[diegosouzapw]

Closes #13894

Root cause

omitOversizedPipeline() / buildMinimalArtifactForSizeLimit() (src/lib/usage/callLogArtifacts.ts) do not drop a size-limited pipeline payload — they write an explicit marker in its place: { error: { _omniroute_truncated: true, reason: "call_log_artifact_size_limit_exceeded" } }, a non-empty object. /api/logs/[id]'s fallback check (!pipelinePayloads || Object.keys(pipelinePayloads).length === 0) never fires on it, so the request never reaches the bounded in-flight preview path the issue's title describes. Instead, RequestLoggerDetail.tsx fed that marker straight into the generic JSON/<pre> renderer under a plain "Pipeline Error" title — indistinguishable from a real upstream error. Same problem for requestBody/responseBody, which get replaced by the [omitted: call log artifact size limit exceeded] string marker and were rendered as raw text.

This PR makes the fallback observable instead of widening any bound: the marker is now detected by shape and rendered as an explicit, labeled notice.

Also fixed a confirmed doc-drift: .env.example documented CHAT_LOG_ARRAY_TAIL_ITEMS=128 / CHAT_LOG_MAX_DEPTH=6, which no longer match src/lib/logEnv.ts's actual defaults (1000 / 20).

Changes

• src/shared/constants/callLogSizeLimitMarkers.ts (new): single source of truth for the size-limit marker shapes (isPipelineSizeLimitMarker, isSizeLimitOmissionMarker), shared between the artifact writer (server-only, fs-dependent) and the client-side detail view.
• src/lib/usage/callLogArtifacts.ts: re-exports isSizeLimitOmissionMarker from the new shared module instead of defining it locally (no behavior change).
• src/shared/components/RequestLoggerDetail.sections.tsx: adds notice support to PayloadSection (renders an explicit "payload omitted — exceeded the call log size limit" box instead of a JSON/<pre> dump) and exports buildPipelinePayloadSections() / isBodySizeLimitOmission() to detect the marker shapes.
• src/shared/components/RequestLoggerDetail.tsx: wires the pipeline/request/response sections through the new helpers (net -1 line — the refactor into buildPipelinePayloadSections() more than pays for the added notice wiring, keeping the file under its 1200-line new-file cap).
• src/i18n/messages/en.json + all 65 other locales: new requestLogger.detail.payload.sizeLimitOmitted key (__MISSING__:-prefixed everywhere but en.json, per the i18n-key convention).
• .env.example: fixed the stale CHAT_LOG_ARRAY_TAIL_ITEMS/CHAT_LOG_MAX_DEPTH doc-drift.

Regression test — RED → GREEN

tests/unit/dashboard/payload-section-size-limit-notice.test.tsx (new, vitest/jsdom, following the existing payload-section-collapsible-json.test.tsx pattern).

• RED: ran the exact same test against origin/release/v3.8.51's copy of RequestLoggerDetail.sections.tsx (via git show) — 6/7 assertions failed: the marker rendered verbatim (_omniroute_truncated visible in the DOM, no payloadSizeLimitOmitted text) and buildPipelinePayloadSections/isBodySizeLimitOmission did not exist.
• GREEN: npx vitest run tests/unit/dashboard/payload-section-size-limit-notice.test.tsx → 7/7 pass against this branch.

Gates run

• node scripts/check/check-file-size.mjs → no new violation (only the pre-existing, unrelated tests/unit/chatcore-translation-paths.test.ts base-red).
• node scripts/check/check-complexity.mjs → OK (2858 ≤ baseline 3218).
• node scripts/check/check-cognitive-complexity.mjs → OK (1291 ≤ baseline 1437).
• npm run typecheck:core → exit 0.
• npm run check:dashboard-typecheck → OK, 206 pre-existing errors, all within frozen baseline (0 new).
• npx eslint --suppressions-location config/quality/eslint-suppressions.json <changed files> → clean.
• node scripts/check/check-changelog-integrity.mjs → OK.
• npm run check:env-doc-sync → confirms the two vars I fixed are no longer flagged; the remaining OMNIROUTE_STRIP_SYSTEM_PREAMBLE/COMBO_LOOP_SAFETY_TIMEOUT_MS mismatches are the pre-existing, unrelated base-red (🔴 Release branch not green: release/v3.8.51 #14004).
• Regression test (above) + existing area tests, all green: tests/unit/dashboard/payload-section-collapsible-json.test.tsx, tests/unit/request-logger-detail-copy-all.test.ts, tests/unit/dashboard/timestamp-titles.test.tsx, tests/unit/ui/request-logger-cache-tokens.test.tsx, tests/unit/ui/issue-7845-log-detail-structured-error.test.tsx, tests/unit/ui/log-detail-conversation-link-12646.test.tsx, tests/unit/request-log-detail-layout.test.ts, tests/unit/request-log-detail-stream.test.ts, tests/unit/request-logger-stream-concatenated-json.test.ts, tests/unit/i18n-hardcoded-ui-regressions.test.ts, tests/unit/log-export-runner.test.ts, tests/unit/call-log-file-rotation.test.ts, tests/unit/call-log-artifact-bodies-first.test.ts, tests/unit/call-log-size-limit-error.test.ts, tests/unit/completed-detail-pipeline-precedence.test.ts (40/40 native + all vitest files).

Scope note

The plan file's lower-priority/optional items were left out of this PR to keep the diff surgical: (1) the route.ts fallback-condition widening (explicitly marked optional/lower-priority — kept additive if ever done, out of scope here), and (2) surfacing CALL_LOG_PIPELINE_MAX_SIZE_KB as a read-only dashboard field next to the pipeline-logging toggle (a separate settings-UI change). Both are UX polish on top of the core fix (the silent fallback is now observable) rather than required for it.

⚠️ base-red inherited: #14004 — docs env/docs contract (fixed separately in #14022), chatHelpers file-size drift