Prove the trace wrapper records before trusting an empty trace

The `notools` check reads an absence: it passes when the trace file contains no
compiler, git or brew invocation. A shim directory that never reached PATH
produces exactly the same empty file as an installer that touched nothing, so
the single leg carrying that assertion would stay green no matter what the
installer did. "Verify the simulation actually took effect" only ran for mask
mode, which left the trace leg with nothing checking its own instrumentation.

Call git explicitly after sourcing the environment and require it to appear in
the trace, then truncate the file so the self-test entry does not count against
the install. The call has to be explicit because macOS reaches _has_working_git
only under STUDIO_LOCAL_INSTALL (install.sh:2026), so no consumer leg on that
platform probes git on its own.

.github/workflows/clean-machine-install-ci.yml

@@ -123,6 +123,25 @@ jobs:
           UNSLOTH_CLEAN_ALLOW_WORKING='${{ matrix.allow_working }}' \
             bash .github/scripts/clean-machine-assert.sh absent
 
+      - name: Verify the trace actually records
+        if: matrix.mode == 'trace'
+        run: |
+          # `notools` reads an absence, so a shim dir that never reached PATH is
+          # indistinguishable from an installer that touched nothing, and the one leg
+          # carrying that assertion would pass no matter what the installer did.
+          # Prove the wrapper records before trusting an empty file. macOS never
+          # probes git off the --local path, so this must be an explicit call.
+          set -a; . ./clean-machine.env; set +a
+          [ -n "$UNSLOTH_TOOL_TRACE" ] || { echo "::error::trace mode set no UNSLOTH_TOOL_TRACE"; exit 1; }
+          git --version >/dev/null 2>&1 || true
+          if ! grep -q "^git[[:space:]]" "$UNSLOTH_TOOL_TRACE"; then
+            echo "::error::the trace wrapper did not record a git call, so notools proves nothing"
+            echo "PATH=$PATH"; command -v git; cat "$UNSLOTH_TOOL_TRACE" || true
+            exit 1
+          fi
+          echo "trace wrapper records; clearing the self-test entry"
+          : > "$UNSLOTH_TOOL_TRACE"
+
       - name: Install
         id: install
         env: