v4 T-4 Phase-3: dissolve python.dag PythonNumericTower wrapper → flat-nullary PythonScalar (#3309 fwd-port)

[briansrls]

Issue

#3338 landed canonical-B bool grounding for python.dag but retained a hollow nested PythonNumericTower / Numeric-tower wrapper: PythonScalar = Numeric { tower: PythonNumericTower } | Singleton { kind }. The single-field Numeric { tower } wrapper is a Practice-8 hollow prong (a wrapper adding no field of its own) and PythonNumericTower is a classifier reading zero spec facts.

Operator A-vs-B ruling (2) (2026-05-19, relayed via vivid-carp-207): #3309's Practice-8 dissolution of that wrapper carries unique value and is forward-ported onto post-#3338 main.

The dissolution

PythonScalar is reseeded into a flat-nullary coproduct:

type PythonScalar
  = IntScalar
  | FloatScalar
  | ComplexScalar
  | BoolScalar
  | Singleton { kind: PythonSingletonKind }

PythonNumericTower is dissolved. The flat coproduct mirrors rust.dag RustScalar's structure (flat scalar coproduct with nullary variants), not its facts: Python's numeric primitives have zero intra-kind variance (one int, one float, one complex — Python Language Reference §3.2), so the variants carry no fabricated kind/width carrier.

Preserved byte-exact (the #3338 canonical-B grounding mechanism)

• data py_bool_grounding: BooleanAlgebra<Bool> = bool_boolean_algebra (data row untouched)
• import v4.std.logic { Bool, bool_boolean_algebra } / import v4.std.algebra { BooleanAlgebra }

Header/ledger references to the dissolved PythonNumericTower.BoolLevel are re-anchored to PythonScalar.BoolScalar (python.dag scope/owns/bool-header/grounding-comment; DECISIONS.md python.dag / singletons bullet). New SL-3309-PYTHON-SCALAR-RESEED ledger row added.

Acceptance criteria (runnable)

1. v2 compiles 0 diagnostics (python.dag is in the closure):

   cargo run -p v2-compiler --bin v2-compiler -- compile --source-root src/v4 --output-dir /tmp/v4out --target rust
   

   -> compiled: 76 files emitted, 0 diagnostics
2. PythonScalar is flat-nullary -- no Numeric-tower / PythonNumericTower remain:

   grep -n 'PythonNumericTower\|Numeric {' src/v4/extdeps/languages/python.dag   # -> no matches
   

3. fix-language-files #3338 bool grounding byte-identical to main:

   git diff origin/main HEAD -- src/v4/extdeps/languages/python.dag | grep -E '^[-+].*(py_bool_grounding|import v4.std)'   # -> no matches
   

🤖 Generated with Claude Code

[briansrls]

Thanks for the review. The exploratory observation — docs/modeling/grounding-worked-examples.md mentioning PythonNumericTower.BoolLevel — is already addressed. The review artifact was generated against commit 4550b5c31; the subsequent commit 7a3dc65dd ("Reconcile dissolved-type ref in grounding-worked-examples.md") reconciles that line to PythonScalar.BoolScalar. grep -n PythonNumericTower docs/modeling/grounding-worked-examples.md on the current PR head returns no matches. The only surviving PythonNumericTower strings repo-wide are inside the new SL-3309-PYTHON-SCALAR-RESEED decision prose, where they deliberately describe the dissolved before-state ("dissolves the bare PythonNumericTower enum", "formerly anchored at"). No further change needed.\n\n— sent from stern-eagle-698