Fix #117 — Validate FeeConfig to reject zero and negative fees

[peace-cyber09]

PR: Fix #117 — Validate FeeConfig to reject zero and negative fees

Summary

initialize and update_fee_config previously accepted a FeeConfig with
any fee field set to 0 or a negative value, including contact_fee_stroops.
This would allow scouts to contact players for free and break subscription
pricing. This PR adds a validate_fee_config guard that rejects any such
configuration before it is stored on-chain.

Changes

contracts/scout_access/src/errors.rs

• Added InvalidInput = 15 to ScoutAccessError.

contracts/scout_access/src/lib.rs

• Added private helper validate_fee_config(config: &FeeConfig) -> Result<(), ScoutAccessError>:
  • Returns ScoutAccessError::InvalidInput if any of contact_fee_stroops,
    basic_sub_stroops, pro_sub_stroops, or elite_sub_stroops is <= 0.
  • Returns ScoutAccessError::InvalidInput if sub_duration_secs == 0.
• Called validate_fee_config in initialize (before require_auth).
• Called validate_fee_config in update_fee_config (after require_admin).
• Added 11 unit tests covering every validation path:

Test	Scenario
test_initialize_zero_contact_fee_returns_invalid_input	contact_fee_stroops = 0 → InvalidInput
test_initialize_zero_basic_sub_returns_invalid_input	basic_sub_stroops = 0 → InvalidInput
test_initialize_zero_pro_sub_returns_invalid_input	pro_sub_stroops = 0 → InvalidInput
test_initialize_zero_elite_sub_returns_invalid_input	elite_sub_stroops = 0 → InvalidInput
test_initialize_zero_sub_duration_returns_invalid_input	sub_duration_secs = 0 → InvalidInput
test_initialize_negative_fee_returns_invalid_input	contact_fee_stroops = -1 → InvalidInput
test_initialize_valid_fee_config_succeeds	All fields positive → Ok(())
test_update_fee_config_zero_contact_fee_returns_invalid_input	contact_fee_stroops = 0 → InvalidInput
test_update_fee_config_zero_subscription_fee_returns_invalid_input	basic_sub_stroops = 0 → InvalidInput
test_update_fee_config_zero_duration_returns_invalid_input	sub_duration_secs = 0 → InvalidInput
test_update_fee_config_valid_succeeds	All fields positive → Ok(()), stored value verified

Acceptance Criteria

• initialize with a zero contact fee returns InvalidInput (error code 15).
• update_fee_config with a zero subscription fee returns InvalidInput.
• Valid fee config succeeds in both initialize and update_fee_config.
• Unit tests cover all validation cases.

Testing

cargo test -p scoutchain-scout-access

Related

Closes #117

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