upload command does not accept accessibility tree refs (fill/click do)

[pleasedodisturb]

Description

The upload command rejects accessibility tree refs (e29) that fill and click accept. It only works with CSS selectors. This is an API inconsistency — users expect refs from snapshot output to work uniformly across all commands.

Reproduction

# Take a snapshot to get refs
agent-browser snapshot
# Output includes: button "Attach" [ref=e29]

# These work with refs:
agent-browser fill 'e26' 'Jane'          # ✓
agent-browser click 'e3'                  # ✓

# This works with CSS selector:
agent-browser upload 'input[type="file"]' resume.pdf  # ✓

# This fails with ref:
agent-browser upload 'e29' resume.pdf     # ✗ "Element not found"

Expected Behavior

upload 'e29' resume.pdf should resolve the ref to the underlying <input type="file"> element, same as fill and click resolve their refs.

Environment

• agent-browser v0.23.4 (Homebrew)
• macOS Darwin 25.4.0 (Apple Silicon)
• Target page: Greenhouse job application form (job-boards.greenhouse.io)

Context

Found during a web agent comparison benchmark testing 5 browser automation tools against real job application flows. agent-browser performed well overall (7.6/10) — this was the only API inconsistency found.