diff --git a/config/quality/file-size-baseline.json b/config/quality/file-size-baseline.json
index e99bbd3d44..fd6df33e3c 100644
--- a/config/quality/file-size-baseline.json
+++ b/config/quality/file-size-baseline.json
@@ -233,10 +233,10 @@
     "src/shared/constants/cliTools.ts": 875,
     "src/shared/constants/pricing.ts": 1662,
     "src/shared/constants/providers.ts": 3276,
-    "src/shared/constants/sidebarVisibility.ts": 1100,
+    "src/shared/constants/sidebarVisibility.ts": 1198,
     "src/shared/services/cliRuntime.ts": 1090,
     "src/shared/validation/schemas.ts": 2523,
-    "src/sse/handlers/chat.ts": 1560,
+    "src/sse/handlers/chat.ts": 1575,
     "src/sse/services/auth.ts": 2336,
     "open-sse/executors/default.ts": 876,
     "open-sse/translator/request/openai-responses.ts": 902,
@@ -337,5 +337,6 @@
   "_rebaseline_2026_06_22_phase4b_slm_tier_ultra": "Compression Phase 4 (B) SLM tier own growth: open-sse/services/compression/strategySelector.ts 783->818 (+35 at the existing applyUltraAsync chokepoint). The no-modelPath ultra branch (previously a one-line passthrough to the sync applyCompression) now runs the two-tier resolver: it adapts the body, builds the ultraConfig (threading config.ultraEngine + preserveSystemPrompt), awaits the now-async ultraCompress (SLM Tier-B when ultraEngine===slm and the worker backend is available, else fail-open to the Tier-A heuristic), and threads result.stats.ultraTier into the returned CompressionStats so the resolved tier reaches the D0 telemetry persister. The sync applyCompression ultra branch is also re-pointed to the new pure ultraCompressHeuristic. The two-tier resolver + the pure heuristic live in open-sse/services/compression/ultra.ts and the thin SLM entry in engines/llmlingua/ultraEntry.ts (both <cap, fully unit-tested); strategySelector.ts is cohesive dispatch wiring at the existing ultra chokepoint, not extractable without hiding the dispatch boundary. Covered by tests/unit/compression/ultra-slm-tier.test.ts (applyCompressionAsync ultraTier:slm) + ultra.test.ts (39 regression) + the integration suites. Structural shrink of this file tracked in #3501.",
   "_rebaseline_2026_06_22_phase4c_adaptive_context_budget": "Compression Phase 4 (C) adaptive context-budget wiring own growth: open-sse/services/compression/strategySelector.ts 818->848 (+30 at the existing selectCompressionPlan dispatch chokepoint). selectCompressionPlan gains an 8th optional `adaptiveOptions` param (modelContextLimit/requestMaxTokens/onAdaptive sink) and, after resolveBasePlan and before the caching-aware pass, runs the PURE resolveAdaptivePlan when config.contextBudget.mode is floor|replace-autotrigger; the new adaptiveEnabled(config) helper also gates the legacy shouldAutoTrigger branch inside resolveBasePlan off when adaptive owns automatic-by-size escalation (D-C4). The escalation ladder, target computation, and the resolver itself live in open-sse/services/compression/adaptiveCompression/{computeTarget,ladder,resolveAdaptivePlan,types}.ts (all <cap, fully unit-tested by Tasks 1-4). strategySelector.ts is cohesive dispatch wiring at the existing compression chokepoint, not extractable without hiding the dispatch boundary, mirroring the prior compression rebaselines (#4217/#4210/phase4b). Covered by tests/unit/compression/adaptive-select-plan-wiring.test.ts (4 tests) + adaptive-chatcore-source-guard.test.ts (2). chatCore.ts also grows ~30 lines at the same call site (threads getTokenLimit(provider,effectiveModel) + request max_tokens into adaptiveOptions and records the adaptive telemetry block onto compression.completed) but stays under its frozen cap. Structural shrink of this file tracked in #3501.",
   "_rebaseline_2026_06_25_rc17_pr_batch": "rc17 PR batch own growth (cohesive, not extractable): responseSanitizer.ts 1103->1122 (+19 = SanitizeOpenAIResponseOptions interface + stripReasoning option, #4678); tokenRefresh.ts 2070->2090 (+20 = codex 401 defense-in-depth unrecoverable-refresh guard, #4686); token-refresh-service.test.ts 1322->1353 (+31 = 401-unfamiliar-payload regression case, #4686); translator-openai-responses-req.test.ts 1047->1050 (+3 = reasoning_effort non-Copilot assertion update, #4688). All are the merged PRs own surgical additions at existing chokepoints.",
-  "_rebaseline_2026_06_25_rc17b_leva2": "rc17 leva2 PR batch own growth (cohesive, not extractable): providerLimits.ts 950->955 (#4786 generalized accesstoken fallback); default.ts NEW frozen entry at 828 (#4729 anthropic-compatible Bearer + #4766 json_schema fallback + #4787 cline workos headers — three provider-specific header branches); openai-to-kiro.ts 807->814 (#4763 Claude-capability image gate); openai-responses.ts 923->937 (#4764 computeFinishReason guard); executor-default-base.test.ts 1339->1440 (#4766 json_schema fallback tests); translator-openai-to-kiro.test.ts 918->980 (#4763 non-Claude image gate tests)."
+  "_rebaseline_2026_06_25_rc17b_leva2": "rc17 leva2 PR batch own growth (cohesive, not extractable): providerLimits.ts 950->955 (#4786 generalized accesstoken fallback); default.ts NEW frozen entry at 828 (#4729 anthropic-compatible Bearer + #4766 json_schema fallback + #4787 cline workos headers — three provider-specific header branches); openai-to-kiro.ts 807->814 (#4763 Claude-capability image gate); openai-responses.ts 923->937 (#4764 computeFinishReason guard); executor-default-base.test.ts 1339->1440 (#4766 json_schema fallback tests); translator-openai-to-kiro.test.ts 918->980 (#4763 non-Claude image gate tests).",
+  "_rebaseline_2026_06_27_v3838_filesize_drift": "Mid-cycle drift on release/v3.8.38 — feature/fix growth from already-merged PRs that the fast-path (PR->release skips check:file-size) let accumulate without a bump. src/shared/constants/sidebarVisibility.ts 1100->1198 (+98 = #3812 colored menu-icon support, per-item accent map across the sidebar entries; #5142 then dropped one orphan settings entry, net still above the frozen). src/sse/handlers/chat.ts 1560->1575 (+15 = #5064 self-inflicted-timeout cooldown skip + #5124 long OpenAI-compatible SSE hardening + #5110 embed-WS LIVE_WS_HOST honour / early empty-message reject). Localized feature/fix code next to existing branches, each covered by its own PR tests; not extractable without hiding the chokepoint. Structural shrink of chat.ts tracked in #3501."
 }