Report prescan errors on their source lines

Reviewed-on: #42

.gitea/workflows/ci.yaml

@@ -17,7 +17,7 @@ jobs:
           # Not recursive, deliberately. The top-level build needs
           # deps/libakerror and deps/libakstdlib, via add_subdirectory, and
           # nothing else: the golden corpus and the Commodore font now live in
-          # this repository (tests/reference/ and assets/fonts/), so
+          # this repository (tests/language/ and assets/fonts/), so
           # deps/basicinterpret is no longer a build dependency at all.
           # It does *not* need deps/libakgl, which is guarded behind
           # AKBASIC_WITH_AKGL and defaults OFF -- and recursing into it would
@@ -26,19 +26,45 @@ jobs:
           # skipped for the same reason: our CMakeLists declares akerror::akerror
           # first and libakstdlib guards on if(NOT TARGET ...).
           submodules: true
+      # moreutils is load-bearing, not incidental: it supplies errno(1), which
+      # deps/libakerror/scripts/generrno.sh shells out to at build time to
+      # generate its errno name table and to stamp AKERR_LAST_ERRNO_VALUE into
+      # the generated akerror.h.
+      #
+      # Its absence does not fail the build, which is what made this expensive to
+      # find. The script prints "errno: command not found" twice, emits an empty
+      # akerr_init_errno() so no errno ever gets a name, and substitutes an empty
+      # AKERR_LAST_ERRNO_VALUE -- so every code in libakerror's reserved band
+      # collapses from (134 + n) to ( + n), i.e. to n. AKERR_OUTOFBOUNDS is
+      # (AKERR_LAST_ERRNO_VALUE + 2), so it becomes literally 2, and ERR(2)
+      # answers "Out Of Bounds Error" where ENOENT's "No such file or directory"
+      # belongs. That is the docs_examples failure at docs/15-error-codes.md:105
+      # that this job carried on every run since #2.
       - name: dependencies
         run: |
           sudo apt-get update -y
-          sudo apt-get install -y cmake gcc
+          sudo apt-get install -y cmake gcc moreutils
+      # --parallel 2 rather than a bare --parallel, and that bound is measured
+      # rather than cautious. All five jobs in this file say runs-on:
+      # ubuntu-latest and land on the same runner, so a bare --parallel asks for
+      # nproc compilers *per job* and the runner is handed five times that at
+      # once. Run #30 never showed it because akgl_build and coverage were still
+      # dying early; run #31 was the first push on which all five did real work
+      # simultaneously, and the sanitizers job went from a 55-second link phase
+      # to a 14-minute one -- individual `Linking C executable` steps taking two
+      # minutes each, starting at the exact second akgl_build began its SDL tree
+      # -- before the runner's Docker daemon fell over outright and took the job
+      # with it. That is memory exhaustion, and the only lever on it is the
+      # number of concurrent compiler and linker processes. Applied at all four
+      # build sites for the same reason; mutation_test drives its own builds
+      # through the harness and is not bounded here.
       - name: build
         run: |
           cmake -S . -B build
-          cmake --build build --parallel
-      # The suite is 78 cases: 41 golden files byte-compared against the Go
-      # reference's own corpus (checked in at tests/reference/, see its README),
-      # 9 local golden cases for verbs the reference never implemented, 25 unit
-      # tests, 2 embedding examples, and 1 known-failing test that asserts the
-      # *correct* contract for defects carried over from the reference (TODO.md
+          cmake --build build --parallel 2
+      # The suite is 112 cases: 65 language files with sibling expectations,
+      # 43 unit tests, 3 embedding examples, and docs_examples.
+      # Some unit tests assert the *correct* contract for known defects (TODO.md
       # section 6). A green run therefore does not mean defect-free -- see
       # AKBASIC_KNOWN_FAILING_TESTS.
       #
@@ -74,7 +100,7 @@ jobs:
       - name: dependencies
         run: |