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What is Tee Recovery?

When RTK filters command output to save tokens, critical debugging information (stack traces, assertion messages) can be lost. If a command fails, LLM agents may re-run the same command multiple times to retrieve the full output. The tee recovery feature solves this by automatically saving raw, unfiltered output to a file when commands fail. Instead of re-executing the command, the agent reads the saved file — saving tokens and time.

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How It Works

On command failure (exit code ≠ 0), RTK saves the full unfiltered output to ~/.local/share/rtk/tee/ and prints a one-line hint for the LLM to read.
Example workflow: 
rtk cargo test
# Output: ✓ cargo test: 15 passed (1 suite, 0.01s)
# [full output: ~/.local/share/rtk/tee/1707753600_cargo_test.log]
The agent can now read ~/.local/share/rtk/tee/1707753600_cargo_test.log directly instead of running cargo test again.

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File Naming

Tee files use the format: {epoch}_{sanitized_command}.log
  • Epoch timestamp: Sorts files chronologically
  • Sanitized command: Alphanumeric/underscore/hyphen only, truncated at 40 chars
  • Example: 1707753600_cargo_test.log

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Minimum Output Size

Tee skips outputs smaller than 500 bytes — these are short enough to re-run without significant overhead.

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Configuration

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Default Settings

Create or edit ~/.config/rtk/config.toml: 
[tee]
enabled = true          # Enable tee feature
mode = "failures"       # When to save: "failures", "always", or "never"
max_files = 20          # Keep only the last 20 files (oldest auto-deleted)
max_file_size = 1048576 # 1MB max per file (larger outputs truncated)
# directory = "/custom/path"  # Optional: override default location

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Tee Modes

[tee]
mode = "failures"  # Save output only on command failures (exit code != 0)
mode = "always" can consume significant disk space. Use max_files to limit retention.

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Environment Overrides

Environment variables take precedence over config.toml: 
# Disable tee temporarily
RTK_TEE=0 rtk cargo test

# Override output directory
export RTK_TEE_DIR="/tmp/rtk-tee"
rtk cargo test
Priority: RTK_TEE / RTK_TEE_DIR > config.toml > defaults

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File Rotation and Size Limits

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Automatic Cleanup

Tee maintains a fixed number of files (default: 20). When this limit is exceeded:
  1. Files are sorted by timestamp (oldest first)
  2. Oldest files are deleted to maintain the limit
  3. Only .log files in the tee directory are affected
Example: With max_files = 20, if you run 25 failing commands, the first 5 tee files are automatically deleted.

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Size Truncation

Outputs larger than max_file_size (default: 1MB) are truncated: 
{first 1MB of output}

--- truncated at 1048576 bytes ---
This prevents disk exhaustion from extremely verbose commands.

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Supported Commands

Tee recovery is available for these RTK commands:
  • cargo build
  • cargo test
  • cargo clippy
  • cargo check
  • cargo install
  • cargo nextest
  • vitest run
  • pytest
  • go test
  • go build
  • go vet
  • lint (eslint/biome)
  • tsc
  • ruff check
  • ruff format
  • pylint
  • mypy
  • golangci-lint run
  • err <command> — errors/warnings only
  • test <command> — failures only

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Examples

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Example 1: Default Behavior (Failures Only)

# ~/.config/rtk/config.toml
[tee]
mode = "failures"

# Success — no tee file created
rtk cargo build
# Output: ✓ cargo build (0.5s)

# Failure — tee file created
rtk cargo test
# Output: FAILED: 2/15 tests
#   ✗ test_edge_case: assertion failed at src/lib.rs:42
# [full output: ~/.local/share/rtk/tee/1707753600_cargo_test.log]

# Agent reads the file instead of re-running
cat ~/.local/share/rtk/tee/1707753600_cargo_test.log

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Example 2: Always Save Output

# ~/.config/rtk/config.toml
[tee]
mode = "always"
max_files = 50  # Increase retention for always mode

# Every command saves output (success + failure)
rtk cargo test
# [full output: ~/.local/share/rtk/tee/1707753600_cargo_test.log]

rtk cargo build
# [full output: ~/.local/share/rtk/tee/1707753610_cargo_build.log]

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Example 3: Disable Tee Temporarily

# Disable via environment variable
RTK_TEE=0 rtk cargo test
# No tee file created, even on failure

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Example 4: Custom Tee Directory

# ~/.config/rtk/config.toml
[tee]
directory = "/var/log/rtk"

# Or via environment
export RTK_TEE_DIR="/tmp/rtk-tee"
rtk cargo test
# [full output: /tmp/rtk-tee/1707753600_cargo_test.log]

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Example 5: Large Output Truncation

# ~/.config/rtk/config.toml
[tee]
max_file_size = 524288  # 512KB limit

rtk cargo test  # Generates 5MB of output
# Tee file contains first 512KB + truncation notice
cat ~/.local/share/rtk/tee/1707753600_cargo_test.log
# ... 512KB of output ...
# --- truncated at 524288 bytes ---

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Troubleshooting

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Tee Files Not Created

Check tee is enabled: 
rtk config  # Look for [tee] section
Verify mode allows saving: 
[tee]
mode = "failures"  # Must NOT be "never"
Check environment override: 
echo $RTK_TEE  # Should NOT be "0"

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Disk Space Issues

Reduce retention: 
[tee]
max_files = 10       # Keep fewer files
max_file_size = 262144  # 256KB limit
Change directory to larger partition: 
[tee]
directory = "/mnt/large-disk/rtk-tee"

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Tee Hint Not Visible

Tee hints are printed to stdout after the filtered output. If you’re capturing output to a file, check both: 
rtk cargo test 2>&1 | tee output.log
# Check output.log for the hint line

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Implementation Details

Tee failures never affect command output or exit codes. If tee cannot write the file (permissions, disk full, etc.), RTK silently continues without interrupting the user workflow.
From src/tee.rs: 
/// Write raw output to tee file if conditions are met.
/// Returns file path on success, None if skipped/failed.
pub fn tee_raw(raw: &str, command_slug: &str, exit_code: i32) -> Option<PathBuf> {
    // Check RTK_TEE=0 env override (disable)
    if std::env::var("RTK_TEE").ok().as_deref() == Some("0") {
        return None;
    }

    let config = Config::load().ok()?;
    let tee_dir = get_tee_dir(&config)?;
    let tee_dir = should_tee(&config.tee, raw.len(), exit_code, Some(tee_dir))?;

    write_tee_file(raw, command_slug, &tee_dir,
                   config.tee.max_file_size, config.tee.max_files)
}
Key behaviors:
  • Checks RTK_TEE=0 first (fastest exit)
  • Skips outputs < 500 bytes (hardcoded MIN_TEE_SIZE)
  • Respects mode (failures/always/never)
  • Returns None on any error (graceful degradation)

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See Also

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