fix: Test suite stability - fix failures, reduce skips, clean warnings

[vybe]

Summary

The test suite has 3 failures, 97 skipped tests, and 289 deprecation warnings. While the 99.9% pass rate indicates platform health, we need to improve test reliability and coverage by fixing configuration issues.

Test Failures (3)

1. Async Task Execution Flakiness

Files: tests/test_parallel_task.py:595, tests/test_parallel_task.py:731
Tests:

• TestAsyncModeExecution::test_async_mode_execution_completes
• TestAsyncModeActivities::test_async_mode_creates_task_activity

Problem: These tests depend on a live Claude Code agent successfully completing a task. When the agent fails (missing API key, out of context, transient Docker issue), both tests fail.

Fix:

• Add pytest.mark.dependency to cascade skip when execution fails
• Consider mocking execution results for unit tests
• Add retry logic or longer polling timeout
• Verify test agent has valid API key in fixture setup

2. Subscription State Leak

File: tests/test_subscriptions.py:528
Test: TestSubscriptionAutoAssign::test_create_agent_no_subscriptions

Problem: Test expects agent to have no subscription, but subscription from prior test is still assigned.

Fix:

• Add explicit clear_agent_subscription call in fixture or test setup
• Ensure module-scoped fixtures don't leak subscription state

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Skipped Tests to Enable (97 total)

Priority 1: Missing Test Environment Config

Category	Count	Fix Required
Agent Server Direct	14	Set TEST_AGENT_NAME env var in test config
Internal API	7	Set INTERNAL_API_SECRET in test environment
Git tests	10	Configure a test agent with git template
SSH access	7	Configure SSH service for test env

Priority 2: Missing Python Packages

Package	Tests Enabled	Command
docker	6 (test_log_archive.py)	pip install docker
markdown-it-py	13 (unit/test_slack_rich_text.py)	pip install markdown-it-py

Priority 3: Test Design Improvements

Category	Count	Action
Public links	4	Require running agent with public URL - consider mocking
Public user memory	9	Same as above
Setup tests	3	Can only run on fresh install - document as expected
Slack integration	3	Mock Slack or configure test workspace
Validation DB	3	Verify VALIDATE-001 tables exist in test DB

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Deprecation Warnings (289)

datetime.utcnow() Deprecation (Python 3.12+)

Replace with datetime.now(datetime.UTC) in:

• src/scheduler/service.py
• src/scheduler/database.py
• src/backend/logging_config.py
• src/backend/services/backlog_service.py
• src/backend/services/ssh_service.py
• tests/scheduler_tests/*.py

Pydantic V2 Deprecations

• Update AgentStatus, Activity, Execution models in src/backend/models.py to use Pydantic V2 config syntax

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Acceptance Criteria

• All 3 test failures resolved
• Skipped test count reduced from 97 to <30 (only tests requiring external services)
• Zero deprecation warnings in test output
• Test suite runs reliably on CI without flaky failures
• Document any intentionally skipped tests with clear skip reasons