FA-11708 / Graph algorithm invariants / Member archive

Duplicate dependency declarations strand a valid topological vertex · case 03

Duplicate dependency declarations strand a valid topological vertex.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Treat repeated directed edges as one dependency. Return the lexicographically smallest topological order, or None if any cycle exists. Include isolated vertices.

Why this case matters

A deterministic in-memory graph model isolates this invariant; no large-graph performance or production graph engine behavior is claimed.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
duplicate dependency	`null`	`[3, 4]`	Failed

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