v2.18.7 — jsonEsc NUL/control-char fix (field failure: Kubernetes pod names)

v2.18.7 (2026-09-08)

Fix: jsonEsc incomplete — NUL and other control chars not escaped (field failure)

Root cause: jsonEsc() in TemporalIndex.cls and TraversalBFS.cls handled
\, ", and 5 named control chars (BS/TAB/LF/FF/CR) but omitted the other 26
characters in U+0000–U+001F. Kubernetes embeds a NUL byte (\x00, U+0000) as a
C string terminator in process/pod names. Any metric series whose label included
such a name stored the NUL in ^KG("tout") verbatim, then QueryWindow emitted
it into the JSON string — causing json.loads to raise ValueError: Invalid control character and dropping the entire window for that tenant.

Fix: Both jsonEsc implementations now loop over i = 0:1:7, 11, 14:1:31
(the 26 remaining control chars) and emit \uXXXX. The 5 named escapes are kept
as-is for readability.

Downstream note for opsreview: MetricIngest.SeriesTarget should also strip
control characters before storing the series node ID — defense-in-depth so IVG
never receives malformed data regardless of what Kubernetes delivers. The IVG fix
ensures the JSON layer is safe even if bad bytes reach storage.

Regression tests: 2 new tests in tests/integration/test_temporal_json_safety.py
(TestControlCharEscaping): NUL byte round-trip + full 13-char control set.
All 19 JSON safety tests pass.