docs(debug): resolve asyncio nested loop debug session

Root cause: BilibiliExtractor sync wrappers use asyncio.run() internally,
which fails when called from async context in BilibiliAdapter.

Fix: Call async methods directly instead of sync wrappers.

Verified: Human confirmed fix works (bilibili_BV16cNMzpExh)

.planning/debug/resolved/kb-workflow-asyncio-nested-loop.md

@@ -0,0 +1,60 @@
+---
+status: resolved
+trigger: "kb-workflow skill fails to download Bilibili videos with asyncio nested loop error"
+created: 2026-03-15T00:00:00Z
+updated: 2026-03-15T19:00:00Z
+---
+
+## Current Focus
+
+hypothesis: N/A - root cause confirmed and fix verified
+test: Ran kb-workflow process command - metadata extraction succeeded
+expecting: No asyncio nested loop error, successful metadata extraction
+next_action: Await human verification to confirm fix works in their environment
+
+## Symptoms
+
+expected: kb-workflow skill should successfully download Bilibili videos (BV16cNMzpExh)
+actual: Download fails with asyncio nested event loop error
+errors: `asyncio.run() cannot be called from a running event loop`
+reproduction: CLI command (e.g., `/kb-workflow download <url>`)
+started: Never worked properly - this is a new feature with a bug
+
+## Eliminated
+
+<!-- APPEND only -->
+
+## Evidence
+
+- timestamp: 2026-03-15T00:00:01Z
+  checked: kb-workflow/kb_workflow.py line 387
+  found: process_command() calls asyncio.run(run_pipeline()) - this is the outer event loop
+  implication: Creates an async context that all nested code runs within
+
+- timestamp: 2026-03-15T00:00:01Z
+  checked: kb_pipeline/pipeline.py line 106
+  found: Pipeline.run() is an async method that calls await processor.process()
+  implication: All processors run within the async event loop
+
+- timestamp: 2026-03-15T00:00:01Z
+  checked: kb_pipeline/processors/download.py line 66
+  found: DownloadProcessor.process() calls await adapter.fetch_metadata()
+  implication: BilibiliAdapter.fetch_metadata() is called from async context
+
+- timestamp: 2026-03-15T00:00:01Z
+  checked: kb_pipeline/platforms/bilibili.py line 173
+  found: BilibiliAdapter._fetch_metadata_with_retry() calls self._extractor.extract_video_metadata(content_id) which is a SYNC method
+  implication: Calls sync wrapper from async context
+
+- timestamp: 2026-03-15T00:00:01Z
+  checked: kb-bilibili-metadata/bilibili_extractor.py line 91
+  found: BilibiliExtractor.extract_video_metadata() calls asyncio.run(self._extract_video_async(bvid)) - this is the ROOT CAUSE
+  implication: asyncio.run() CANNOT be called when an event loop is already running, causing the nested loop error
+
+## Resolution
+
+root_cause: BilibiliExtractor provides sync wrapper methods (extract_video_metadata, extract_article_metadata, etc.) that use asyncio.run() internally. When BilibiliAdapter.fetch_metadata() (which is async) calls these sync methods, it triggers asyncio.run() from within an already-running event loop, which is forbidden in Python's asyncio model.
+fix: Modified BilibiliAdapter._fetch_metadata_with_retry() to call the underlying async methods directly (await self._extractor._extract_video_async() and await self._extractor._extract_article_async()) instead of the sync wrappers that use asyncio.run()
+verification: Self-verified - ran kb-workflow process command successfully. No asyncio nested loop error. Metadata extracted correctly including title, author, stats, description. Human-verified - user confirmed fix works (bilibili_BV16cNMzpExh executed successfully, asyncio error resolved).
+files_changed:
+  - kb_pipeline/platforms/bilibili.py