master does not parse — orphan else: in dispatch.py breaks every ebuild command

[srpatcha]

ebuild/build/dispatch.py on master does not parse. The package cannot be
imported, so no ebuild command runs at all.

$ git show origin/master:ebuild/build/dispatch.py > /tmp/d.py
$ python3 -c "import ast; ast.parse(open('/tmp/d.py').read())"
  File "dispatch.py", line 133
        else:
        ^^^^
SyntaxError: invalid syntax

The line:

128         raise ValueError(
129             f"Unknown build backend '{backend}'. "
130             f"Supported backends: {', '.join(sorted(ALL_BACKENDS))}"
131         )
132
133         else:                        <-- no `if` to attach to
134             raise RuntimeError(
135                 f"BackendDispatcher cannot configure backend '{backend}'. "

An else: with nothing to bind to, immediately after a completed raise.

Cause

Two different designs for the unknown-backend error path — one raising
ValueError, one raising RuntimeError — were each green on their own branch
and squash-merged onto a base that had moved. The merge kept the first raise and
the second's else:, producing a file that no version of the code ever looked
like. Nothing recompiled the result before it became master.

Identical in shape to eos#92, where sync.c ended up referencing original_prio
from one priority-inheritance design and g_blocked_on from another. Same root
cause, different repository.

Impact

Total. dispatch.py is imported by the CLI, so ebuild build, ebuild configure, ebuild info — every command — fails at import. The suite reports
11 failures / 190 passed on master once the file is made parseable by hand;
until then it does not collect.

Why nothing caught it

$ gh api repos/embeddedos-org/ebuild/branches/master/protection
{"checks": null, "reviews": 1, "sigs": false}

required_status_checks is null. Nothing builds or imports the merge result
before it lands. This is the third repository in the organisation with the same
gap — none has a required status check — and the second where it has already
allowed a non-compiling master.

Fixes already open

PR	parses after?
#66	yes — also unifies the two error paths behind one _unknown_backend() helper. Already approved.
#78	yes
#75	no — despite the title. Its dispatch.py still fails at line 133 with the identical error. Its toolchain-flag validation is real and worth keeping, but it does not repair the syntax.

#66 is the one to take: it removes the duplication that caused this rather than
just deleting the stray else:.

The durable fix

Once #66 lands, make the existing workflow a required status check on master.
A PR whose merge result does not import then cannot merge, which is precisely
what did not happen here.

[srpatcha]

master parses again and the suite runs. Verified from a fresh
git clone --depth 1:

dispatch.py parses OK
287 passed, 1 skipped

The orphan else: is gone.

Leaving this open for the same reason as eos#92: the syntax error was the
symptom, and the cause is still in place.

$ gh api repos/embeddedos-org/ebuild/branches/master/protection
{"checks": null, "reviews": 1, "sigs": false}

required_status_checks is null. Nothing imports the package before the merge
lands, which is how a file that does not parse became master in the first
place — every command in the CLI broken, and no gate that would notice.

A required check that does no more than python -c "import ebuild.build.dispatch"
would have caught this exact failure. The suite already runs in CI; making it
required is a settings change, not work.

Worth doing now while the build is green rather than after the next splice.