docs(readme): the cost-distortion finding, rendered from the ledger (#646)

[eaitbrahim]

Partial. #646 also asks for a ~10-second terminal capture with committed generation tooling. That's unbuilt and the issue stays open for it. This is the research half.

The README already leads with the fee-drag table (shipped earlier). This adds the finding that came out of measuring it properly.

What it says

Every backtest here used to price fills at the floor of keel's own slippage model — the best case the model can produce, reached only at a $500M/day anchor. 0 of 24 assets reach it. Re-pricing per product moved the median profit factor across 120 cells from 0.309 → 0.219.

	profit factor
the cost-model correction	−0.090
the best strategy improvement we have measured	+0.033

2.7× — derived at render time from two separate hash-chained ledger rows, not typed. A literal would survive either number changing underneath it, which is exactly the trap a headline ratio sets, and a test asserts the ratio is computed.

What it deliberately does not say

Nothing about any other framework.

The tempting version of this section framed crypto backtesting generally as living on fantasy friction assumptions. We have not measured anyone else's defaults, and an unsourced claim about a named third party is the exact failure this section exists to avoid making about ourselves. #646 forbids competitor naming in the asset on trademark grounds; the stronger reason is that the finding needs no help.

A test asserts six framework names are absent and that the scope sentence — "keel mis-pricing keel, on one venue" — is present.

The headline is narrower than proposed

"Strategy optimization is irrelevant under flat slippage assumptions" generalises from one comparison, one universe, one venue. What's written instead — "we mis-priced our own execution by more than any strategy change we ever made" — is checkable line by line, and is the more damaging claim precisely because it's about us.

Two rendering bugs the tests caught

Both invisible in the source, both obvious on the page:

• textwrap broke the source link mid-URL, so it rendered as literal text.
• A blank line after every paragraph turned one four-row table into four one-row tables.

Verification

Tests: tests/test_fee_reality_block.py (+6, 16 total).
6 mutants, 6 killed: a hardcoded ratio, a dropped scope disclaimer, a named competitor, a hand-edited README number, a wrapped link, a split table.

Full suite 5253 passed / 3 skipped; ruff and mypy clean.

Regenerate with python scripts/render_fee_reality.py --write; the drift pin fails if the README and the ledger disagree.