fix(ui): always show Full Report link when runId exists in session history

[toanalien]

Summary

• Fix "Full Report" link disappearing when loading sessions from a different browser or remote device
• loadSessionMessages and SSE handler now always render the run_complete card when runId exists in message metadata, even if api.getRun() fails (auth error, 404, network issue)
• Improve RunDetail error page with diagnostic hints (API auth, run directory) and a back button

Root Cause

When reloading a session from history, if metrics was missing from message metadata, the code called api.getRun(runId) to fetch run data. If that call failed (common for remote/cross-browser access due to auth), the error was silently caught and the card was never added — so the "Full Report" link disappeared entirely. The original browser still showed it because the card was cached in Zustand's in-memory store from the live SSE session.

Test plan

• Open a session with completed backtest runs in the original browser — verify "Full Report" link still appears with metrics/chart
• Open the same session in a new browser (or incognito) — verify "Full Report" link now appears
• Click "Full Report" when run data is available — verify RunDetail page loads normally
• Click "Full Report" when run data is unavailable — verify improved error page with hints and back button
• cd frontend && npx vite build passes

[warren618]

Thanks for the fix — the root cause is real and the RunDetail not-found diagnostic page is a nice improvement. But the "always render the card when runId exists" approach is too broad and introduces a regression. Requesting changes before merge.

The regression

Every assistant turn carries a run_id, not just backtests. In service.py, every agent.run() creates a run directory (loop.py state_store.create_run_dir), and the reply metadata gets run_id whenever a run dir exists:

# session/service.py
if attempt.run_dir:
    reply_metadata["run_id"] = Path(attempt.run_dir).name

There is no separate lightweight chat path — a plain conversational answer also gets a run_id. Verified end-to-end against a local server:

# sent: "what is a moving average? answer in one sentence, do not run any backtest"
assistant metadata: {"run_id": "20260530_062432_41_d7d2d9", "status": "completed"}  # run_id present, no metrics
getRun(run_id) -> status=success, metrics=None, equity_curve=None, artifacts=[]
isReportWorthyRun(...) === false

On main, the else branch (if (isReportWorthyRun)) and the SSE branch (if (hasReport || shadowId)) correctly skip the card for these turns. With this PR, every plain chat answer now renders a spurious "Full Report →" link, and clicking it lands on a RunDetail page with no metrics / chart / trades.

The case worth preserving

The genuine bug is narrower: a run that is report-worthy but has no metrics in metadata (e.g. a Pine-only or equity-curve-only run). Metrics-bearing backtests already render from metadata alone (first branch, no getRun, so they're fine cross-browser). The link only disappears cross-browser when getRun fails (401/404/network) and we can't confirm report-worthiness.

Suggested fix

Only fall back to a bare card when getRun actually throws — i.e. distinguish "succeeded but not report-worthy" (plain chat → render nothing) from "couldn't fetch" (unknown → show the link):

let fetchedMetrics, fetchedCurve, runUnavailable = false;
try {
  const runData = await api.getRun(runId);
  if (isReportWorthyRun(runData)) {
    fetchedMetrics = runData.metrics;
    fetchedCurve = runData.equity_curve?.map(e => ({ time: e.time, equity: Number(e.equity) }));
  } else {
    // succeeded but not report-worthy (plain chat) -> no card
    continue; // or skip the addMessage in the SSE path
  }
} catch {
  runUnavailable = true; // can't tell -> still show the link
}
// push run_complete card only when we have data OR the run couldn't be fetched

This keeps the cross-browser fix (auth failure → catch → link still shows) without putting a "Full Report" link under every conversational reply. The RunDetail.tsx changes are good as-is.