Claude Code v2.1.305 Update Breakdown: Sandbox Isolation and Multi-Platform Compatibility Fixes

A Release Defined by Fixes

Anthropic has shipped Claude Code v2.1.305. Judging from the length composition of the release notes, this is not an update headlined by new features, but rather a concentrated effort to fix problems exposed in real-world usage scenarios. There are only two additions at the environment-variable level, while the vast majority of entries fall under the "Fixed" section, covering modules including cloud platforms like Vertex/Bedrock, self-hosted runners, Cloud sessions, the VS Code extension, Code Review, and Slack integration.

For developers who use Claude Code long-term, the value of this kind of release often exceeds that of feature-stacking updates — it determines whether the tool can run reliably in complex network environments, enterprise gateways, and automated pipelines.

New Capabilities: An Opening for Namespaces in the Linux Sandbox

Giving Sandboxed Commands More System Capabilities

This release adds sandbox.allowNestedUserNamespaces, which allows sandboxed commands on Linux to create user namespaces. The release notes explicitly call out the typical beneficiaries: Chromium and rootless podman. These kinds of applications themselves rely on namespace isolation to run, and previously were blocked by Claude Code's sandbox file protection mechanism.

The positioning of this switch is worth noting. It effectively opens a gap between the "security boundary" and "command usability": once enabled, commands inside the sandbox can bypass some file protection restrictions. In other words, this is an option that users must weigh for themselves, rather than a capability that is enabled by default.

User namespace is an isolation mechanism provided by the Linux kernel that gives processes an independent user ID mapping within the namespace: root inside the namespace can be mapped to an ordinary unprivileged user on the host, thereby enabling operations such as mounting and creating network stacks without real root privileges. Rootless containers (such as rootless podman) and Chromium's sandbox rely on precisely this mechanism to achieve "unprivileged yet isolated" execution. Claude Code's sandbox by default narrows command permissions through file protection and restrictions on namespace creation, so applications that depend on nested user namespaces get blocked. sandbox.allowNestedUserNamespaces effectively explicitly lifts this restriction, at the cost of granting processes inside the sandbox stronger system operation capabilities — users need to decide whether to enable it based on their actual trust boundary.

Usage-Limit Awareness in Unattended Retry Mode

The other new variable, CLAUDE_CODE_RETRY_WATCHDOG_USAGE_LIMIT_RECHECK_MS, serves the unattended retry mode (CLAUDE_CODE_RETRY_WATCHDOG). Its purpose is to let that mode become aware of usage limits that are "lifted before the reset time." For users running long tasks unattended, this avoids unnecessary waiting time.

Key Fixes: From the 2.1.304 Regression to Multi-Platform Compatibility

Fix for the Regression That Caused All Cloud Platform Requests to Fail

This is a fix item with broad impact. The release notes mention that when an endpoint or gateway rejects tool search, or when the gateway forbids ToolSearch and does not include it in --tools, every single request to Vertex, Bedrock, and other providers would fail. This was a regression introduced in 2.1.304. The current handling is that Claude Code will automatically retry without that feature.

For teams accessing Claude through enterprise gateways, this fix directly determines whether the service is usable after upgrading.

Tool search is a capability in Claude Code that lets the model retrieve and select available tools on demand, changing the previous approach of stuffing all tool definitions into the context at once, which helps control token consumption when there are many tools. But this capability requires the endpoint or gateway to support the corresponding request fields and protocol extensions. Enterprise-common Vertex AI, Bedrock, and self-built LLM gateways often validate or whitelist-filter request bodies, and upon encountering an unrecognized field they reject the entire request rather than merely ignoring the feature. This is exactly why the impact of this regression was amplified: a single point of incompatibility gets magnified into "every request fails." The fix's degradation-retry strategy — detecting rejection, then removing tool search and sending again — is a common compatibility-layer approach in cloud vendor adaptation.

Disk Full and MCP Configuration Conflicts

When the disk is full, Bash commands previously threw a raw ENOSPC file path error. Now the error message clearly states that the disk is full and the command was not executed — this kind of "plain-language" error message may seem like a small change, but its impact on troubleshooting efficiency is quite direct.

On the MCP side, a configuration override issue was fixed: servers passed in via setMcpServers from cloud sessions or the SDK were previously replaced later in the session by servers of the same name in the user's own settings. This kind of silent override is a hidden bug that is hard to pin down.

State Consistency of Subagents and Worktrees

Two Git worktree-related behaviors were fixed: creating a new worktree in a bare repository sometimes started from the local HEAD instead of the default branch; unchanged subagent worktrees were sometimes not cleaned up. In addition, after a subagent switched to a fallback model, Claude would incorrectly use it to name that subagent's working model — this issue has also been corrected.

Git worktree allows multiple working directories to be checked out simultaneously on the same repository, each pointing to a different branch and sharing the same object database. It is a common means of parallel development and isolating changes for automated agents: each subagent modifies code in its own worktree without interfering with others. A bare repository has no working tree, only version history, so when creating a worktree on it the starting branch must be explicitly specified; otherwise it easily defaults to the local HEAD rather than the remote default branch. Understanding this helps judge the actual impact of this fix: a wrong worktree starting point causes subagents to work from an outdated code baseline, while failing to clean up unchanged worktrees continuously consumes disk and repository metadata — long-running multi-agent pipelines are especially sensitive to this.

Continuous Polish at the Interaction Level

Improved Usability of /usage and /effort

The diagnostic information from /usage has been restructured into single-line fixable items; each warning indicates its source, and pressing f applies the fix. The same fix also appears in VS Code and /doctor. The issue of /usage lines being truncated in narrow terminals has also been resolved.

The /effort and /autocompact settings previously did not take effect when there was a case difference between the model name and the modelOverrides value, or when a [1m] tag was present; this has now been fixed.

Startup Warnings and Accessibility Improvements

Startup warnings are no longer printed as raw text above the logo, but instead routed to the debug log; permission rules with no actual binding force are now displayed as warning lines below the banner. Screen reader mode fixed how the search box is read — previously VoiceOver would read the symbol as "telephone recorder," but now it clearly reads "Search:"; the issue of spaces appearing inside words in Ctrl+R search matches and highlighted text such as "ultrathink" has also been addressed.

Interaction Adjustments for Remote Control and Artifact Deletion

Remote Control fixed an issue where empty (session) entries remained in the /resume list after switching sessions with /resume. The deletion confirmation for /artifacts has been changed to key 1 to keep, 2 to delete, and Esc to cancel; y and n no longer respond to that dialog — this is a change that will break muscle memory, so watch out for it after upgrading.

Stability of Self-Hosted Runners and Cloud Sessions

Self-hosted runners fixed three issues: startup scripts that share only stdout with the runner or orchestrator reported Resource temporarily unavailable when TERM was set (a 2.1.300 regression); since 2.1.296, repository access failed when a git credential helper or askpass program read settings through GIT_CONFIG; and the orchestrator incorrectly reported a background-started runner as a spawn-runner hook timeout.

On the Cloud sessions side, the cloud environment management page previously refused to save an existing environment with an "installs packages" error; this has now been fixed. The deletion dialog for self-hosted environments has also been improved to clearly explain the blocking reason and scope of impact.

git credential helper and askpass are the two standard paths by which Git obtains credentials: the former is an external program specified by the credential.helper configuration item, responsible for returning the username and password/token to Git when needed; the latter is a graphical or script program specified via GIT_ASKPASS, which answers credential prompts in a terminal-less environment. The GIT_CONFIG environment variable is used to make Git read a configuration file at a specified location, and is often used by self-hosted environments to inject isolated repository configuration. When the runner is started in a way that shares only stdout, and environment variables are trimmed or rewritten, these paths can fail, manifesting as repository access failure rather than an explicit authentication error. This kind of problem is hard to reproduce because it often works fine in an interactive terminal and only surfaces under specific process startup methods.

Detail Corrections in Integration Modules

Claude Tag fixed several issues related to Slack threads: when another routine restarts the conversation in a DM thread, the previously set routine no longer posts; after a thread conversation ends, the routine reports success but actually does not post — now such runs are skipped and the creator is informed. A repository can be re-added after being migrated to another GitHub account. The management page in large organizations can now properly edit plugins, skills, and bundles even while the channel list is loading.

Code Review fixed an issue where, when a PR received multiple pushes during review, it sometimes did not review the latest commit; the review opening logic was also adjusted so that it no longer opens with LGTM when earlier blocking findings remain unresolved.

Summary

The density of fixes in v2.1.305 shows that Claude Code's usage scenarios have become quite dispersed: enterprise gateways, self-hosted infrastructure, IDE plugins, code review pipelines, collaboration platform integrations — any inconsistency in any link gets amplified in real teams. For users, if you previously encountered all requests failing on Vertex/Bedrock or repository access failures on self-hosted runners, this version is worth prioritizing for upgrade.