Test files in packages/codev are never typechecked — a signature change cannot break a test caller visibly

[pseudoseed]

packages/codev/tsconfig.json is the only tsconfig in the package, and it excludes tests:

"include": ["src/**/*"],
"exclude": ["node_modules", "dist", "**/__tests__/**"]

build is … && tsc && …. There is no second config and no noEmit pass. So no test file in
packages/codev has ever been typechecked.

Why that matters more than it sounds

A change to a function's signature is invisible to tsc at every test call site. The compiler
cannot tell you which test callers you broke, and "typecheck clean" is a true statement that checks
nothing about them.

Measured today. bugfix-196 changed heldRecoveryKeystroke(action) to
heldRecoveryKeystroke(action, clearDraft). A helper introduced by #203 still called it with one
argument, so clearDraft was undefined, CLEAR_DRAFT_BYTES[undefined] was undefined, and the
fake session was written the string undefined instead of \x03.

It surfaced at runtime, in one test, and only because that test happened to exist:

FAIL pty-session-geometry.test.ts > POSITIVE CONTROL: the harness DOES record a keystroke when one is sent
 expected [ undefined ] to deeply equal [ '\x03' ]

That positive control was added during #203's review for an unrelated reason — so that the
neighbouring expect(writes).toEqual([]) assertions could not pass on a harness that observes
nothing. It caught a real break in the harness itself, which is exactly the case it was written for,
and it is the only reason this was found before merge.

Two contributing errors the builder named, both worth recording because they are the normal way this
stays hidden:

• It grepped tsc output for filenames matching the modules it had touched.
  pty-session-geometry matched none of them, so even a real error would have been filtered out.
• It had fixed some callers by hand earlier and they worked, which made it believe the compiler was
  watching. It was not; it had simply been careful in the file it was already editing.

Do not "fix" this by deleting the exclude line

The exclude is there for a reason: include is src/**/* and tsc emits, so removing the
exclusion would compile test files into dist/. That is worse than the current state.

The fix is a separate noEmit pass:

1. Add packages/codev/tsconfig.test.json extending the base, "noEmit": true, with __tests__
   included.
2. Add a typecheck script that runs it, and run it in CI alongside the build.
3. Leave tsconfig.json and the build script untouched.

Worth checking whether the other packages have the same shape before fixing only this one.

The general form

"Typecheck clean" was reported honestly all session and was never false. It simply did not cover the
files it appeared to cover, and nothing in the output said so — a check reporting a value about a
scope it does not include. See #199.

Related: #199, #203 (the positive control that caught it), #205 (where it surfaced).

[pseudoseed]

This is no longer hypothetical — there is a type error sitting in the repo right now

Found by bugfix-214 while working on an unrelated pre-publish scrub:

packages/codev/src/__tests__/spec-146-t3-contract.test.ts:323

const noInterpreterEnv = { ...process.env, T3CODE_ROOT: checkout };
delete noInterpreterEnv.T3_NODE;

A delete on a property of a spread of process.env. It has been in the tree undetected, because
packages/codev/tsconfig.json excludes **/__tests__/** and vitest does not type-check.

Reported by the builder, not independently reproduced by me — confirming it requires the very
config this issue asks for. Recording it with that caveat rather than asserting it.

Why it matters for this issue's priority

The issue as filed argued from a mechanism: a signature change cannot break a test caller visibly.
That was demonstrated once, by a runtime failure that a positive control happened to catch.

This is different. It is a standing error, in the tree today, that nothing will ever surface —
not a green run, not CI, not a reviewer. It was found only because someone happened to point a
compiler at a file the build never compiles.

So the question this issue answers is not "could errors hide here" but "how many are hiding here
now", and nobody can answer that until the noEmit pass exists. The count is unknown by
construction.

Unchanged

The fix is still a separate tsconfig.test.json with noEmit, run as its own script in CI —
not deleting the exclude line, since include is src/**/* and tsc emits, so that would
compile test files into dist/.

Worth running the new pass once and publishing the count before fixing anything, so the scale is on
the record rather than discovered one file at a time.