Add helpers for detecting open-ended activations (#26)

[craigmcchesney]

Implements the plan merged in #64 (plan/tickets/26/plan.md).

Helpers — activation_is_open() and activation_end_time() in machine_config_client, exported from dp_python_lib.client. Module-level so they cover get, query, iterate, and get_active_configurations() alike (D1). Reading .endTime directly on an open activation silently yields a zero Timestamp (1970); activation_end_time() returns None instead, which also makes end_time=activation_end_time(current) the correct carry-forward in a full-replace re-save (D3). Presence is the only test: an endTime present with value 0 is closed (D5).

Tests — new TestActivationOpenEndedHelpers (open, bounded, epoch-zero, reading .endTime does not set presence, re-save round trip, open record carried forward stays open, filtering a mixed query page). The integration open-ended round trip asserts the helpers beside the existing raw HasField checks, which remain the wire verification.

Cookbook (doc/cookbook/machine-configuration.md)

• "Open-ended activations" uses the helpers and warns about the 1970 value.
• "Copy every field forward" covers end_time.
• New "When you do not have the activation's id" recipe: finds the activation to close at a changeover by the incoming configuration's category plus CA.timestamp(changeover), the same terms as the server's overlap check (category as well as name). Deliberately not narrowed to open records, since a bounded activation ending after the changeover blocks the next save just as an open one does. Handles zero / one / more-than-one results. (Revised in review; the plan carries a dated note.)
• get_active_configurations() match rule now includes an absent endTime.
• "Every interval a configuration was in effect" no longer prints 0 for an open interval.

Also — CLAUDE.md, doc/release-notes/NEXT.md section, cookbook checker preamble.

Verification — pytest tests/unit/ (746 passed), ruff check ., ruff format --check ., mypy src/, cookbook snippet checker, release-notes checker all clean. tests/integration/test_machine_config_client_integration.py against a live stack: 3 passed, including the open-ended round trip with the new helper assertions. The revised recipe was also exercised against the live stack with a throwaway script: an empty result with nothing in effect, an open activation of a different configuration found through the category, the next save rejected while it stays open, a bounded activation ending after the changeover still found, and the next save succeeding once it is closed.

Closes #26

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https://claude.ai/code/session_01PgJ3cRwMrh8UzxzZwraLCT

[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved review comments remain, and all approval-readiness assessments approve the changes.

Review effort: Lite
Findings: None

What changed in this PR

Adds public helpers for detecting open-ended activations and safely retrieving optional end times.

Changes:

• Adds and exports activation_is_open() and activation_end_time().
• Adds unit and integration coverage for presence and epoch-zero behavior.
• Updates documentation, release notes, guidance, and snippet checks.

File	Summary
tests/​unit/​test_machine_config_activation_client.py	Tests helper behavior and edge cases.
tests/​integration/​test_machine_config_client_integration.py	Adds round-trip assertions.
src/​dp_python_lib/​client/​machine_config_client.py	Implements activation helpers.
src/​dp_python_lib/​client/​__init__.py	Exports the helpers.
doc/​release-notes/​NEXT.md	Documents the user-visible change.
doc/​cookbook/​machine-configuration.md	Documents safe activation handling.
CLAUDE.md	Updates project guidance.
.dev/​tools/​check-cookbook-snippets.py	Makes helpers available to snippet checks.

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