Affected Repositories

• PyAutoFit (tests only, pending-release)

Branch Survey

Suggested branch: feature/search-ext-a0a2-backend-conformance, stacked on feature/search-ext-a0b-hygiene in the A0b worktree; PR base = the A0b branch until it merges.

Implementation Steps

1. Read test_conformance.py and conformance_roster.py for the roster, capability attributes and golden-table conventions.
2. Write the backend module and fixtures; budgets via apply_test_mode only.
3. Emulate the no-jax leg with an import hook; confirm exactly NSS, BlackJAXNUTS, SMC, MultiStart×4 skip by capability.
4. Full pytest test_autofit; runtime of the new module under 90 s.

Validation checklist (--auto run — plan was not pre-approved)

• Effective level: safe (header: safe, cap: test → safe)
• Gate legs recorded in the PR body at ship

Search conformance suite, layer (ii): backend execution on the full-extras legs (epic search-extensibility, phase A0a(ii))

Type: test
Target: autofit
Repos:

• PyAutoFit
  Themes:
• searches
• jax
• ci
  Difficulty: medium
  Autonomy: safe
  Consequence: judge
  Witness: layer (ii) green on the [optional] CI legs for all 15 searches; on an emulated no-jax leg NSS, BlackJAXNUTS, SMC and the MultiStart×4 are skipped by declared capability (never by importorskip) and the rest pass
  Unattended: ready
  Priority: high
  Epic: search-extensibility
  Blocked-by: search-ext-a0b-hygiene (PyAutoFit, A0b must merge first; implemented stacked on its branch)
  Status: draft
  Filed: 2026-10-08

Phase A0a(ii) of the search-extensibility epic (draft/research/autofit/search_extensibility_epic.md; plan
search_extensibility_epic_report.md §4 A0a layer (ii)). Tests only. Layer (i) is merged (PyAutoFit#1667,
test_autofit/non_linear/search/{test_conformance,conformance_roster}.py). Lands after A0b so Drawer/NullPaths
is not an xfail. Human launch 2026-10-08: --auto for every A0 phase.

Original request (verbatim from the epic plan)

"Layer (ii), backend execution, Heart full-extras legs only (lib-tests.yml installs [optional], :114),
explicitly skipped by declared capability on unittest-nojax: capability-matched fixtures (numpy MockAnalysis for
jax_use none/optional, a JAX MockAnalysis for required) at PYAUTO_TEST_MODE=1 with real DirectoryPaths; it
asserts the output file set, the completed-path resume, a NullPaths fit, the samples_from(model, None) fallback
and the samples_info key sets. The module docstring states the coverage contract: every backend executes on the
full-extras leg, and importorskip may not hide a required backend there. Layer (ii) lands after A0b, so
Drawer/NullPaths is not an xfail. Verify: pytest test_autofit/non_linear on a full-extras env and with
jax/blackjax/optax uninstalled. Witness: layer (i) green on all legs; layer (ii) green on [optional] legs, with
NSS/NUTS/SMC/MultiStart skipped on the no-jax leg by declared capability."

Scope

• New test_autofit/non_linear/search/test_conformance_backend.py reusing conformance_roster.searches_under_test().
  Per search, at PYAUTO_TEST_MODE=1: (a) a fit with real DirectoryPaths into tmp_path asserting the expected
  output file set per search (search.json, model.json, samples.csv/samples_info.json, the backend's own
  checkpoint name from survey 01 §8), (b) a second fit on the completed path resumes without rerunning (assert via
  the backend's call count or the timer file), (c) a NullPaths fit returns a Result, (d) samples_from(model, None)
  falls back (A0b's narrowed except), (e) samples_info key set per family.
• Capability gate: skip by the declared capability attributes A0a(i) introduced (jax_use or equivalent), never
  importorskip; the no-jax emulation (import-hook block) must show exactly NSS, BlackJAXNUTS, SMC and MultiStart×4
  skipped.
• Fixtures: numpy MockAnalysis for jax_use none/optional; a JAX MockAnalysis (jnp log-likelihood) for required.
• Mark the whole module to run only when [optional] extras are installed on CI (the unittest legs), skipping
  per-search on unittest-nojax by capability.
• Not in scope: any library source. If a search cannot satisfy (a)-(e) without a library change, add a strict xfail
  naming the later phase (A2/A3) and list it on the issue.

Verification

pytest test_autofit/non_linear/search -x; full pytest test_autofit; no-jax leg emulated; runtime of the new
module under 90 s on a laptop (reduce budgets via apply_test_mode, never by editing searches).

Shape

One PyAutoFit PR (pending-release). Implemented on a branch stacked on feature/search-ext-a0b-hygiene with the PR
based on that branch; after A0b merges the human retargets to main (or it retargets automatically) and merges.
Tier judge.