Draft: narrow JuliaLowering generator/filter seam for #99

This draft PR packages a very narrow first JuliaLowering-facing slice for #99. ## Scope - generator/filter representative slice only - default/manual path unchanged - JuliaLowering remains experimental and gated - nested comprehensions remain explicitly out of scope ## What is included - a readiness false-negative fix in the experimental seam (`Base.show_unquoted` for Expr source) - guarded seam behavior that can distinguish: - out-of-slice expressions - in-slice but not-ready expressions - in-slice expressions whose contract is met - a branch-local smoke example for the representative generator/filter case - maintainer-facing notes / handoff docs / patch relay bundle for the validated path ## Key files - `src/macro.jl` - `src/utils.jl` - `test/test_main.jl` - `examples/experimental_julialowering_seam_readiness.jl` - `reports/resumablefunctions-99-maintainer-handoff-2026-03-23.md` - `reports/patches/resumablefunctions-99-2026-03-23/README.md` ## Validation - `~/.juliaup/bin/julia --project=. -e 'using Pkg; Pkg.test(test_args=["main"])'` passes on Julia 1.11 - representative seam smoke reports the expected fallback status on Julia < 1.12 - in a temporary Julia 1.12.5 environment with local `JuliaLowering`, the representative smoke path reaches `POSTLOAD_CONTRACT_MET=true` - local benchmark script also completed successfully on this branch after benchmark-project instantiation: - `~/.juliaup/bin/julia --project=benchmark -e 'using Pkg; Pkg.instantiate()'` - `~/.juliaup/bin/julia --project=benchmark benchmark/benchmarks.jl` ## CI note - the visible `benchmark` check is currently red on this PR - GitHub refused rerun of that failed workflow with `workflow file may be broken` - six other Actions workflows on this PR head are in `action_required` with no jobs started from this account's view - so the current red/idle CI surface appears at least partly workflow/approval-side rather than a straightforward local reproduction of branch breakage ## Why this PR exists The issue discussion notes that a branch on which a JuliaLowering-based path succeeds can count as bounty completion even before merge readiness. This PR is meant to give maintainers a concrete review/delivery artifact for that narrow first slice rather than claiming the full migration is done. Related to #99.