feat(sector): implement the gocomb fuse recombination sub-step (default-off)#267
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Completes TNT combined analysis for large sectors: after the sectorCombStarts RAS+drift starts, recombine them with tree_fuse (best start as recipient, the others as donors) and keep the fused tree only if it beats every start. Previously gocomb was RAS+drift keep-best; the fuse step was deferred because tree_fuse re-roots the reduced tree at tip 0, dropping the (HTU, sr_mapped) synthetic-root layout reinsert_sector needs. Re-anchoring: parsimony is rooting-invariant, so reanchor_fused_at_htu simply re-roots the fused tree at the HTU pseudo-tip. The HTU represents the rest of the tree at the sector boundary and stays adjacent to the content root, so its sibling after re-rooting is the whole non-HTU clade -- exactly what reinsert_sector grafts back, with the content clade still rooted at sr_mapped. The fused tree is accepted only through the SAME root_ok gate + reinsert path as the drift starts (no reduced-score shortcut); if fuse ever floated the HTU into the interior -- the move the drift path already reverts -- root_ok fails and the best RAS+drift start stands, so a fused tree is reinserted only when its id mapping is already valid. Default-OFF (needs sectorGoComb > 0); env TS_SECT_FUSE=0 disables only the fuse step (drift-only comb) to isolate its marginal contribution in an A/B. Reuses the existing tree_fuse and ts_tbr's reroot_at_tip; no new scoring code. Local correctness gate (Zanol2014 74t, Giles2015 78t -- the wps>=2 regime): fuse fires and wins, and every reinserted tree's C++ score equals an independent by-label TreeLength. An initial permutation-remap for the HTU-float case was implemented, found empirically unreachable (the content root always keeps id sr_mapped), and removed to avoid shipping untested pointer surgery. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Adds dev/benchmarks/sector_fuse_ab.R: within each combStarts level the fuse and drift-only arms differ only by TS_SECT_FUSE, so any delta is fuse alone. Records the pre-committed decision rule (beat drift-only -> opt-in, else stay default-off). This is the harness behind the null marginal result. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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…#266) * feat(sector): TNT-style in-sector drifting for large sectors (opt-in) Large sectorial sub-problems have more reach but get stuck in their own local optima under plain RAS+TBR. Add TNT `sectsch godrift`/`gocomb`: sectors with >= sectorGoDrift real tips are re-solved by tree-drifting; >= sectorGoComb by combined analysis (sectorCombStarts RAS+drift starts, keep-best). Reuses the existing drift_search; default-OFF (both thresholds 0) so every current search is byte-identical. Anchoring: an unmasked drift on the HTU-anchored reduced sector tree floats the HTU (re-roots the sector vs the rest of the tree) in ~80% of solves, which the root-structure check then reverts to a NON-TBR'd topology -> net-negative. Fixed by threading an optional sector_mask through drift_search -> drift_phase and its internal tbr_search calls (additive, default nullptr; top-level driven_search drift unaffected): search_sector pins the synthetic root, HTU, content root and its two children per RAS start, cutting the HTU-float revert rate ~80% -> ~12%. Residual reverts stay safe via the existing root_ok check. Validated (Hamilton matched-wall A/B, 4 EW sector-resolve datasets x 5 seeds, rasStarts=3 both arms, sectorMaxSize=80): pinned godrift wins-or- ties every dataset with zero regressions for 3-cycle arms (sectorGoDrift 25-40, sectorDriftCycles=3). Shipped OPT-IN only; the recipe-default flip is gated on a separate preset-level (rasStarts- matched) A/B. The gocomb fuse recombination sub-step is deferred (sectorFuseRounds reserved/unused). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * feat(sector): implement the gocomb fuse recombination sub-step (default-off) (#267) * feat(sector): implement the gocomb fuse recombination sub-step Completes TNT combined analysis for large sectors: after the sectorCombStarts RAS+drift starts, recombine them with tree_fuse (best start as recipient, the others as donors) and keep the fused tree only if it beats every start. Previously gocomb was RAS+drift keep-best; the fuse step was deferred because tree_fuse re-roots the reduced tree at tip 0, dropping the (HTU, sr_mapped) synthetic-root layout reinsert_sector needs. Re-anchoring: parsimony is rooting-invariant, so reanchor_fused_at_htu simply re-roots the fused tree at the HTU pseudo-tip. The HTU represents the rest of the tree at the sector boundary and stays adjacent to the content root, so its sibling after re-rooting is the whole non-HTU clade -- exactly what reinsert_sector grafts back, with the content clade still rooted at sr_mapped. The fused tree is accepted only through the SAME root_ok gate + reinsert path as the drift starts (no reduced-score shortcut); if fuse ever floated the HTU into the interior -- the move the drift path already reverts -- root_ok fails and the best RAS+drift start stands, so a fused tree is reinserted only when its id mapping is already valid. Default-OFF (needs sectorGoComb > 0); env TS_SECT_FUSE=0 disables only the fuse step (drift-only comb) to isolate its marginal contribution in an A/B. Reuses the existing tree_fuse and ts_tbr's reroot_at_tip; no new scoring code. Local correctness gate (Zanol2014 74t, Giles2015 78t -- the wps>=2 regime): fuse fires and wins, and every reinserted tree's C++ score equals an independent by-label TreeLength. An initial permutation-remap for the HTU-float case was implemented, found empirically unreachable (the content root always keeps id sr_mapped), and removed to avoid shipping untested pointer surgery. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * test(sector): matched-wall harness isolating the gocomb-fuse margin Adds dev/benchmarks/sector_fuse_ab.R: within each combStarts level the fuse and drift-only arms differ only by TS_SECT_FUSE, so any delta is fuse alone. Records the pre-committed decision rule (beat drift-only -> opt-in, else stay default-off). This is the harness behind the null marginal result. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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Stacks on #266 (base is that branch, so this diff is just the fuse commit — retarget to
cpp-searchonce #266 merges).What
Completes TNT combined analysis for large sectors: after the
sectorCombStartsRAS+drift starts, recombine them withtree_fuse(best start = recipient, the others as donors) and keep the fused tree only if it beats every start. Previouslygocombwas RAS+drift keep-best; the fuse step was deferred becausetree_fusere-roots the reduced tree at tip 0, dropping the(HTU, sr_mapped)synthetic-root layoutreinsert_sectorneeds.Re-anchoring (the deferral obstacle, resolved)
Parsimony is rooting-invariant, and the HTU pseudo-tip represents the rest of the tree at the sector boundary — so it stays structurally adjacent to the content root.
reanchor_fused_at_htujust re-roots the fused tree at the HTU (reusing ts_tbr's existingreroot_at_tip); its sibling is then the whole non-HTU clade, with the content still rooted atsr_mapped. The existingroot_okgate accepts it, and the fused tree is reinserted through the same gate + path as the drift starts (no reduced-score shortcut). If fuse ever floats the HTU into the interior — the move the drift path already reverts —root_okfails and the best RAS+drift start stands, so a fused tree is reinserted only when its id mapping is already valid. An initial permutation-remap for the float case was implemented, found empirically unreachable, and removed to keep untested pointer surgery out of the merge.Validation
TreeLength.comb_fuse − comb_drift= +0.00 (1/18/1) at combStarts=3, −0.15 (4/14/2) at combStarts=6. The drift path carries the whole gain (comb_drift − base= −1.55). Cause: fuse gets ≥2 distinct donors only ~1/20 comb solves — the RAS+drift starts converge, so there is usually nothing to recombine.Scope
Default-OFF (needs
sectorGoComb > 0); envTS_SECT_FUSE=0disables only the fuse step. Landed for TNT combined-analysis parity / completeness — not a wall-clock lever, and deliberately not enabled in any recipe. The wall-clock lever is godrift (#266). Reusestree_fuseandreroot_at_tip; no new scoring code.🤖 Generated with Claude Code