Add rodney discover command for listing data-testid elements

[jstockdi]

Add rodney discover — scan pages for testable elements

What this adds

A new rodney discover command that scans the current page for elements with a test attribute (default: data-testid) and outputs them grouped by type with suggested rodney commands. This makes it easy to explore an unfamiliar page and quickly build automation scripts.

rodney open https://example.com
rodney discover              # scan for data-testid elements
rodney discover --json       # machine-readable output
rodney discover --attr data-cy  # use a custom attribute

Example output

Page: https://example.com/dashboard

Readable:
  heading                All systems operational              rodney text '[data-testid="heading"]'
  results-table          Name, Status (2 rows)                rodney text '[data-testid="results-table"]'

Interactive:
  search                 Search...                            rodney input '[data-testid="search"]' "<text>"
  submit-btn             Submit                               rodney click '[data-testid="submit-btn"]'
  filter                 All, Active                          rodney select '[data-testid="filter"]' "<value>"

Hidden:
  hidden-el              Hidden content                       rodney text '[data-testid="hidden-el"]'

Why

When automating against an app that uses data-testid (or data-cy, data-test, etc.), the first step is usually figuring out what elements are available. Today you'd need to open DevTools or pipe rodney html through grep. rodney discover makes this a single command that also suggests the exact rodney commands to interact with each element.

This is especially useful when rodney is used by AI agents or in scripted workflows where the page structure isn't known in advance.

Implementation

• queryDiscoverEntries(page, attrName) — runs a JS query on the page, classifies each element by tag/type (button→click, input→input, select→select, a→click, table→text, etc.), and returns structured discoverEntry results
• formatDiscoverText(entries, attrName, pageURL) — groups entries into Readable/Interactive/Hidden and formats with suggested commands
• cmdDiscover — wires up --json and --attr flags, delegates to the above functions

Tests

13 new tests covering:

• Element detection across all supported types (button, input, textarea, link, select, table)
• Hidden element visibility detection
• Custom attribute via --attr
• Empty page (no matches)
• Text output grouping and suggested commands
• JSON round-trip serialization

All 75 tests pass (62 existing + 13 new).