Goal / Objective                                                                                          

Ensure that all QE stages that read internalQuerySpillingMinAvailableDiskSpaceBytes see a consistent, snapshotted value for the full lifetime of a query. The value must be read once (at query initialization or stage construction) and held stable — not re-read from the underlying atomic on each spill or each stage — so that multiple spilling stages within the same query (e.g., two $sort stages, a $group  and a $lookup) all operate against the same threshold.

Concretely, this means:
  - Pipeline stages with access to ExpressionContext must read the value through a static getter from via the QueryKnobCofiguration (the getter is currently not implemented)
  - SBE stages and sorter infrastructure that do not have ExpressionContext must snapshot the value at
  construction or open() time and store it as a member, rather than calling .loadRelaxed() at spill time.

Context & Background

 internalQuerySpillingMinAvailableDiskSpaceBytes is an AtomicWord<long long> server parameter (default 500
  MB) that controls the minimum free disk space required before any spilling is permitted. Because it is an atomic, it can be read by calling .load()/.loadRelaxed() anywhere in the codebase. However, calling this way means we don't get a consistent internalQuerySpillingMinAvailableDiskSpaceBytes throughout a query.

Call sites that should be considered to be updated

  The following query-execution-owned call sites currently call .load() directly on
  internalQuerySpillingMinAvailableDiskSpaceBytes and must be replaced with the appropriate snapshotted access
   pattern:

  File: src/mongo/db/exec/sort_executor.h
  Location: SortExecutor constructor
  ────────────────────────────────────────
  File: src/mongo/db/exec/sbe/stages/sort_stage_sort_impl.cpp
  Location: _makeSortOptions()
  ────────────────────────────────────────
  File: src/mongo/db/exec/sbe/stages/hashagg_base.cpp
  Location: HashAggBaseStage constructor
  ────────────────────────────────────────
  File: src/mongo/db/exec/sbe/stages/lookup_hash_table.cpp
  Location: LookupHashTable::open()
  ────────────────────────────────────────
  File: src/mongo/db/exec/sbe/stages/window.cpp
  Location: WindowStage constructor
  ────────────────────────────────────────
  File: src/mongo/db/exec/sbe/util/spilling.cpp
  Location: SpillingStore two-arg constructor
  ────────────────────────────────────────
  File: src/mongo/db/sorter/sorter_template_defs.h – I know this is under storex ownership, but I believe QE owns this spilling behavior.
  Location: InMemIterator::spill() (~line 193)
  ────────────────────────────────────────
  File: src/mongo/db/sorter/sorter_template_defs.h
  Location: InMemSorter::spill() (~line 738)
  ────────────────────────────────────────
  File: src/mongo/db/sorter/sorter_template_defs.h
  Location: BoundedSorter::_spill() (~line 1507)

Acceptance Criteria

All QE-owned stages have internalQuerySpillingMinAvailableDiskSpaceBytes see a consistent, snapshotted value for the full lifetime of a query, and to each sorter instance a QE stage constructs.

Behavioral expectations
  - With default parameter settings, observable behavior of spilling is unchanged.
  - All stages within a single query use the same threshold value, regardless of when their spill operations occur relative to one another.