feat: improve channel message chunking boundary quality

docs/plans/state.json

@@ -5363,10 +5363,22 @@
         "docs/plans/state.json"
       ],
       "test_status": "pnpm test:run src/cli/setup/summary.test.ts src/cli/setup/channels.test.ts src/cli/setup/integration.test.ts + pnpm typecheck passing"
+    },
+    "streaming-chunking-quality-tier-b5": {
+      "status": "completed",
+      "date": "2026-02-18",
+      "updated": "2026-02-18",
+      "summary": "Implemented Tier B5 chunking-quality improvements by upgrading shared channel message splitting to prefer natural boundaries (paragraph/newline/sentence/space), while preserving markdown code-fence integrity across multi-part chunks. Added regression coverage for sentence-boundary preference and code-fence balancing.",
+      "files_modified": [
+        "src/channels/utils.ts",
+        "src/channels/utils.test.ts",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/channels/utils.test.ts src/channels/telegram/adapter.test.ts src/channels/discord/adapter.test.ts src/channels/slack/adapter.test.ts src/channels/whatsapp/adapter.test.ts + pnpm typecheck passing"
     }
   },
   "overall_progress": {
-    "total_test_count": 1918,
+    "total_test_count": 1924,
     "all_tests_passing": true,
     "p0_completion": "3/3 (100%)",
     "p1_completion": "4/4 (100%)",
@@ -5386,7 +5398,7 @@
     "gmail_auth_cli": "flynn gmail-auth command implemented with OAuth2 flow, doctor check, config routed to Telegram",
     "native_audio_support": "completed — smart routing for native audio (Gemini/OpenAI/GitHub) vs Whisper transcription fallback",
     "remaining_phases_completion": "Phase 1: 3/3 (100%) — context levels, command registry, memory structure. Phase 2: 3/3 (100%) — component registry, confidence routing, history index. Phase 3: 2/2 (100%) — adaptive memory/compaction, truthfulness/autonomy hardening",
-    "next_up": "Implement Tier B5 streaming chunking quality parity checks"
+    "next_up": "Implement Tier B2 minimal companion app client"
   },
   "soul_md_and_cron_create": {
     "date": "2026-02-11",