Assess US equities as a tradeable asset class for keel (Coinbase or any other broker)

[eaitbrahim]

US stocks have come up as a candidate asset class. Before any adapter or rule work, establish whether keel can trade them at all — from Coinbase, whose key keel already holds, or from any other broker — and record the answer so the question is not re-litigated from scratch.

This is the third assessment in the series set by #201 (cTrader) and #204 (Trade Nation), and should follow the same house form.

Scope

• Determine whether Coinbase Advanced Trade actually exposes an equities order path, and whether keel's own account can use it. Re-run the committed probe rather than relying on the 2026-08-05 measurement.
• Determine whether equity market data is available at any granularity keel's rules can consume — every rule in keel/strategy/rules/ takes candles_by_tf.
• Decide the decisive question: would keel's charter permit holding an instrument that represents equity in an issuer, independent of any venue? Map §71.6 onto keel/compliance/screen.py and the asset_attestations schema.
• Map the answer onto keel's own gates — the Broker port, OrderSpec, the rails in keel/execution/guards.py, and the live-path wiring.
• Survey alternative brokers if Coinbase is unsuitable.
• If it is a capability gap rather than a prohibition, say so plainly and scope what building the capability would cost.

Acceptance

• A feasibility document in docs/experiments/ following the house form set by docs/experiments/2026-08-05-coinbase-asset-class-feasibility.md.
• A real KB basis: line — this is a halal question, not only an architectural one.
• Every file:line citation verified against the working tree.
• An explicit statement of which refusals are independent and which are stacked, so a later reader does not treat one correction as flipping the verdict.
• Any premise from the brief that does not survive checking must be corrected in the document itself, not quietly dropped.
• Independent review of the finished assessment before merge.

Note on the distinction that matters

If the blocker turns out to be a screening capability keel does not have, rather than a property of the instrument, then the answer is "not yet" — materially different from the "never" returned for CFDs in #201 and #204. The document must not blur the two.

[eaitbrahim]

Duplicate — this was already assessed and shipped by a concurrent session while this issue was being written.

• docs(experiments): assess US equities and refuse on screening capability #211 merged the assessment (docs/experiments/2026-08-09-equities-feasibility.md)
• docs(experiments): correct the equities assessment after independent review #213 merged the corrections after independent review

The merged document answers everything in the scope above, and reaches the distinction this issue asked for: the blocker is keel's own screening capability, not the instrument — so US equities are "not yet", where a CFD (#201, #204) is "never". Closing as duplicate; no work is outstanding.