CB-WP-0008-T02: cb-play — INTENT stage 0's CLI player

A human seat is a Policy like any bot, so the CLI adds no second driver:
HumanPolicy renders the projection, lists the legal commands and reads an
index or `pass`. `make play` runs it; `--all-bots` watches one.

K13's Project trait gains its first implementor after six passes with
none. Hidden: other seats' face-down selections until Reveal, hands and
deck (counts only), a face-down Problem's suit and value, and the seed —
not secret content, but a seat holding it can compute the deck.

A played session becomes an artifact: --record writes it as a scenario
the runner executes, --replay writes a .cbreplay bundle. record.rs is the
inverse of parse_command and its warrant is a round-trip test over every
command shape.

The acceptance test for the projection passed vacuously twice. First it
asserted the text contained "face-down", which every render does because
of Problems. Counted, it then reported zero inspected entries: seats are
asked in order, so a human at P1 is prompted before anyone has selected.
Seated at P3 it inspects ten entries and dies when the projection is
mutated to reveal everything. Counting what the harness examined caught
both, which is the second time that remedy has worked where a stronger
predicate would not have.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

history/260801-cb-wp-0008-log.md

@@ -62,3 +62,41 @@ stated reason. Third recorded instance of the weak-mutation class — the
 retrospective in `260801-instrument-the-table-retrospective.md` predicted
 mutation strength would stay a standing maintenance cost, and this is
 that cost arriving on the next pass.
+
+## T02 — `cb-play`
+
+`tools/cb-play` (`make play`), 6 tests. A human seat is a `Policy` like
+any bot, so the CLI adds no second driver: `HumanPolicy` renders the
+projection, lists the legal commands, and reads an index or `pass`.
+
+- **K13's first implementor** is `games/ground/src/view.rs`. Hidden:
+  other seats' face-down selections until Reveal, hands (count only), the
+  undealt deck (count only), a face-down Problem's suit and value, and
+  **the seed** — not secret content, but a seat holding it can compute the
+  deck.
+- **A played session becomes an artifact.** `--record FILE` writes it as a
+  scenario the runner executes; `--replay DIR` writes a `.cbreplay`
+  bundle. `games/ground/src/record.rs` is the inverse of
+  `parse_command`, and its warrant is a round-trip test over every
+  command shape — an encoder checked against hand-written expectations
+  only agrees with itself.
+
+### Two vacuous tests, caught by counting
+
+The acceptance clause *"a seat's projection never contains another seat's
+hidden selection"* passed twice while asserting nothing.
+
+1. The first version asserted the rendered text contained `face-down` —
+   which it does, from **Problems**, in every game ever rendered.
+2. The counted version then reported **0 inspected entries**: seats are
+   asked in order, so a human at P1 is always prompted before anyone has
+   selected and never sees a hidden selection at all.
+
+Seating the human at **P3** exercises the rule; the test now counts what
+it inspected and requires at least four. Mutating the projection
+(`revealed = true`) fails it for its stated reason.
+
+This is the same class as the AM-2 `expect` that matched passing output —
+an assertion that cannot distinguish the two worlds. The remedy that
+worked both times was **counting what the harness examined**, not
+strengthening the predicate.