feat: implement pod snapshot method

[shrutiyam-glitch]

Depends on: #338 #337

This PR completes the Pod Snapshot extension for the Python SDK by implementing the snapshot() method and the underlying logic to monitor snapshot completion.

Core Logic Implementation:

• Manual Trigger Workflow: The snapshot() method creates a PodSnapshotManualTrigger resource for the target pod, using a unique hash suffix to avoid name collisions.
• Snapshot Status Watcher: Implements _wait_for_snapshot_to_be_completed, which uses the Kubernetes watch API to block until the snapshot controller marks the trigger as Complete. It specifically looks for the Triggered condition with a True status and Complete reason.
• Response Handling: Captures the snapshot_uid from the resource status and returns a structured SnapshotResponse, providing the user with the unique identifier needed for future restores.
• Lifecycle Cleanup: Updates the __exit__ method to ensure that all PodSnapshotManualTrigger resources created during the session are automatically deleted, maintaining a clean namespace.

Testing Done:

• Integration Test: Added test_podsnapshot_extension.py which verifies the full E2E flow:
  -- Starts a sandbox with a counter application.
  -- Creates two sequential snapshots (test-snapshot-10 at 10 seconds and test-snapshot-20 at 20 seconds).

• Unit tests are added

Follow-up PR:
Restore example, is_restored() check added in the following PR (#249)
List_snapshots, delete_snapshots and restoring from dedicated snapshot will be added in the following PRs.

Output:

• Integration Test (clients/python/agentic-sandbox-client/test_podsnapshot_extension.py):

$ python3 test_podsnapshot_extension.py --template-name python-counter-template --namespace sandbox-test
--- Starting Sandbox Client Test (Namespace: sandbox-test, Port: 8888) ---

***** Phase 1: Starting Counter *****

======= Testing Pod Snapshot Extension =======
Creating first pod snapshot 'test-snapshot-10' after 10 seconds...
Trigger Name: test-snapshot-10-20260306-190022-b6016fa2
Snapshot UID: 69debd3e-3518-4185-8d09-720f933b2100
Success: True
Error Code: 0
Error Reason: 

Creating second pod snapshot 'test-snapshot-20' after 10 seconds...
Trigger Name: test-snapshot-20-20260306-190035-874a66a1
Snapshot UID: a10f67a6-bd84-4684-b8bd-506cde0f7757
Success: True
Error Code: 0
Error Reason: 
Recent snapshot UID: a10f67a6-bd84-4684-b8bd-506cde0f7757
--- Pod Snapshot Test Passed! ---

--- Sandbox Client Test Finished ---

• Unit test (clients/python/agentic-sandbox-client/k8s_agent_sandbox/gke_extensions/test_podsnapshot_client.py):

$ python3 k8s_agent_sandbox/gke_extensions/test_podsnapshot_client
.py
.......ERROR:k8s_agent_sandbox.gke_extensions.podsnapshot_client:Failed to create PodSnapshotManualTrigger 'test-trigger-fe4e166a': (Create failed)
Reason: None
Traceback (most recent call last):
  File "/usr/local/google/home/shrutiyam/Documents/python-test/split1/agent-sandbox/clients/python/agentic-sandbox-client/k8s_agent_sandbox/gke_extensions/podsnapshot_client.py", line 214, in snapshot
    created_obj = self.custom_objects_api.create_namespaced_custom_object(
        group=PODSNAPSHOT_API_GROUP,
    ...<3 lines>...
        body=manifest,
    )
  File "/usr/lib/python3.13/unittest/mock.py", line 1169, in __call__
    return self._mock_call(*args, **kwargs)
           ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/unittest/mock.py", line 1173, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/unittest/mock.py", line 1228, in _execute_mock_call
    raise effect
kubernetes.client.exceptions.ApiException: (Create failed)
Reason: None

...ERROR:k8s_agent_sandbox.gke_extensions.podsnapshot_client:Snapshot creation timed out for trigger 'test-trigger-7faa61c6': Snapshot manual trigger 'test-trigger-7faa61c6' was not processed within 1 seconds.
Traceback (most recent call last):
  File "/usr/local/google/home/shrutiyam/Documents/python-test/split1/agent-sandbox/clients/python/agentic-sandbox-client/k8s_agent_sandbox/gke_extensions/podsnapshot_client.py", line 224, in snapshot
    snapshot_result = self._wait_for_snapshot_processed(
        trigger_name, resource_version
    )
  File "/usr/local/google/home/shrutiyam/Documents/python-test/split1/agent-sandbox/clients/python/agentic-sandbox-client/k8s_agent_sandbox/gke_extensions/podsnapshot_client.py", line 176, in _wait_for_snapshot_processed
    raise TimeoutError(
        f"Snapshot manual trigger '{trigger_name}' was not processed within {self.podsnapshot_timeout} seconds."
    )
TimeoutError: Snapshot manual trigger 'test-trigger-7faa61c6' was not processed within 1 seconds.
.
----------------------------------------------------------------------
Ran 11 tests in 1.452s

OK

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[k8s-ci-robot]

Hi @shrutiyam-glitch. Thanks for your PR.

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[janetkuo]

/ok-to-test

[SHRUTI6991]

/lgtm

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[vicentefb]

import os seems to be unused in this file. Consider removing it to keep the imports clean.

[vicentefb]

snapshot_timestamp is extracted and stored in SnapshotResult, but it is never utilized or returned in SnapshotResponse. Should we add it to the final SnapshotResponse so the user knows when the snapshot occurred

[vicentefb]

If the the API responds with an explicit null for conditions ({"conditions": null}), status.get("conditions", []) will return None. Iterating over None on the next line will raise a TypeError. Please use conditions = status.get("conditions") or [] to ensure it always defaults to a list.

[vicentefb]

It is safer to write: snapshot_created = status.get("snapshotCreated") or {} and then snapshot_uid = snapshot_created.get("name"). Similar case as the on ebaove where the API can return a null value...

[vicentefb]

is this utc ?

[shrutiyam-glitch]

No, it is the local time of the system wherever the code is running. Should it be UTC ?

[vicentefb]

that's fine

[vicentefb]

To improve test coverage, you could use assert_called_once_with(...) instead of assert_called_once(). This ensures that the generated manifest payload accurately includes the generated trigger_name and the correct targetPod.

[vicentefb]

When asserting result.success, we could use self.assertTrue(result.success, result.error_reason). This will print the actual error message in the test output if the test fails unexpectedly.

[vicentefb]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shrutiyam-glitch, vicentefb

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