docs(tools): name the boundary that rejects a padded integer, and what the flavor-guard test actually reads

pyScalar's docstring attributed the rejection of a String-spelled
beyond-safe-range integer to "the Python runtime". No published backend
makes that call on this base. The fact that does not depend on one: the
padded digits name an integer no double holds, and passing it back would
have to cross the argument boundary as a JSON number. Say that, and say
why String rounds at all -- Number::toString is shortest round-trip, so
2 ** 60 emits the 16 digits that re-read to the same double and pads.
Mirror both in the test comment.

The note's Decision sentence said a test covers the flavor guard through
ctx.tools.schemas(). The test reads the definition's getter directly,
under a language absent from both tables; schemas() reaches the same
getter but has no assertion. Name what is read, and record that a
renderer-without-flavor language is drift this guards against rather
than an existing input -- the two key sets are identical today.

packages/core/tools/src/py-types.ts

@@ -259,11 +259,14 @@ function childClassName(base: string, segment: string): string {
  * `String`: Python integers are arbitrary-precision, so the emitted digits ARE
  * the value the model programs against, and `String` gives a different integer
  * than the double holds (`2 ** 60` prints the rounded `...847000`, not the
- * exact `...846976`) or no integer literal at all (`1e21` prints `1e+21`). The
- * Python runtime then rejects the advertised literal as not exactly
- * representable as a JavaScript number, so the SDK would document a value no
- * program can pass. The TS flavor needs no counterpart: its literal is re-read
- * by a JS parser back into the same double.
+ * exact `...846976`) or no integer literal at all (`1e21` prints `1e+21`).
+ * `String`'s rounding is not a bug in it: `Number::toString` is shortest
+ * round-trip, so it emits the 16 digits that re-read to the same double and
+ * pads with zeros, and those padded digits name an integer no double holds.
+ * Passing one back would have to cross the argument boundary as a JSON number
+ * — a double again — so the SDK would document a value no program can pass.
+ * The TS flavor needs no counterpart: its literal is re-read by a JS parser
+ * back into the same double.
  *
  * `JSON.stringify` is also what keeps this path's output parseable, and it is
  * the only thing that does. It covers both classes of hazard: the two kinds of