fix(coprocessor): make ciphertext compression fallible

[Eikix]

Summary

This is the standalone fix for zama-ai/fhevm-internal#1020.

• Make SupportedFheCiphertexts::compress() fallible and remove panic/expect usage.
• Convert TFHE compression failures (including panic payloads from internal asserts) into typed FhevmError values.
• Bubble compression errors at caller sites instead of killing execution:
  • scheduler compression paths
  • tfhe-worker server compression paths
  • zkproof-worker handle creation path
• Add a focused unit test for scalar compression error behavior.

Scope

Compression error propagation only.
No gRPC-refactor changes, no unrelated cleanup.

Validation

• cd coprocessor/fhevm-engine && SQLX_OFFLINE=true cargo check -p fhevm-engine-common -p scheduler -p zkproof-worker -p tfhe-worker
• cd coprocessor/fhevm-engine && SQLX_OFFLINE=true cargo test -p fhevm-engine-common -p scheduler -p zkproof-worker -p tfhe-worker --no-run
• cd coprocessor/fhevm-engine && SQLX_OFFLINE=true cargo test -p fhevm-engine-common compress_scalar_returns_error -- --nocapture

closes https://github.com/zama-ai/fhevm-internal/issues/1020

[mergify]

🧪 CI Insights

Here's what we observed from your CI run for 1ddbdc2.

🟢 All jobs passed!

But CI Insights is watching 👀

[Eikix]

normally ready for re review

[Eikix]

@mergify queue

[mergify]

queue

✅ The pull request has been merged automatically

Details

The pull request has been merged automatically at bed88b0

[mergify]

Merge Queue Status

Rule: main

---

• ✅ Entered queue — 2026-02-09 13:40 UTC
• ✅ Checks passed · on draft merge queue: embarking main (5fa5b7c) and [#1928 + #1944] together #1948
• ✅ Merged — 2026-02-09 16:21 UTC · at 1ddbdc2a54e4a4c2a2c066f5e58bcd272fdf4ed9

This pull request spent 2 hours 41 minutes 4 seconds in the queue, including 9 hours 54 minutes 56 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • fix(coprocessor): make ciphertext compression fallible #1928
  • chore(kms-connector): enforce acl check #1944
• #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
  • fix(coprocessor): make ciphertext compression fallible #1928
  • chore(kms-connector): enforce acl check #1944
• #review-threads-unresolved = 0 [🛡 GitHub branch protection]
  • fix(coprocessor): make ciphertext compression fallible #1928
  • chore(kms-connector): enforce acl check #1944
• branch-protection-review-decision = APPROVED [🛡 GitHub branch protection]
  • fix(coprocessor): make ciphertext compression fallible #1928
  • chore(kms-connector): enforce acl check #1944
• check-success = run-e2e-tests / fhevm-e2e-test
• any of [🛡 GitHub branch protection]:
  • check-success = common-pull-request/lint (bpr)
  • check-neutral = common-pull-request/lint (bpr)
  • check-skipped = common-pull-request/lint (bpr)
• any of [🛡 GitHub branch protection]:
  • check-skipped = coprocessor-cargo-listener-tests/cargo-tests (bpr)
  • check-neutral = coprocessor-cargo-listener-tests/cargo-tests (bpr)
  • check-success = coprocessor-cargo-listener-tests/cargo-tests (bpr)
• any of [🛡 GitHub branch protection]:
  • check-success = coprocessor-cargo-test/cargo-tests (bpr)
  • check-neutral = coprocessor-cargo-test/cargo-tests (bpr)
  • check-skipped = coprocessor-cargo-test/cargo-tests (bpr)
• any of [🛡 GitHub branch protection]:
  • check-success = coprocessor-dependency-analysis/dependencies-check (bpr)
  • check-neutral = coprocessor-dependency-analysis/dependencies-check (bpr)
  • check-skipped = coprocessor-dependency-analysis/dependencies-check (bpr)
• any of [🛡 GitHub branch protection]:
  • check-skipped = gateway-contracts-deployment-tests/sc-deploy (bpr)
  • check-neutral = gateway-contracts-deployment-tests/sc-deploy (bpr)
  • check-success = gateway-contracts-deployment-tests/sc-deploy (bpr)
• any of [🛡 GitHub branch protection]:
  • check-success = kms-connector-tests/test-connector (bpr)
  • check-neutral = kms-connector-tests/test-connector (bpr)
  • check-skipped = kms-connector-tests/test-connector (bpr)