react tree prints only "✓ Done" without --json, so agents conclude React introspection is unsupported

Summary

react tree produces no tree at all unless --json is passed. The plain invocation prints ✓ Done and exits 0. Because that is indistinguishable from "this page has no React tree to show", an agent reasonably concludes React introspection does not work on the target app and stops using it.

Version: agent-browser 0.38.0/0.38.1, macOS (darwin arm64).

Reproduce

Against any React app (below: a Next.js pages-router app on localhost:8999):

$ agent-browser open --session demo --enable react-devtools http://localhost:8999/some/page
✓ <page title>

$ agent-browser react tree --session demo
✓ Done          # <- no tree, exit 0

$ agent-browser react tree --session demo --json
{"success":true,"data":{"lifecycle":…,"tree":"# React component tree\n# Columns: depth id parent name …\n0 2985 - Root\n…"}}

The --json form returns 1004 lines covering 81 levels of depth, correctly naming every application component. So the introspection itself works fine; only the default output path is empty.

Why this matters more than a cosmetic gap

Two things compound:

1. data.tree is a preformatted, human-readable string — the exact text a user would want on stdout. So --json is the only way to obtain the non-JSON rendering, which is the inverse of the usual convention and unlikely to be guessed.
2. --enable react-devtools must be set at session launch. An agent that reads ✓ Done as "no React here" has already paid for a relaunch and will not pay again to re-test the same conclusion.

I hit this while measuring how well coding agents can verify their own UI changes in a browser. Of four independent agents given the same instructions, one ran the documented react tree, saw ✓ Done, concluded React introspection was broken on Next.js, and completed its task without it — while a second agent on the sibling SPA found react inspect to be the only way to distinguish "feature flag off" from "component never mounted". The capability was decisive in one case and discarded in another purely on output formatting.

Suggested fix

Print data.tree to stdout when --json is absent. If the empty output is intentional pending a formatter, an explicit hint (use --json to see the tree) would be enough to stop the false negative.