docs(node): move confirmation rationale off the pure helper

Per review: attestation_expiry_changed is a plain comparison, so drop the
system-behavior doc from it and state the assumption once at the decision site
(submitted_attestation_landed), linking DEFAULT_EXPIRATION_DURATION_SECONDS so
the cross-crate reference is checked. Trim remaining where-used / paraphrasing
comments.

Author: barakeinav1

crates/node/src/indexer.rs

@@ -405,9 +405,8 @@ impl ReadSupportedForeignChain for RealForeignChainPolicyReader {
 }
 
 pub(crate) trait ReadAttestationExpiry: Send + Sync {
-    /// Reads the Dstack attestation expiry currently stored for `tls_public_key`, or `None` if
-    /// none is stored. Used as the pre-submit baseline for the submit_participant_info
-    /// confirmation.
+    /// The Dstack attestation expiry currently stored for `tls_public_key`, or `None` if none is
+    /// stored.
     fn read_stored_dstack_expiry<'a>(
         &'a self,
         tls_public_key: &'a dtos::Ed25519PublicKey,

crates/node/src/indexer/tx_sender.rs

@@ -181,21 +181,21 @@ async fn submit_tx(
     })
 }
 
-/// Whether our `submit_participant_info` landed: a successful submit re-stamps the stored expiry to
-/// a new value, a failed one leaves it unchanged, so a change from the baseline (or no prior entry)
-/// means it landed. Inequality rather than `>` because a lowered expiry constant can make a landed
-/// submit stamp an *earlier* expiry.
-// TODO(#1639): match a certificate-derived identity instead of this expiry heuristic.
 fn attestation_expiry_changed(pre_submit_expiry: Option<u64>, stored_expiry: u64) -> bool {
     match pre_submit_expiry {
         Some(expiry_before_submit) => stored_expiry != expiry_before_submit,
         None => true,
     }
 }
 
-/// Whether the attestation we submitted is the one now stored. Mock carries a full identity and is
-/// matched directly; a Dstack entry has none to match (it's a different stored type), so it's
-/// confirmed indirectly via [`attestation_expiry_changed`].
+/// Whether the attestation we submitted is now the one stored on chain.
+///
+/// Mock is matched by identity. A Dstack entry keeps no stored per-submission identity, so it is
+/// confirmed via [`attestation_expiry_changed`]: an accepted submit re-stamps the entry's expiry
+/// (to the submit block time plus
+/// [`DEFAULT_EXPIRATION_DURATION_SECONDS`](mpc_attestation::attestation::DEFAULT_EXPIRATION_DURATION_SECONDS)),
+/// and only the owning account may rewrite it, so a changed expiry means our submit landed.
+// TODO(#1639): match a certificate-derived identity instead of this expiry heuristic.
 fn submitted_attestation_landed(
     pre_submit_expiry: Option<u64>,
     stored: &VerifiedAttestation,

crates/node/src/indexer/types.rs

@@ -68,8 +68,8 @@ pub enum ChainSendTransactionRequest {
     SubmitParticipantInfo {
         #[serde(flatten)]
         args: Box<contract_args::SubmitParticipantInfoArgs>,
-        /// Attestation expiry stored on chain before this submission, captured once by the caller
-        /// for the landing check in observe_tx_result. Node-internal; NOT part of the on-chain call.
+        /// Pre-submit expiry baseline for the landing check. Skipped from serialization so it never
+        /// reaches the on-chain call args.
         #[serde(skip)]
         pre_submit_expiry: Option<u64>,
     },

crates/node/src/tee/remote_attestation.rs

@@ -192,7 +192,7 @@ pub async fn periodic_attestation_submission<T: TransactionSender + Clone, I: Ti
             .read_stored_dstack_expiry(&tls_public_key)
             .await
         {
-            Ok(baseline) => baseline, // Some = prior expiry; None = nothing stored yet (first submit) -- both proceed
+            Ok(baseline) => baseline, // None just means nothing stored yet (e.g. first submit)
             Err(error) => {
                 tracing::warn!(%error, "could not read pre-submit attestation baseline; skipping this round");
                 continue; // next tick. Do NOT submit with an unknown baseline.
@@ -310,7 +310,7 @@ pub async fn monitor_attestation_removal<T: TransactionSender + Clone>(
                 .read_stored_dstack_expiry(&tls_public_key)
                 .await
             {
-                Ok(baseline) => baseline, // Some = prior expiry; None = nothing stored yet (first submit) -- both proceed
+                Ok(baseline) => baseline, // None just means nothing stored yet (e.g. first submit)
                 Err(error) => {
                     tracing::warn!(%error, "could not read pre-submit attestation baseline; skipping this round");
                     was_available = is_available;