docs(experiments): the honest-cost restatement and the DCA dip-bonus ablation (#339)

[eaitbrahim]

What & why

Closes #339's measurement checkboxes. Two firsts, one date:

The honest-cost simulate re-run — the first keel simulate under per-product slippage (#334, v0.9.0): verdict TRAIN MORE, unchanged, and the correction runs exactly the conservative direction — BTC identical (floor-anchored), XLM 4.7567→4.4435, ADA 1.7638→1.7087, PAXG capped at 50bp. No flattered outlier survived; the TON-class 3.751-on-n=9 result can no longer print at thin-book pricing. This is the measurement that decides #335: the gate opt-in stays precautionary (nothing promotes on thin assets today), with the evidence now on record.

The DCA dip-bonus ablation — first-ever coverage of the only unswept rule family, three cells (dip_bonus_pct 0/1/2) through sim/portfolio_sim at keel's real costs over ~5 years of BTC hourly. The pre-registered ordinal expectation was NOT confirmed: cells within 0.65% relative, no monotone direction (1.40742 / 1.40424 / 1.41325). The honest reading is stated: mechanism mismatch (the citation holds cash until threshold dips; the param always buys and scales size) plus single-asset/single-window power. No cell preferred; the live rule stays at 0.

Both trials appended to the hash-chained ledger (chain verified clean). Also records the deployment actions: DCA twins re-enabled via keel rules enable + promote --force (the documented bypass, warnings logged), so the paper pipeline now has an always-firing family. v0.9.0 was cut and deployed first (PR #346; four distributions verified, keel versions clean, both DBs at schema 10).

Tests-first evidence

Measurement PR: the instruments' outputs are quoted verbatim; the ledger rows were appended through keel.research.ledger.append_trial with verify_chain returning []. Gates: 2947 passed / 1 skipped; ruff clean; mypy clean.

Gates

• uv run ruff check keel tests packages — All checks passed!
• uv run mypy — Success: no issues found in 238 source files
• uv run pytest -q — 2947 passed, 1 skipped

Scope check

• Documentation, experiment records, and ledger rows only — no code, rails, rules, or classifications touched.