feat: add financial governance evaluators (spend limits + transaction policy)

evaluators/contrib/financial-governance/README.md

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+# Financial Governance Evaluators for Agent Control
+
+Evaluators that enforce financial spend limits and transaction policies for autonomous AI agents.
+
+As agents transact autonomously via protocols like [x402](https://github.com/coinbase/x402) and payment layers like [agentpay-mcp](https://github.com/AI-Agent-Economy/agentpay-mcp), enterprises need governance over what agents spend. These evaluators bring financial policy enforcement into the Agent Control framework.
+
+## Evaluators
+
+### `financial_governance.spend_limit`
+
+Tracks cumulative agent spend and enforces rolling budget limits. Stateful — records approved transactions and checks new ones against accumulated spend.
+
+- **Per-transaction cap** — reject any single payment above a threshold (`BudgetLimit` with no window)
+- **Rolling period budget** — reject payments that would exceed a time-windowed budget (`BudgetWindow(kind="rolling", ...)`)
+- **Calendar-aligned budget** — reject payments that exceed a day/week/month budget (`BudgetWindow(kind="fixed", ...)`)
+- **Scoped budgets** — independent counters per channel, agent, or session via `scope_by`
+- **Pluggable storage** — abstract `SpendStore` protocol with built-in `InMemorySpendStore`; bring your own PostgreSQL, Redis, etc.
+- **Atomic enforcement** — `check_and_record()` prevents TOCTOU races in single-process deployments
+
+### `financial_governance.transaction_policy`
+
+Static policy checks with no state tracking. Enforces structural rules on individual transactions.
+
+- **Currency allowlist** — only permit specific currencies (e.g., `["USDC", "USDT"]`)
+- **Recipient blocklist/allowlist** — control which addresses an agent can pay
+- **Amount bounds** — minimum and maximum per-transaction limits
+
+## Installation
+
+```bash
+# From the repo root (development)
+cd evaluators/contrib/financial-governance
+pip install -e ".[dev]"
+```
+
+## Configuration
+
+### Spend Limit
+
+The `spend_limit` evaluator is configured via a list of `BudgetLimit` objects. Each limit is evaluated independently — the first violation wins.
+
+```yaml
+controls:
+  - name: spend-limit
+    evaluator:
+      type: financial_governance.spend_limit
+      config:
+        limits:
+          # Per-transaction cap: single payment ≤ 100 USDC
+          - amount: "100.00"
+            currency: USDC
+          # Per-channel rolling 24h budget: each channel limited to 1000 USDC/day
+          - amount: "1000.00"
+            currency: USDC
+            scope_by: [channel]
+            window:
+              kind: rolling
+              seconds: 86400
+    selector:
+      path: input                     # Extract step.input (transaction dict)
+    action: deny
+```
+
+### Transaction Policy
+
+```yaml
+controls:
+  - name: transaction-policy
+    evaluator:
+      type: financial_governance.transaction_policy
+      config:
+        allowed_currencies: [USDC, USDT]
+        blocked_recipients: ["0xDEAD..."]
+        allowed_recipients: ["0xALICE...", "0xBOB..."]
+        min_amount: "0.01"
+        max_amount: "5000.00"
+    selector:
+      path: input
+    action: deny
+```
+
+## Selector Paths
+
+Both evaluators support two selector configurations:
+
+- **`selector.path: "input"`** (recommended) — The evaluator receives `step.input` directly, which should be the transaction dict.
+- **`selector.path: "*"`** — The evaluator receives the full Step object. It automatically extracts `step.input` for transaction fields and `step.context` for channel/agent/session metadata.
+
+## Input Data Schema
+
+The transaction dict (from `step.input`) should contain:
+
+```python
+# step.input — transaction payload
+{
+    "amount": "50.00",             # required — Decimal or numeric string
+    "currency": "USDC",            # required — payment currency
+    "recipient": "0xABC...",       # required — payment recipient
+    # optional context fields (used for scope_by)
+    "channel": "slack",
+    "agent_id": "agent-42",
+    "session_id": "sess-1",
+}
+```
+
+> **Note:** Use `Decimal` or string representations for `amount` — never raw `float`. Floating-point arithmetic is imprecise for money. The evaluator internally converts to `Decimal`.
+
+## BudgetLimit Model
+
+```python
+from decimal import Decimal
+from agent_control_evaluator_financial_governance.spend_limit import (
+    BudgetLimit, BudgetWindow, SpendLimitConfig, SpendLimitEvaluator,
+)
+
+# Per-transaction cap (no window)
+cap = BudgetLimit(amount=Decimal("100"), currency="USDC")
+
+# Rolling 24-hour budget, scoped per channel
+rolling = BudgetLimit(
+    amount=Decimal("1000"),
+    currency="USDC",
+    scope_by=("channel",),
+    window=BudgetWindow(kind="rolling", seconds=86400),
+)
+
+# Calendar-day budget (UTC)
+daily = BudgetLimit(
+    amount=Decimal("500"),
+    currency="USDC",
+    window=BudgetWindow(kind="fixed", unit="day"),
+)
+
+config = SpendLimitConfig(limits=[cap, rolling, daily])
+evaluator = SpendLimitEvaluator(config)
+```
+
+### BudgetWindow
+
+| kind | Required fields | Notes |
+|------|----------------|-------|
+| `"rolling"` | `seconds` | Sliding window from `now - seconds` |
+| `"fixed"` | `unit` (`"day"`, `"week"`, or `"month"`) | Calendar-aligned, UTC by default |
+
+### scope_by semantics
+
+`scope_by` lists the context dimension keys to isolate spend buckets. Each dimension is **independent**:
+
+- `scope_by=()` (default) — global budget: all spend in that currency shares one counter
+- `scope_by=("channel",)` — one counter per unique `channel` value
+- `scope_by=("agent_id",)` — one counter per unique `agent_id`
+- `scope_by=("channel", "agent_id")` — one counter per unique `(channel, agent_id)` pair
+
+Spend in `channel-A` does **not** count against `channel-B`'s budget.
+
+## Context-Aware Limits
+
+Context fields (`channel`, `agent_id`, `session_id`) can be provided in two ways:
+
+**Option A: Via `step.context`** (recommended for engine integration)
+
+```python
+step = Step(
+    type="tool",
+    name="payment",
+    input={"amount": "75.00", "currency": "USDC", "recipient": "0xABC"},
+    context={
+        "channel": "experimental",
+        "agent_id": "agent-42",
+    },
+)
+```
+
+When using `selector.path: "*"`, the evaluator merges `step.context` fields into the transaction data automatically. Fields already present in `step.input` are never overwritten by context.
+
+**Option B: Inline in the transaction dict** (simpler, for direct SDK use)
+
+```python
+result = await evaluator.evaluate({
+    "amount": "75.00",
+    "currency": "USDC",
+    "recipient": "0xABC",
+    "channel": "experimental",
+    "agent_id": "agent-42",
+})
+```
+
+## Custom SpendStore
+
+The `SpendStore` protocol requires three methods. Implement them for your backend:
+
+```python
+from decimal import Decimal
+from agent_control_evaluator_financial_governance.spend_limit import (
+    SpendStore, SpendLimitConfig, SpendLimitEvaluator,
+)
+
+class PostgresSpendStore:
+    """Example: PostgreSQL-backed spend tracking."""
+
+    def __init__(self, connection_string: str):
+        self._conn = connect(connection_string)
+
+    def record_spend(
+        self,
+        amount: Decimal,
+        currency: str,
+        metadata: dict | None = None,
+    ) -> None:
+        self._conn.execute(
+            "INSERT INTO agent_spend (amount, currency, metadata, recorded_at)"
+            " VALUES (%s, %s, %s, NOW())",
+            (str(amount), currency, json.dumps(metadata)),
+        )
+
+    def get_spend(
+        self,
+        currency: str,
+        start: float,
+        end: float | None = None,
+        scope: dict[str, str] | None = None,
+    ) -> Decimal:
+        # Build WHERE clause for scope filtering
+        clauses = [
+            "currency = %s",
+            "recorded_at >= to_timestamp(%s)",
+        ]
+        params = [currency, start]
+        if end is not None:
+            clauses.append("recorded_at <= to_timestamp(%s)")
+            params.append(end)
+        if scope:
+            for k, v in scope.items():
+                clauses.append(f"metadata->>{k!r} = %s")
+                params.append(v)
+        where = " AND ".join(clauses)
+        row = self._conn.execute(
+            f"SELECT COALESCE(SUM(amount), 0) FROM agent_spend WHERE {where}",
+            params,
+        ).fetchone()
+        return Decimal(str(row[0]))
+
+    def check_and_record(
+        self,
+        amount: Decimal,
+        currency: str,
+        limit: Decimal,
+        start: float,
+        end: float | None = None,
+        scope: dict[str, str] | None = None,
+        metadata: dict | None = None,
+    ) -> tuple[bool, Decimal]:
+        # Use a DB transaction for atomicity
+        with self._conn.transaction():
+            current = self.get_spend(currency, start, end, scope)
+            if current + amount > limit:
+                return False, current
+            self.record_spend(amount, currency, metadata)
+            return True, current
+
+# Use it:
+store = PostgresSpendStore("postgresql://...")
+evaluator = SpendLimitEvaluator(config, store=store)
+```
+
+> **Single-process atomicity note:** `InMemorySpendStore.check_and_record()` uses a `threading.Lock` to atomically check-and-record within a single process. For multi-process or distributed deployments, your custom store must implement true database-level atomics (e.g., PostgreSQL `SELECT ... FOR UPDATE`, Redis Lua scripts).
+
+## Running Tests
+
+```bash
+cd evaluators/contrib/financial-governance
+pip install -e ".[dev]"
+pytest tests/ -v
+```
+
+## Design Decisions
+
+1. **Decimal for money** — All monetary amounts use `Decimal`, never `float`. Floating-point arithmetic is unsuitable for financial calculations.
+2. **BudgetLimit + BudgetWindow models** — Expressive, composable budget definitions that replace the previous flat config. Each limit is independent; first violation wins.
+3. **Independent scope dimensions** — `scope_by=("channel",)` creates a separate counter for each channel value. Spend in one channel is completely isolated from another.
+4. **Atomic check_and_record()** — Eliminates the TOCTOU race of separate `get_spend()` + `record_spend()` calls. Single-process safe with `threading.Lock`; production stores should use DB-level atomics.
+5. **Decoupled from data source** — The `SpendStore` protocol means no new tables in core Agent Control. Bring your own persistence.
+6. **Fail-open on malformed input** — Missing or malformed data returns `matched=False, error=None`, following Agent Control conventions. The `error` field is reserved for evaluator crashes, not policy decisions.
+
+## Related Projects
+
+- [x402](https://github.com/coinbase/x402) — HTTP 402 payment protocol
+- [agentpay-mcp](https://github.com/up2itnow0822/agentpay-mcp) — MCP server for non-custodial agent payments
+
+## License
+
+Apache-2.0 — see [LICENSE](../../../LICENSE).

evaluators/contrib/financial-governance/pyproject.toml

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+[project]
+name = "agent-control-evaluator-financial-governance"
+version = "0.1.0"
+description = "Financial governance evaluators for agent-control — spend limits and transaction policy enforcement"
+readme = "README.md"
+requires-python = ">=3.12"
+license = { text = "Apache-2.0" }
+authors = [{ name = "agent-control contributors" }]
+keywords = ["agent-control", "evaluator", "financial", "spend-limit", "x402", "agentpay"]
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "License :: OSI Approved :: Apache Software License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.12",
+    "Topic :: Software Development :: Libraries",
+]
+dependencies = [
+    "agent-control-evaluators>=3.0.0",
+    "agent-control-models>=3.0.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0.0",
+    "pytest-asyncio>=0.23.0",
+    "pytest-cov>=4.0.0",
+    "ruff>=0.1.0",
+    "mypy>=1.8.0",
+]
+
+[project.entry-points."agent_control.evaluators"]
+"financial_governance.spend_limit" = "agent_control_evaluator_financial_governance.spend_limit:SpendLimitEvaluator"
+"financial_governance.transaction_policy" = "agent_control_evaluator_financial_governance.transaction_policy:TransactionPolicyEvaluator"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/agent_control_evaluator_financial_governance"]
+
+[tool.ruff]
+line-length = 100
+target-version = "py312"
+
+[tool.ruff.lint]
+select = ["E", "F", "I"]
+
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
+
+[tool.uv.sources]
+agent-control-evaluators = { path = "../../builtin", editable = true }
+agent-control-models = { path = "../../../models", editable = true }