fix(scripts): require --actor, the way --files is required

[os-elon]

Fixes#116

What changed

check-translation-ownership.mjs documented --actor LOGIN as part of its invocation but
defaulted the value to the empty string and judged the PR anyway. An empty actor can never
equal a non-empty TRANSLATION_BOT_LOGIN, so isBot was false and a translation-account PR
invoked without the flag was rejected as hand-written — a confident verdict reached with the
discriminator the whole check rests on absent, and nothing saying so.

--actor is now required unconditionally, exactly the way --files is: same UsageError
class from #117, same usage block, no stack, exit 1. Declared, therefore enforced — one usage
convention for the whole file.

This is the governing ruling on the card: the triage adjudication (option 1), issue comment
5331667901. It answers a malformed invocation and nothing else. What the check means for
a well-formed call while TRANSLATION_BOT_LOGIN is unset — the inert report-and-pass path — is
the subject of #68 and is not addressed here; rows 01-03 and 09-14 of the matrix below pin it
byte for byte.

The transcript below is verbatim except for one thing: GitHub strips an angle bracket followed
by a letter from stored bodies (measured on an earlier revision of this description, which lost
every placeholder inside this very code fence), so each placeholder here carries a space the
script does not print.

✗ --actor < login> is required
usage: node .github/scripts/check-translation-ownership.mjs --actor < login> --files < path>
--actor < login> PR author login (workflows pass github.event.pull_request.user.login)
--files < path> file listing one changed path per line (git diff --name-only)

Argument validation runs before the list file is read, so a call that is wrong in two ways
reports the missing --actor rather than the unreadable path.

Declared second change: the unguarded ENOENT

Authorised on dispatch as a rider, same species and named in the card's tail: a --files path
that does not exist died with a raw seven-line ENOENT stack, which reads as "this script is
broken" rather than "I called it wrong". It is now the same usage failure as omitting --files.
The catch is narrowed to error.code === 'ENOENT' — every other way the read can fail (a
directory, a permission error) still rethrows and keeps its stack — and the UsageError doc
comment was corrected to match, since it previously promised a stack for "an unreadable list
file", which now means a file that exists but cannot be read.

Invocation matrix, before and after

25 invocation shapes recorded against 69204ab and against this branch, then compared block by
block (env spelling, argv, exit status, stdout, stderr). 13 byte-identical, 12 changed — and
every changed row is either the defect, the intended requirement, or the rider.

Unchanged — the invariant set, including every shape the real caller produces:

#	env	argv	before	after
01-03	unset	actor + files (human clean / human artifacts / bot mixed)	0	0, identical
09	transbot	human, clean	0	0, identical
10	transbot	human, artifacts	1	1, identical
11	transbot	bot, artifacts only	0	0, identical
12	transbot	bot, mixed	1	1, identical
13	transbot	bot, login case-flipped	0	0, identical
14	transbot	--actor=…--files=… equals form	0	0, identical
19-21	unset / transbot	no --files at all	1	1, identical (usage block is unchanged from #117)
25	transbot	relative --files (the translations.yml shape)	1	1, identical

Intended change — a missing or empty actor is now a usage failure everywhere:

#	env	argv	before	after
04-05	unset	no --actor, clean / artifacts	0, inert pass	1, usage error
06	unset	empty --actor, artifacts	0, inert pass	1, usage error
07-08	empty / all-blank	no --actor, clean	0, inert pass	1, usage error
15	transbot	no --actor, artifacts	1, wrong reason	1, usage error
16	transbot	no --actor, clean	0, silent	1, usage error
17	transbot	empty --actor, clean	0, silent	1, usage error
18	transbot	blank --actor, artifacts	1, wrong reason	1, usage error

Rider:

#	env	argv	before	after
22-23	unset / transbot	--files nonexistent	1, ENOENT stack	1, usage error
24	transbot	no --actorand nonexistent --files	1, ENOENT stack	1, missing-actor usage error

Rows 04-08 are the behaviour change the ruling asks for: an invocation that omits the
documented discriminator now says so instead of returning a verdict. The one thing that had to
survive did: the only real caller, .github/workflows/translations.yml:48, always passes
--actor, and every shape it produces (rows 09-14, plus row 25 for its relative --files
path) is byte-identical before and after. Rows 07-08 also record that TRANSLATION_BOT_LOGIN
set to the empty string or to whitespace still behaves as unset, unchanged by this PR.

Gates

All on Node 22.22.2, matching CI, at commit 1778d4a:

• pnpm install --frozen-lockfile — 0
• pnpm turbo run type-check --continue --force — 0
• pnpm turbo run build --force — 0
• pnpm turbo run test --force — 0 (includes the self-test runner)
• node .github/scripts/check-translations.mjs — 0
• node .github/scripts/check-translation-output.mjs --self-test — 0
• node .github/scripts/check-translation-output.mjs --files on this PR's changed list — 0
• the ownership script itself on this PR's own changed list, both paths — 0 and 0
• the workflow's own invocation shape reproduced verbatim (relative --files, actor passed) — 0

No changeset: this repo does not use them.

---

Generated by Claude Code