Add CLI prompt for unknown variable descriptions

[Mandyx22]

Summary

• After data processing and metadata options, the CLI now detects user-data variables whose descriptions could not be resolved from plugin source
• Shows an optional gate prompt: users can skip the entire step or fill in descriptions one by one (pressing Enter skips an individual variable)
• Suppressed automatically when all three flags (--psych-ds-dir, --data-dir, --metadata-options) are provided (non-interactive mode)

Test plan

• Run CLI interactively against a data directory — confirm gate prompt appears with correct variable count
• Choose "Fill in descriptions", type a description for one variable, press Enter to skip another — verify dataset_description.json reflects filled-in and "unknown" values correctly
• Choose "Skip" at the gate — verify no per-variable prompts appear and all descriptions remain "unknown"
• Run with all three flags — confirm no prompt appears and CLI completes silently

🤖 Generated with Claude Code

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🦋 Changeset detected

Latest commit: 58ebde8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@jspsych/metadata-cli	Minor

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[jodeleeuw]

🔴 Stale "unknown" value persists after filling in a description

When a user fills in a description via the new prompt, the old "unknown" value isn't removed — the output ends up containing both.

promptUnknownDescriptions calls:

metadata.updateVariable(name, "description", { user: description.trim() });

This routes into VariablesMap.updateDescription, which is append-only by design (it accumulates descriptions across plugins). Tracing a typical user-data variable:

• Its description ends up as e.g. { "default, html-keyboard-response": "unknown" }.
• After fill-in, Object.assign adds the new key without touching the old one → { "default, html-keyboard-response": "unknown", "user": "my desc" }.

So the resulting dataset_description.json contains both the new description and the stale "unknown". The user's input doesn't actually resolve the unknown — it just sits alongside it.

If the intent is for the user value to replace "unknown", clear the existing description first, e.g.:

const variable = metadata.getVariable(name) as any;
variable["description"] = {}; // or delete the unknown-valued keys
metadata.updateVariable(name, "description", { user: description.trim() });

(Worth a comment too, since the append semantics of updateDescription are non-obvious.)

Side effect: because the unknown key survives, the description becomes a mixed map (one "unknown", one real value), so hasUnknownDescription returns false on a re-run (every(v => v === "unknown") is false) and a partially-filled variable won't be re-prompted.