Claude Code v1.0.120

What: File backup snapshots are now persisted to session logs and restored when resuming previous sessions, preserving the complete file modification history across Claude Code restarts.

How it works:

• During execution, file history snapshots are automatically saved to the session log file
• When resuming a session (e.g., claude --resume <session-id>), backup files from the previous session are hard-linked or copied to the new session directory
• The file history UI state is fully restored, showing which files were tracked and their modification history

Details:

• Session log entries now include a new type: "file-history-snapshot" at insertFileHistorySnapshot() at line 438449
• New function a_1() at line 384641 handles cross-session backup file migration
• New function t11() at line 384611 generates session-specific backup file paths
• New function n_1() at line 384636 processes snapshots to extract tracked files for UI restoration
• Session log class now includes fileHistorySnapshots Map at line 438396
• Backup files are stored per session in ~/.config/claude/file-history/<sessionId>/

What: MCP server configurations can now specify a shell command that generates HTTP headers dynamically at runtime, enabling secure credential management and token rotation.

How to use:

{
  "mcpServers": {
    "my-api": {
      "transport": {
        "type": "sse",
        "url": "https://api.example.com/sse",
        "headers": {
          "X-Static-Header": "value"
        },
        "headersHelper": "~/scripts/get-auth-token.sh"
      }
    }
  }
}

Details:

• The headersHelper command must output valid JSON with string key-value pairs
• Dynamic headers override static headers (merge strategy: {...static, ...dynamic})
• Includes workspace trust security checks for project/local-scoped servers at Xo6() at line 393477
• Comprehensive validation ensures proper JSON format and string values
• Errors are logged with telemetry event tengu_mcp_headersHelper_missing_trust
• Use cases: fetching tokens from credential managers, generating time-based auth, reading secrets from environment-specific sources

What: Network permissions now support Unix domain sockets for local IPC, enabling tools like SSH agents and Docker to work within the sandbox.

How to configure:

{
  "permissions": {
    "network": {
      "allowUnixSockets": true  // Allow all Unix sockets
    }
  }
}

Or with specific paths:

{
  "permissions": {
    "network": {
      "allowUnixSockets": [
        "/var/run/docker.sock",
        "~/.ssh/agent.sock"
      ]
    }
  }
}

Details:

• Three modes: true (allow all), false (block all - default), or array of specific socket paths
• Currently implemented for macOS sandbox profiles using (remote unix-socket) directive
• Essential for Docker, SSH agents, and other development tools requiring local IPC
• Type: boolean | string[]

What: The internal SlashCommand tool now includes comprehensive input validation before execution, catching errors early and providing clear error messages.

Details:

• Validates command format with error code 1 at validateInput() at line 425333
• Checks if command exists with error code 2
• Verifies command can be loaded with error code 3
• Detects disableModelInvocation conflicts with error code 4
• Ensures command is prompt-based with error code 5
• Validation occurs before permission checks, improving error reporting

What: File permission checks now resolve symlinks and verify that BOTH the symlink path AND its target are allowed, preventing permission bypass attacks via symlinks.

How it works:

• When checking read/edit permissions for /home/user/project/link, Claude Code now resolves it to its real path (e.g., /etc/passwd)
• Both paths are checked against permission rules
• Access is denied if EITHER path is restricted

Details:

• New function CD1() at line 339792 returns array of [original_path, resolved_path]
• Helper function fW() at line 339783 performs symlink resolution using realpathSync()
• Integrated into read permissions at o11() at line 439057
• Integrated into edit permissions at dd() at line 439126
• Integrated into working directory checks at QE() at line 438915
• Gracefully handles non-existent files and resolution errors

What: Improved detection of shell variable expansion and command substitution in bash commands for more accurate file path extraction.

Details:

• Now detects patterns like $VARIABLE and $(command) in command arguments at Ng6() at line 382386
• Sets mayHaveUnknownFiles flag when variable expansion is detected
• Prevents false positives in automatic file reading after bash execution
• More conservative approach to file permission pre-approval

What: The filesystem permissions configuration has been completely redesigned with a simplified, asymmetric approach: reads use denylist-only mode, writes use allowlist-only mode.

Old model (v1.0.119):

{
  "permissions": {
    "filesystem": {
      "read": {
        "allowAllExcept": ["/etc/", "/private/"]
      },
      "write": {
        "denyAllExcept": ["/home/user/project/"]
      }
    }
  }
}

New model (v1.0.120):

{
  "permissions": {
    "filesystem": {
      "read": {
        "denyOnly": ["/etc/passwd", "/private/keys/"]
      },
      "write": {
        "allowOnly": ["/home/user/project/"],
        "includeDefaults": true,
        "denyWithinAllow": ["./.claude/"]
      }
    }
  }
}

Key differences:

• Read permissions: Only denyOnly mode (assumes open by default, deny specific paths)
• Write permissions: Only allowOnly mode (assumes closed by default, allow specific paths)
• Lost feature: Can no longer do restrictive read permissions (denyAllExcept for reads is removed)
• New feature: denyWithinAllow allows exceptions within allowed write paths
• Breaking change: Existing v1.0.119 configurations are incompatible

What: Several tools now include explicit outputSchema definitions alongside their existing inputSchema, improving type safety and documentation.

Tools updated:

• Read tool: outputSchema at th6 at line 381201
• Edit tool: outputSchema at yGB at line 395229
• MultiEdit tool: outputSchema at xo6 at line 395850
• Write tool: outputSchema at co6 at line 396008
• Bash tool: outputSchema at np6 at line 387039
• Grep tool: outputSchema at sW5 at line 420771
• WebFetch tool: outputSchema at bW5 at line 417012
• SlashCommand tool: outputSchema at XX5 at line 425324

What: Internal documentation URLs have been updated from docs.anthropic.com to docs.claude.com.

Examples:

• Permissions docs: https://docs.claude.com/en/docs/claude-code/iam#configuring-permissions
• Environment variables: https://docs.claude.com/en/docs/claude-code/settings#environment-variables
• Hooks documentation: https://docs.claude.com/en/docs/claude-code/hooks
• Claude Code docs map: https://docs.claude.com/en/docs/claude-code/claude_code_docs_map.md

What: Two new UI components display information about updates to Anthropic's Consumer Terms and Privacy Policy.

Details:

• Pre-acceptance message function pW5() at line 418651 (effective September 28, 2025)
• Post-acceptance message function iW5() at line 418738
• Includes information about model training opt-in and data retention changes
• Provides links to updated terms, privacy policy, and announcement

What: Session log transcripts now include a fileHistorySnapshots field in addition to existing fields.

Format change:

{
  date, messages, fullPath, value, created, modified,
  firstPrompt, messageCount, isSidechain, leafUuid,
  summary, checkpoints,
  fileHistorySnapshots,  // NEW
  gitBranch
}

What: Removed duplicate condition check in slash command processing that always evaluated to true.

Details:

• Old code at line 1373: if (!0) Y(!0); - condition always true, always executed
• New code at line 1499: Y(!0); - executes directly without redundant check
• No functional change, just cleaner code

What: Changed stream module import from default import to named import for better clarity.

Details:

• Old: import dFQ from "stream"; (line 338181 removed)
• New: import { PassThrough as rr5 } from "stream"; (line 443623 added)
• More explicit about what's being imported
• Better tree-shaking support

What: New cleanup function removes expired file history backup directories based on the configured retention period.

Details:

• Function yr5() at line 442733 removes backup directories older than retention threshold
• Respects cleanupPeriodDays setting from configuration
• Returns statistics: { messages: count, errors: count }
• Integrated into session cleanup routine at rQQ() at line 442760
• Empty directories are removed after cleanup

What: Internal documentation and error message references updated across the codebase.

Details:

• Version updated from 1.0.119 to 1.0.120 in constants
• README URL updated: https://docs.claude.com/s/claude-code
• Issue reporting: https://github.com/anthropics/claude-code/issues

What: Several internal functions were removed as part of the permissions model refactoring.

Removed functions:

• sBB() - Generic allow/deny rule generator (line 374871-374901)
• pBB() - Old read permission default paths (line 374680-374713)
• i9B() - Old bash file path analyzer (line 382301-382346)
• Various permission getter functions: ZQB(), GQB(), YQB(), pb6(), ib6(), JQB() (lines 375215-375242)

Reason: Replaced by new permission model implementation with separate read/write functions.

What: GitHub Actions workflow YAML templates updated (renamed internal variables).

Details:

• Variables wDB and qDB renamed to PDB and jDB
• No functional changes to the workflows themselves
• Both templates remain identical in content

• [x] File history persistence verified as NEW in v1.0.120 (did not exist in v1.0.119)
• [x] Permissions model verified as completely redesigned, not enhanced
• [x] MCP headersHelper verified as NEW functionality
• [x] Symlink resolution verified as NEW security feature
• [x] Unix socket support verified as NEW capability
• [x] All major claims include specific function names and line numbers
• [x] Distinguished between NEW and ENHANCED features
• [x] Excluded internal refactoring with no user impact
• [x] Provided concrete usage examples for new features