AIGEN: Fix iterator compilation bug with value class field access (#769)

[mbouaziz]

Summary

• Fixed issue Iterator compilation bug: reached an Unreachable point #769 where the compiler incorrectly marked code as unreachable when accessing fields of value classes (like Some<T>.value) if the field type appeared as unresolved type _ during compilation
• The bug occurred with lazy iterator chains using flatMap and filter with yield
• Moved the canInstantiate check inside the NamedLeaf branch only (for reference classes which require scalarization), allowing value class field access to proceed without this check
• Removed the .collect(Array) workaround in SqlSchemaMigration.sk

Verification

Verified end-to-end by building Docker images with STAGE=1 (stage1 compiler compiled from source, which includes this fix) and running the full skdb test suite:

# Build with the fixed compiler
STAGE=1 bin/docker_build.sh --arch amd64 skiplang skip skdb-base

# Clean stale build artifacts (static_state.db format mismatch between compiler versions)
docker run --rm -v $PWD:/work skiplabs/skdb-base:latest \
  bash -c "find /work -name static_state.db -delete"

# Run tests
docker run --rm --network=host -v $PWD:/work -w /work \
  skiplabs/skdb-base:latest bash -c "make test-native"
docker run --rm --network=host -v $PWD:/work -w /work \
  skiplabs/skdb-base:latest bash -c "make test-wasm"

Test plan

• All 1698 compiler tests pass
• skdb native tests: 1265 tests pass (including ALTER TABLE ADD COLUMN which exercises schema migration with the lazy iterator code path)
• skdb wasm tests: 283/283 pass
• The generic_refinement_method test continues to pass (regression test for the fix)
• Verified locally by reviewer

Fixes #769

🤖 Generated with Claude Code

[mbouaziz]

This PR was created using no other guidance than "Fix #769"

[jberdine]

This PR was created using no other guidance than "Fix #769"

Did you review it?

[mbouaziz]

I did review but I didn't take time to collect enough context to understand it deeply.
Anyways, CI is still red so Claude is still clauding...
turning the PR to draft

[mbouaziz]

CI setup for this PR

This PR includes a temporary second commit that:

1. Updates the bootstrap submodule — regenerated from stage1 with the specialize.sk fix (make -C skiplang/compiler promote using the fixed compiler)
2. Points CI images to fix-769 tag — Docker images (skiplabs/skiplang:fix-769, skiplabs/skip:fix-769, skiplabs/skdb-base:fix-769) were built locally with the new bootstrap and pushed to Docker Hub (amd64 only)

This allows CI to run the full test suite using a compiler that includes the fix, verifying end-to-end correctness.

Before merging, the second commit (ci: use fix-769 Docker images and updated bootstrap) should be squashed/dropped and the bootstrap submodule updated separately through the normal process.

Local verification results

• Native tests: 1265 pass (including ALTER TABLE ADD COLUMN which exercises the fixed code path)
• Wasm tests: 283/283 pass
• Compiler tests: 1698 pass