docs(llms): setup agents documentation

docs/agent-guides/testing.md

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+# Testing strategy
+
+Use for changed behaviour or tests.
+
+## Layers
+
+### Pure unit
+
+Put detailed business-rule coverage on pure functions. Test public inputs/outputs with Vitest: relevant boundaries, invalid input, ordering, rollover, errors.
+
+Every bug fix needs a regression test that fails before the fix. Prefer behaviour over mocks/implementation assertions.
+
+### Service and state
+
+Use service, DAO, store, or hook tests for orchestration: transitions, transactions, persistence, cache, notifications, external effects.
+
+Do not repeat all pure cases here. Prove delegation and sequencing.
+
+### End-to-end
+
+Reserve Playwright for key journeys and high-risk cross-layer integrations: edit/run rundown, playback, imports, rundown switching, cloud-prefixed navigation.
+
+No E2E for edges already proven in lower layers. Add E2E only when lower layers cannot prove the user-facing integration.
+
+## Compact before handoff
+
+Development harnesses may be broad, repetitive, diagnostic, temporary. Before handoff:
+
+1. Identify distinct required behaviours/regressions.
+2. Keep the smallest readable set that catches them.
+3. Parameterise repetition only when the table reads better.
+4. Remove diagnostic assertions, redundant permutations, temporary fixtures, private-detail coupling.
+5. Keep rare cases that encode real domain rules.
+
+Optimise for future readers, not minimum line count.
+
+## Quality
+
+- Name tests by observable behaviour.
+- Keep setup local/explicit unless a fixture improves comprehension.
+- Avoid arbitrary waits, wall-clock dependence, cross-test state, weak assertions.
+- Prefer realistic typed fixtures over large snapshots or masking casts.
+- Test non-mutation when promised.
+- No tests for trivial type/format changes or framework behaviour Ontime does not own.
+
+## Review prompts
+
+- Business logic directly unit-testable?
+- Test catches the reported bug/regression?
+- Cases distinct, not repeated path?
+- Temporary harness leaked?
+- E2E justified by cross-layer risk?