ci(server): hold unmeasured methods and only SQL errors to the probe baseline

The Postgres probe only ratcheted the methods it managed to call. A method
it could not build arguments for, one that threw before its first
statement and one that timed out were counted and logged but held to
nothing, so a new repository method with a callback parameter could land
SQLite-only SQL unseen, and the part of the code the probe reaches could
shrink without anyone noticing.

pg-probe-baseline.json gains an `uncovered` list of those methods. A
method outside it that goes unmeasured fails the run, and so does an
entry whose method is measured now or gone, so the list only shrinks.
It is seeded from the same first measurement as `failing`; a baseline
without the key reads as unmeasured.

The failing count also counted every refusal, including data errors the
sample values cause (a "probe" string in a date column, SQLSTATE 22007),
so renaming a parameter could fail the gate on a change that never
touched the SQL. Only classes 42 and 0A count now; the rest is reported
in the log and the step summary without being held.

The docs said the probe measures every repository statement. They now
say it measures what each method reaches with sample arguments against
empty tables, and that the methods it cannot reach are held to the list.

.github/workflows/test.yml

@@ -20,8 +20,8 @@ permissions:
 #     gates cleared in preflight, they can only fail because tests failed.
 #     client-e2e drives the real app in Chromium and WebKit, client-bundle
 #     builds the client and checks each map engine keeps a chunk of its own,
-#     and postgres-probe runs the dialect helpers and every repository
-#     statement against a Postgres service. None of them feeds the scan.
+#     and postgres-probe runs the dialect helpers and the repository
+#     statements it reaches against a Postgres service. None of them feeds the scan.
 #   - Scan `needs:` exactly the four coverage jobs. A coverage job failing
 #     must stop the scan — a missing lcov file would make every line of that
 #     package report as uncovered, and the dashboard would show a collapse
@@ -529,9 +529,10 @@ jobs:
   # Postgres it derives a schema from the entities, runs every dialect helper
   # on SQLite and Postgres (every case must pass), and calls every public
   # repository method once, each statement in its own rolled-back transaction.
-  # The statements Postgres refuses are held per method to
-  # server/scripts/pg-probe-baseline.json, which may only shrink; an unmeasured
-  # baseline (failing: null) or a run that called no method fails. The measured
+  # The statements Postgres refuses as SQL are held per method to
+  # server/scripts/pg-probe-baseline.json, and so is the list of methods it
+  # could not measure (uncovered); both may only shrink. An unmeasured
+  # baseline (failing or uncovered null) or a run that called no method fails. The measured
   # baseline and the full report are uploaded either way, so the first run's
   # artifact seeds the file and a change that fixes a statement can lower it
   # without a local Postgres.