chore: TIER-2 READ conductor/code_styleguides/error_handling.md lines 462-540 + §0-§11 (full) before Phase 9
Phase 9 = Patch Phase per Tier 1's spec.md §12 (added 2026-06-20). Tier 1
corrected my Phase 8 completion report: the actual git history of the
tier-2-clone (per the remote-tracking branch at 8f6d044d) showed only
6 wrapper-obliteration commits + 7 failing baseline tests. The user
demanded a real Phase 9 patch that verifies with actual test output,
not claimed counts.
Sections re-read for Phase 9:
- §0 TL;DR (the data-oriented error handling convention)
- §5 Patterns (Nil-Sentinel, Zero-Init, Fail-Early, AND over OR, Error Info)
- §6 Anti-Patterns (the 5 heurstics for INTERNAL_COMPLIANT)
- §7 Boundary Types (3 categories + 'What is NOT a boundary')
- §8 Drain Points (the 5 patterns + 'What is NOT a drain point')
- §9 The Broad-Except Distinction (the classification table)
- §10 Constructors Can Raise
- §11 Re-Raise Patterns (1, 2, 3 + the suspicious re-raise)
- §12 AI Agent Checklist (5 MUST-DO + 7 MUST-NOT-DO + 3 boundary patterns)
Key principle applied to Phase 9: 'logging is NOT a drain' (extended
to 'error dropping is NOT a drain'). A claimed completion without
audit-script exit 0 + actual pytest output is NOT a completion. The
sub-track 2 Phase 12-13 pattern's final lesson: the test runner
script crash hid 6 tiers from the count.
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