chart/docs/plan_diagnostics_improvements.md

Diagnostic Access Improvements

Goal

Make it practical for an agent on a separate SSH machine to diagnose browser and production failures without granting broad production control or asking the user to paste console output.

Browser Captures

Diagnostic mode (?diag=1) offers Capture diagnostic. Upload and metadata remain authenticated. The PNG URL at /api/debug/captures/{id} is public by its 72-bit id, which is the explicit handoff capability a user shares with an agent.

After inspecting a user-shared capture, the agent must immediately call:

DELETE /api/debug/captures/{id}

The 24-hour expiry and 50-capture cap remain a backstop. Do not inspect capture URLs that the user has not explicitly supplied.

Production Diagnostics

Do not grant an agent a general production shell or Docker-group membership. Docker access is effectively root access, and arbitrary shell access can expose environment variables, OAuth tokens, and mounted volumes.

Instead create a dedicated chart-debug production account with a forced-command SSH wrapper. It accepts only a small, read-oriented command set:

logs --since <duration>
status
container-state
recent-deploy
capture-read <capture-id>
capture-delete <capture-id>

The wrapper must reject arbitrary commands and paths. It should cap output, redact known secret patterns, and log every request. Use a dedicated SSH key that can be revoked without affecting deployment or normal administration.

Expected agent usage:

ssh chart-debug@production logs --since 20m

Observability

Keep browser performance telemetry separate from production access. A future frontend recorder should locally aggregate frame timing, long tasks, tick rate, visible bars, and rendered line/level counts, then periodically upload compact, authenticated summaries. Pair it with server timing for bar handling, level rebuilds, WebSocket serialization, and the existing loop-lag measure.

This separates rendering, feed, transport, and backend pressure without logging prices, drawing text, cursor positions, screenshots, or per-tick event history.