Add failing tests for #1617: provider unavailability abort missing backoff + misclassification

[prompt-driven-github]

Summary

Adds 7 failing tests across 5 files that detect the two bugs reported in #1617.

Test Files

• tests/test_agentic_checkup_orchestrator.py — backoff sleep test for checkup orchestrator
• tests/test_agentic_bug_orchestrator.py — backoff sleep test for bug orchestrator
• tests/test_agentic_change_orchestrator.py — backoff sleep test for change orchestrator
• tests/test_agentic_e2e_fix_orchestrator.py — backoff sleep test for e2e-fix orchestrator
• tests/test_final_pr_gate.py — 3 tests for _classify_layer1_failure_category returning "provider_unavailable"

Prompt Files

• pdd/prompts/agentic_checkup_orchestrator_python.prompt — updated to require 30s backoff before each consecutive_provider_failures increment
• pdd/prompts/agentic_checkup_python.prompt — updated to specify new "provider_unavailable" failure category

What This PR Contains

• 4 backoff tests (Tests 1–4): Assert time.sleep(30) is called at least 3 times when all steps return "All agent providers failed". Currently call_count == 0 → AssertionError. After fix adds PROVIDER_FAILURE_BACKOFF_SECONDS = 30 and time.sleep(PROVIDER_FAILURE_BACKOFF_SECONDS) before each counter increment, these pass.
• 3 classification tests (Tests 5–7): Assert _classify_layer1_failure_category("Aborting: 3 consecutive steps failed - agent providers unavailable") returns "provider_unavailable" (not "layer1_failed"). Currently falls through to the catch-all "layer1_failed" → AssertionError. After fix adds a new branch, these pass.
• All 7 tests are verified to fail on current code and will pass once the bug is fixed.
• Prompt specs updated to reflect the required behavior.

Root Cause

Bug 1 (pdd/agentic_checkup_orchestrator.py:3283-3298 and 3 siblings): The consecutive_provider_failures counter is incremented immediately on each provider-failure step with no time.sleep(). Three back-to-back steps during a transient provider blip fill the counter and abort permanently with no recovery window.

Bug 2 (pdd/agentic_checkup.py:346-389): The abort string "Aborting: 3 consecutive steps failed - agent providers unavailable" matches no specific branch in _classify_layer1_failure_category and falls through to "layer1_failed" with severity: blocker, making a transient infrastructure outage look like a real PR-level code defect.

Next Steps

1. Add PROVIDER_FAILURE_BACKOFF_SECONDS = 30 and time.sleep(PROVIDER_FAILURE_BACKOFF_SECONDS) before consecutive_provider_failures += 1 in all four orchestrators; add import time to the three missing it
2. Add FINAL_GATE_CATEGORY_PROVIDER_UNAVAILABLE = "provider_unavailable" to pdd/checkup_review_loop.py, import in pdd/agentic_checkup.py, add branch in _classify_layer1_failure_category before the catch-all
3. Verify all 7 generated tests pass
4. Run full test suite for regressions
5. Mark PR ready for review

Fixes #1617

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