Batch 244-A ACCEPTED -- the book's (8.6.15)--(8.6.24) assembled along the book's own path: the one remaining computation is located at the (8.6.2) pairs

New file Definitions/MMFLM86SpanningDisplayAligned.lean (MM.FLM86SDA):

* MEASUREMENT: the landed pieces of the book's chain, checked at source -- (8.6.6) all k
  (MM.FLM86D866T.display866SecondEqK_all), (8.6.9)/(8.6.10) at all states (MM.FLM86MFC.modeFieldCommInput),
  the (8.4.25)/(8.4.20) assembly (MM.FLM810NOC.assemblyDiagonal_antidiagonal, MM.FLM86AR.assemblyDiagonal),
  the coefficient engine MM.FLM86FB.flatBinomialExpansion (Chu--Vandermonde), and the whole
  (8.6.11)--(8.6.27) absorption at the datum (batch 234/235).
* KEY FINDING: the lift from the (8.6.2) pairs to all states -- Remark 8.3.9's spanning step -- is
  ALREADY LANDED: batch 223-B's modeFieldCommInsertionStep8625_iff_spanningEventual is an equivalence
  whose backward direction takes the window-synchronized (8.5.13) at the (8.5.4) states
  (MM.FLM86SL.Corollary851SpanningEventualWindows, via exists_stateFinset_mem_span and the bilinearity
  MM.FLM85Fock.corollary851_of_mem_span at a common window) to the commutator half at ALL states.
* THEREFORE the one remaining computation of the display side is AT the (8.6.2) pairs.  REGISTERED:
  MM.FLM86SDA.spanningDisplay_evenCocycle : MM.FLM86SL.Corollary851SpanningGroundedWindows (ZAligned E)
  -- the window-synchronized (8.5.13) at the (8.5.4) states, i.e. the book's coefficient extraction
  (8.6.15)--(8.6.21) and display (8.6.23)/(8.6.24) at the labelled pairs.
* ASSEMBLED (no new content, all pieces landed): spanningEventualWindows_evenCocycle (the landed
  two-way spelling equivalence), crossContraction_of_spanningDisplay (the (8.4.25) step, via batch
  223-B), and commutatorInsertion8625_of_spanningDisplay (the commutator half (8.6.24) at all states,
  via the landed composition with the proved (8.6.9)/(8.6.10) input).
* The register reads: the grounded all-states display (batch 242-A's entry, to be absorbed into the
  (8.6.2)-pair entry by the all-states bilinear lift -- next batch), the (8.6.2)-pair display (this
  batch), and the l < 0 residual (batch 243-A's entry).  All three are the section 8.6 engine.

Build: the new module --- OK ---; FinalCheck.lean GREEN; HANDOVER.md section 1.1 and NOTES.md
section 143 record the assembly and the location of the remaining computation.
