* fix(agent): stop the tool-schema ratchet meaning a different thing per host
TestEagerToolSchemaTokenBudget counted exec_command shell guidance along with
the schemas, and that guidance is host-specific. The same tree measured 3498 on
Linux, about 3600 on a Windows host with pwsh 7, and 3653 on Windows PowerShell
5.1, because shellGuidanceForRuntime appends a longer block for 5.1 (it has to
explain that && and || do not work there).
5.1 is stock Windows, and that case has been over the 3650 ceiling since
view_image landed. So `go test ./...` failed for anyone on a stock Windows box
while CI stayed green: the runners have pwsh 7 and take the cheaper branch. The
workflow does run the tests on windows-latest, so this was never a coverage gap,
just a ceiling sized against whichever shell the runner happened to have.
The two halves are now charged separately. The schema ceiling measures the
schemas alone and reads 3498 on Linux and on Windows PowerShell 5.1, so it
ratchets the same thing everywhere. The host guidance gets its own ceiling at
200, above the worst case rather than above this machine: 5.1 is 155 tokens,
pwsh 7 is 110, cmd.exe is 87, POSIX is 0.
No guidance text was trimmed. It is what stops the model writing bash on Windows,
and the 5.1 note is the reason a chained command does not silently do half its
work. Paying 155 tokens for it is the right trade; measuring it as if it were a
schema was not.
HostExecCommandShellGuidance is exported for the budget, which is production
surface added for a test. It is one accessor over existing logic, and the
alternative is a ratchet that cannot tell the two costs apart. A guard in
internal/tools pins that the guidance really is the tail of the description, so
the subtraction cannot silently start measuring the wrong thing.
* test(tools,agent): make the guidance contract checkable off Windows
The ratchet separates the fixed tool schemas from this host's exec_command
shell guidance, and both halves of that separation were only being checked on
Windows.
The description test returned early off Windows once the accessor reported no
guidance, so it never looked at the description. Dropping the GOOS condition in
the constructor would have a POSIX host append its own guidance (about 150
characters on darwin) with the accessor still reporting none and the ratchet
charging every byte of it to the schemas, and nothing would fail. Both the
description and the accessor now take goos, so the contract is checked for all
three platforms from any one of them.
The budget also went from subtracting a separately rounded guidance estimate to
removing the guidance from the description before estimating. ApproxTextTokens
is an integer division, so floor((schema+guidance)/4) - floor(guidance/4) is one
token high whenever the two remainders add past four, and which side of that a
host lands on depends on the length of its guidance. That is the same
host-dependence the ratchet was being fixed for, one token smaller.
No behaviour change: exec_command's description is byte for byte what it was on
every platform.
