test: add unit tests for `main.py`, `tracer.py`, `telemetry/`

[KRRT7]

Parent: #2079

Phase 1 — Small zero-coverage modules

Module	Stmts	Current coverage
main.py	95	0%
tracer.py	268	0%
telemetry/	33	15%

These are small files that should be straightforward to test with mocks for external services (Sentry, PostHog, sys.settrace).

Target

100% coverage for these 3 modules (~396 statements).