Declare CB-WP-0023: SOLVE is offered only where it can do something

ground-game ruled SOLVE's legality on 2026-08-03: not offered on a
face-down or Denied Problem, not offered without a matching Solution in
hand, and not offered on a Problem claimed in a prior round. The bluff
reading CB-WP-0018 raised is dead -- it was a filter bug, and the engine
has been offering an inert move since legal_commands was written.

Only SOLVE is ruled on, so only SOLVE is touched. Implementing more than
was ruled would be inventing rules, which is what this exchange exists
to stop.

Chaos d8=6, no override.

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

workplans/CB-WP-0023-solve-legality.md

@@ -0,0 +1,97 @@
+---
+id: CB-WP-0023
+kind: product
+title: "SOLVE is offered only where it can do something"
+status: active
+---
+
+# Purpose
+
+```
+structural tier  S   (implements a ruling inside an existing capability —
+                      no new port, no canonical interface, no dependency)
+chaos            d8 = 6  → no override
+declared tier    S
+```
+
+Declaration 6 of chaos window 2.
+
+## A ruling, not a judgment call
+
+`ground-game` ruled SOLVE's legality on 2026-08-03 (GROUND-WP-0002 T02),
+after clay-borg raised it from play:
+
+| sub | ruling |
+|---|---|
+| **(a)** face-down Problem | **Not offered — illegal target.** *"only face-up, non-Denied. Browser no-ops were a filter bug, not a bluff mechanic."* |
+| **(b)** no matching Solution in hand | **Not offered.** *"the engine only offers SOLVE when a matching suit is held."* |
+| **(c)** already-claimed Problem | **Same-round race legal; prior-round claim not offered.** |
+
+**The bluff reading is dead.** CB-WP-0018 raised (a) as *possibly* an
+intended bluff in a commit/reveal game and deferred to ground-game rather
+than deciding. The answer is that it was a filter bug, and the engine has
+been offering an inert move since the day `legal_commands` was written.
+
+`legal_commands` offers Investigate and SOLVE on **every** problem key,
+with no reference to `face_up`, `denied`, `claimed_by` or the hand.
+
+**Only SOLVE is ruled on. Investigate is not touched** — implementing more
+than was ruled would be inventing rules, which is what this whole exchange
+exists to stop.
+
+## Task: filter SOLVE to what the ruling allows
+
+```task
+id: CB-WP-0023-T01
+status: todo
+priority: high
+```
+
+SOLVE is offered on problem `p` for seat `s` **iff** `p.face_up`,
+`!p.denied`, `p.claimed_by.is_none()`, and `s`'s hand holds a card of
+`p.suit`.
+
+On (c): at Select time every `claimed_by` is from a prior round — claims
+land at Resolve — so *"prior-round claim not offered"* is exactly
+`claimed_by.is_none()`, and the same-round race is already legal because
+both seats select before either resolves. **Say this in the code**, or the
+next reader will add a round comparison that does nothing.
+
+**Controls:**
+- each of the four conditions must be independently mutation-provable —
+  drop one filter, and a test naming *that* condition goes red;
+- the maintainer's reported case must be reproduced and then fixed: SOLVE
+  on a face-down Problem is offered before, not offered after;
+- **`make sim` must still pass**, or the ruling has broken a scenario that
+  encoded the old behaviour — in which case the scenario was encoding a
+  bug and must be updated with a note, not quietly edited.
+
+## Task: retire what the ruling settles
+
+```task
+id: CB-WP-0023-T02
+status: todo
+priority: medium
+```
+
+Update `specs/GroundRules.md` §Underdetermined for the SOLVE items, and
+retire the provisional flags the ruling closes. **A ruling that lands in
+code but not in the spec leaves the next reader with two sources.**
+
+Report to `ground-game` that the ruling is implemented — closing the loop
+is the part that has failed twice.
+
+## Task: evidence
+
+```task
+id: CB-WP-0023-T03
+status: todo
+priority: high
+```
+
+`evidence/CB-EV-0020-*.md`. Short.
+
+- **How long the inert move survived**, and what it cost: a maintainer
+  played SOLVE three rounds running with no effect and no explanation.
+- **Whether any scenario encoded the bug.**
+- **Quote CB-WP-0022's cost by re-running the instrument.**