Brummel
f5e00a9c72
Cycle 5 of milestone #148 (cost-model graph in R): the per-cycle-held accrual mechanism — C10's "per-cycle-held factors accrue over the hold". A carry/funding cost is charged for every cycle a position is held, so the net_r_equity equity curve bleeds continuously over the hold (approach B, "ja, mach B") rather than stepping at close. Mechanism (logged on #148): ChargeMode { AtClose, PerHeldCycle } is a property of the cost factor, read by the one shared CostRunner (no second runner type). The AtClose arm is the pre-cycle-5 eval tokens VERBATIM (IEEE-754 byte-identity). The PerHeldCycle arm accrues `per` into `acc` each held cycle, dumps the accrued total into `cum` at close (resetting acc), and marks the open position via a growing open_cost_in_r. The bleed lives in open_cost_in_r, which the net_r_equity tap already subtracts — so summarize_r and the CLI net_eq wiring are UNCHANGED, and the cycle-0083/0084 net_expectancy_r goldens (-614.3134020253314 flat, -615.0304388396047 composed) + the C18 no-cost golden stay byte-identical. CarryCost is a ConstantCost twin differing only in charge_mode() -> PerHeldCycle (a labelled stress parameter, the flat base of the accrual family). Wired through the existing cost_graph/CostSum aggregation; a per-trade ConstantCost and a per-held-cycle CarryCost compose in one run (the costs sum per-field — the composed golden is exactly the sum of the two single-cost charges). New run-path --carry-per-cycle flag (sweep/walkforward/mc pass None, as the existing cost flags do). Tests: 2 RED-first unit B-proofs (open_cost grows over the hold, dumps the total at close, acc resets between trades — the discriminator a scalar net_expectancy_r cannot see); the CarryCost twin's 5 unit tests; 2 captured net_expectancy_r goldens (-768.2095026600887 carry, -1383.7939051991182 composed); a net_r_equity-bleeds-over- the-hold integration test (the terminal open hold's r_equity-net_r_equity gap strictly grows); plus negative-rate-refused-exit-2, monotone-in-rate, and zero-rate-exactly-free guards. Verified: cargo test --workspace (0 failures), cargo build --workspace, cargo clippy --workspace --all-targets -- -D warnings clean. summarize_r / aura-analysis untouched. Deferred to later #148 cycles (logged there): notional-based carry, the calendar-aware overnight swap, sweep-path cost. refs #148