#36584 kernel: make btck_LogEntry opaque

Replaces the public struct definition of `btck_LogEntry` in the libbitcoinkernel C API with an opaque handle and explicit getter functions (`btck_log_entry_get_*`). String fields are returned as non-owning `btck_StringView` structs rather than raw pointer and length pairs. Field values are extracted lazily upon access rather than eagerly converted before calling the registered logging callback.

Problem: Exposing `btck_LogEntry` as a public C struct fixes its memory layout in the library ABI, preventing the addition or alteration of log fields without breaking backwards compatibility. It also deviates from almost all other libbitcoinkernel types, which use opaque handles.

Evidence of importance:

• Author note in description: 'This allows adding or changing fields without breaking the ABI, and is consistent with ~all other kernel objects. Follow-up to https://github.com/bitcoin/bitcoin/pull/34374#discussion_r4207440088.'
• Author microbenchmarks show negligible overhead: callback log statement duration shifts between −2.5 ns and +5.4 ns depending on how many fields are read.

Risk of a mistake: low (other). Mistakes are confined to libbitcoinkernel logging callback wrappers and getters, causing corrupted log fields or compilation issues for external kernel consumers.

Changed since the previous assessment: Diff provided; matches the previous description.

Ready

Nothing known that would invalidate a review now.

Waiting on (from the thread read):

• nothing

Strong

substantive support, no open objection (musaHaruna)

Thread notes: Initial record. sedited raised a style suggestion regarding docstring comments on getters, which the author answered, and both sedited and musaHaruna have ACKed the PR. / Initial record for the PR. sedited raised a minor docstring style suggestion which stickies-v answered, followed by ACKs from both sedited and musaHaruna.

Objections, suggestions, and questions:

Support:

• sedited (member) (ACK, 2026-10-21): (no reason given) [not substantive]
• musaHaruna (contributor) (ACK, 2026-10-21) [tested]: Tested locally, including calling all nine getters from the logging callback and checking the message, timestamp, source location, level, and category for the connection and disconnection messages.

Participants:

• musaHaruna (contributor, support, 1 statements 2026-10-21 to 2026-10-21): ACKed; tested getters and logging callback locally
• sedited (member, support, 2 statements 2026-10-21 to 2026-10-21): ACKed; suggested one-line comments for trivial getters

0 lines under test/bench/ci.

• src/kernel/bitcoinkernel.h +103/-38
• src/kernel/bitcoinkernel.cpp +53/-24
• src/kernel/bitcoinkernel_wrapper.h +19/-16

The short text the ranking pass compares across PRs.

Makes btck_LogEntry an opaque handle in the libbitcoinkernel C interface, exposing fields via btck_log_entry_get_* accessor functions. A public struct layout made it impossible to add or change log metadata fields without breaking ABI compatibility for kernel consumers, unlike other kernel API handles. Fields are now converted lazily when read, and author benchmarks show no meaningful performance impact (delta between -2.5 ns and +5.4 ns per log statement).

P3 · cleanup

Making `btck_LogEntry` opaque aligns it with other kernel types and avoids fixing struct layout in the ABI. As the author notes, this 'allows adding or changing fields without breaking the ABI, and is consistent with ~all other kernel objects.' While it improves library ABI extensibility, the work is an internal C API refinement and reasonably deferrable.

Membership: Modifies `src/kernel/bitcoinkernel.h`, `bitcoinkernel.cpp`, and `bitcoinkernel_wrapper.h` to change the public libbitcoinkernel C API logging interface.

Factors: security/stability 0, bug 0, performance 0, user value 1, leverage 1