docs(agents): streamline instruction routing (#6358)

.agents/skills/adversarial-validation/references/test-coverage.md

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+# Test-Coverage Lens
+
+- For every behavior claim, name the focused test/check that fails if the
+  changed hunk is reverted. If none is practical, require the reason and
+  residual risk.
+- Confirm tests exercise the real production path and assert returned values,
+  exact bytes, stored state, or the specific error variant—not only success,
+  `is_err()`, or no panic.
+- For new flags/modes, verify each branch and ask which test fails if the branch
+  is inverted.
+- For new error propagation, inject the failure and assert the caller observes
+  it; mentally replacing `?`/`return Err` with success must break a test.
+- Streaming GET tests assert the complete body and length under degraded reads.
+- Disk/wire-format tests use pinned foreign/legacy fixtures; same-code
+  round-trips are insufficient for compatibility.
+- Concurrency tests use readiness polling, isolate global state, and avoid fixed
+  sleeps or unrealistically short timeouts. Use nextest groups when process-level
+  serialization is required.
+- Internal metadata tests assert both RustFS and MinIO keys, not only read-back
+  through a helper that prefers one key.
+- Boundary companions are distinct coverage: `n == max` vs `max + 1`, and
+  absent vs empty vs nil UUID.
+- A focused test proves only the targets/features it builds. Add compilation or
+  Clippy only for uncovered changed targets.