fix: remove stale lru_cache from FlowGraphMiddleware.get_block

The lru_cache on get_block() caused three cache coherence bugs:

1. Removed blocks remained accessible — set_block_params would
   modify a detached block object that no longer exists in the
   flowgraph, so save_flowgraph would serialize stale state.

2. Re-created blocks with the same auto-generated name would
   return the cached (removed) block instead of the new one.

3. Renamed blocks (via set_block_params id=...) left phantom
   cache entries under the old name.

Fix: always look up blocks from the live flowgraph. Block lookup
is a linear scan of typically <20 blocks — no cache needed.
Raises KeyError instead of StopIteration for missing blocks.

src/gnuradio_mcp/middlewares/flowgraph.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-from functools import lru_cache
 from typing import TYPE_CHECKING, Optional
 
 from gnuradio.grc.core.blocks.block import Block
@@ -45,11 +44,18 @@ class FlowGraphMiddleware(ElementMiddleware):
         block_middleware = self.get_block(block_name)
         self._flowgraph.remove_element(block_middleware._block)
 
-    @lru_cache(maxsize=None)
     def get_block(self, block_name: str) -> BlockMiddleware:
-        return BlockMiddleware(
-            next(block for block in self._flowgraph.blocks if block.name == block_name)
+        """Look up a block by name from the live flowgraph.
+
+        Always queries the actual flowgraph state — no caching — so that
+        block renames, removals, and re-creations are immediately visible.
+        """
+        block = next(
+            (b for b in self._flowgraph.blocks if b.name == block_name), None
         )
+        if block is None:
+            raise KeyError(f"Block {block_name!r} not found in flowgraph")
+        return BlockMiddleware(block)
 
     def connect_blocks(
         self, src_port_model: PortModel, dst_port_model: PortModel

tests/unit/test_flowgraph.py

@@ -119,6 +119,48 @@ def test_block_disconnection(flowgraph_middleware: FlowGraphMiddleware, block_ke
     assert len(flowgraph_middleware.get_connections()) == 0
 
 
+def test_get_block_after_removal_raises(flowgraph_middleware: FlowGraphMiddleware):
+    """Removed blocks must not be accessible — prevents stale references."""
+    model = flowgraph_middleware.add_block("analog_sig_source_x")
+    flowgraph_middleware.remove_block(model.name)
+    with pytest.raises(KeyError):
+        flowgraph_middleware.get_block(model.name)
+
+
+def test_recreated_block_gets_fresh_state(flowgraph_middleware: FlowGraphMiddleware):
+    """Re-creating a block after removal must return the new instance."""
+    model = flowgraph_middleware.add_block("analog_sig_source_x")
+    block_mw = flowgraph_middleware.get_block(model.name)
+    block_mw.set_params({"freq": "99999"})
+
+    flowgraph_middleware.remove_block(model.name)
+    model2 = flowgraph_middleware.add_block("analog_sig_source_x", model.name)
+
+    block_mw2 = flowgraph_middleware.get_block(model2.name)
+    freq_param = next(p for p in block_mw2.params if p.key == "freq")
+    # New block should have default value, not the one we set before removal
+    assert freq_param.value != "99999"
+
+
+def test_renamed_block_accessible_by_new_name(
+    flowgraph_middleware: FlowGraphMiddleware,
+):
+    """After renaming via set_params(id=...), the new name must resolve."""
+    model = flowgraph_middleware.add_block("variable")
+    old_name = model.name
+    block_mw = flowgraph_middleware.get_block(old_name)
+    block_mw.set_params({"id": "my_var", "value": "42"})
+
+    # New name works
+    new_block = flowgraph_middleware.get_block("my_var")
+    val = next(p for p in new_block.params if p.key == "value")
+    assert val.value == "42"
+
+    # Old name is gone
+    with pytest.raises(KeyError):
+        flowgraph_middleware.get_block(old_name)
+
+
 def test_default_flowgraph_errors(flowgraph_middleware: FlowGraphMiddleware):
     for error in flowgraph_middleware.get_all_errors():
         assert isinstance(error, ErrorModel)