**, where each player selects a tile to mark on their turn.
+
+---
+
+## 2. Roles and Win Condition
+
+- **Players**:  
+  - Player 1: *Solar Scribe* (places **Sun Runes, ☼**)  
+  - Player 2: *Lunar Scribe* (places **Moon Runes, ☽**)
+  
+- **Win Condition**:  
+  A player wins immediately upon forming three of their runes in a continuous line—horizontal, vertical, or diagonal—on the Runic Tablet.
+
+- **Loss Condition**:  
+  The opponent achieves a triad alignment first.
+
+- **Draw Condition**:  
+  All nine cells are occupied with no winning triad.
+
+---
+
+## 3. Turn Structure and Determinism
+
+- Turns alternate between Solar and Lunar Scribe starting with Solar Scribe.
+- One action per turn.
+- Deterministic: No randomness; the entire environment is reproducible from the same sequence of moves and initial seed.
+- Maximum turn count: **9** (since there are 9 cells).
+- Each step is deterministic; random seed affects only initial player ordering if randomized (optional).
+
+---
+
+## 4. Action Grammar (Machine-Parseable)
+
+**Allowed Action Format**:  
+Each player submits an action inside `\boxed{{}}`.  
+Inside the braces, the content must follow one of the following patterns:
+
+### 4.1 `[Inscribe:x,y]`
+
+Places the player's rune at coordinates `(x, y)` on the 3×3 Runic Tablet.
+
+- **Pattern**:  
+  ```
+  ^\[Inscribe:(?:[0-2]),(?:[0-2])\]$
+  ```
+  where `x` and `y` are integers 0, 1, or 2 representing row and column indexes.
+
+- **Interpretation**:  
+  (0,0) = top-left, (2,2) = bottom-right.
+
+- **Example Valid Action**:  
+  ```
+  [Inscribe:1,2]
+  ```
+  → Marks the middle-right cell.
+
+- **Example Invalid Action**:  
+  ```
+  [draw:1,2]
+  ```
+  → Invalid because the verb “draw” does not match required token “Inscribe”.
+
+Another invalid example:  
+  ```
+  [Inscribe:3,0]
+  ```
+  → Invalid because coordinate 3 is outside permitted range 0–2.
+
+**Only one grammar token exists**; the rest of the system enforces availability, legality, and turn order.
+
+---
+
+## 5. Game State Schema
+
+Full run-time `game_state` example:
+
+```json
+{
+  "turn_count": 4,
+  "current_player": "Solar Scribe",
+  "board": [
+    ["☼", "☽", null],
+    [null, "☼", null],
+    ["☽", null, null]
+  ],
+  "players": {
+    "Solar Scribe": {
+      "symbol": "☼",
+      "actions": ["[Inscribe:0,0]", "[Inscribe:1,1]"]
+    },
+    "Lunar Scribe": {
+      "symbol": "☽",
+      "actions": ["[Inscribe:0,1]", "[Inscribe:2,0]"]
+    }
+  },
+  "winner": null,
+  "outcome": "ongoing",
+  "observations": [
+    {"player": "Solar Scribe", "action": "[Inscribe:0,0]"},
+    {"player": "Lunar Scribe", "action": "[Inscribe:0,1]"},
+    {"player": "Solar Scribe", "action": "[Inscribe:1,1]"},
+    {"player": "Lunar Scribe", "action": "[Inscribe:2,0]"}
+  ]
+}
+```
+
+---
+
+## 6. Initialization Rules
+
+- The board initializes as a 3×3 matrix of `null`.
+- Turn count = 0.
+- `current_player` defaults to *Solar Scribe*, unless overridden by a deterministic seed-controlled random choice.
+- No randomness affects board contents.
+- `game_state["observations"]` starts empty.
+- At reset, the first observation returned describes player identities, symbol assignments, and available actions.
+
+---
+
+## 7. Validation and Error Handling
+
+On each step, before updating the state:
+
+1. **Extract content** between `\boxed{{}}` using `_extract_answer_content(action: str) → str`.  
+   If missing or malformed, mark move invalid with reason `"Malformed boxed syntax"`.
+
+2. **Check Regex Pattern**:  
+   Must match `^\[Inscribe:[0-2],[0-2]\]$`.  
+   If not, invalid with reason `"Action does not match grammar [Inscribe:x,y]"`.
+
+3. **Check Turn Ownership**:  
+   If action comes from incorrect player, invalid with reason `"Action out of turn"`.
+
+4. **Check Tile Availability**:  
+   If the chosen cell is already marked, invalid with reason `"Tile already inscribed"`.
+
+Invalid actions trigger `set_invalid_move(player, reason)` and the turn passes without board change.
+
+---
+
+## 8. Terminal Conditions and Scoring
+
+**Terminal Checks each turn:**
+
+1. **Triad Alignment**:  
+   After a valid inscription, check all possible lines for three identical rune symbols belonging to the acting player.
+   - If true → `winner = that player`, `outcome = "win"`.
+2. **Draw**:  
+   If the board is full (`9 moves`) and no winner → `outcome = "draw"`.
+3. **Otherwise** → `outcome = "ongoing"`.
+
+**Scoring Rules**:
+- Win: +1 point to the winner, 0 to loser.
+- Draw: 0 points both sides.
+
+No fractional or cumulative scoring beyond the single session.
+
+**Tie-Breaker**: None; draw is final.
+
+---
+
+## 9. Player Prompt Specification
+
+### Prompt Outline for `_generate_player_prompt`
+
+Identity:
+> You are a **mystic scribe** engraving the sacred **Runic Tablet** to align divine energies.  
+> On your turn, you use the `[Inscribe:x,y]` action to claim an empty slot on the 3×3 grid.  
+> Your goal: form a continuous line of your rune symbols before your opponent does.
+
+Rules Recap:
+- Solar Scribe marks **☼**, Lunar Scribe marks **☽**.  
+- Valid format: `\boxed{{[Inscribe:x,y]}}` where `x` and `y` are 0–2.  
+- You may not inscribe an already-occupied tile.  
+- Example grid coordinate map:
+  ```
+  (0,0) (0,1) (0,2)
+  (1,0) (1,1) (1,2)
+  (2,0) (2,1) (2,2)
+  ```
+
+Response Format Requirement:
+- Provide any reasoning text first.
+- Conclude with your action token within `\boxed{{}}`.
+
+### Few-Shot Examples
+
+```
+Example valid response:
+I shall inscribe my rune on the center tile for strength.
+\boxed{{[Inscribe:1,1]}}
+
+Example invalid response:
+I think I will go middle-right.
+\boxed{{Move:1,2}}
+```
+
+Ensure every response ends with exactly one `\boxed{{}}` block containing the action token.
+
+---
+
+## 10. API Mapping Plan
+
+| Method | Purpose | Reads / Writes | Outcome Handling |
+|---------|----------|----------------|------------------|
+| **`reset(seed)`** | Initializes `game_state`, applies seed (e.g., random start player if supported), returns initial observation of empty board and player roles. | Sets `turn_count=0`, clears `observations`, resets `winner/outcome`. | Returns observation for both players with board layout and available format instructions. |
+| **`step(player_id, action)`** | Processes player’s action each turn, updates `board`, verifies legality, appends to `observations`, checks for terminal conditions. | Reads current board, writes updated cell, increments `turn_count`, flips `current_player`. | Returns updated observation, `done` flag if terminal, and optional reward dictionary `{+1,0}`. |
+| **`_generate_player_prompt(player_id)`** | Constructs human-readable prompt describing game status, coordinates, runes, and legal actions. | Reads entire `game_state` to present board, current turn, valid syntax. | Ensures prompt ends with instruction: *“Put your final answer within \boxed{{}} at the end of your response.”* |
+
+---
+
+## 11. Copy-Check Against Example
+
+- **Theme Check**: Distinct from negotiation example—no trading, communication, or offers.
+- **Objective Check**: Pattern-alignment on a Runic Tablet vs. any negotiation outcomes.
+- **Terminology**: Original names—*Runic Tablet*, *Solar Rune*, *Lunar Rune*, *Inscribe*—entirely unique.
+- **Game state keys**: `"board"`, `"players"`, `"observations"`, `"turn_count"`, `"winner"`, `"outcome"` are original to this schema.
+- **Prompt and grammar**: Use custom `[Inscribe:x,y]` format unseen in example sources.
+
+---
+
+**End of Design Document for “Runic Grid”**
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