[guluchen]

For #157 (hub #15). Adoption PR per the PI's decisions of 2026-10-29. Do not merge without the PI's go.

What this PR does

• Adds the CC node lower bound charge ([Mac agent] CC engine: fractional-charge / edge-cover node lower bounds #157; fractional LP-dual charge, exact integer arithmetic) and makes it part of the default -cc-rules: excl,pack,orbf,parity,leaf,overlap,charge, on top of the -cc-aut=on default from Make -cc-aut=on the CC default (GH-152; do not merge before PI says merge) #155. -cc-rules=excl,pack,orbf,parity,leaf,overlap restores the previous CC search.
• It is evaluated only after the packing fails, at remaining budget >= 3 (-cc-lb-minr), where the packing is exactly at its limit (-cc-lb-gap=0). It switches itself off per half after a level with >= 100 000 evaluations of which < 40 % pruned (-cc-lb-auto=40). -cc-lb-raise=off drops the raise step.
• ecover (Gallai edge cover) was evaluated in the round and removed at the PI's request.
• Merged with main 6083e662 (includes Make -cc-aut=on the CC default (GH-152; do not merge before PI says merge) #155 and Rename six tier5 TN stems with GH-152 CC lower bounds #163). MaxSAT path unchanged.

Evidence (optimization/experiments/GH-157/REPORT.md)

• Tier 0 of the adopted default (764b011): make test-cc PASS (Part I: bound vs brute-force tau, 345 600 ladders, mutant 15 caught; all main mutants as on main); flags 442/442; tier 0-3 answers 61/61 equal to the stem (CC default with seeds 0 and 1, MaxSAT tier 0-1); identity vs main: MaxSAT deterministic 30/30, old CC path 45/45, MaxSAT default 26/30 identical (the rest differ only in finder-timing lines).
• Tiers 1-4 (opt-in evaluation, 5-seed medians, vs main CC / vs -cc-aut=on on both sides): Tier 1 1.000 / 1.012 (process floor), Tier 2 0.889 / 0.919, Tier 3 0.925 / 0.911, Tier 4 0.946 / 0.975; max cell 1.105 / 1.133.
• Tier 5: new CC lower bounds TN_360 >= 23, TN_396 >= 23, TN_504 >= 24, TN_648_10 >= 22 (all four reproduced with a different search order, mrv with original labels, within 12 h: REPRODUCTION.md). TN codes reach the old values in 0.72-0.80x of the same-session main time.
• A default change requires re-recording the baselines afterwards (PI rule), unless the PI waives it. No stems are renamed.

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