fix(telemetry): record an allowlist of HTTP headers on Maple's Workers - #1453

🟢 Confidence 9/10 · safe to merge
Header capture is a bounded allowlist pinned by tests on both the alchemy bridge and the client path; the tracer fix only narrows when a ResponseError is treated as a rendered 5xx.
_{quality 100/100 · no findings · tests covered · risk medium}

Restores an allowlisted set of HTTP request/response headers on Maple's Worker spans and stops the SDK relabelling a failed response write as a rendered 5xx. Contained to telemetry wiring; safe to merge.

• MapleHttpTracingLive allowlists the request and response headers recorded on HTTP spans
• runtimeTelemetry adds the allowlist to the three Durable Object runtimes via telemetry.layer
• isStatusOnlyResponseError keeps a write-failure ResponseError as its own exception

Before merge

• Manual · Confirm the three prod alerts and five Agent Sessions widgets updated outside the code are live against the new span data

_{4c8b40e · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}