refactor: decode Cycles from little-endian bytes via TryFrom

[mraszyk]

Cycles was decoded from its little-endian byte representation through an infallible From<&Vec<u8>> impl, which left it with no way to report a length mismatch to its caller. Replace it with TryFrom<&Vec<u8>>.

The two protobuf conversions built on it, state.queues.v1.Cycles and canister_state_bits.v1.CyclesAccount, become TryFrom impls returning ProxyDecodeError::ValueOutOfRange, so a length mismatch is now reported like any other proto decoding error. This matches how NominalCycles and CompoundCycles already decode in the same crate.

The try_from_option_field call sites (Request::cycles_payment, Response::cycles_refund, CallContext::available_cycles, CanisterStateBits::cycles_balance, Refund::amount) need no change: they already required a TryFrom whose error converts into ProxyDecodeError and were satisfied through the blanket impl. The callers that used the infallible impls directly now propagate the error instead: CompoundCycles::real, Callback::cycles_sent, the three RefundStatus fields, and four CanisterStateBits fields in state_layout.

The encoding is unchanged, so this only affects the decoding failure path.

[Copilot]

Pull request overview

Refactors Cycles decoding to report invalid byte lengths instead of panicking.

Changes:

• Adds fallible byte-slice and protobuf conversions.
• Propagates decode errors through state deserialization.
• Updates tests and direct decoding call sites.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rs/types/types/src/methods.rs	Propagates callback cycle decode errors.
rs/types/types/src/canister_http.rs	Validates refund cycle fields.
rs/types/cycles/src/cycles.rs	Implements fallible decoding and tests.
rs/types/cycles/src/compound_cycles.rs	Propagates real-cycle decode errors.
rs/state_layout/src/state_layout/proto.rs	Validates persisted cycle fields.
rs/execution_environment/tests/hypervisor.rs	Updates test decoding calls.
rs/embedders/tests/system_api.rs	Updates system API test decoding.

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[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to dbb9ec6.

Security Overview

• 🔎 Scanned files: 7 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f5e9d2bb-29a4-4b64-902a-391d65fd8b2d?scanId=6cdad95d-23c7-4812-abca-7890d36c8847&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► rs/embedders/tests/system_api.rs     Use Cycles::try_from(&heap) instead of Cycles::from(&heap) where decoding from bytes is performed ► rs/execution_environment/tests/hypervisor.rs     Switch to Cycles::try_from(&bytes).unwrap() for cost decoding ► rs/state_layout/src/state_layout/proto.rs     Use Cycles::try_from with transpose for optional fields (cycles_debit, reserved_balance, reserved_balance_limit, minimum_incoming_canister_call_cycles)
Enhancement	► rs/types/cycles/src/compound_cycles.rs     Decode real field with Cycles::try_from(real) instead of Cycles::from(real)
Enhancement	► rs/types/cycles/src/cycles.rs     Introduce TryFrom<&Vec> for Cycles using try_from on LE bytes     Change PbCycles -> Cycles and pbCyclesAccount -> Cycles implementations to TryFrom with proper error handling     Add helper try_from_le_bytes to map length errors to ProxyDecodeError     Add tests for roundtrip, wrong length handling, and proto mismatch cases
Enhancement	► rs/types/types/src/canister_http.rs     In CanisterHttpRequestContext, convert Cycles fields using Cycles::try_from with proper transpose handling
Enhancement	► rs/types/types/src/methods.rs     In Callback, convert cycles_sent using Cycles::try_from instead of Cycles::from