fix(ergo-sigma): evaluator carrier/type/serialize fidelity (#215 findings 2, 4, 5)

[arkadianet]

All three deferred #215 Critical evaluator findings. Each verified against sigmastate-interpreter v6.0.2 source and confirmed by a live JVM-oracle differential.

#	Fix	Kind
#5	Coll.patch accepts every element carrier (was Byte/Int/Long only → rejected valid Coll[Short]/Coll[Boolean]/tuple/box/header) via the generic updateMany path	reject-valid
#4	flatMap recovers the output element type B from the mapper body for an empty receiver instead of collapsing to Coll[Byte]	type divergence
#2	SGlobal.serialize resolves context-backed box carriers (SELF/INPUTS/OUTPUTS/Coll[Box]) via resolve_box → canonical OpaqueBoxBytes	reject-valid

JVM-oracle validation ✅

ergo-difftest reduce-surface differential vs sigma-state 6.0.2 (cargo test -p ergo-difftest --lib reduce_diff_serialize_and_flatmap -- --ignored), all matching node==JVM on prop and JIT cost:

serialize(SELF)==SELF.bytes   node=P:d3|142  jvm=P:d3|142
serialize(INPUTS).size>0      node=P:d3|145  jvm=P:d3|145
empty flatMap type            node=P:d3|166  jvm=P:d3|166

• chore: make CI green — regenerate OpenAPI golden + clear RustSec advisories #2: serialize(SELF)/serialize(INPUTS) produce the JVM's canonical bytes at the JVM's cost (a pre-fix node rejected these → would diverge).
• chore(ci): fix two pre-existing main CI blockers (cargo-deny wildcard + b4 byte-parity fixture) #4: the empty-flatMap output is tagged Coll[Long], serializing byte-for-byte identically to an empty Coll[Long] (a type mismatch reduces to false/P:d2).

Validation

ergo-sigma suite 499 → 504 (+5 unit tests) + the live oracle differential; clippy -D warnings + fmt clean.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved serialization of context-backed boxes and nested collection values.
  • Added clearer errors when box values are serialized without the required evaluation context.
  • Fixed flatMap on empty collections to preserve the mapper’s output type.
  • Improved patch support across collection types, including Boolean and Short collections.
  • Added runtime type validation when applying collection patches.
• Validation
  • Expanded evaluator coverage and cross-checked reduction behavior against the JVM oracle.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

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Configuration used: Path: .coderabbit.yaml

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Run ID: 01a6c126-c895-40de-8feb-ceedf01d233e

📥 Commits

Reviewing files that changed from the base of the PR and between 5892073 and d48502d.

📒 Files selected for processing (6)

• ergo-difftest/src/oracle.rs
• ergo-sigma/src/evaluator/helpers/serialize.rs
• ergo-sigma/src/evaluator/helpers/subst_constants.rs
• ergo-sigma/src/evaluator/opcodes/method_call/coll.rs
• ergo-sigma/src/evaluator/opcodes/method_call/global.rs
• ergo-sigma/src/evaluator/tests.rs

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📝 Walkthrough

Walkthrough

The evaluator now supports context-aware box serialization, preserves collection element types for empty flatMap results, generically patches collections, and adds Rust-to-JVM differential validation.

Changes

Evaluator updates

Layer / File(s)	Summary
Context-aware serialization ergo-sigma/src/evaluator/helpers/serialize.rs, ergo-sigma/src/evaluator/helpers/subst_constants.rs, ergo-sigma/src/evaluator/opcodes/method_call/global.rs, ergo-sigma/src/evaluator/tests.rs	value_to_typed_sigma propagates ReductionContext, resolves context-backed boxes to canonical SBox bytes, and rejects unsupported context-backed values without context.
Typed collection method evaluation ergo-sigma/src/evaluator/opcodes/method_call/coll.rs, ergo-sigma/src/evaluator/tests.rs	flatMap recovers empty-result element types from mapper expressions, while patch validates compatible elements and reconstructs collections generically.
Cross-runtime validation ergo-difftest/src/oracle.rs	An ignored integration test compares Rust reduction verdicts with the Scala JVM serde oracle across targeted ErgoTree cases.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• arkadianet/ergo#98: Introduces JVM oracle infrastructure used by the new differential test.

✨ Finishing Touches

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• Commit unit tests in branch fix/sigma-evaluator-carriers

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