Policy: Cycle breaks

Concern: What happens when the dependency graph has a cycle?

PMS / Portage: Emerge often proceeds through bootstrap / circular runtime edges with little ceremony. portage-ng’s inductive prover must break a cycle to finish the proof; that break is recorded explicitly.

Literals:

• Prover cycle-break proof key: assumed(rule(Lit))
• Model side: assumed(Lit)
• Distinct from domain rule(assumed(X))

Owns: Source/Pipeline/prover.pl (cycle detection / assume), benignity checks in Rules/Resolving/heuristic.pl, printer cycle section (config:print_prover_cycles/1).

Invariants:

• Cycle-breaks are not domain assumptions; do not lump them into “assumptions” counts without saying which kind.
• Self-deps and mutual compile/runtime cycles typically produce benign breaks (CI exit 1 when alone).
• Domain assumptions and cycle-breaks can co-exist; exit 2 if any domain assumption is present.
• PDEPEND cycles use the same break mechanism; PDEPEND is never disabled to avoid them.

Examples: test03 and test05 (actual cycle-break assumptions); test06, test47, test61 and test79 (cycles dissolved by the install/run action split — no break needed).
See also: Assumptions, Run, Chapter 9.