V0.26 Scope - KS Revisit Decision, Promotion Deferred to V0.26b#

Status: COMPLETE

Summary#

v0.26 is a Kuramoto-Sivashinsky revisit decision release.

It revisits the v0.11/v0.12 KS no-go with modern confidence diagnostics, but does not promote public KS runtime APIs.

Stable investigation path:

internal normalized KS fixture
-> spectral_fd derivatives through u_xxxx
-> internal KS residual feasibility
-> translation fit / verification / confidence report
-> explicit v0.26 decision label

Release conclusion:

current_no_go_reference_fallback

KS remains deferred because the primary frozen fixture still relies on reference-fallback translation fitting. Public KS promotion, if justified later, is reserved for a separate v0.26b scope freeze.

Decision Labels#

  • current_no_go_reference_fallback: residual and verification evidence are feasible, but direct residual-based SVD fitting still drifts and requires reference fallback.

  • residual_feasible_fit_not_promotable: residual and verification evidence pass, but fit evidence is not promotable.

  • direct_strong_candidate_for_v0_26b_promotion: the frozen primary fixture passes direct-SVD/no-fallback criteria and may justify opening v0.26b.

  • deferred_no_go: core evidence is not sufficient for either residual feasibility or future promotion candidacy.

Frozen Decision Criteria#

Promotion candidacy in v0.26 requires all of:

  • residual max < 5e-2

  • residual RMS < 1e-2

  • first verification error < 5e-4

  • verification classification not failed

  • selected/SVD span distance within frozen tolerance

  • fit evidence label direct_svd_in_tolerance

  • reference_fallback_used is False

confidence_label == "strong" is necessary but not sufficient for future promotion. Direct SVD in tolerance and reference_fallback_used is False are required.

Minimal KS Reproduction Matrix#

v0.26 records test-only evidence for:

  • frozen primary fixture

  • one seed sweep

  • one fit-epsilon sweep

  • one resolution variant

  • fit/fallback diagnostics

  • verification diagnostics

  • generator confidence report

All matrix variants are diagnostic-only. Promotion evidence must come from the frozen primary fixture, not from the best-performing variant in a sweep.

V0.26b Follow-Up Contract#

v0.26b is reserved for the actual KS promotion release if a future scope freeze accepts the direct_strong_candidate_for_v0_26b_promotion evidence.

Candidate v0.26b surface, if opened later:

  • KS data generator under pdelie.data

  • KS residual evaluator under pdelie.residuals

  • KS vertical-slice example under pdelie.examples

No weak KS, custom KS coefficients, custom KS initial conditions, broad KS regimes, or root exports are included unless explicitly frozen in v0.26b.

Explicit Non-goals#

  • no public KS data generator

  • no public KS residual evaluator

  • no public KS vertical-slice example

  • no public KS status example

  • no residual-only KS API

  • no weak KS API

  • no custom KS initial-condition API

  • no configurable KS coefficient API

  • no broad KS regime support

  • no root KS export

  • no broad adapters or file loaders

  • no multidimensional or nonuniform stable support

  • no time-translation APIs

  • no neural or callable generator APIs

  • no operator-facing APIs

Milestone Status#

  • Milestone 0: COMPLETE

  • Milestone 1: COMPLETE

  • Milestone 2: COMPLETE

  • Milestone 3: COMPLETE

  • Milestone 4: COMPLETE

  • Milestone 5: COMPLETE

  • Milestone 6: COMPLETE

Release Gate#

v0.26 is complete only if:

  • the primary KS fixture records current_no_go_reference_fallback

  • residual and verification evidence remain feasible but fit evidence remains fallback-backed

  • the confidence report is included and does not override the direct-SVD/no-fallback rule

  • minimal matrix evidence remains diagnostic-only

  • no best-of-sweep promotion path exists

  • no public KS runtime API, weak KS API, status example, or root KS export lands

  • API_STABILITY.md records the decision-only status without adding stable KS runtime contracts

  • CI uses one compact current release gate plus full editable tests and package smoke

  • package-index publishing remains deferred until v1.0 or later