**U9, PR7.** One test file, +15 lines, no production change.
## Two safety tests that could never pass
`reviewer.test.ts`'s `vi.mock("../pi.js")` is missing
`wrapToolsWithOutputBudget`, which `wrapCustomToolsForPluginRuntime`
(`agent-session-helpers.ts:104`) calls as the outermost tool wrapper.
Both test-mode-forcing cases therefore threw:
```
No "wrapToolsWithOutputBudget" export is defined on the "../pi.js" mock
```
They have been **permanently red on main** — dead enforcement on the
invariant that **testMode never issues real AI calls**.
`reviewer.test.ts`: 83 passed | 2 failed → **85 passed**.
Found while characterizing the reviewer lane for U9: they surfaced as
pre-existing baseline failures under an unrelated mutation run. This is
exactly why the delta harness records a baseline — under the old
absolute-count method these two would have been silently credited to
whatever mutation was running.
**Not a product bug.** testMode forcing works correctly; its guard did
not.
## Verified the revived tests actually guard something
A dead test can also be a vacuous one, so passing again is not
sufficient evidence. Mutating `isTestModeActive` in
`model-resolution.ts` to ignore `settings.testMode` fails **exactly
these two** (`NEW-failures=2`). Both assert
`expect(mockedCreateFnAgent).not.toHaveBeenCalled()` — no live agent
spawn.
## Why the existing gate didn't catch it
`pnpm check:mock-completeness` runs in the merge gate and passes. It
inspects only the `@fusion/engine` and `@fusion/dashboard` **barrels**,
under `cli/` and `dashboard/` test dirs — never a relative intra-package
mock like `"../pi.js"`. So the whole class of engine-internal mock drift
is outside it.
**Deliberately not fixed here.** Extending the checker is its own change
and I want the violation count measured before proposing it, rather than
opening a PR that turns out to touch dozens of files. That's the next
PR.
## Also observed, stated rather than buried
Mutating `useMockRuntime` in `agent-session-helpers.ts` produces **no**
failure in this file — the reviewer path routes through model resolution
instead. That downstream seam has its own coverage question which I have
not answered; flagging it rather than implying this PR closes it.
## Scope note
This was initially committed onto #2541's branch. I split it onto its
own branch so each PR stays independently revertable — #2541 is now one
commit (the FN-7720 verdict assertion) and this is one commit.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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