[nightshift] fix documentation drift

[marin-ops-agent]

Seed hums, digits drift —
the doc still names a river
the code rerouted.

docs/design/finelog-exact-analytics.md describes Finelog's segment index
family in the present tense, and the implementation moved past it.

The IndexSpec enum listed four variants; it now has six. Document
AdaptiveValueCounts and AdaptiveGroupExtrema, their query families, and the
Schema.grouped_extrema declaration that drives the second one. Adaptive
sections are best-effort: a segment that declines one above its cardinality or
byte budget stays complete, while a missing declared ValueCounts section still
makes the bundle stale.

Value-count substitution no longer requires complete coverage across visible
segments. Contained segments read summaries, boundary and L0 segments keep an
ordinary aggregate, and a final aggregate merges both exactly; grouped extrema
use the same shape under FinelogGroupExtrema.

Correct the training-status projection column list, which was missing
run_id, job_id, and attributes_json, and record that the telemetry schema
now declares fourteen projections rather than one. Mark the benchmark section as
the acceptance run for the original four-method family so its numbers are not
read as current.

The other five docs under docs/design/ were checked against the code in the
same pass. Their file paths, symbols, and config values still resolve, and the
markdown links are intact.

[marin-ops-agent]

🤖 Note on the agentic-lint label: the per-lane review harness could not run in
this runner. ./infra/pre-commit.py --review spawned claude -p for each lane
and every lane exited immediately with Not logged in, so no findings were
produced (logs under /tmp/marin-linter/nightshift-docs-design-drift/).

I ran the infra/lint/ catalog over the branch diff directly instead. The diff
is prose-only in one design doc. The applicable prose rules are
ml-stale-docstring and ml-docstring-contradicts-impl, which this change
fixes rather than introduces. Two wordings were tightened in the follow-up
commit: a not an exception stock contrast and a redundant clause in the
benchmark caveat.

[chatgpt-codex-connector]

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