feat(code): add built-in thread inspector skill

libs/code/deepagents_code/built_in_skills/deepagents-thread-inspector/SKILL.md

@@ -0,0 +1,50 @@
+---
+name: deepagents-thread-inspector
+description: Inspect and explain conversations in the local Deep Agents Code SQLite session store. Use as a fallback when LangSmith trace tooling is unavailable, for offline or untraced sessions, or when asked to identify or summarize a local dcode thread, inspect checkpoint metadata, list recent local threads, or parse ~/.deepagents/.state/sessions.db and a thread UUID or prefix.
+license: MIT
+compatibility: designed for deepagents-code
+---
+
+# Deep Agents Thread Inspector
+
+If LangSmith tooling is available for a traced thread, prefer it. Otherwise, use `scripts/inspect_sessions.py` instead of manually decoding database blobs. It opens the database read-only and deserializes the root message channel with LangGraph's strict MsgPack loader — reading the materialized messages from the latest checkpoint, or replaying writes in checkpoint order when that fast path is unavailable — and emits JSON.
+
+## Inspect local state
+
+Resolve `SKILL_DIR` to the directory containing this `SKILL.md`; do not assume a user, project, or installation-specific location. Start with the smallest useful view:
+
+```bash
+python3 "$SKILL_DIR/scripts/inspect_sessions.py" THREAD_ID --mode latest-turn
+```
+
+A unique thread-ID prefix is accepted. Select another view when needed:
+
+```bash
+python3 "$SKILL_DIR/scripts/inspect_sessions.py" THREAD_ID --mode summary
+python3 "$SKILL_DIR/scripts/inspect_sessions.py" THREAD_ID --mode transcript
+```
+
+Use `--include-metadata` only when run, repository, model, checkpoint, or LangGraph metadata matters. Use `--max-content N` to raise or lower the default 4,000-character limit per message, tool result, or tool-call argument.
+
+If the user does not know the ID, list recent threads first:
+
+```bash
+python3 "$SKILL_DIR/scripts/inspect_sessions.py" --list 20
+```
+
+Pass `--db PATH` only for a non-default session store. The default is `~/.deepagents/.state/sessions.db`; `DEEPAGENTS_SESSIONS_DB` can override it.
+
+## Explain the result
+
+Synthesize the JSON rather than pasting it verbatim.
+
+- State the user's request, the assistant's conclusion, and significant tool actions or failures.
+- Distinguish stored facts from your interpretation.
+- For the latest turn, describe only the final user message and subsequent activity unless earlier context is required to make it understandable.
+- Mention truncation when a relevant record has `content_truncated` or `args_truncated` set.
+- Surface reconstruction problems when the result includes a top-level `warnings` array (for example, a corrupt checkpoint, a skipped write, or malformed metadata) so conclusions are appropriately hedged.
+- Do not expose unrelated credentials, tokens, personal data, or hidden reasoning that may appear in local records.
+
+## Safety
+
+Keep inspection read-only. Do not deserialize an untrusted database: checkpoint deserialization is intended for trusted local Deep Agents state. Do not mutate or delete session rows unless the user separately and explicitly requests it.