An "unknown"/empty node_name silently produced evt-unknown-* event files. One
landed in events/piha/ and, being lexically greater than every evt-piha-* name,
pinned the observer's (then lexical) checkpoint and blocked PIHA for ~34 days.
Defense in depth, two layers, both refuse rather than emit poison:
- config.py: node_name field_validator rejects ""/"unknown" (case-insensitive,
trimmed); validate_default=True so the "unknown" default itself is rejected
when NODE_NAME never reaches the process. main() catches ValidationError and
exits 1 with a clear FATAL message instead of a raw traceback.
- event_emitter.py: EventEmitter.__init__ guards node_name at the exact poison
site (node_name is embedded in the filename), so no future call path can
reintroduce evt-unknown-*.
Precedence unchanged and correct: Settings.load() uses os.environ.setdefault, so
env NODE_NAME wins over YAML; YAML only supplies node_name when env is absent.
api.py never writes event files (only /health, /trigger), so its _node_name
global cannot produce poison — verified, left as-is.
Tests (services/ha-diag-agent/tests/): new test_config.py (env load, env>YAML
precedence, fail-fast on unknown/empty/whitespace/default/YAML-unknown) and
EventEmitter guard tests. Full unit suite: 139 passed, 0 regressions.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
