feat(governance): decouple minimum dissolve delay to vote from propose

rs/nns/governance/src/governance.rs

@@ -285,6 +285,12 @@ pub const MAX_NEURONS_FUND_PARTICIPANTS: u64 = 5_000;
 /// in the same limit.
 const NEURON_RATE_LIMITER_KEY: &str = "ADD_NEURON";
 
+/// The minimum dissolve delay (in seconds) a neuron must have to submit a
+/// non-ManageNeuron proposal. This is intentionally decoupled from the voting
+/// eligibility threshold (`neuron_minimum_dissolve_delay_to_vote_seconds`),
+/// which can be lower.
+pub const NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS: u64 = 6 * ONE_MONTH_SECONDS;
+
 // The maximum dissolve delay allowed for a neuron.
 pub const MAX_DISSOLVE_DELAY_SECONDS_PRE_MISSION_70: u64 = 8 * ONE_YEAR_SECONDS;
 pub const MAX_DISSOLVE_DELAY_SECONDS_POST_MISSION_70: u64 = 2 * ONE_YEAR_SECONDS;
@@ -5226,18 +5232,16 @@ impl Governance {
             ));
         }
 
-        let min_dissolve_delay_seconds_to_vote = if action.manage_neuron().is_some() {
+        let min_dissolve_delay_seconds_to_propose = if action.manage_neuron().is_some() {
             0
         } else {
-            self.neuron_minimum_dissolve_delay_to_vote_seconds()
+            NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS
         };
 
-        // The proposer must be eligible to vote. This also ensures that the
-        // neuron cannot be dissolved until the proposal has been adopted or
-        // rejected.
-        if proposer_dissolve_delay_seconds < min_dissolve_delay_seconds_to_vote {
+        // The proposer must have sufficient dissolve delay to submit proposals.
+        if proposer_dissolve_delay_seconds < min_dissolve_delay_seconds_to_propose {
             return Err(GovernanceError::new_with_message(
-                ErrorType::InsufficientFunds,
+                ErrorType::PreconditionFailed,
                 "Neuron's dissolve delay is too short.",
             ));
         }

rs/nns/governance/src/network_economics.rs

@@ -1,3 +1,4 @@
+use crate::governance::NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS;
 use crate::pb::v1::{
     NetworkEconomics, NeuronsFundEconomics, NeuronsFundMatchedFundingCurveCoefficients,
     VotingPowerEconomics,
@@ -380,6 +381,16 @@ impl VotingPowerEconomics {
                 );
                 defects.push(defect);
             }
+
+            if delay > NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS {
+                let defect = format!(
+                    "neuron_minimum_dissolve_delay_to_vote_seconds ({:?}) must not exceed \
+                     the minimum dissolve delay required to submit proposals ({}).",
+                    self.neuron_minimum_dissolve_delay_to_vote_seconds,
+                    NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS,
+                );
+                defects.push(defect);
+            }
         } else {
             defects.push("neuron_minimum_dissolve_delay_to_vote_seconds must be set.".to_string());
         }

rs/nns/governance/src/network_economics_tests.rs

@@ -112,10 +112,18 @@ fn test_neuron_minimum_dissolve_delay_to_vote_seconds_bounds() {
         ),
         (
             Some(UPPER_BOUND_SECONDS + 1),
-            Err(vec![format!(
-                "neuron_minimum_dissolve_delay_to_vote_seconds (Some({})) must be between two weeks and six months.",
-                UPPER_BOUND_SECONDS + 1
-            )]),
+            Err(vec![
+                format!(
+                    "neuron_minimum_dissolve_delay_to_vote_seconds (Some({})) must be between two weeks and six months.",
+                    UPPER_BOUND_SECONDS + 1
+                ),
+                format!(
+                    "neuron_minimum_dissolve_delay_to_vote_seconds (Some({})) must not exceed \
+                     the minimum dissolve delay required to submit proposals ({}).",
+                    UPPER_BOUND_SECONDS + 1,
+                    crate::governance::NEURON_MINIMUM_DISSOLVE_DELAY_TO_PROPOSE_SECONDS,
+                ),
+            ]),
         ),
         (Some(DEFAULT_SECONDS), Ok(())),
         (Some(LOWER_BOUND_SECONDS), Ok(())),

rs/nns/governance/unreleased_changelog.md

@@ -13,6 +13,8 @@ on the process that this file is part of, see
 
 ## Changed
 
+* The minimum dissolve delay required to submit non-manage-neuron proposals is now
+  a fixed 6 months, decoupled from the voting eligibility threshold which can be lower.
 * Mission 70 voting rewards adjustment has been re-calculated. Now: 63.29%. Before: 65.5%.
 
 ## Deprecated