T-208/T-211: random_constrained_tree() and impose_constraint() fixes#229
Merged
ms609 merged 6 commits intocpp-searchfrom Mar 25, 2026
Merged
T-208/T-211: random_constrained_tree() and impose_constraint() fixes#229ms609 merged 6 commits intocpp-searchfrom
ms609 merged 6 commits intocpp-searchfrom
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…ilder Build random binary tree that satisfies topological constraints by: 1. Ordering constraint splits smallest-to-largest 2. Assigning each tip to its tightest enclosing split 3. Bottom-up: randomly resolve each split's children into binary subtree 4. Wire root-level items (unconstrained tips + top-level splits) Replaces Wagner fallback (T-214 workaround) for RANDOM_TREE strategy, restoring uniform random topology sampling diversity under constraints. Tests: 916 constraint + 24 random-constrained + 373 simplify/driven pass.
Three issues in impose_one_pass / impose_constraint: 1. Bail-out threshold n_tip/4 was too aggressive. For n_tip=5 the threshold was 1, so any split requiring 2+ moves caused an immediate bail-out before making any repairs. Raised to n_tip. 2. impose_one_pass returned 0 both for 'no violations' and 'bailed out', so impose_constraint couldn't distinguish the two. Now returns -1 on bail-out, allowing the caller to know the repair may be incomplete. 3. Documented the root-child limitation: spr_clip() doesn't fully handle root children, so impose_one_pass skips them. The fuse path's post-repair verification guard (T-214) catches these cases. Tests: 940 constraint + 308 simplify/driven/sector pass.
spr_clip() can't detach root children (root is its own parent, so the bypass logic fails). All search callers skip root children, but impose_constraint needs them for constraint repair. New topology_spr() helper in ts_constraint.cpp handles the root-child case by absorbing the sibling into root and repurposing it as the insertion node. No changes to spr_clip or any search caller. Also removes the build_postorder call that was missing between individual moves within impose_one_pass — each topology_spr is now followed by a postorder rebuild so edge enumeration stays valid. Tests: 942 constraint (90 impose-constraint, incl 2 new root-child tests) + 308 simplify/driven/sector pass.
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Summary
Implements
random_constrained_tree()and fixes three bugs inimpose_constraint().New:
random_constrained_tree()(T-208)Constraint-aware random topology builder. Orders constraint splits smallest→largest,
assigns tips to tightest enclosing split, randomly resolves each split's children
into a binary subtree, then wires root level. Replaces the Wagner tree fallback
that T-214 introduced as a workaround.
Fix:
impose_constraint()bugs (T-211)Three interconnected bugs prevented constraint repair from working correctly:
n_tip/4too aggressiven_tipspr_clip()can't detach root childrentopology_spr()helper (65 lines)Testing
Agent A (Claude Sonnet 4).