[BUG] Assertion of Validity causes crash.

[SamHSmith]

After responding to a ProcessSyncedValue message with a proposal marked valid we get this crash. (Sometimes.)

The application panicked (crashed).
Message:  assertion left == right failed
  left: Invalid
 right: Valid
Location: /home/sam/.cargo/git/checkouts/malachite-ea1aa1be87e998cc/8a64f82/code/crates/core-consensus/src/handle/decide.rs:64

[cason]

Can you please detail you setup? What is the ValuePayload mode?

From a generic overview, you have a full_proposal reported as invalid that was decided. This probably happens because the full proposal was previously received by the node and the application reported it as invalid. Now, since a certificate for it was received from ValueSync, it became decide, despite being invalid.

It is expected the process to panic in this case, but I am curious to understand the scenario better.

[SamHSmith]

So it is not possible for values to change from being invalid to valid?

[cason]

So it is not possible for values to change from being invalid to valid?

Good point, it should be (as for https://github.com/circlefin/malachite/blob/main/specs/consensus/overview.md#validation)! But I am not sure if the software actually supports this, apparently it does not.

[cason]

But in any case, your application should tell consensus that v was invalid, then that v has became valid. Not sure how this can be done, this "change of mind" is supposed to happen after a node restart.

[cason]

Indeed, we ignore a Input::Proposal(p, true) if a Input::Proposal(p, false) was already stored:

malachite/code/crates/core-driver/src/proposal_keeper.rs

Lines 70 to 78 in 76d25e5

	pub fn add(
	&mut self,
	proposal: SignedProposal<Ctx>,
	validity: Validity,
	) -> Result<(), RecordProposalError<Ctx>> {
	// Ignore exact duplicates
	if self.proposals.iter().any(|(p, _)| p == &proposal) {
	return Ok(());
	}

[Ridwannurudeen]

I'd like to work on this. The root cause is clear — proposal_keeper.rs silently drops a valid proposal if an invalid one was already stored for the same value. The fix should allow validity to be upgraded from false to true, consistent with the spec's position that validity can change after a restart.

I'll look into the proposal keeper logic and the assertion in decide.rs to make sure both paths handle the upgrade correctly.

Could you assign this to me?