fix(browser): downgrade non-Error unhandled rejections to warnings

[posthog]

Problem

• A noise $exception issue opened for Non-Error promise rejection captured with value: Object Not Found Matching Id:4, MethodName:update, ParamCount:4 — the well-known artifact of a Microsoft Outlook-family link/email scanner injecting a script that rejects a promise with a plain object. The string exists nowhere in Autter source.
• Zero user impact: a single Chrome/Windows session, a sub-second burst, no recurrence. The only cost is triage attention sitting next to real errors.
• The observed event was captured by posthog-js on the marketing site (autter-website-new, a separate repo) — the direct fix for it (a before_send filter + suppressing the existing issue) lives there and in the PostHog UI, not in this repo. See the report below.
• This repo's SDK has the same class of gap: the browser runtime's unhandledrejection handler reports a non-Error rejection — no stack, no real type — at the default error severity, so customers shipping it will mint spurious first-class issues from injected-script noise too.

Change

• Non-Error promise rejections are now reported as warning instead of error, so they no longer open a first-class error/issue.
• Still captured and visible for debugging; a customer's beforeSend can drop them entirely. Error-typed rejections are unchanged.

  if (isError) {
      e.errorType = reason.name;
      if (reason.stack) e.stack = String(reason.stack).slice(0, 32000);
+ } else {
+     // no stack, no meaningful type — almost always injected 3rd-party
+     // scripts, not a real app fault. Warn, don't raise a first-class issue.
+     e.severity = "warning";
  }

The ingester already honors an SDK-supplied severity (asSeverity in normalize-browser.ts), so warning-level rejections flow through and group correctly.

Scope / what this does NOT do

• Does not change the observed marketing-site event — that originates from posthog-js in autter-website-new and needs its own before_send filter plus issue suppression in error tracking.
• This is the in-repo half of the report's proposal: hardening Autter's own SDK against the same noise class. Additive and low-risk.

Verification

• build succeeds; size-limit 1.1 kB (limit 5 kB). tsc --noEmit clean.

Agent context

• Confirmed no competing open PRs/branches/issues on this repo. autter-website-new is not present here, so the posthog-js filter could not be applied in this PR.

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Created with PostHog Desktop from this inbox report.