tests(cli): add test coverage for jj run stub command

[RajPabnani03]

Summary

• Adds cli/tests/test_run_command.rs with 6 tests covering the jj run stub command
• Registers mod test_run_command in runner.rs in correct alphabetical order

Background

jj run is a stub command that unconditionally returns "This is a stub, do not use" after
performing argument parsing and revision resolution. It had zero test coverage, identified
during a broader test-coverage audit of the codebase.

Tests added

Test	What it verifies
test_run_is_stub	Baseline: stub error is returned for a valid in-repo invocation
test_run_accepts_jobs_flag	--jobs N / -j N are parsed without a spurious pre-stub error
test_run_accepts_revset_flag	-r @ resolves the revset before the stub is reached
test_run_accepts_hidden_x_flag	Hidden -x compat flag (mirrors git rebase -x) is silently accepted
test_run_outside_repo	workspace_helper check fires before the stub — returns "no jj repo" error
test_run_invalid_revset	A bad revset returns a parse error, not the stub error, proving resolution runs first

Why test a stub?

1. Regression guard — any future wiring of real implementation code must update these
   tests, making the activation visible in review rather than silently activating.
2. CLI contract — the flags (--jobs, --revisions, -x) and their accepted values
   are part of the public CLI surface even before the command is implemented.
3. Repo requirement — confirms workspace_helper takes priority over the stub for
   out-of-repo invocations.

Test plan

• All 6 new tests pass: cargo test --package jj-cli --test runner test_run
• test_no_forgotten_test_files guard passes
• No regressions in existing tests

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[martinvonz]

I'm sorry, but I don't think we need tests for a stub command. I'm very tempted to close this.

[PhilipMetzger]

I'm sorry, but I don't think we need tests for a stub command. I'm very tempted to close this.

It being mostly AI generated also is something you should consider in this.

[martinvonz]

I'm fine with it being AI generated as long as the quality is good and the author doesn't just throw it over the wall and waste the reviewer's time by having the reviewer find all the problems the author should have found before sending it. That's basically what the proposed policy in #8897 says.

[martinvonz]

@RajPabnani03: I just realized that my comment above could have been interpreted as being directed at you, so I wanted to clarify that it wasn't. I have only spent a few seconds looking at the code, so I couldn't say if it was well written. I think it's just not time for tests of the jj run command at this point regardless of how well-written they are.