Working strategy — migrate the core while keeping prod alive

Answers ask #3: fork? branch? new repo? — and how to keep maintaining prod nirs4all locally and remotely throughout a multi-month chantier.

PROPOSAL — pending open decisions #1/#2/#7 in README.md.

Constraints this must respect

  • nirs4all main is production (tags 0.10.x; webapp depends on the frozen 0.9.x surface). It must keep shipping hotfixes/features the whole time.

  • The team already works feature-branch-on-one-repo (GBeurier/nirs4all): cache_refactoring, feat/heterogeneous-repetitions, parquets_refactoring, … This migration should ride that workflow, not fight it.

  • dag-ml is a separate, contract-frozen submodule (0.2.0) co-evolving with dag-ml-data under the ADR-10 release train. It is already pip install-able (dag-ml / import dag_ml, maturin).

  • nirs4all/CLAUDE.md mandates phased execution (≤5 files/phase, dead-code cleanup committed separately first) and no long-lived backward-compat shims (ADR-14 wants a temporary exception — open decision #3).

Recommendation — not a fork, not a new repo: selector-on-main + integration branch + worktree

The load-bearing insight is ADR-17: a runtime backend selector engine ∈ {legacy, dag-ml, dual} that defaults to legacy. With that flag, migration code can be merged into main incrementally without changing a single production code path — prod simply never flips the flag. This collapses the classic “giant long-lived branch that rots” problem.

So the model is three layers:

2. Integration lives on main behind the selector, in flag-gated increments

  • New code path: nirs4all/pipeline/engine/ (or similar) holding the dag-ml bridge (DSL serialization → dag_ml importer, host process-adapter, result re-hydration). Selected by engine= kwarg / N4A_ENGINE env / config — default legacy.

  • Each PR is small (≤5 files), parity-gated (see PARITY_AND_PERF_HARNESS.md), and merges to main because it is inert at engine=legacy. Prod stays green; rollback = “don’t set the flag” (zero-cost, per ADR-17).

  • The god-class decomposition (orchestrator/merge/branch/base_model/SpectroDataset) is pure refactor that benefits prod too — it lands on main as normal, behind the project’s phased rule, before the bridge needs to cross those seams. This is the “extract-protocols-first” order the externalization notes recommend.

3. A long-lived branch + worktree only for the churny, not-yet-flag-isolatable spikes

  • For exploratory work that can’t yet be made inert (e.g. the first end-to-end bridge spike, serialization-format experiments), use one integration branch core/dagml, rebased on main frequently, and collapsed into flag-gated PRs as soon as a slice is parity-passing. Don’t let it accumulate.

Local setup — maintain prod and migrate at the same time, zero context-switch

Use a git worktree so prod main and the migration branch are two directories at once:

# from the existing prod checkout
cd /home/delete/nirs4all/nirs4all
git worktree add ../nirs4all-core core/dagml      # second working dir on the migration branch
# prod hotfixes:   work in   nirs4all/        (main)
# migration work:  work in   nirs4all-core/   (core/dagml)

# editable, co-evolving dag-ml in the migration venv only:
cd ../nirs4all-core && python -m venv .venv && . .venv/bin/activate
pip install -e '.[dagml,all]'
maturin develop -m ../dag-ml/crates/dag-ml-py/Cargo.toml --release   # local editable engine

Prod venv (nirs4all/.venv) never gets dag-ml → it cannot accidentally change behaviour.

Remote & release

  • Prod releases continue from main exactly as today (ADR-10 release train; engine defaults to legacy, so 0.10.x/0.11.x ship with dag-ml dormant).

  • Migration CI: push core/dagml; CI runs the parity suite in dual mode + perf benchmarks (see harness doc). PRs to main run the fast parity-compile gate + legacy baseline.

  • Cutover is then just a normal PR that flips the default once the parity + perf gates are green for the targeted scope — and is reversible by flipping back.

  • Cross-repo pinning: extend the ecosystem meta-repo with a tested (nirs4all branch/rev × dag-ml rev × dag-ml-data rev) compatibility triple per ADR-10, so the three stay in lockstep.

Why not the alternatives

Option

Verdict

Fork nirs4all

✗ Splits issues/PRs/community; merge-back is a nightmare; no upside over a flag on main.

New repo nirs4all-next / pipeforge

✗ Only justified if destination = the generic-core detour (open decision #1), which the recon argues against. Doubles maintenance.

One giant long-lived branch

✗ Rots against a main that ships weekly; the selector makes it unnecessary.

Selector-on-main + worktree (recommended)

✓ Prod inert by default, incremental & reviewable, zero-cost rollback, matches existing workflow, decomposition benefits prod immediately.

First concrete steps (once decisions #1/#2 are set)

  1. Land the backend-selector skeleton on main (engine=legacy|dag-ml|dual, default legacy; dag-ml path raises NotImplemented for now). Inert, tiny, unblocks everything.

  2. Stand up the parity gold-baseline + dual-run hook (harness doc) — needed before any bridge code is trustworthy.

  3. Begin god-class decomposition along the dag-ml seam (phased, ≤5 files, cleanup-first), starting with the orchestrator/executor OOF + refit boundary.

  4. Build the DSL serialization frontend (live pipeline objects → portable JSON descriptors the dag_ml importer accepts) — the #1 dag-ml-side gap.