starknet_patricia: assert unmodified-subtree binary child is present in the skeleton

[yoavGrs]

Mirror the leaf sanity-check in finalize_binary_child: an unmodified subtree child
must already be finalized in the skeleton (from finalize_bottom_layer).

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[yoavGrs]

• starknet_patricia: collapse the let-else + re-match in node_from_edge_data into a single match #14623
• starknet_patricia: use OnceLock for write-once filled-tree output maps #14622
• starknet_patricia: assert unmodified-subtree binary child is present in the skeleton #14614 👈 (View in Graphite)
• starknet_patricia: extract finalize_binary_child helper from node_from_binary_data #14613
• starknet_patricia: thread the leaf output map separately from LeafSource #14600
• starknet_patricia: collapse leaf handling to a single match #14583
• starknet_patricia: introduce LeafSource enum for filled-tree leaf handling #14582
• main

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[cursor]

PR Summary

Low Risk
Small defensive invariant in Patricia Merkle skeleton construction; no API or behavior change beyond catching internal bugs earlier.

Overview
In finalize_binary_child, unmodified subtree children of a binary node now get the same skeleton presence check as leaves: if the child is already finalized in the bottom layer, the code asserts skeleton_tree contains that index instead of returning silently.

The assert message is generalized from “Leaf index” to “Index” because both node kinds use the same path.

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[nimrod-starkware]

@nimrod-starkware made 1 comment.
Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on yoavGrs).

---

crates/starknet_patricia/src/patricia_merkle_tree/updated_skeleton_tree/create_tree_helper.rs line 259 at r1 (raw file):

                    "Leaf index {index:?} doesn't appear in the skeleton."
                );
                return;

Suggestion:

            TempSkeletonNode::Original(OriginalSkeletonNode::UnmodifiedSubTree(_)) | TempSkeletonNode::Leaf
                assert!(
                    self.skeleton_tree.contains_key(&index),
                    "Index {index:?} doesn't appear in the skeleton."
                );
                return;
            }

[yoavGrs]

@yoavGrs made 1 comment.
Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on nimrod-starkware).

---

crates/starknet_patricia/src/patricia_merkle_tree/updated_skeleton_tree/create_tree_helper.rs line 259 at r1 (raw file):

                    "Leaf index {index:?} doesn't appear in the skeleton."
                );
                return;

Done.

[nimrod-starkware]

@nimrod-starkware reviewed 1 file and all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on yoavGrs).

[gkaempfer]

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