Implement the text reconstruction pipeline (§4.1 steps 2-5) for the M0
Spike B gate:
- GlyphRun.h: input model (Glyph, GlyphRun, Line, Paragraph, GroundTruth)
mirroring §3.2/§3.3
- Reconstruct.cpp: flatten → line detection (baseline cluster, 0.25×font
tolerance) → reading order (descending-y for PDF coords) → paragraph
grouping → boundary-F1 scorer
- Corpus.cpp: deterministic synthetic corpus generator (3-8 paras/doc,
1-5 lines/para, realistic leading + paragraph gaps + short last lines)
- main.cpp: emits the contract JSON; exit 0 if F1 ≥ target
Gate MET: F1=0.963 (precision 0.929, recall 1.000) on 500 synthetic docs,
target ≥0.85. Verified clean under ASan+UBSan. The result and findings are
recorded in docs/spike-results/0002-spike-b-reconstruction.md.
Key findings: (1) the leading-gap signal is primary for paragraph breaks;
treating short-last-line as primary over-segmented (F1 0.37→0.96 fixed).
(2) PDF coordinate orientation (y-up) inverts reading order — easy to get
backwards. (3) column-width inference must use a percentile not the max.
(4) the 80/20 boundary is visible in the 166/500 imperfect docs (single-line
paras, list items) — the real labelled corpus (§8.1) is needed for the 0.93
release gate.
Step 1 (glyph→Unicode via cmap/ToUnicode) is deliberately not exercised
here — the synthetic corpus knows Unicode by construction; it is the next
reconstruction work and the highest-risk step.
CI: add a spike-gates job to .gitea/workflows/build.yml that runs Spike A
(informational — the byte-identity gate is met by §4.4 surgical splice in
M2, not by QPDFWriter) and Spike B (fails the build on regression) on Linux.
Signed-off-by: ai-ad4 <ai-ad4@users.noreply.gitea.lm.je>
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