[BREAKING] Python: Checkpoint refactor: encode/decode, checkpoint format, etc (#3744)

* WIP: Checkpoint refactor: encode/decode, checkpoint format, etc

* WIP: Remove workflow ID in checkpoints

* Refactor checkpointing

* Add get_latest tests

* Increase test coverage

* Fix formatting

* Fix unit tests

* Fix samples

* fix unit tests

* fix pipeline

* Copilot comments

* Fix tests

* Fix more tests

* Address comments part 1

* Address comments part 2

* Comments

python/packages/orchestrations/tests/test_concurrent.py

@@ -224,13 +224,10 @@ async def test_concurrent_checkpoint_resume_round_trip() -> None:
 
     assert baseline_output is not None
 
-    checkpoints = await storage.list_checkpoints()
+    checkpoints = await storage.list_checkpoints(workflow_name=wf.name)
     assert checkpoints
     checkpoints.sort(key=lambda cp: cp.timestamp)
-    resume_checkpoint = next(
-        (cp for cp in checkpoints if (cp.metadata or {}).get("checkpoint_type") == "superstep"),
-        checkpoints[-1],
-    )
+    resume_checkpoint = checkpoints[1]
 
     resumed_participants = (
         _FakeAgentExec("agentA", "Alpha"),
@@ -270,14 +267,13 @@ async def test_concurrent_checkpoint_runtime_only() -> None:
 
     assert baseline_output is not None
 
-    checkpoints = await storage.list_checkpoints()
-    assert checkpoints
-    checkpoints.sort(key=lambda cp: cp.timestamp)
-
-    resume_checkpoint = next(
-        (cp for cp in checkpoints if (cp.metadata or {}).get("checkpoint_type") == "superstep"),
-        checkpoints[-1],
+    checkpoints = await storage.list_checkpoints(workflow_name=wf.name)
+    assert len(checkpoints) >= 2, (
+        "Expected at least 2 checkpoints. The first one is after the start executor, "
+        "and the second one is after the first round of agent executions."
     )
+    checkpoints.sort(key=lambda cp: cp.timestamp)
+    resume_checkpoint = checkpoints[1]
 
     resumed_agents = [_FakeAgentExec(id="agent1", reply_text="A1"), _FakeAgentExec(id="agent2", reply_text="A2")]
     wf_resume = ConcurrentBuilder(participants=resumed_agents).build()
@@ -320,8 +316,8 @@ async def test_concurrent_checkpoint_runtime_overrides_buildtime() -> None:
 
         assert baseline_output is not None
 
-        buildtime_checkpoints = await buildtime_storage.list_checkpoints()
-        runtime_checkpoints = await runtime_storage.list_checkpoints()
+        buildtime_checkpoints = await buildtime_storage.list_checkpoints(workflow_name=wf.name)
+        runtime_checkpoints = await runtime_storage.list_checkpoints(workflow_name=wf.name)
 
         assert len(runtime_checkpoints) > 0, "Runtime storage should have checkpoints"
         assert len(buildtime_checkpoints) == 0, "Build-time storage should have no checkpoints when overridden"