refactor(storage): remove the dead state-based comparisons sync path

[chefsale]

What

Removes the legacy state-based Merkle comparison sync (compare_trees / StorageDelta::Comparisons), which is superseded by the HashComparison / level-wise / DAG-CausalActions protocols and is unreachable in production. Net −680 lines.

Why it's safe (evidence, not just static analysis)

Follow-up to the probe PR (#3209). Static analysis showed the path was dead; to confirm it independent of log capture, that PR made all three of its entry points hard-abort:

• emit — commit_root producing a Comparisons artifact,
• receive — Root::sync → apply_comparisons,
• trigger — the Action::Compare receive-arm in apply_actions.

CI ran the full multi-node divergence e2e suite (partition, peer-restart, peer-pause, 8-node mesh-soak, concurrent-rotation-converge, HashComparison-reconcile, member-removed-catchup). None of the aborts fired → the path is exercised by neither production sync nor the test suite.

Removed

• Interface::{compare_trees, compare_affective, generate_comparison_data}
• StorageDelta::Comparisons variant; Comparison (integration.rs — file deleted); ComparisonData (action.rs)
• Root::apply_comparisons + the Comparisons arm of Root::sync
• delta::push_comparison, DeltaContext.comparisons, and the Comparisons branch of commit_root / commit_causal_delta
• Index::get_collection_names_for (only the removed path used it)
• the inert Action::Compare pushes in apply_action (they only fed the removed protocol) and the now-false "ships in the next outbound delta" comment

Kept / compatibility

• The Action::Compare enum variant stays — it's referenced defensively across op-adapter / node delta_store / signing / runtime. Its Root::sync and apply_action arms are now inert (no-op / reject).
• Wire tags preserved: StorageDelta gains a hand-rolled BorshSerialize so CausalActions keeps tag 2 (tag 1 — the removed variant — is now rejected). Every persisted and in-flight delta stays decodable; this is wire-stability, not a migration shim. The zero-byte no-op sentinel now decodes to Actions(vec![]).

Verification

• cargo clippy --workspace --all-targets --features calimero-storage/testing -- -D warnings — clean
• cargo test -p calimero-storage --features testing — 667 passed, 0 failed (incl. rewritten StorageDelta wire-format roundtrip tests)

🤖 Generated with Claude Code

[meroreviewer]

🤖 MeroReviewer

Reviewed by 1 agents | Quality score: 85% | Review time: 527.2s

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✅ No Issues Found

All agents reviewed the code and found no issues. LGTM! 🎉

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_{🤖 Generated by MeroReviewer | Review ID: review-3fa9af2b}

[meroreviewer]

Documentation Review

The following documentation may need updates based on the changes in this PR:

• 🟡 AGENTS.md: AGENTS.md exists but was not updated — consider updating it to reflect the architecture changes in this PR.
• 🟡 CONTRIBUTING.md: CONTRIBUTING.md exists but was not updated — consider updating it to reflect the architecture changes in this PR.
• 🟡 architecture/migrations.html: Files matching crates/storage/** were deleted but architecture/migrations.html was not updated — references to removed code may now be stale (per source_to_docs_mapping).
• 🟡 architecture/storage-schema.html: Files matching crates/storage/** were deleted but architecture/storage-schema.html was not updated — references to removed code may now be stale (per source_to_docs_mapping).
• 🟡 docs/: Static HTML docs in docs/ may need updating — architecture-impacting changes detected. On merge, update-docs will scan this directory and open a PR if any pages need to change.

[meroreviewer]

🤖 AI Code Reviewer

Reviewed by 3 agents | Quality score: 95% | Review time: 1180.4s

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⚠️ Review Incomplete

1 of 3 agent(s) did not finish (security-reviewer) and no findings were produced. Treat this PR as not yet reviewed, not as approved.

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_{🤖 Generated by AI Code Reviewer | Review ID: review-d135c8bf}

[chefsale]

Superseded by #3216, which merged the identical removal to master (same hand-rolled StorageDelta BorshSerialize keeping CausalActions at tag 2, same get_collection_names_for/IndexMap cleanup, same retained Action::Compare variant). This branch is based on pre-#3208 master and adds nothing over what's already merged. Closing as duplicate.