feat(progression): capabilities the adapters need (commit A of the swap)

no behaviour change - additive only.

GrantSkill: pickups are free unlocks, and collecting one already owned is
a no-op rather than a free upgrade.
RevokeSkill: for skills that consume themselves (brick shield).
AbandonAttempt: leaving a level without dying, so no life is charged.

ApplyCheat rewrites the Playthrough through its snapshot rather than via
SetLives/AddCoins mutators, which ADR-0005 rules out - a bare mutator is
an invitation, and the old code had two paths to exactly that. Every
value is re-validated on the way back in and a rejected cheat leaves the
Playthrough untouched, which is asserted.

73 tests.

progression/ProgressionService.cs

@@ -176,6 +176,65 @@ public sealed class ProgressionService
         return PurchaseOutcome.Purchased;
     }
 
+    /// <summary>
+    /// Grants a Skill for free, as a pickup does. No coins change hands, and collecting one already
+    /// owned is a no-op rather than a free upgrade.
+    /// </summary>
+    public bool GrantSkill(SkillId skill)
+    {
+        if (_playthrough is null || _attempt is null) return false;
+        if (IsOwned(skill)) return false;
+
+        if (!_attempt.TryRecordPurchase(skill, SkillLevel.First, Coins.Zero)) return false;
+
+        AnnounceChanges();
+        return true;
+    }
+
+    /// <summary>
+    /// Takes a Skill away, from this Attempt's purchases and from the Playthrough alike. For Skills
+    /// that consume themselves rather than as a cheat.
+    /// </summary>
+    public bool RevokeSkill(SkillId skill)
+    {
+        if (_playthrough is null) return false;
+
+        var revoked = _playthrough.RevokeSkill(skill);
+        AnnounceChanges();
+        return revoked;
+    }
+
+    /// <summary>
+    /// Throws the current Attempt away without charging a life — leaving a Level rather than dying in
+    /// it. The ledger is discarded, so coins found and Skills bought during it are lost.
+    /// </summary>
+    public void AbandonAttempt()
+    {
+        _attempt = null;
+        AnnounceChanges();
+    }
+
+    /// <summary>
+    /// Console only. Rewrites the Playthrough by transforming its snapshot.
+    /// </summary>
+    /// <remarks>
+    /// Deliberately shaped this way rather than as <c>SetLives</c> / <c>AddCoins</c> mutators, which
+    /// ADR-0005 rules out — a bare mutator is an invitation, and the code being replaced had two paths
+    /// to exactly that. Going through the snapshot means every value is re-validated on the way back
+    /// in, and a rejected cheat leaves the Playthrough untouched.
+    /// </remarks>
+    public void ApplyCheat(Func<PlaythroughSnapshot, PlaythroughSnapshot> change)
+    {
+        if (_playthrough is null) return;
+
+        var rewritten = Playthrough.Restore(change(_playthrough.Export()));
+
+        _playthrough = rewritten;
+        _attempt = null;
+        _playthroughs.Save(_playthrough);
+        AnnounceChanges();
+    }
+
     /// <summary>
     /// Charges the active Attempt's death to the Playthrough and persists it. Repeated calls for one
     /// Attempt cost one life — the Playthrough defers to the Attempt's terminal outcome (ADR-0005),