Claude Code v2.1.163: Hooks, TMPDIR, and Session Fixes
This update covers smarter lifecycle hooks that can return structured context directly to the model, making stop-phase workflows cleaner for testing and automation. It also fixes temporary directory handling for local builds and improves session ID propagation for stdio MCP servers when using resume and continue flows.
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Chapter 1
Claude Code v2.1.163 Hook Control and Sandbox Fixes
Lachlan Reed
Welcome to the show everybody! I'm Lachlan Reed, here with James Turner for a quick v2.1.163 update for Claude Code, and first, a quick shoutout to Jellypod for helping us bring you these daily logs. Now, James, let's talk about the developer hooks in this patch. Claude's `Stop` and `SubagentStop` lifecycle hooks can now return JSON payload objects containing `hookSpecificOutput.additionalContext`.
James Turner
Wait, [curious] so instead of a hook execution being a binary pass-fail where a non-zero exit code throws an error and halts execution, the hook itself can now directly feed JSON structured runtime data right back into the model's context window?
Lachlan Reed
Spot on, mate! It keeps the model's turn running completely uninterrupted. Think of it like a developer's guardrail that doesn't just trip the breaker but actually whispers, "Hey, here is what you need to fix," right in the middle of a transaction.
James Turner
That is incredibly clean for automated testing or linting runs during a stop phase. But speaking of environments, what is the story with this `$TMPDIR` fallback logic? I saw it was breaking local Bazel builds and EDR-monitored Go compilation.
Lachlan Reed
Oh, absolute nightmare for local builds. [chuckles] Basically, Claude Code was aggressively overriding the system temporary directory fallback to `/tmp/claude-{uid}` across the board. Now, they've restricted that override *strictly* to isolated sandbox environments.
James Turner
Ah, [measured] because security agents like Endpoint Detection and Response—EDR—and hermetic build systems like Bazel expect very specific, deterministic paths for compiler operations. If Claude Code is forcing `/tmp/claude-{uid}` on a non-sandboxed host machine, the Go compiler or Bazel's sandboxed actions just fall over.
Lachlan Reed
Exactly! It was tripping security policies and breaking caching. If you're building locally now, your standard `$TMPDIR` is respected. Finally, there's the session propagation fix. The environmental variable `CLAUDE_CODE_SESSION_ID` now propagates consistently to stdio Model Context Protocol servers.
James Turner
And this specifically fixes the state loss when developers use the `--resume` or `--continue` flags, right? Previously, standard Bash and hook scripts kept the session ID, but stdio MCP servers were left in the dark about who was talking to them after a session restart.
Lachlan Reed
Spot on. Now those stdio MCP servers can seamlessly track state and authorize actions across resumed sessions without skipping a beat. That's a wrap on v2.1.163. Catch you next time!