Stage 2 of 4. Read the project prerequisites before starting; this stage builds on the preceding contracts.
What changes
Checking available budget without reserving it allows multiple queued requests to spend the same capacity. Store reservations separately from settled spending. A new request must fit after both quantities are counted.
This single-process state machine teaches the invariant. It does not claim distributed concurrency safety. A service version needs an atomic transaction or lock around this exact transition.
Work through one concrete case
Start at limit 100, spent 20, holds={A:30}. Available capacity is 50, so reserving B:60 fails without changing A. A second reservation using id A also fails even if its amount is 1.
pj agent budget planner 2
Change the lab inputs and calculate the result before reading its metrics. The figure computes from those inputs; the implementation tests below remain the source of completion evidence.
Implement the contract
Implement reserve against the stated contract.
Use the public API contract and the typed starter signatures. Return values from core functions and let the supplied driver own file input, argument parsing and presentation.
Build a new holds dictionary only after validating the identity and amount. Admission and reservation must be one state transition; an earlier available() check alone permits double spending.
Verify and inspect
From the repository root, initialize once with python3 scripts/project_test.py agent-budget-planner --init learning-artifacts/agent-budget-planner. Then grade cumulatively:
python3 scripts/project_test.py agent-budget-planner --stage 2 --path learning-artifacts/agent-budget-planner --strictA fresh workspace should fail until you implement the contract. After every stage is complete, run your actual artifact from the supplied sample:
cd learning-artifacts/agent-budget-planner
python3 cli.py samples/input.json --mode execute --output budget.jsonInvestigate the failure boundary
Trace two callers both observing 50 free units. Name the lock or database transaction a service needs around reserve.