bug(cli): wrong exit code on too many args for review submit and preview

[DS123-ally]

I'd like to work on this — planning a small CLI-only fix.

Scope: backend/internal/cli/ only — wrap arg-count validators for ao review submit and ao preview (including ao preview clear) so misuse returns usageError and exits 2, matching AGENTS.md and the rest of the CLI.

Approach:

• Add/reuse an atMostOneArg helper (same pattern as noArgs in root.go)
• Wire it into review submit and preview
• Use noArgs for preview clear instead of bare cobra.NoArgs
• Add table tests asserting exit code 2 for too-many-args cases

No daemon/API/OpenAPI changes. I'll open a PR once tests pass locally.

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## Issue description (full body)

### Summary

`AGENTS.md` documents a CLI convention: **usage errors exit 2; runtime/daemon failures exit 1**. Two commands break that convention for **argument-count misuse** — they exit **1** instead of **2** when too many positional args are passed.

Affected commands:

- `ao review submit`
- `ao preview`
- `ao preview clear`

### Expected behavior

When a user passes the wrong number of positional arguments, the process should exit **2** (usage error), consistent with other commands like `ao session get`, `ao completion`, and `ao project add`.

### Actual behavior

Passing too many args exits **1** (generic failure), which misleads scripts and wrappers that distinguish usage misuse from daemon/runtime errors.

### Reproduction

```bash
$ ao review submit mer-1 mer-2
Error: accepts at most 1 arg(s), received 2
$ echo $?
1   # expected 2

$ ao preview http://localhost:5173 extra
Error: accepts at most 1 arg(s), received 2
$ echo $?
1   # expected 2

$ ao preview clear extra
Error: unknown command "extra" for "ao preview clear"
# (or similar arg-count error — should exit 2, not 1)
$ echo $?
1   # expected 2

Root cause

In backend/internal/cli/:

File	Current validator
review.go	Args: cobra.MaximumNArgs(1) on review submit
preview.go	Args: cobra.MaximumNArgs(1) on preview
preview.go	Args: cobra.NoArgs on preview clear

Cobra's built-in arg validators return plain errors.New(...). The root command's SetFlagErrorFunc only wraps flag parse errors as usageError, not Args validation errors. So arg-count failures are not recognized as usage errors and ExitCode() returns 1.

Other commands already follow the correct pattern — they wrap Cobra validators so misuse becomes usageError:

• noArgs in root.go (used by ao start, ao stop, etc.)
• oneSessionIDArg, sessionRenameArgs in session.go
• Inline wrappers in project.go, completion.go

Existing tests for these commands already assert exit 2 for other usage errors (e.g. TestReviewSubmitMissingVerdictIsUsageError, TestPreview_MissingSessionIDIsUsageError), but no test covers arg-count misuse for review/preview.

Proposed fix (CLI-only)

1. Add a shared helper in root.go:

   func atMostOneArg(cmd *cobra.Command, args []string) error {
       if err := cobra.MaximumNArgs(1)(cmd, args); err != nil {
           return usageError{err}
       }
       return nil
   }

2. Use atMostOneArg for review submit and preview.

3. Use existing noArgs for preview clear instead of cobra.NoArgs.

4. Add tests:

   • TestReviewSubmitTooManyArgsIsUsageError
   • TestPreview_TooManyArgsIsUsageError
   • TestPreviewClear_TooManyArgsIsUsageError

Out of scope

• No daemon, HTTP, SQLite, or OpenAPI changes
• No new CLI commands or flags
• No changes to flag-validation paths (those already work)

Test plan

cd backend
go test ./internal/cli/ -run 'TestReviewSubmit|TestPreview' -count=1
go test ./internal/cli/ -count=1

Manual smoke:

ao review submit a b; echo $?    # should print 2
ao preview a b; echo $?          # should print 2
ao preview clear x; echo $?      # should print 2

References

• Contributor convention: AGENTS.md — "Return usage errors as usageError so CLI misuse exits 2"
• Exit code mapping: backend/internal/cli/root.go — usageError + ExitCode()
• Prior art: noArgs, oneSessionIDArg, completion.go arg wrapper

---

Files to change

File	Change
backend/internal/cli/root.go	Add atMostOneArg helper
backend/internal/cli/review.go	Args: atMostOneArg on review submit
backend/internal/cli/preview.go	Args: atMostOneArg on preview; Args: noArgs on preview clear
backend/internal/cli/review_test.go	TestReviewSubmitTooManyArgsIsUsageError
backend/internal/cli/preview_test.go	TestPreview_TooManyArgsIsUsageError, TestPreviewClear_TooManyArgsIsUsageError

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[DS123-ally]

I want to Work on this issue can you assign to me