Review of the modern exec wire protocol surfaced defects the committed
suite did not pin.
The Pi bridge dropped frame arguments: `pi_read`'s offset/limit (ranged
reads returned whole files), `pi_grep`'s literal (fixed strings ran as
regexes), and the path/glob join emitted `./`-prefixed specs. These are
`optional int32`, so a present `0` is a value, not "unset" — `limit: 0`
now answers empty rather than reading everything, and `pi_find` clamps
to 1 like the reference client.
The provider synthesized its transcript block from a second, divergent
translation of the same frame, so the displayed operation differed from
the executed one. Both sides now share one mapper in `exec-modern.ts`.
End-of-transport cleanup reparsed every open block's streamed argument
buffer; blocks whose args arrive whole never set that buffer, and
`parseStreamingJson(undefined)` is `{}`, so a truncated turn erased
their arguments.
All fixes are mutation-verified: reverting each one fails a test.
(cherry picked from commit bb7bcfebce4200d436e17d6e39320da13fc85ca8)
