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Codecov Report

❌ Patch coverage is 83.75000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.11%. Comparing base (964a84f) to head (53e156a).
⚠️ Report is 46 commits behind head on main.

@@            Coverage Diff             @@
##             main    #4580      +/-   ##
==========================================
- Coverage   86.18%   86.11%   -0.07%     
==========================================
  Files         156      157       +1     
  Lines      108528   108871     +343     
  Branches   108528   108871     +343     
==========================================
+ Hits        93532    93752     +220     
- Misses      12386    12504     +118     
- Partials     2610     2615       +5     

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I've completed a thorough review of every file and hunk in this PR. The changes are well-structured — the reserve functions now properly reject cases where the channel value is below the dust limit or minimum reserve, the cmp::min(channel_value, ...) cap is correctly replaced by early error returns, and the for_splice path correctly uses context.holder_dust_limit_satoshis instead of MIN_CHAN_DUST_LIMIT_SATOSHIS.

No new issues found.

Prior review status: My previous inline comment at channel.rs:2828 appears to have been incorrect — the current code already uses context.holder_dust_limit_satoshis in the error message, matching the value passed to get_v2_channel_reserve_satoshis.

Verification notes:

• All callers of the now-Result-returning functions handle Err properly via map_err with descriptive messages.
• The unwrap() calls in tx_builder.rs are inside #[cfg(debug_assertions)] blocks and are safe because channel_value >= dust_limit is guaranteed by the constraint computation for existing channels.
• The cmp::min(prop, 1_000_000) cap in get_holder_selected_channel_reserve_satoshis matches the documented behavior in ChannelHandshakeConfig.
• The removal of cmp::min(channel_value, ...) is safe: the early Err checks ensure the reserve never exceeds the channel value on the Ok path, preserving the "no larger than channel_value_satoshis" doc guarantee.
• The is_0reserve short-circuit after the error check means 0-reserve channels with value below thresholds are now rejected, which is correct and intentional per the PR description.
• Test visibility for counterparty_dust_limit_satoshis follows the existing #[cfg(test)]/pub(crate) pattern used by holder_dust_limit_satoshis.

Dropped the move of the no_outputs check in tx_builder, and made this diff:

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index e59855d28..137bdd28f 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -2825,14 +2825,25 @@
                                .expect("counterparty reserve is set")
                                == 0,
                )
-               .map_err(|()| format!("The post-splice channel value {post_channel_value_sat} is smaller than our dust limit {MIN_CHAN_DUST_LIMIT_SATOSHIS}"))?;
-               let their_dust_limit_satoshis = context.counterparty_dust_limit_satoshis;
+               .map_err(|()| {
+                       format!(
+                               "The post-splice channel value {post_channel_value_sat} is smaller \
+                               than our dust limit {}",
+                               context.holder_dust_limit_satoshis
+                       )
+               })?;
                let holder_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
                        post_channel_value_sat,
-                       their_dust_limit_satoshis,
+                       context.counterparty_dust_limit_satoshis,
                        prev_funding.holder_selected_channel_reserve_satoshis == 0,
                )
-               .map_err(|()| format!("The post-splice channel value {post_channel_value_sat} is smaller than their dust limit {their_dust_limit_satoshis}"))?;
+               .map_err(|()| {
+                       format!(
+                               "The post-splice channel value {post_channel_value_sat} is smaller \
+                               than their dust limit {}",
+                               context.counterparty_dust_limit_satoshis,
+                       )
+               })?;

                Ok(Self {
                        channel_transaction_parameters: post_channel_transaction_parameters,