# intraday-shortability-sample — a second, different-hour sample of the borrow-flag panel to capture intraday ETB→HTB onset: considered and REJECTED

status: dismissed · considered panel run 22 (2026-09-14), frontier scout ·
verdict: passes bar 1, fails bars 2 and 3 independently; aggravated by a
live pre-registration it would corrupt

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**What was considered.** Alpaca serves borrow state as *current state only*,
never history, so the incumbent daily snapshot records one observation per
day and the **time within the day** at which a name flips easy-to-borrow →
hard-to-borrow is irrecoverable the moment the day ends. A second capture at
a different hour would own that onset timing. No prior art.

**Bar 1 (un-backfillable): PASSES cleanly** — this is exactly the class the
capture doctrine is built for.

Rejected on two independent bars:

3. **Mechanism — fails.** The mechanism on offer is borrow-constraint
   arrival. This shop's own registration screens that class **out** rather
   than harvesting it (the Muravyev–Pearson–Pollet artifact class): the
   constraint is treated as a contaminant of the skew measurement, not as a
   signal. And the quantity is tiny — the Russell-1000 hard-to-borrow
   positive class runs about 1.5 names per day out of ~885 (measured this
   run across 33 snapshots; see BTB-1) and is mostly non-persistent. Finer
   time resolution on a variable that small resolves nothing a long-only
   book could act on.
2. **~Zero marginal cost — fails as written.** It does not ride the existing
   cron; a *different hour* is the entire point, so it is a new scheduled
   job, a new beacon, and a new capture-QA surface.

**Aggravating, and the reason this one should stay shut even if the bars
were argued:** the shortability stream is 32 of its pre-registered 60
trading days into its own accrual. Changing the sampling design mid-panel
would corrupt the panel the pinned test is going to read — the B4 lesson
(pin the exam before any student can see it) applied to sampling rather than
to thresholds.

## Reopens if

Both of these become true together:

- **(a)** the Russell-1000 hard-to-borrow positive class becomes
  **persistent** — a name debounced HTB across ≥5 consecutive sessions,
  which the store has never yet shown (CPB's 8 appearances are recurrent,
  not consecutive); **and**
- **(b)** the incumbent stream's **60-trading-day test has completed**, so a
  design change can no longer contaminate a live pre-registration.

Until both hold, re-proposing a second intraday sample is C0 relitigation.