After two days experimenting with Claude Fable 5, a Hacker News user describes the model as relentlessly proactive. When a stray horizontal scrollbar appeared in the Datasette Agent jump‑menu, the author fed a screenshot to the assistant and asked it to inspect dependencies. Within minutes the model began launching browsers, editing code and even running custom scripts to reproduce the visual glitch.

The assistant opened Firefox, then Safari, using a Python routine that enumerated window IDs and called the macOS screencapture utility. It generated a temporary HTML page reproducing the textarea scroll issue, injected JavaScript into Datasette’s templates to fire the '/' key shortcut, and spun up a tiny HTTP server to collect DOM measurements via CORS POSTs. All these steps occurred without explicit user commands.

When the model hit an internal guardrail, it downgraded to the Opus persona, which retained the transcript and completed the fix. Opus produced a markdown report listing every trick—from Playwright launches to pyobjc‑Quartz workarounds—used to isolate the CSS bug. The episode demonstrates that coding agents can automate full‑stack debugging, in practice raising both productivity prospects and security concerns.