#36318 validation: Ensure Invalid ValidationState has result

Enforces that invalid `ValidationState` instances always have a concrete failure `Result` enum and a non-empty `reject_reason`. Adds `BlockValidationResult::BLOCK_INCONCLUSIVE` across consensus validation, net processing, and the kernel C API to represent tests where block validity cannot be evaluated, replacing an unset result in `TestBlockValidity`.

Problem: Callers could construct an invalid `ValidationState` with an unset result enum or an empty reject reason string, leaving downstream consumers like P2P punishment logic and the kernel C API with ambiguous state. Specifically, `TestBlockValidity` used an unset result when a block did not connect to the active chain tip.

Evidence of importance:

• Commit message (ee04f82075): 'A violating usage in `TestBlockValidity` is being changed: instead of the default `BLOCK_RESULT_UNSET`, it now uses `BLOCK_INCONCLUSIVE`.'
• PR description notes that PR #31981 moved a check into `TestBlockValidity` that introduced a `BlockValidationState` with an unset result, which was noted in review on #35570.

Risk of a mistake: medium (validation, p2p). A faulty validation result invariant or misclassification could trigger debug assertions or improperly punish or fail to penalize P2P peers.

Ready

Nothing known that would invalidate a review now.

Waiting on (from the thread read):

• reviewer: review after undrafting 2026-09-23
• reviewer: initial review after undrafting 2026-09-23

Crickets

no substantive comment either way

Thread notes: Initial read. No objections or reviews yet; hodlinator provided context pointing to a previous discussion. / Initial record. No substantive reviews or objections yet.

Objections, suggestions, and questions: none recorded.

Participants:

• hodlinator (member, neutral, 1 statements 2026-09-23 to 2026-09-23): noted origin of the defaulted result enum and suggested pinging ryanofsky

15 lines under test/bench/ci.

• src/consensus/validation.h +6/-3
• src/test/fuzz/txdownloadman.cpp +3/-3
• src/test/txdownload_tests.cpp +3/-3
• src/bitcoin-chainstate.cpp +3/-0
• src/kernel/bitcoinkernel_wrapper.h +2/-1
• src/net_processing.cpp +3/-0
• src/test/kernel/test_kernel.cpp +3/-0
• src/kernel/bitcoinkernel.cpp +2/-0
• src/validation.cpp +1/-1
• src/kernel/bitcoinkernel.h +1/-0

The short text the ranking pass compares across PRs.

validation: Ensure Invalid ValidationState has result enforces that all invalid validation states specify both an explicit failure enum and a non-empty reject reason. It introduces `BLOCK_INCONCLUSIVE` to represent checks whose validity could not be resolved (e.g., when a block does not connect to the current chain tip in `TestBlockValidity`) and updates the kernel C API and net processing accordingly. This addresses an unset result introduced in PR #31981 and adds an `Assume` invariant to prevent incomplete validation error states.

P3 · bug fix

Extends the kernel C API to report the new inconclusive block validation state rather than exposing an ambiguous unset result. Error reporting at the kernel library boundary is directly improved, though the change is a straightforward extension of internal validation semantics.

Membership: Touches src/kernel/bitcoinkernel.h and src/kernel/bitcoinkernel.cpp to add BLOCK_INCONCLUSIVE to the kernel C API result reporting.

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

P3 · bug fix

Enforces that invalid ValidationState instances cannot be left in an unset or empty state, preventing ambiguous results in callers like TestBlockValidity. This strengthens validation invariants and retires a hazard for downstream validation state consumers.

Membership: Labeled Validation; changes ValidationState invariant enforcement in src/consensus/validation.h and updates TestBlockValidity in src/validation.cpp.

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