fix: validate force_small_change_as_fee in the API server

[eval-exec]

The API server's transfer method accepted force_small_change_as_fee as a free-form string and passed it straight through to WalletSubCommand::transfer, while the equivalent --max-tx-fee CLI flag is validated by clap.

Changes

• ApiRpc::transfer validates force_small_change_as_fee before any wallet lock is taken, so a value that cannot be parsed as a capacity is reported as -32602.
• WalletSubCommand::transfer propagates the parse error rather than assuming success.
• Saturates the capacity arithmetic used to build the --max-tx-fee suggestion.
• Documents the field in docs/API-Server.md.

Compatibility

No wire-format change: force_small_change_as_fee stays an optional capacity string in CKB, the same unit as the --max-tx-fee CLI flag. Existing clients are unaffected.

Tests

Three unit tests cover the validation and the field's wire format:

cargo test --bin ckb-cli api_server::tests

[Copilot]

Copilot review overview

🟡 Changes recommended

The changelog entry should explicitly flag the wire-format breaking change for force_small_change_as_fee, and a small naming clarity fix is needed in the new conversion code.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

• Document the wire-format breaking change for shannon fees · New

What changed in this PR

This PR tightens validation and error handling for the API server transfer flow by changing force_small_change_as_fee from a free-form string into a typed u64 (shannons), aligning the API behavior with CLI validation and preventing panics in downstream parsing.

Changes:

• Change force_small_change_as_fee in the API server transfer args to Option<u64> and convert it back via HumanCapacity for internal CLI-compatible handling.
• Propagate parse failures in WalletSubCommand::transfer instead of unwrap()-ing and potentially panicking.
• Prevent overflow in the --max-tx-fee suggestion calculation by using saturating arithmetic, and document the field in the API docs.

File	Description
src/​subcommands/​wallet.rs	Avoids panic by propagating parse errors; prevents overflow in fee suggestion capacity math.
src/​subcommands/​api_server.rs	Makes force_small_change_as_fee typed (u64) at the JSON-RPC boundary and adds unit tests for deserialization/conversion.
docs/​API-Server.md	Documents force_small_change_as_fee and clarifies its unit (Shannon).
CHANGELOG.md	Notes the fixes in Unreleased (should also call out the breaking wire-format change).

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Copilot]

Copilot review overview

🟡 Changes recommended

The new API documentation for force_small_change_as_fee should explicitly show it is a JSON string (quoted) to prevent client-side type mistakes, and there is also a small typo in the transfer log message.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• Document force_small_change_as_fee as a string · New
• Fix typo in log message to match RPC method · New

Resolved since last review (1)

• Document the wire-format breaking change for shannon fees

[Copilot]

Copilot review overview

🟢 Approval recommended

The change is small, self-contained, consistent with existing parsing/error-handling conventions, and covered by new tests with docs and changelog updated.

Review effort: Balanced
Findings: None

Resolved since last review (2)

• Fix typo in log message to match RPC method
• Document force_small_change_as_fee as a string