fix(rpc): reject non-positive fund account amounts

[vikions]

Summary

Rejects non-positive sim_fundAccount amounts before creating or crediting a funding transaction.

Why

sim_fundAccount is expected to create funding transactions only for positive values. Accepting 0 can create useless transactions, while negative values can lead to invalid transfer semantics later in the simulator flow.

Changes

• Validate amount > 0 in fund_account
• Return JSON-RPC invalid params for non-positive amounts
• Add focused tests for 0 and negative amounts
• Assert invalid inputs do not instantiate the transaction processor or create crediting side effects

Test plan

• python3 -m py_compile backend/protocol_rpc/endpoints.py tests/unit/test_simulator_sessions.py
• git diff --check -- backend/protocol_rpc/endpoints.py tests/unit/test_simulator_sessions.py
• python3 -m pytest tests/unit/test_simulator_sessions.py -q

Summary by CodeRabbit

Bug Fixes

• The account funding endpoint now validates that the amount must be greater than 0, rejecting non-positive values with a clear error message (code -32602). Request validation checks now occur earlier in the process for improved efficiency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: bd834a80-29d5-4764-87eb-a2b3c2943e74

📥 Commits

Reviewing files that changed from the base of the PR and between 6736a15 and eb0ec6d.

📒 Files selected for processing (2)

• backend/protocol_rpc/endpoints.py
• tests/unit/test_simulator_sessions.py

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📝 Walkthrough

Walkthrough

The pull request adds input validation to the fund_account RPC endpoint. The function now validates the account address and rejects non-positive amounts before creating a transaction processor, raising a standardized JSON-RPC error when validation fails. Unit tests verify both the rejection behavior and the existing successful transaction path.

Changes

fund_account Input Validation

Layer / File(s)	Summary
Validation Logic backend/protocol_rpc/endpoints.py	fund_account validates account_address before instantiation and rejects amount <= 0 with JSONRPCError (code -32602); TransactionsProcessor is created after validations pass.
Test Infrastructure & Validation Cases tests/unit/test_simulator_sessions.py	Import JSONRPCError and add parametrized test ensuring fund_account rejects amounts 0 and -1, asserting correct error code, message, and no side effects.
Happy Path Verification tests/unit/test_simulator_sessions.py	Extended existing test assertions to verify account manager's credit_tx_value_once is called with generated transaction hash, funded address, and amount.

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

A rabbit hops through validation gates,
Checking amounts before creating fates,
"No zeros or negatives!" the function declares,
With errors well-formed and tests that declare,
Transactions now guarded with mathematical care! 🐰✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 16.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically summarizes the main change: adding validation to reject non-positive amounts in the fund_account function.
Description check	✅ Passed	The description covers the what (changes), why (reasons), and testing done sections required by the template, with clear explanations and specific test execution details.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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