Spike D cannot be built in the M0 development environment: PDFium has no
system package and its Chromium-scale build exceeds the available disk
(29 GB free) and RAM (7.8 GB); Skia likewise builds from source. The spike
specifically tests the divergence between *our own Skia display-list
renderer* (which is M2 work, doesn't exist yet) and *PDFium* — it cannot be
substituted with another renderer without testing a different question.
This is not a go/no-go block on M0: the four buildable spikes (A, B, C, E)
give go signals, and the §2.5 predictive tier is an optimisation whose
fallback (authoritative tier alone) is recorded in ADR-0001. Spike D is
naturally a late-M0/early-M2 activity — it depends on M2's L3 renderer —
and must run on a machine with the bandwidth to build PDFium and Skia
(a CI runner or build server). The pixel-diff harness scaffolding is
already in place for when the renderers exist.
Signed-off-by: ai-ad4 <ai-ad4@users.noreply.gitea.lm.je>
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