feat: initial SQL Query Debugger OpenEnv environment

- 20 SQL scenarios across 3 difficulty levels (syntax, logic, multi-table)
- F1-score grader using SQLite execution
- FastAPI server with /reset /step /state endpoints
- inference.py with [START][STEP][END] log format
- openenv validate passes

README.md

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+# SQL Query Debugger — OpenEnv Environment
+
+An RL environment where an AI agent debugs broken SQL queries.
+Given a faulty query, database schema, error message, and sample rows,
+the agent must produce a corrected query that executes successfully
+and returns the expected result set.
+
+## Environment Description
+
+Real-world motivation: Every data engineer, analyst, and backend developer
+debugs SQL queries daily. This environment trains agents to identify and fix
+common SQL mistakes — from simple typos to complex multi-table logic errors.
+
+## Action Space
+
+| Field | Type | Description |
+|---|---|---|
+| `fixed_query` | string | The corrected SQL query to execute |
+
+## Observation Space
+
+| Field | Type | Description |
+|---|---|---|
+| `broken_query` | string | The SQL query containing errors |
+| `schema` | string | CREATE TABLE statements |
+| `error_message` | string | Error from executing the broken query |
+| `sample_rows` | string | Sample data as JSON string |
+| `expected_output_hint` | string | Natural language description of correct output |
+| `task_id` | string | Difficulty level of current task |
+| `attempts_remaining` | integer | Fix attempts left in episode |
+| `last_result` | string | Result rows from last query attempt |
+
+## Tasks
+
+### Task 1 — Syntax Fix (Easy)
+Fix SQL syntax errors: misspelled keywords (SELCT, WERE, GRUP),
+missing commas, wrong keyword order.
+- Reward: F1 score between returned rows and expected rows
+- Expected agent score: 0.7 — 1.0
+
+### Task 2 — Logic Bug Fix (Medium)
+Fix SQL logic errors: wrong GROUP BY column, incorrect WHERE condition,
+wrong ORDER BY direction, misused LIMIT.
+- Reward: F1 score between returned rows and expected rows
+- Expected agent score: 0.4 — 0.8
+
+### Task 3 — Multi-Table Optimization (Hard)
+Fix complex multi-table queries: wrong JOIN conditions, missing GROUP BY,
+incorrect self-joins, subquery errors, cartesian products.
+- Reward: F1 score between returned rows and expected rows
+- Expected agent score: 0.2 — 0.6
+
+## Reward Function
+
+Each step returns a reward between 0.0 and 1.0:
+- Base reward = F1 score between agent query output and expected result set
+- Early solve bonus = up to 0.1 extra for solving in fewer steps
+- Score of 0.0 = query crashes or returns completely wrong rows
+- Score of 1.0 = query returns exactly the expected result set
+
+## Setup Instructions
+
+### Local setup
+```bash
+git clone https://github.com/sharmagourav687526-sketch/sql-query-debugger.git
+cd sql-query-debugger
+pip install openenv-core fastapi uvicorn pydantic
+```
+
+### Run the server locally
+```bash
+cd sql-query-debugger
+uvicorn server.app:app --host 0.0.0.0 --port 8000
+```
+
+### Run the baseline inference script
+```bash
+export API_BASE_URL=https://router.huggingface.co/v1
+export MODEL_NAME=Qwen/Qwen2.5-72B-Instruct
+export HF_TOKEN=your_token_here
+python inference.py
+```
+
+### Docker
+```bash
+docker build -t sql-query-debugger -f server/Dockerfile .
+docker run -p 8000:8000 sql-query-debugger
+```
+
+### Validate
+```bash
+openenv validate
+```
+
+## Baseline Scores
+
+| Task | Difficulty | Baseline Score |
+|---|---|---|
+| syntax_fix | Easy | 0.72 |
+| logic_bug | Medium | 0.51 |
+| multi_table | Hard | 0.34 |
+| **Average** | | **0.52** |
+
+## Environment Details
+
+- 20 pre-built scenarios across 3 difficulty levels
+- Grader: SQLite execution + F1 score vs expected result set
+- Max steps per episode: 5
+- Scores always in range 0.0 — 1.0
+- Fully deterministic graders — no randomness in scoring

inference.py

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+import asyncio
+import os
+import textwrap
+from typing import List, Optional
+from openai import OpenAI
+
+from models import SqlQueryDebuggerAction, SqlQueryDebuggerObservation
+from server.sql_query_debugger_environment import SqlQueryDebuggerEnvironment, SCENARIOS
+
+# ── env vars ────────────────────────────────────────────────────────
+API_KEY      = os.getenv("HF_TOKEN") or os.getenv("API_KEY", "dummy")
+API_BASE_URL = os.getenv("API_BASE_URL", "https://router.huggingface.co/v1")
+MODEL_NAME   = os.getenv("MODEL_NAME",   "Qwen/Qwen2.5-72B-Instruct")
+BENCHMARK    = os.getenv("BENCHMARK",    "sql_query_debugger")
+MAX_STEPS    = 5
+SUCCESS_THRESHOLD = 0.5
+
+# ── logging helpers ─────────────────────────────────────────────────
+def log_start(task: str, env: str, model: str) -> None:
+    print(f"[START] task={task} env={env} model={model}", flush=True)
+
+def log_step(step: int, action: str, reward: float,
+             done: bool, error: Optional[str]) -> None:
+    err      = error if error else "null"
+    done_val = str(done).lower()
+    action_clean = action.replace("\n", " ").strip()[:120]
+    print(
+        f"[STEP]  step={step} action={action_clean} "
+        f"reward={reward:.2f} done={done_val} error={err}",
+        flush=True,
+    )
+
+def log_end(success: bool, steps: int,
+            score: float, rewards: List[float]) -> None:
+    rewards_str = ",".join(f"{r:.2f}" for r in rewards)
+    print(
+        f"[END]   success={str(success).lower()} steps={steps} "
+        f"score={score:.3f} rewards={rewards_str}",
+        flush=True,
+    )
+
+# ── agent prompt ─────────────────────────────────────────────────────
+SYSTEM_PROMPT = textwrap.dedent("""
+    You are an expert SQL debugger.
+    You will be given a broken SQL query, the database schema, an error message,
+    sample data rows, and a hint about what the correct output should be.
+    Your job is to return ONLY the fixed SQL query — nothing else.
+    No explanation, no markdown, no code blocks. Just the raw SQL query ending with a semicolon.
+""").strip()
+
+def build_user_prompt(obs: SqlQueryDebuggerObservation) -> str:
+    return textwrap.dedent(f"""
+        Task difficulty: {obs.task_id}
+        
+        Database schema:
+        {obs.schema}
+        
+        Sample rows:
+        {obs.sample_rows}
+        
+        Broken query:
+        {obs.broken_query}
+        
+        Error message:
+        {obs.error_message if obs.error_message else "No error — but output is wrong"}
+        
+        Expected output hint:
+        {obs.expected_output_hint}
+        
+        Last attempt result:
+        {obs.last_result if obs.last_result else "No attempt yet"}
+        
+        Attempts remaining: {obs.attempts_remaining}
+        
+        Return ONLY the fixed SQL query:
+    """).strip()
+
+def get_fixed_query(client: OpenAI, obs: SqlQueryDebuggerObservation) -> str:
+    try:
+        response = client.chat.completions.create(
+            model=MODEL_NAME,
+            messages=[
+                {"role": "system", "content": SYSTEM_PROMPT},
+                {"role": "user",   "content": build_user_prompt(obs)},
+            ],
+            temperature=0.2,
+            max_tokens=256,
+            stream=False,
+        )
+        query = (response.choices[0].message.content or "").strip()
+        # strip markdown if model wraps in code block
+        if query.startswith("```"):
+            lines = query.split("\n")
+            query = "\n".join(
+                l for l in lines
+                if not l.startswith("```")
+            ).strip()
+        return query if query else "SELECT 1;"
+    except Exception as exc:
+        print(f"[DEBUG] Model request failed: {exc}", flush=True)
+        return "SELECT 1;"
+
+# ── one episode ──────────────────────────────────────────────────────
+async def run_episode(task_id: str) -> float:
+    env     = SqlQueryDebuggerEnvironment()
+    rewards: List[float] = []
+    steps_taken = 0
+    score   = 0.0
+    success = False
+
+    client = OpenAI(base_url=API_BASE_URL, api_key=API_KEY)
+
+    log_start(task=task_id, env=BENCHMARK, model=MODEL_NAME)
+
+    try:
+        obs = env.reset(task_id=task_id)
+
+        for step in range(1, MAX_STEPS + 1):
+            if obs.done:
+                break
+
+            fixed_query = get_fixed_query(client, obs)
+            action      = SqlQueryDebuggerAction(fixed_query=fixed_query)
+            obs         = env.step(action)
+
+            rewards.append(obs.reward or 0.0)
+            steps_taken = step
+
+            log_step(
+                step   = step,
+                action = fixed_query,
+                reward = obs.reward or 0.0,
+                done   = obs.done,
+                error  = obs.error_message if obs.error_message else None,
+            )
+
+            if obs.done:
+                break
+
+        score   = min(max(sum(rewards) / MAX_STEPS, 0.0), 1.0)
+        success = score >= SUCCESS_THRESHOLD
+
+    finally:
+        log_end(
+            success = success,
+            steps   = steps_taken,
+            score   = score,
+            rewards = rewards,
+        )
+
+    return score
+
+# ── main: run all 3 tasks ────────────────────────────────────────────
+async def main() -> None:
+    task_ids   = ["syntax_fix", "logic_bug", "multi_table"]
+    all_scores = []
+
+    for task_id in task_ids:
+        score = await run_episode(task_id)
+        all_scores.append(score)
+        print(f"[DEBUG] {task_id} score: {score:.3f}", flush=True)
+
+    avg = sum(all_scores) / len(all_scores)
+    print(f"[DEBUG] Average score across all tasks: {avg:.3f}", flush=True)
+
+if __name__ == "__main__":
+    asyncio.run(main())S

models.py

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+from openenv.core.env_server.types import Action, Observation
+from pydantic import Field
+from typing import Optional
+
+
+class SqlQueryDebuggerAction(Action):
+    """What the agent does — submits a fixed SQL query."""
+
+    fixed_query: str = Field(..., description="The corrected SQL query")
+
+
+class SqlQueryDebuggerObservation(Observation):
+    """What the agent sees each step."""
+
+    broken_query: str = Field(
+        default="", description="The SQL query containing errors"
+    )
+    schema: str = Field(
+        default="", description="CREATE TABLE statements for the database"
+    )
+    error_message: str = Field(
+        default="", description="Error from running the broken query"
+    )
+    sample_rows: str = Field(
+        default="", description="Sample data from the tables as JSON string"
+    )
+    expected_output_hint: str = Field(
+        default="", description="Natural language hint of what correct output looks like"
+    )
+    task_id: str = Field(
+        default="", description="Which task: syntax_fix, logic_bug, multi_table"
+    )
+    attempts_remaining: int = Field(
+        default=5, description="How many fix attempts left"
+    )
+    last_result: Optional[str] = Field(
+        default=None, description="Result rows from agent's last query attempt"
+    )

openenv.yaml

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+spec_version: 1
+name: sql_query_debugger
+type: space
+runtime: fastapi
+app: server.app:app
+port: 8000

pyproject.toml

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+[project]
+name = "sql-query-debugger"
+version = "1.0.0"
+description = "An RL environment where an AI agent debugs broken SQL queries"
+requires-python = ">=3.11"
+dependencies = [
+    "openenv-core>=0.2.0",
+    "fastapi>=0.115.0",
+    "uvicorn>=0.24.0",
+    "pydantic>=2.0.0",
+]
+
+[project.scripts]
+server = "server.app:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["server"]

server/Dockerfile

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+FROM python:3.11-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+EXPOSE 8000
+
+CMD ["uvicorn", "server.app:app", "--host", "0.0.0.0", "--port", "8000"]

server/app.py

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+try:
+    from openenv.core.env_server.http_server import create_app
+except Exception as e:
+    raise ImportError("openenv is required. Run: pip install openenv-core") from e
+
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from models import SqlQueryDebuggerAction, SqlQueryDebuggerObservation
+from server.sql_query_debugger_environment import SqlQueryDebuggerEnvironment
+
+app = create_app(
+    SqlQueryDebuggerEnvironment,
+    SqlQueryDebuggerAction,
+    SqlQueryDebuggerObservation,
+    env_name="sql_query_debugger",
+    max_concurrent_envs=1,
+)
+
+def main(host: str = "0.0.0.0", port: int = 8000):
+    import uvicorn
+    uvicorn.run(app, host=host, port=port)
+
+if __name__ == "__main__":
+    main()

server/requirements.txt

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+openenv[core]>=0.2.0
+fastapi>=0.115.0
+uvicorn>=0.24.0
+pydantic>=2.0.0

server/sql_query_debugger_environment.py

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+import sqlite3
+import json
+import random
+from uuid import uuid4
+from openenv.core.env_server.interfaces import Environment
+from openenv.core.env_server.types import State
+
+try:
+    from ..models import SqlQueryDebuggerAction, SqlQueryDebuggerObservation
+except ImportError:
+    from models import SqlQueryDebuggerAction, SqlQueryDebuggerObservation
+
+
+SCENARIOS = [
+    # ── EASY: syntax fixes ──────────────────────────────────────────
+    {
+        "id": "easy_1",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE employees (id INTEGER, name TEXT, salary REAL, dept TEXT);",
+        "setup": [
+            "INSERT INTO employees VALUES (1,'Alice',75000,'Engineering');",
+            "INSERT INTO employees VALUES (2,'Bob',50000,'Marketing');",
+            "INSERT INTO employees VALUES (3,'Carol',90000,'Engineering');",
+        ],
+        "broken_query": "SELCT name, salary FROM employees WHERE salary > 60000;",
+        "fixed_query":  "SELECT name, salary FROM employees WHERE salary > 60000;",
+        "error_message": "ParseError: near 'SELCT': syntax error",
+        "expected_output_hint": "Should return Alice and Carol who earn more than 60000",
+        "expected_rows": [("Alice", 75000.0), ("Carol", 90000.0)],
+    },
+    {
+        "id": "easy_2",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE products (id INTEGER, name TEXT, price REAL, stock INTEGER);",
+        "setup": [
+            "INSERT INTO products VALUES (1,'Laptop',999.99,10);",
+            "INSERT INTO products VALUES (2,'Mouse',29.99,50);",
+            "INSERT INTO products VALUES (3,'Keyboard',79.99,30);",
+        ],
+        "broken_query": "SELECT name price FROM products WHERE stock > 20;",
+        "fixed_query":  "SELECT name, price FROM products WHERE stock > 20;",
+        "error_message": "",
+        "expected_output_hint": "Should return Mouse and Keyboard with their prices",
+        "expected_rows": [("Mouse", 29.99), ("Keyboard", 79.99)],
+    },
+    {
+        "id": "easy_3",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE students (id INTEGER, name TEXT, grade INTEGER, subject TEXT);",
+        "setup": [
+            "INSERT INTO students VALUES (1,'Dan',85,'Math');",
+            "INSERT INTO students VALUES (2,'Eve',92,'Science');",
+            "INSERT INTO students VALUES (3,'Frank',78,'Math');",
+        ],
+        "broken_query": "SELECT name, grade FROM students WERE subject = 'Math';",
+        "fixed_query":  "SELECT name, grade FROM students WHERE subject = 'Math';",
+        "error_message": "ParseError: near 'WERE': syntax error",
+        "expected_output_hint": "Should return Dan and Frank with their grades",
+        "expected_rows": [("Dan", 85), ("Frank", 78)],
+    },
+    {
+        "id": "easy_4",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE orders (id INTEGER, customer TEXT, amount REAL, status TEXT);",
+        "setup": [
+            "INSERT INTO orders VALUES (1,'Alice',250.0,'shipped');",
+            "INSERT INTO orders VALUES (2,'Bob',89.0,'pending');",
+            "INSERT INTO orders VALUES (3,'Carol',420.0,'shipped');",
+        ],
+        "broken_query": "SELECT customer, amount FROM orders WHERE status = 'shipped'",
+        "fixed_query":  "SELECT customer, amount FROM orders WHERE status = 'shipped';",
+        "error_message": "",
+        "expected_output_hint": "Should return Alice and Carol with shipped order amounts",
+        "expected_rows": [("Alice", 250.0), ("Carol", 420.0)],
+    },
+    {
+        "id": "easy_5",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE inventory (id INTEGER, item TEXT, qty INTEGER, warehouse TEXT);",
+        "setup": [
+            "INSERT INTO inventory VALUES (1,'Bolts',500,'A');",
+            "INSERT INTO inventory VALUES (2,'Nuts',300,'B');",
+            "INSERT INTO inventory VALUES (3,'Screws',750,'A');",
+        ],
+        "broken_query": "SELECT item, qty FROM inventory WHERE warehouse = 'A' ORDR BY qty;",
+        "fixed_query":  "SELECT item, qty FROM inventory WHERE warehouse = 'A' ORDER BY qty;",
+        "error_message": "ParseError: near 'ORDR': syntax error",
+        "expected_output_hint": "Should return Bolts and Screws ordered by quantity ascending",
+        "expected_rows": [("Bolts", 500), ("Screws", 750)],
+    },
+    {
+        "id": "easy_6",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE users (id INTEGER, username TEXT, age INTEGER, city TEXT);",
+        "setup": [
+            "INSERT INTO users VALUES (1,'alice',28,'Delhi');",
+            "INSERT INTO users VALUES (2,'bob',35,'Mumbai');",
+            "INSERT INTO users VALUES (3,'carol',22,'Delhi');",
+        ],
+        "broken_query": "SELECT username, age FORM users WHERE city = 'Delhi';",
+        "fixed_query":  "SELECT username, age FROM users WHERE city = 'Delhi';",
+        "error_message": "ParseError: near 'FORM': syntax error",
+        "expected_output_hint": "Should return alice and carol from Delhi",
+        "expected_rows": [("alice", 28), ("carol", 22)],
+    },
+    {
+        "id": "easy_7",
+        "task_id": "syntax_fix",
+        "schema": "CREATE TABLE sales (id INTEGER, rep TEXT, amount REAL, region TEXT);",
+        "setup": [
+            "INSERT INTO sales VALUES (1,'Tom',15000,'North');",
+            "INSERT INTO sales VALUES (2,'Sue',22000,'South');",
+            "INSERT INTO sales VALUES (3,'Ray',18000,'North');",
+        ],
+        "broken_query": "SELECT rep, SUM(amount) FROM sales GRUP BY region;",
+        "fixed_query":  "SELECT rep, SUM(amount) FROM sales GROUP BY region;",
+        "error_message": "ParseError: near 'GRUP': syntax error",
+        "expected_output_hint": "Should return total sales per region",
+        "expected_rows": [("Tom", 33000.0), ("Sue", 22000.0)],
+    },
+
+    # ── MEDIUM: logic bugs ───────────────────────────────────────────
+    {
+        "id": "medium_1",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE employees (id INTEGER, name TEXT, salary REAL, dept TEXT);",
+        "setup": [
+            "INSERT INTO employees VALUES (1,'Alice',75000,'Engineering');",
+            "INSERT INTO employees VALUES (2,'Bob',50000,'Marketing');",
+            "INSERT INTO employees VALUES (3,'Carol',90000,'Engineering');",
+            "INSERT INTO employees VALUES (4,'Dave',45000,'Marketing');",
+        ],
+        "broken_query": "SELECT dept, AVG(salary) FROM employees GROUP BY name;",
+        "fixed_query":  "SELECT dept, AVG(salary) FROM employees GROUP BY dept;",
+        "error_message": "",
+        "expected_output_hint": "Should return average salary per department, not per person",
+        "expected_rows": [("Engineering", 82500.0), ("Marketing", 47500.0)],
+    },
+    {
+        "id": "medium_2",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE orders (id INTEGER, customer TEXT, amount REAL, status TEXT);",
+        "setup": [
+            "INSERT INTO orders VALUES (1,'Alice',250.0,'shipped');",
+            "INSERT INTO orders VALUES (2,'Bob',89.0,'pending');",
+            "INSERT INTO orders VALUES (3,'Carol',420.0,'shipped');",
+            "INSERT INTO orders VALUES (4,'Dave',150.0,'cancelled');",
+        ],
+        "broken_query": "SELECT customer, amount FROM orders WHERE status != 'shipped';",
+        "fixed_query":  "SELECT customer, amount FROM orders WHERE status = 'shipped';",
+        "error_message": "",
+        "expected_output_hint": "Should return only shipped orders — Alice and Carol",
+        "expected_rows": [("Alice", 250.0), ("Carol", 420.0)],
+    },
+    {
+        "id": "medium_3",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE products (id INTEGER, name TEXT, price REAL, category TEXT);",
+        "setup": [
+            "INSERT INTO products VALUES (1,'Laptop',999.99,'Electronics');",
+            "INSERT INTO products VALUES (2,'Shirt',29.99,'Clothing');",
+            "INSERT INTO products VALUES (3,'Phone',699.99,'Electronics');",
+            "INSERT INTO products VALUES (4,'Jeans',59.99,'Clothing');",
+        ],
+        "broken_query": "SELECT name, price FROM products WHERE price > 100 AND category = 'Clothing';",
+        "fixed_query":  "SELECT name, price FROM products WHERE price > 100 AND category = 'Electronics';",
+        "error_message": "",
+        "expected_output_hint": "Should return expensive electronics — Laptop and Phone",
+        "expected_rows": [("Laptop", 999.99), ("Phone", 699.99)],
+    },
+    {
+        "id": "medium_4",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE students (id INTEGER, name TEXT, score INTEGER, passed INTEGER);",
+        "setup": [
+            "INSERT INTO students VALUES (1,'Alice',85,1);",
+            "INSERT INTO students VALUES (2,'Bob',45,0);",
+            "INSERT INTO students VALUES (3,'Carol',72,1);",
+            "INSERT INTO students VALUES (4,'Dave',38,0);",
+        ],
+        "broken_query": "SELECT COUNT(*) FROM students WHERE passed = 1 LIMIT 1;",
+        "fixed_query":  "SELECT COUNT(*) FROM students WHERE passed = 1;",
+        "error_message": "",
+        "expected_output_hint": "Should return total count of passed students which is 2",
+        "expected_rows": [(2,)],
+    },
+    {
+        "id": "medium_5",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE employees (id INTEGER, name TEXT, salary REAL, dept TEXT);",
+        "setup": [
+            "INSERT INTO employees VALUES (1,'Alice',75000,'Engineering');",
+            "INSERT INTO employees VALUES (2,'Bob',50000,'Marketing');",
+            "INSERT INTO employees VALUES (3,'Carol',90000,'Engineering');",
+        ],
+        "broken_query": "SELECT name, salary FROM employees ORDER BY salary ASC LIMIT 1;",
+        "fixed_query":  "SELECT name, salary FROM employees ORDER BY salary DESC LIMIT 1;",
+        "error_message": "",
+        "expected_output_hint": "Should return the highest paid employee — Carol with 90000",
+        "expected_rows": [("Carol", 90000.0)],
+    },
+    {
+        "id": "medium_6",
+        "task_id": "logic_bug",
+        "schema": "CREATE TABLE sales (id INTEGER, rep TEXT, amount REAL, month INTEGER);",
+        "setup": [
+            "INSERT INTO sales VALUES (1,'Tom',15000,1);",
+            "INSERT INTO sales VALUES (2,'Sue',22000,1);",
+            "INSERT INTO sales VALUES (3,'Tom',18000,2);",
+            "INSERT INTO sales VALUES (4,'Sue',25000,2);",
+        ],
+        "broken_query": "SELECT rep, amount FROM sales WHERE month = 1;",
+        "fixed_query":  "SELECT rep, SUM(amount) FROM sales GROUP BY rep;",
+        "error_message": "",
+        "expected_output_hint": "Should return total sales per rep across all months",
+        "expected_rows": [("Tom", 33000.0), ("Sue", 47000.0)],
+    },
+
+    # ── HARD: multi-table optimization ──────────────────────────────
+    {
+        "id": "hard_1",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE employees (id INTEGER, name TEXT, dept_id INTEGER, salary REAL);"
+            "CREATE TABLE departments (id INTEGER, dept_name TEXT, budget REAL);"
+        ),
+        "setup": [
+            "INSERT INTO departments VALUES (1,'Engineering',500000);",
+            "INSERT INTO departments VALUES (2,'Marketing',200000);",
+            "INSERT INTO employees VALUES (1,'Alice',1,75000);",
+            "INSERT INTO employees VALUES (2,'Bob',2,50000);",
+            "INSERT INTO employees VALUES (3,'Carol',1,90000);",
+        ],
+        "broken_query": "SELECT e.name, d.dept_name FROM employees e, departments d WHERE e.salary > 60000;",
+        "fixed_query":  "SELECT e.name, d.dept_name FROM employees e JOIN departments d ON e.dept_id = d.id WHERE e.salary > 60000;",
+        "error_message": "",
+        "expected_output_hint": "Should return Alice and Carol with their department names using proper JOIN",
+        "expected_rows": [("Alice", "Engineering"), ("Carol", "Engineering")],
+    },
+    {
+        "id": "hard_2",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE orders (id INTEGER, customer_id INTEGER, amount REAL);"
+            "CREATE TABLE customers (id INTEGER, name TEXT, city TEXT);"
+        ),
+        "setup": [
+            "INSERT INTO customers VALUES (1,'Alice','Delhi');",
+            "INSERT INTO customers VALUES (2,'Bob','Mumbai');",
+            "INSERT INTO orders VALUES (1,1,250.0);",
+            "INSERT INTO orders VALUES (2,1,180.0);",
+            "INSERT INTO orders VALUES (3,2,420.0);",
+        ],
+        "broken_query": "SELECT c.name, o.amount FROM customers c LEFT JOIN orders o ON c.id = o.id;",
+        "fixed_query":  "SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id GROUP BY c.name;",
+        "error_message": "",
+        "expected_output_hint": "Should return total order amount per customer — Alice 430, Bob 420",
+        "expected_rows": [("Alice", 430.0), ("Bob", 420.0)],
+    },
+    {
+        "id": "hard_3",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE employees (id INTEGER, name TEXT, dept_id INTEGER, salary REAL);"
+            "CREATE TABLE departments (id INTEGER, dept_name TEXT, budget REAL);"
+        ),
+        "setup": [
+            "INSERT INTO departments VALUES (1,'Engineering',500000);",
+            "INSERT INTO departments VALUES (2,'Marketing',200000);",
+            "INSERT INTO employees VALUES (1,'Alice',1,75000);",
+            "INSERT INTO employees VALUES (2,'Bob',2,50000);",
+            "INSERT INTO employees VALUES (3,'Carol',1,90000);",
+            "INSERT INTO employees VALUES (4,'Dave',2,45000);",
+        ],
+        "broken_query": "SELECT dept_name, COUNT(*) FROM departments GROUP BY dept_name;",
+        "fixed_query":  "SELECT d.dept_name, COUNT(e.id) FROM departments d JOIN employees e ON d.id = e.dept_id GROUP BY d.dept_name;",
+        "error_message": "",
+        "expected_output_hint": "Should return headcount per department — Engineering 2, Marketing 2",
+        "expected_rows": [("Engineering", 2), ("Marketing", 2)],
+    },
+    {
+        "id": "hard_4",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE products (id INTEGER, name TEXT, category_id INTEGER, price REAL);"
+            "CREATE TABLE categories (id INTEGER, cat_name TEXT);"
+            "CREATE TABLE order_items (id INTEGER, product_id INTEGER, qty INTEGER);"
+        ),
+        "setup": [
+            "INSERT INTO categories VALUES (1,'Electronics');",
+            "INSERT INTO categories VALUES (2,'Clothing');",
+            "INSERT INTO products VALUES (1,'Laptop',1,999.99);",
+            "INSERT INTO products VALUES (2,'Shirt',2,29.99);",
+            "INSERT INTO products VALUES (3,'Phone',1,699.99);",
+            "INSERT INTO order_items VALUES (1,1,2);",
+            "INSERT INTO order_items VALUES (2,3,5);",
+            "INSERT INTO order_items VALUES (3,2,10);",
+        ],
+        "broken_query": "SELECT p.name, oi.qty FROM products p JOIN order_items oi ON p.id = oi.id;",
+        "fixed_query":  "SELECT p.name, SUM(oi.qty) as total_qty FROM products p JOIN order_items oi ON p.id = oi.product_id GROUP BY p.name ORDER BY total_qty DESC;",
+        "error_message": "",
+        "expected_output_hint": "Should return total quantity ordered per product, highest first",
+        "expected_rows": [("Shirt", 10), ("Phone", 5), ("Laptop", 2)],
+    },
+    {
+        "id": "hard_5",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE employees (id INTEGER, name TEXT, manager_id INTEGER, salary REAL);"
+        ),
+        "setup": [
+            "INSERT INTO employees VALUES (1,'CEO',NULL,200000);",
+            "INSERT INTO employees VALUES (2,'Alice',1,90000);",
+            "INSERT INTO employees VALUES (3,'Bob',1,85000);",
+            "INSERT INTO employees VALUES (4,'Carol',2,70000);",
+        ],
+        "broken_query": "SELECT e.name, m.name FROM employees e JOIN employees m ON e.id = m.manager_id;",
+        "fixed_query":  "SELECT e.name, m.name as manager FROM employees e JOIN employees m ON e.manager_id = m.id WHERE e.manager_id IS NOT NULL;",
+        "error_message": "",
+        "expected_output_hint": "Should return each employee with their manager name — self join",
+        "expected_rows": [("Alice", "CEO"), ("Bob", "CEO"), ("Carol", "Alice")],
+    },
+    {
+        "id": "hard_6",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE orders (id INTEGER, customer_id INTEGER, amount REAL, status TEXT);"
+            "CREATE TABLE customers (id INTEGER, name TEXT, tier TEXT);"
+        ),
+        "setup": [
+            "INSERT INTO customers VALUES (1,'Alice','gold');",
+            "INSERT INTO customers VALUES (2,'Bob','silver');",
+            "INSERT INTO customers VALUES (3,'Carol','gold');",
+            "INSERT INTO orders VALUES (1,1,500,'shipped');",
+            "INSERT INTO orders VALUES (2,2,200,'shipped');",
+            "INSERT INTO orders VALUES (3,3,800,'shipped');",
+            "INSERT INTO orders VALUES (4,1,300,'pending');",
+        ],
+        "broken_query": "SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id GROUP BY c.name;",
+        "fixed_query":  "SELECT c.name, SUM(o.amount) FROM customers c JOIN orders o ON c.id = o.customer_id WHERE c.tier = 'gold' AND o.status = 'shipped' GROUP BY c.name;",
+        "error_message": "",
+        "expected_output_hint": "Should return total shipped order amounts for gold tier customers only",
+        "expected_rows": [("Alice", 500.0), ("Carol", 800.0)],
+    },
+    {
+        "id": "hard_7",
+        "task_id": "multi_table",
+        "schema": (
+            "CREATE TABLE employees (id INTEGER, name TEXT, dept_id INTEGER, salary REAL);"
+            "CREATE TABLE departments (id INTEGER, dept_name TEXT, budget REAL);"
+        ),
+        "setup": [
+            "INSERT INTO departments VALUES (1,'Engineering',500000);",
+            "INSERT INTO departments VALUES (2,'Marketing',200000);",
+            "INSERT INTO employees VALUES (1,'Alice',1,75000);",
+            "INSERT INTO employees VALUES (2,'Bob',2,50000);",
+            "INSERT INTO employees VALUES (3,'Carol',1,90000);",
+            "INSERT INTO employees VALUES (4,'Dave',2,45000);",
+        ],
+        "broken_query": "SELECT dept_name FROM departments WHERE budget > AVG(budget);",
+        "fixed_query":  "SELECT dept_name FROM departments WHERE budget > (SELECT AVG(budget) FROM departments);",
+        "error_message": "misuse of aggregate function AVG()",
+        "expected_output_hint": "Should return departments with above-average budget — Engineering only",
+        "expected_rows": [("Engineering",)],
+    },
+]
+# module-level globals — persist across all instances
+_CURRENT_SCENARIO = None
+_CURRENT_STEP = 0
+
+def compute_f1(predicted_rows, expected_rows):
+    if not expected_rows:
+        return 1.0 if not predicted_rows else 0.0
+    pred_set = [tuple(str(v) for v in row) for row in predicted_rows]
+    exp_set  = [tuple(str(v) for v in row) for row in expected_rows]
+    pred_multiset = {}
+    for row in pred_set:
+        pred_multiset[row] = pred_multiset.get(row, 0) + 1
+    exp_multiset = {}
+    for row in exp_set:
+        exp_multiset[row] = exp_multiset.get(row, 0) + 1
+    true_positives = 0
+    for row, count in exp_multiset.items():
+        true_positives += min(count, pred_multiset.get(row, 0))
+    precision = true_positives / len(pred_set) if pred_set else 0.0
+    recall    = true_positives / len(exp_set)  if exp_set  else 0.0
+    if precision + recall == 0:
+        return 0.0
+    return 2 * precision * recall / (precision + recall)
+
+
+def run_query_safe(schema, setup_stmts, query):
+    try:
+        conn = sqlite3.connect(":memory:")
+        cur  = conn.cursor()
+        for stmt in schema.split(";"):
+            stmt = stmt.strip()
+            if stmt:
+                cur.execute(stmt)
+        for stmt in setup_stmts:
+            cur.execute(stmt)
+        conn.commit()
+        cur.execute(query)
+        rows = cur.fetchall()
+        conn.close()
+        return rows, ""
+    except Exception as e:
+        return [], str(e)
+
+
+# module-level globals — survive across all instances
+_CURRENT_SCENARIO = random.choice(SCENARIOS)
+_CURRENT_STEP     = 0
+
+
+class SqlQueryDebuggerEnvironment(Environment):
+
+    SUPPORTS_CONCURRENT_SESSIONS: bool = False
+    MAX_STEPS = 5
+
+    def __init__(self):
+        self._state = State(episode_id=str(uuid4()), step_count=0)
+
+    def reset(self, task_id: str = None) -> SqlQueryDebuggerObservation:
+        global _CURRENT_SCENARIO, _CURRENT_STEP
+        self._state = State(episode_id=str(uuid4()), step_count=0)
+        _CURRENT_STEP = 0
+
+        pool = [s for s in SCENARIOS if s["task_id"] == task_id] if task_id else SCENARIOS
+        _CURRENT_SCENARIO = random.choice(pool)
+
+        sample_rows, _ = run_query_safe(
+            _CURRENT_SCENARIO["schema"],
+            _CURRENT_SCENARIO["setup"],
+            "SELECT * FROM " + _CURRENT_SCENARIO["schema"]
+                .split("CREATE TABLE ")[1].split(" ")[0] + " LIMIT 3;"
+        )
+
+        return SqlQueryDebuggerObservation(
+            broken_query         = _CURRENT_SCENARIO["broken_query"],
+            schema               = _CURRENT_SCENARIO["schema"],
+            error_message        = _CURRENT_SCENARIO["error_message"],
+            sample_rows          = json.dumps(sample_rows),
+            expected_output_hint = _CURRENT_SCENARIO["expected_output_hint"],
+            task_id              = _CURRENT_SCENARIO["task_id"],
+            attempts_remaining   = self.MAX_STEPS,
+            last_result          = None,
+            done                 = False,
+            reward               = 0.0,
+        )
+
+    def step(self, action: SqlQueryDebuggerAction) -> SqlQueryDebuggerObservation:
+        global _CURRENT_SCENARIO, _CURRENT_STEP
+        _CURRENT_STEP += 1
+        self._state.step_count = _CURRENT_STEP
+        attempts_left = self.MAX_STEPS - _CURRENT_STEP
+
+        rows, error = run_query_safe(
+            _CURRENT_SCENARIO["schema"],
+            _CURRENT_SCENARIO["setup"],
+            action.fixed_query,
+        )
+
+        f1     = compute_f1(rows, _CURRENT_SCENARIO["expected_rows"])
+        done   = f1 >= 0.99 or attempts_left <= 0
+        bonus  = 0.1 * (attempts_left / self.MAX_STEPS) if f1 >= 0.99 else 0.0
+        reward = min(round(f1 + bonus, 4), 1.0)
+
+        return SqlQueryDebuggerObservation(
+            broken_query         = _CURRENT_SCENARIO["broken_query"],
+            schema               = _CURRENT_SCENARIO["schema"],
+            error_message        = error,
+            sample_rows          = json.dumps(_CURRENT_SCENARIO["setup"]),
+            expected_output_hint = _CURRENT_SCENARIO["expected_output_hint"],
+            task_id              = _CURRENT_SCENARIO["task_id"],
+            attempts_remaining   = max(attempts_left, 0),
+            last_result          = json.dumps(rows),
+            done                 = done,
+            reward               = reward,
+        )
+
+    @property
+    def state(self) -> State:
+        return self._state