Source default tensor symmetries from the Context

[evaleev]

Stacked on top of #553 (base branch default-tensor-symmetry); this PR shows only the incremental changes on top of it.

Motivation

#553 makes tensors non-symmetric by default, but hardcodes the defaults and leaves the deserializer's column default (Nonsymm) inconsistent with the Tensor ctor's (Symm). That inconsistency made particle-symmetric amplitudes parse as column-Nonsymm (so they canonicalized differently and no longer merged), and broke ~18 unit + 5 integration tests.

Approach

Make the default tensor symmetries a property of the active sequant::Context, so the library default is the safest (fully non-symmetric) while applications fine-tune for ergonomics.

• Core Context gains symmetry, hermiticity, and column_symmetry defaults (Defaults + Options + accessors + set()). Library defaults: Nonsymm / NonHermitian / Nonsymm.
• BraKet symmetry is never a Context knob — it is a derived property, computed per-tensor from the default Hermiticity and base_field, consistent with the earlier removal of Context::braket_symmetry (8c4669d).
• Tensor ctors resolve unspecified perm/column/hermiticity against the active Context, reading it only when something is unspecified, so explicit construction (the hot path) stays lock-free.
• Deserializer default symmetries are sourced from the active Context.
• Context::operator== now compares the new symmetry defaults (otherwise set_scoped_default_context would silently refuse to switch a context that differs only in these — a latent bug surfaced by the new tests).
• mbpt applications (unit-test harness + srcc/stcc integration) opt into the particle-symmetric convention via column = Symm.
• Test expectations updated to the resulting (physically correct) symmetries; new tests cover the Context-driven defaults and the rejection of braket symmetry on (anti)symmetrization operators.

Testing

Built with the full debug config (clang-17, AddressSanitizer, Unity, ccache, all eval backends: TiledArray/BTAS/TAPP/Torch).

• unit_tests-sequant: 7069 assertions / 70 cases pass.
• check-sequant: all tests pass except sequant/unit/python/basic/run, which aborts at AddressSanitizer init (ASan-instrumented module dlopened into a non-ASan Python on macOS) — an environment limitation, unrelated to these changes.
• All changed files pass clang-format-17 --Werror.

[Copilot]

Pull request overview

This PR moves the “default tensor symmetry” behavior out of hardcoded defaults and into the active sequant::Context, so that library defaults are conservative (fully non-symmetric / non-Hermitian / non-column-symmetric) while applications can opt into more ergonomic conventions (e.g., particle/column symmetry for MBPT). It also updates deserialization and tests to reflect Context-sourced defaults and the updated canonicalization/ordering behavior.

Changes:

• Add Context-level defaults for Symmetry, Hermiticity, and ColumnSymmetry, and include them in Context::operator==.
• Update Tensor construction to resolve unspecified symmetry attributes against the active Context (deriving BraKetSymmetry from Hermiticity + base field).
• Update v1 deserialization to source default symmetries from the active Context, and adjust unit/integration tests to match the new defaults and ordering.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
SeQuant/core/context.hpp	Adds Context defaults + Options fields + accessors/setters for symmetry/hermiticity/column symmetry.
SeQuant/core/context.cpp	Wires new Options fields into construction, adds accessors/setters, and updates operator== to compare new defaults.
SeQuant/core/expressions/tensor.hpp	Introduces Context-driven defaulting via resolve_symmetries() and updates constructors accordingly.
SeQuant/core/io/serialization/v1/deserialize.cpp	Sources deserializer default symmetries from get_default_context().
SeQuant/core/io/serialization/v1/ast_conversions.hpp	Clarifies reserved (anti)symmetrizer symmetry handling; converts AST symmetries into Tensor construction.
tests/unit/test_main.cpp	Sets test default Context to column_symmetry = Symm for MBPT-oriented expectations.
tests/unit/test_tensor.cpp	Updates braket/adjoint expectations and adds coverage for Context-driven defaults.
tests/unit/test_parse.cpp	Adds tests for rejecting braket symmetry on reserved (anti)symmetrizers.
tests/unit/test_wick.cpp	Updates latex expectation due to changed canonical ordering under new defaults.
tests/unit/test_tensor_network.cpp	Updates expected index ordering and adjusts a deserialize string to rely on Context defaults.
tests/unit/test_spin.cpp	Updates expected serialized symmetry specifiers to match new defaulting/derivation behavior.
tests/unit/test_mbpt.cpp	Updates expected strings to reflect Context-driven defaults and explicit symmetry tags.
tests/unit/test_canonicalize.cpp	Updates deserialize fixtures to omit now-defaulted braket specifiers for Ŝ where appropriate.
tests/unit/test_biorthogonalization.cpp	Removes per-call def_col_symm overrides, relying on Context defaults instead.
tests/unit/data/sf_r2_direct_real_inc.hpp	Updates a large expected fixture string to match updated defaulting/serialization behavior.
tests/integration/srcc.cpp	Sets MBPT integration Context default column_symmetry = Symm.
tests/integration/stcc.cpp	Sets MBPT integration Context default column_symmetry = Symm.

Comments suppressed due to low confidence (1)

SeQuant/core/io/serialization/v1/ast_conversions.hpp:337

• Deserializing reserved (anti)symmetrization operators (Ŝ/Â) currently inherits the Context-driven default Hermiticity when no explicit braket specifier is provided. If the active Context defaults to Hermitian, this will derive a non-Nonsymm braket symmetry and make plain "Ŝ{...}" / "Â{...}" fail to parse even though the default form should be accepted. These operators should ignore Context braket defaults and remain braket-Nonsymm unless the user explicitly requests otherwise (in which case the ctor should reject it).

    if (tensor.name == reserved::antisymm_label()) {
      perm_symm = Symmetry::Antisymm;
    } else if (tensor.name == reserved::symm_label()) {
      column_symm = ColumnSymmetry::Symm;
    }

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[evaleev]

Also addressed the low-confidence note on ast_conversions.hpp (reserved (anti)symmetrizers inheriting the Context braket default): that was a real latent bug — under a Hermitian-default Context a plain Ŝ{...}/Â{...} would derive a non-Nonsymm braket and fail to construct. Fixed in 7fdb794 by forcing braket = Nonsymm for these operators when no braket spec is given (an explicit spec is still left for the Tensor ctor to reject), with a new regression test parsing them under a Hermitian Context.