test(currency): pin both halves of the dedup key

The existing test varied the move name and the denomination together, so a
name-only or denom-only key would have passed it too. Two assertions nail it:
give_item(gold)+give_item(silver) kills a name-only key, and
give_item(gold)+accept_item(gold) kills a denom-only key.

The spec now records the per-reply ceiling as a decision rather than an
accident, and flags the pre-existing non-currency duplicate-tag path as open.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QYa9u7Kdxv5gX4AnwWexy8

docs/superpowers/specs/2026-07-12-currency-copper-design.md

@@ -196,6 +196,25 @@ func take(item_id: String, qty: int) -> void    # currency -> purse_copper; else
 `take` clamps the purse at `0`. The validator already gates affordability (§4.7); the
 clamp is defence in depth, not the mechanism.
 
+**A currency move applies at most once per reply.** `TagExtractor` returns *every* tag
+occurrence, `MoveValidator` is a pure membership test, and `MoveApplier` loops — so
+without this, a model repeating `[MOVE: accept_item(copper)]` forty-seven times would
+drain a 47c purse, and ten `give_item(gold)` tags would mint 100,000c. That is the model
+choosing an amount **in unary** — the §2 breach that rejecting a quantity argument was
+meant to prevent. `MoveApplier` therefore keys currency moves on `name(denomination)`
+and drops repeats within a reply.
+
+The residual ceiling is deliberate: one reply may still combine *distinct* denominations
+(`give_item(gold)` + `give_item(silver)` + `give_item(copper)` = +10,101c). That is a
+model selecting a subset of a closed, six-element, state-gated set — an NPC handing over
+a gold, a silver and a copper is a legal sentence — not inventing an integer. Unary
+repetition was what made it unbounded, and that is closed.
+
+**The same duplicate-tag path exists for non-currency moves and predates this work**
+(three `give_item(amulet)` tags yield three amulets; a repeated `offer_quest` can
+double-add a quest). It is bounded *across* replies by `gifts_given` / `has_quest`, but
+not *within* one. Deliberately left alone here — it is not a currency bug. **Open.**
+
 **`NpcContent.available_moves`:**
 
 - `accept_item(<denom>)` is offered for each denomination the player can actually