Count streamed text/thinking/tool-call deltas incrementally in model diagnostics instead of repeatedly estimating full event payloads. Updates diagnostics docs and OTEL wording for the new response byte baseline.\n\nVerification: node scripts/run-vitest.mjs run src/agents/embedded-agent-runner/run/attempt.model-diagnostic-events.test.ts; GitHub Actions CI run 27064304709; CodeQL run 27064304710; OpenGrep PR Diff run 27064304716.