Per-Action Approval Thresholds in OpenMontage's Budget Governance System

OpenMontage enforces a default per-action approval threshold of $0.50 USD that triggers a warning when any single operation exceeds this limit, configurable via single_action_approval_usd in the CostTracker class or project configuration files.

The budget governance system in OpenMontage prevents runaway costs by evaluating every individual action against a per-action spending cap. This mechanism ensures that expensive operations receive explicit approval before execution, protecting project budgets from unexpected spikes caused by high-cost API calls or compute-intensive pipeline steps.

How Per-Action Approval Thresholds Work

OpenMontage implements per-action approval thresholds through the CostTracker class located in tools/cost_tracker.py. When the reserve() method estimates costs for an operation, it compares the amount against the single_action_approval_usd parameter.

Default limit: The system sets a hard default of $0.50 per individual action. This value is defined in lib/config_model.py at line 39 and documented in docs/ARCHITECTURE.md at line 358.

Warning trigger: If an operation's estimated cost exceeds the threshold, the tracker sets entry["budget_warning"] to True and populates entry["budget_warning_message"] with "single-action threshold $0.50 exceeded" (see implementation in tools/cost_tracker.py, lines 47-54).

Configuring the Approval Threshold

You can override the default $0.50 limit at instantiation or through project configuration.

Via CostTracker Instantiation

Pass the single_action_approval_usd parameter when creating a CostTracker instance:

from tools.cost_tracker import CostTracker, BudgetMode

# Override the per-action threshold to $2.00

tracker = CostTracker(
    budget_total_usd=10.0,
    mode=BudgetMode.WARN,
    single_action_approval_usd=2.00,
)

estimated_cost = 1.75
entry = {}
tracker.reserve(entry, estimated_cost)     # No warning, because 1.75 < $2.00

print(entry.get("budget_warning", False)) # → False

Via Configuration File

The threshold can also be set globally in the project's config.yaml file, which the configuration model (lib/config_model.py) loads at runtime.

Practical Implementation Examples

When using the default $0.50 threshold, any operation exceeding that amount triggers governance warnings:

from tools.cost_tracker import CostTracker, BudgetMode

# Create a tracker with the default per-action threshold ($0.50)

tracker = CostTracker(budget_total_usd=10.0, mode=BudgetMode.WARN)

# Simulate an operation that costs $0.75

estimated_cost = 0.75
entry = {}
tracker.reserve(entry, estimated_cost)     # Will set entry["budget_warning"] = True

print(entry["budget_warning_message"])

# → "single-action threshold $0.50 exceeded"

Source Code Architecture

According to the OpenMontage source code, the per-action approval mechanism spans three critical components:

• tools/cost_tracker.py — Contains the CostTracker class and its reserve() method, which implements the threshold comparison logic and warning generation.

• lib/config_model.py — Defines the data model default with single_action_approval_usd = 0.50 at line 39.

• docs/ARCHITECTURE.md — Documents the budget governance system and its default thresholds at line 358.

Summary

• Default threshold: OpenMontage limits individual actions to $0.50 USD by default through the single_action_approval_usd field.
• Warning system: The CostTracker.reserve() method marks entries with budget_warning = True when costs exceed the threshold.
• Configurable: Override defaults via constructor parameters or config.yaml.
• Source locations: Core logic resides in tools/cost_tracker.py (lines 47-54) with defaults defined in lib/config_model.py (line 39).

Frequently Asked Questions

What happens when a single action exceeds the per-action approval threshold?

When an operation's estimated cost exceeds the single_action_approval_usd value (default $0.50), the CostTracker sets the entry's budget_warning flag to True and attaches a warning message. In BudgetMode.WARN, execution continues but logs the violation; in stricter modes, this could block execution pending approval.

Can I disable per-action approval thresholds entirely?

While you cannot completely disable the check without modifying the source code, you can effectively neutralize it by setting single_action_approval_usd to an arbitrarily high value (e.g., 999999.00) when instantiating CostTracker or in your config.yaml configuration file.

Where is the default $0.50 value defined in the codebase?

The default value of $0.50 is hard-coded in lib/config_model.py at line 39 within the configuration data model. This default is also referenced in the project documentation at docs/ARCHITECTURE.md line 358 and enforced in the validation logic within tools/cost_tracker.py.

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