The main process's own warnings never reach the session log #1960

The gap

docs/architecture/issue-reports.md lists this under Known gaps:

The main process's own warnings, such as a preference file it could not read, still go to the terminal only.

Why it matters

The session log is meant to be "what this run of the app has logged" — every sidecar's output, the renderer's console warnings and errors, and electron-updater's log. Main's own warnings are the one source missing, and a packaged app has no terminal for them to go to instead, so they go nowhere at all.

These are exactly the lines that explain a puzzling report. A window that opens in the wrong place, a theme that reverts to system every launch, an interface that ignores the chosen language: each of those has a one-line warning from main saying the preference file could not be read or written, and the user filing the issue will never see it and never send it.

Where

• surfsense_local/electron/src/main/sidecars/supervisor.ts — the pattern already exists here. Its note() helper writes the line to process.stderr and to sessionLog.append(...) in one call. Reuse that shape rather than inventing a logger.
• surfsense_local/electron/src/main/session-log/session-log.ts — sessionLog.append(source, text) already strips colour codes, replaces the home directory with ~, and caps line length, so nothing extra is needed to make these lines safe to paste into a public issue.
• The call sites that write to process.stderr and nowhere else:
  • i18n/locale-prefs.ts
  • window-state.ts
  • theme-prefs.ts
  • index.ts — onSidecarCrash(), and the startup failure near the bottom of the file

Three of those already write [main] at the front of the line by hand, which is what the log's source argument is for.

What done looks like

• A warning main writes appears in Report issue's log, tagged as coming from main, and still appears on the terminal in development.
• One helper, used by every site, rather than a sessionLog.append added beside each process.stderr.write. Two ways to log is how the next one gets missed.
• The startup failure in index.ts fires before any window exists, so it can reach the log but nobody will read it there. Leaving it on stderr alone is a defensible answer; say which you chose.
• Update the The session log bullet in docs/architecture/issue-reports.md, which lists the sources the log carries, and delete the Known gaps line in the same PR.

How to verify

surfsense_local/electron/src/main/session-log/session-log.test.ts covers the log's cleaning rules and is the file to extend. Write the failing test first: call the helper and assert the line is in lines() with its source.

cd surfsense_local/electron
pnpm test
pnpm typecheck

Before you start

Read CONTRIBUTING.md and the issue reports doc. These lines are written by the main process and are never translated — the log is not interface text. Open your PR against dev, not main. Comment here to claim this.