revert(b20-mock): drop isAnnouncementActive view and transient flag

The previous commit added an isAnnouncementActive() view backed by an
EIP-1153 transient flag, aiming for parity with the Rust precompile's
is_announcement_active runtime flag. On review the check is unnecessary:
inner-call dispatch in announce(...) is self-delegatecall only, so there
is no reentrancy surface for an external contract to want to detect a
bracket-in-progress against.

Removes the view from IB20Asset, the flag and its set/clear from
MockB20Asset.announce, and the boundary tests.

Author: stevieraykatz

src/interfaces/IB20Asset.sol

@@ -109,20 +109,6 @@ interface IB20Asset is IB20 {
     /// @return Whether `id` is used.
     function isAnnouncementIdUsed(string calldata id) external view returns (bool);
 
-    /// @notice Whether an announcement bracket is currently open on this token. True from the
-    ///         start of `announce` through the dispatch of every entry in `internalCalls` and
-    ///         until `EndAnnouncement` fires; false at all other times, including before the
-    ///         first `announce` call and after the bracket closes. Resets per transaction:
-    ///         a revert anywhere in the bracket leaves no observable side effect on this view.
-    ///
-    /// @dev    Intended for inner-call contracts dispatched via `internalCalls` (or other
-    ///         contracts they reach) to detect they are executing inside an announcement
-    ///         bracket — useful for issuance, multiplier, and metadata flows whose policy
-    ///         differs when run as part of a disclosed corp action vs. ad-hoc.
-    ///
-    /// @return Whether an announcement is currently active.
-    function isAnnouncementActive() external view returns (bool);
-
     /*//////////////////////////////////////////////////////////////
                                MULTIPLIER
     //////////////////////////////////////////////////////////////*/

test/lib/mocks/MockB20Asset.sol

@@ -64,28 +64,6 @@ contract MockB20Asset is MockB20, IB20Asset {
     ///         by this before dividing.
     uint256 public constant WAD_PRECISION = 1e18;
 
-    // ============================================================
-    //                  ANNOUNCEMENT-ACTIVE FLAG
-    // ============================================================
-
-    /// @dev Per-transaction flag set true at the start of `announce`
-    ///      and false at the end, surfaced via `isAnnouncementActive()`.
-    ///      Lives in transient storage (EIP-1153) because the value is
-    ///      meaningful only within the bracket's call frame and MUST
-    ///      reset between transactions; transient storage also means
-    ///      the slot is reclaimed automatically on a revert anywhere in
-    ///      the bracket, so the flag never gets stuck `true`.
-    ///
-    ///      Declared as a contract-level state variable (not an
-    ///      ERC-7201 namespaced struct field) because transient storage
-    ///      lives in its own opcode-distinct address space — slot
-    ///      indices here can't collide with the regular-storage layout
-    ///      written by the factory bootstrap. The Rust precompile
-    ///      exposes the same value via a runtime context flag rather
-    ///      than a storage slot, so there is no persistent layout the
-    ///      Rust impl needs to mirror.
-    bool internal transient _announcementActive;
-
     // ============================================================
     //                           DECIMALS
     // ============================================================
@@ -119,13 +97,6 @@ contract MockB20Asset is MockB20, IB20Asset {
         // selector check were ever weakened.
         $.usedAnnouncementIds[id] = true;
 
-        // Open the bracket — flip the transient flag BEFORE emitting
-        // `Announcement` and before dispatching any inner call, so any
-        // contract reached transitively through `internalCalls` sees
-        // `isAnnouncementActive() == true` for the full lifetime of the
-        // bracket.
-        _announcementActive = true;
-
         emit Announcement(msg.sender, id, description, uri);
 
         for (uint256 i = 0; i < internalCalls.length; i++) {
@@ -135,21 +106,12 @@ contract MockB20Asset is MockB20, IB20Asset {
         }
 
         emit EndAnnouncement(id);
-
-        // Close the bracket. A revert above leaves transient storage
-        // untouched at tx end (per EIP-1153), so an aborted bracket
-        // also resets the flag implicitly.
-        _announcementActive = false;
     }
 
     function isAnnouncementIdUsed(string calldata id) external view returns (bool) {
         return MockB20AssetStorage.layout().usedAnnouncementIds[id];
     }
 
-    function isAnnouncementActive() external view returns (bool) {
-        return _announcementActive;
-    }
-
     // ============================================================
     //                          MULTIPLIER
     // ============================================================