[petlenz]

The producers declare their pure outputs constant (part 2 of 3, split from #161; stacked on #163). As a result, the global mean-field composite of constant phases runs its kernel once: per update, Mori–Tanaka goes from 7.0 to 0.09 µs and self-consistent from 12.6 to 0.5 µs, with identical results.

What

• Producers declaring their pure outputs (with constant_output or add_callback(...).constant() from Constant properties: engine and API #163):

  Producer	Constant output(s)	Reads
  constant_scalar	value	—
  poisson_ratio_from_moduli	value	—
  linear_elasticity	tangent	—
  Depolarisation tensors	tensor	—
  isotropic_tangent	tangent	all inputs (K, G)
  isotropic_moduli	K, G, ν	all inputs (the tangent)
  Eshelby tensors	tensor	all inputs (ν)
  phase (one group; not constant when the tangent comes over a local edge, i.e. the previous pass's)	all outputs	all inputs
  scalar_split	every part	all inputs (the source)
  weighted_sum	tangent	weights, tangents (not the stresses)
  mean_field_composite_global	tangent, concentrations	all inputs (the phase properties)

• phase simplified: each output and the input it republishes form a relay, and input(key) reads the <key>_source/<key>_property pair (null without a source).

  • The optional Eshelby and depolarisation tensors need no branches, and the edge kind of the tangent comes from its input.
  • The constructor ends in one add_callback(...).constant().
  • The parameters are unchanged. An empty tangent_source or fraction_source now fails at construction with a clear message, instead of as a wiring error at finalize().

• Not constant, as before: stresses, the local composites, and anything reading a history or a local edge.

• docs/mean_field.md §3 describes when the global composite is computed once.

Measured

Global composite: matrix plus aligned spheroids (aspect ratio 5, c = 0.2), linear_stress on top, 2000 updates with a changing strain, -O2.

kernel	before	after	stress checksum
Mori–Tanaka	7.01 µs / update	0.09 µs	identical
self-consistent	12.55 µs / update	0.50 µs (mostly the first update)	identical

Tests

• MeanField.ConstantPhasesAreHomogenisedOnce:
  • a counting Mori–Tanaka kernel, registered through kernel_registry::add, is called once over five updates with a changing strain;
  • the stress follows the strain;
  • the tangent equals the plain Mori–Tanaka one exactly.
  • Before the change the kernel was called 5 times.
• Phase.* (3 tests, written before the refactor): inconsistent parameters (initial tangent without a local edge, unknown edge, empty source, Eshelby in 2D), a negative fraction, and which tensors are relayed. Against the old code only the empty-source checks failed.

Gates (GCC 14, fetched dependencies): 1180/1180 tests, each also under ASan, 0 warnings. The build has no NDEBUG, so the whole suite ran with verification on: none of the declarations above changes on a rerun (self-consistent included).