diff --git a/src/lint_cmd.rs b/src/lint_cmd.rs
index 15f3fed..a7f6c71 100644
--- a/src/lint_cmd.rs
+++ b/src/lint_cmd.rs
@@ -525,7 +525,7 @@ fn filter_mypy_output(output: &str) -> String {
 }
 
 /// Filter generic linter output (fallback for non-ESLint linters)
-fn filter_generic_lint(output: &str) -> String {
+pub(crate) fn filter_generic_lint(output: &str) -> String {
     let mut warnings = 0;
     let mut errors = 0;
     let mut issues: Vec<String> = Vec::new();
diff --git a/src/main.rs b/src/main.rs
index bc46fdd..a2240c0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -47,6 +47,7 @@ mod utils;
 mod vitest_cmd;
 mod wc_cmd;
 mod wget_cmd;
+mod yarn_cmd;
 
 use anyhow::{Context, Result};
 use clap::{Parser, Subcommand};
@@ -434,6 +435,13 @@ enum Commands {
         args: Vec<String>,
     },
 
+    /// Yarn workspace commands with filtered output
+    Yarn {
+        /// Yarn arguments (workspace <pkg> [run] <script> [args...])
+        #[arg(trailing_var_arg = true, allow_hyphen_values = true)]
+        args: Vec<String>,
+    },
+
     /// Curl with auto-JSON detection and schema output
     Curl {
         /// Curl arguments (URL + options)
@@ -1392,6 +1400,10 @@ fn main() -> Result<()> {
             }
         }
 
+        Commands::Yarn { args } => {
+            yarn_cmd::run(&args, cli.verbose, cli.skip_env)?;
+        }
+
         Commands::Ruff { args } => {
             ruff_cmd::run(&args, cli.verbose)?;
         }
@@ -1542,4 +1554,84 @@ mod tests {
             _ => panic!("Expected Git Commit command"),
         }
     }
+
+    #[test]
+    fn test_yarn_workspace_basic() {
+        let cli =
+            Cli::try_parse_from(["rtk", "yarn", "workspace", "@server", "run", "test"]).unwrap();
+        match cli.command {
+            Commands::Yarn { args } => {
+                assert_eq!(args, vec!["workspace", "@server", "run", "test"]);
+            }
+            _ => panic!("Expected Yarn command"),
+        }
+    }
+
+    #[test]
+    fn test_yarn_workspace_scoped_package_with_slash() {
+        let cli = Cli::try_parse_from(["rtk", "yarn", "workspace", "@myorg/server", "run", "lint"])
+            .unwrap();
+        match cli.command {
+            Commands::Yarn { args } => {
+                assert_eq!(args, vec!["workspace", "@myorg/server", "run", "lint"]);
+            }
+            _ => panic!("Expected Yarn command"),
+        }
+    }
+
+    #[test]
+    fn test_yarn_workspace_without_run() {
+        let cli =
+            Cli::try_parse_from(["rtk", "yarn", "workspace", "@server", "test", "--coverage"])
+                .unwrap();
+        match cli.command {
+            Commands::Yarn { args } => {
+                assert_eq!(args, vec!["workspace", "@server", "test", "--coverage"]);
+            }
+            _ => panic!("Expected Yarn command"),
+        }
+    }
+
+    #[test]
+    fn test_yarn_workspace_extra_args() {
+        let cli = Cli::try_parse_from([
+            "rtk",
+            "yarn",
+            "workspace",
+            "@server",
+            "run",
+            "vitest",
+            "--reporter=verbose",
+            "--coverage",
+        ])
+        .unwrap();
+        match cli.command {
+            Commands::Yarn { args } => {
+                assert_eq!(
+                    args,
+                    vec![
+                        "workspace",
+                        "@server",
+                        "run",
+                        "vitest",
+                        "--reporter=verbose",
+                        "--coverage"
+                    ]
+                );
+            }
+            _ => panic!("Expected Yarn command"),
+        }
+    }
+
+    #[test]
+    fn test_yarn_workspace_simple_package() {
+        let cli =
+            Cli::try_parse_from(["rtk", "yarn", "workspace", "server", "run", "build"]).unwrap();
+        match cli.command {
+            Commands::Yarn { args } => {
+                assert_eq!(args, vec!["workspace", "server", "run", "build"]);
+            }
+            _ => panic!("Expected Yarn command"),
+        }
+    }
 }
diff --git a/src/runner.rs b/src/runner.rs
index 6ae6599..7b8b522 100644
--- a/src/runner.rs
+++ b/src/runner.rs
@@ -160,7 +160,7 @@ fn filter_errors(output: &str) -> String {
     result.join("\n")
 }
 
-fn extract_test_summary(output: &str, command: &str) -> String {
+pub(crate) fn extract_test_summary(output: &str, command: &str) -> String {
     let mut result = Vec::new();
     let lines: Vec<&str> = output.lines().collect();
 
diff --git a/src/tsc_cmd.rs b/src/tsc_cmd.rs
index 5fabb6d..bd244da 100644
--- a/src/tsc_cmd.rs
+++ b/src/tsc_cmd.rs
@@ -60,7 +60,7 @@ pub fn run(args: &[String], verbose: u8) -> Result<()> {
 }
 
 /// Filter TypeScript compiler output - group errors by file, show every error
-fn filter_tsc_output(output: &str) -> String {
+pub(crate) fn filter_tsc_output(output: &str) -> String {
     lazy_static::lazy_static! {
         // Pattern: src/file.ts(12,5): error TS2322: Type 'string' is not assignable to type 'number'.
         static ref TSC_ERROR: Regex = Regex::new(
diff --git a/src/yarn_cmd.rs b/src/yarn_cmd.rs
new file mode 100644
index 0000000..ac1c951
--- /dev/null
+++ b/src/yarn_cmd.rs
@@ -0,0 +1,704 @@
+use crate::parser::{FormatMode, OutputParser, ParseResult, TokenFormatter};
+use crate::tee;
+use crate::tracking;
+use crate::{lint_cmd, prettier_cmd, runner, tsc_cmd, vitest_cmd};
+use anyhow::{Context, Result};
+use regex::Regex;
+use std::process::Command;
+
+/// Filter yarn output - strip boilerplate, keep meaningful content.
+///
+/// Strips: YN-prefixed info lines, resolution/fetch/link progress,
+/// empty lines, and yarn classic boilerplate (defensive).
+/// Returns "ok checkmark" if all output was boilerplate.
+pub(crate) fn filter_yarn_output(output: &str) -> String {
+    lazy_static::lazy_static! {
+        // YN0000-prefixed info lines from yarn berry (with or without arrow prefix)
+        static ref YN_PREFIX: Regex = Regex::new(r"^[\u{27a4}\u{2794}]?\s*YN\d{4}:").unwrap();
+        // Yarn classic version header: "yarn run v1.22.19"
+        static ref CLASSIC_VERSION: Regex = Regex::new(r"^yarn run v\d").unwrap();
+        // Yarn classic done message: "Done in 3.42s."
+        static ref CLASSIC_DONE: Regex = Regex::new(r"^Done in \d").unwrap();
+    }
+
+    let mut result = Vec::new();
+
+    for line in output.lines() {
+        let trimmed = line.trim();
+
+        // Skip empty/whitespace-only lines
+        if trimmed.is_empty() {
+            continue;
+        }
+
+        // Skip yarn berry YN-prefixed info lines
+        if YN_PREFIX.is_match(trimmed) {
+            continue;
+        }
+
+        // Skip resolution/fetch/link progress from workspace-tools
+        if trimmed.starts_with("Resolution step")
+            || trimmed.starts_with("Fetch step")
+            || trimmed.starts_with("Link step")
+        {
+            continue;
+        }
+
+        // Skip yarn classic boilerplate (defensive)
+        if CLASSIC_VERSION.is_match(trimmed) {
+            continue;
+        }
+        if CLASSIC_DONE.is_match(trimmed) {
+            continue;
+        }
+        if trimmed.starts_with("info ") {
+            continue;
+        }
+
+        result.push(line.to_string());
+    }
+
+    if result.is_empty() {
+        "ok \u{2713}".to_string()
+    } else {
+        result.join("\n")
+    }
+}
+
+/// Which specialized filter to apply to captured yarn workspace output
+enum FilterRoute {
+    /// runner::extract_test_summary (generic test runner -- jest/cargo/pytest/go)
+    TestRunner,
+    /// vitest_cmd::VitestParser::parse (three-tier vitest parser)
+    Vitest,
+    /// lint_cmd::filter_generic_lint (text-based warning/error extraction)
+    Lint,
+    /// tsc_cmd::filter_tsc_output (TypeScript errors grouped by file/code)
+    Tsc,
+    /// prettier_cmd::filter_prettier_output (files needing formatting)
+    Prettier,
+}
+
+/// Prefix exclusions -- compound scripts that should NOT match their prefix route.
+/// These are explicitly excluded because their output format differs from what
+/// the prefix route's filter expects (e.g., test:e2e is likely Playwright, not jest).
+const PREFIX_EXCLUSIONS: &[&str] = &["test:e2e", "test:playwright", "test:cypress", "lint:fix"];
+
+/// Route a yarn workspace script name to a specialized filter.
+///
+/// Priority: prefix exclusions > exact match > prefix match > None (passthrough).
+/// Per locked decision: exact match only, hardcoded table, no fuzzy/alias matching.
+fn route_script(script: &str) -> Option<FilterRoute> {
+    // 1. Check prefix exclusions first (block known-bad prefix matches)
+    if PREFIX_EXCLUSIONS.contains(&script) {
+        return None;
+    }
+
+    // 2. Exact matches (highest priority)
+    match script {
+        "vitest" => return Some(FilterRoute::Vitest),
+        "typecheck" | "tsc" => return Some(FilterRoute::Tsc),
+        "prettier" | "format" => return Some(FilterRoute::Prettier),
+        "lint" => return Some(FilterRoute::Lint),
+        "test" => return Some(FilterRoute::TestRunner),
+        _ => {}
+    }
+
+    // 3. Prefix matches (lower priority, after exclusions)
+    if script.starts_with("test:") {
+        return Some(FilterRoute::TestRunner);
+    }
+    if script.starts_with("lint:") {
+        return Some(FilterRoute::Lint);
+    }
+
+    None
+}
+
+/// Apply a specialized filter to boilerplate-stripped yarn output.
+///
+/// Returns (filtered_output, tracking_label).
+/// On filter panic or empty-output, falls back to clean_stdout with stderr warning (graceful degradation).
+fn apply_filter(
+    route: FilterRoute,
+    clean_stdout: &str,
+    package: &str,
+    script: &str,
+    verbose: u8,
+) -> (String, String) {
+    let clean_owned = clean_stdout.to_string();
+    let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| match route {
+        FilterRoute::Vitest => {
+            let mode = FormatMode::from_verbosity(verbose);
+            let parse_result = vitest_cmd::VitestParser::parse(clean_stdout);
+            let filtered = match parse_result {
+                ParseResult::Full(data) => data.format(mode),
+                ParseResult::Degraded(data, _warnings) => data.format(mode),
+                ParseResult::Passthrough(raw) => raw,
+            };
+            (filtered, "vitest (via yarn workspace)".to_string())
+        }
+        FilterRoute::Tsc => {
+            let filtered = tsc_cmd::filter_tsc_output(clean_stdout);
+            (filtered, "tsc (via yarn workspace)".to_string())
+        }
+        FilterRoute::Lint => {
+            let filtered = lint_cmd::filter_generic_lint(clean_stdout);
+            (filtered, "lint (via yarn workspace)".to_string())
+        }
+        FilterRoute::Prettier => {
+            let filtered = prettier_cmd::filter_prettier_output(clean_stdout);
+            (filtered, "prettier (via yarn workspace)".to_string())
+        }
+        FilterRoute::TestRunner => {
+            let cmd_hint = format!("yarn workspace {} run {}", package, script);
+            let filtered = runner::extract_test_summary(clean_stdout, &cmd_hint);
+            (filtered, "test (via yarn workspace)".to_string())
+        }
+    }));
+
+    match result {
+        Ok((filtered, label)) => {
+            // Empty-output guard: if filter produced empty but input was non-empty,
+            // the filter ate everything -- fall back to passthrough
+            if filtered.is_empty() && !clean_owned.is_empty() {
+                eprintln!(
+                    "[RTK] Filter returned empty output for '{}', falling back to stripped output",
+                    script
+                );
+                (clean_owned, "yarn workspace (passthrough)".to_string())
+            } else {
+                (filtered, label)
+            }
+        }
+        Err(_) => {
+            eprintln!(
+                "[RTK] Filter panicked for '{}', falling back to stripped output",
+                script
+            );
+            (clean_owned, "yarn workspace (passthrough)".to_string())
+        }
+    }
+}
+
+pub fn run(args: &[String], verbose: u8, skip_env: bool) -> Result<()> {
+    // Expect: workspace <pkg> [run] <script> [extra_args...]
+    if args.is_empty() || args[0] != "workspace" {
+        anyhow::bail!("Usage: rtk yarn workspace <pkg> [run] <script> [args...]");
+    }
+
+    if args.len() < 3 {
+        anyhow::bail!("Usage: rtk yarn workspace <pkg> [run] <script> [args...]");
+    }
+
+    let package = &args[1];
+
+    // Determine script name and extra args
+    // args[2] is either "run" (skip it, take script from args[3]) or the script name directly
+    let (script, extra_args) = if args[2] == "run" {
+        if args.len() < 4 {
+            anyhow::bail!("Missing script name after 'run'");
+        }
+        (&args[3], args[4..].to_vec())
+    } else {
+        (&args[2], args[3..].to_vec())
+    };
+
+    let timer = tracking::TimedExecution::start();
+
+    // Always use explicit "run" when constructing the command to avoid ambiguity
+    let mut cmd = Command::new("yarn");
+    cmd.arg("workspace").arg(package).arg("run").arg(script);
+    for arg in &extra_args {
+        cmd.arg(arg);
+    }
+
+    if skip_env {
+        cmd.env("SKIP_ENV_VALIDATION", "1");
+    }
+
+    let extra_args_str = extra_args.join(" ");
+
+    if verbose > 0 {
+        eprintln!(
+            "Running: yarn workspace {} run {} {}",
+            package, script, extra_args_str
+        );
+    }
+
+    let output = cmd
+        .output()
+        .context("Failed to run yarn workspace command")?;
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    let raw = format!("{}\n{}", stdout, stderr);
+
+    let exit_code = output.status.code().unwrap_or(1);
+
+    // Early exit on failure: skip filter routing, show raw output
+    if !output.status.success() {
+        if !stdout.is_empty() {
+            print!("{}", stdout);
+        }
+        if !stderr.is_empty() {
+            eprint!("{}", stderr);
+        }
+
+        // Tee raw output for recovery
+        if let Some(hint) = tee::tee_and_hint(&raw, "yarn_workspace", exit_code) {
+            println!("{}", hint);
+        }
+
+        // Track with failure label
+        let original_cmd = format!(
+            "yarn workspace {} run {} {}",
+            package, script, extra_args_str
+        );
+        timer.track(&original_cmd, "rtk yarn workspace (failed)", &raw, &raw);
+
+        std::process::exit(exit_code);
+    }
+
+    // Step 1: Strip yarn boilerplate (filters see clean output)
+    let clean_stdout = filter_yarn_output(&stdout);
+
+    // Step 2: Route to specialized filter or passthrough
+    // Guard: if boilerplate stripping consumed everything, skip routing
+    let (filtered, tracking_label) = if clean_stdout == "ok \u{2713}" {
+        (
+            clean_stdout.clone(),
+            "yarn workspace (passthrough)".to_string(),
+        )
+    } else {
+        match route_script(script) {
+            Some(route) => apply_filter(route, &clean_stdout, package, script, verbose),
+            None => (
+                clean_stdout.clone(),
+                "yarn workspace (passthrough)".to_string(),
+            ),
+        }
+    };
+
+    // Tee raw output for recovery on failure
+    let final_output = if let Some(hint) = tee::tee_and_hint(&raw, "yarn_workspace", exit_code) {
+        format!("{}\n{}", filtered, hint)
+    } else {
+        filtered.clone()
+    };
+
+    println!("{}", final_output);
+
+    // Pass stderr through as-is to stderr
+    if !stderr.is_empty() {
+        eprint!("{}", stderr);
+    }
+
+    // Track with routing-aware labels
+    let original_cmd = format!(
+        "yarn workspace {} run {} {}",
+        package, script, extra_args_str
+    );
+    let rtk_cmd = format!("rtk yarn {}", tracking_label);
+    timer.track(&original_cmd, &rtk_cmd, &raw, &final_output);
+
+    // Preserve exit code -- must be AFTER tracking and printing
+    if !output.status.success() {
+        std::process::exit(exit_code);
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn count_tokens(text: &str) -> usize {
+        text.split_whitespace().count()
+    }
+
+    #[test]
+    fn test_filter_yarn_output_clean() {
+        // Input with actual tool output (no boilerplate) -> output unchanged
+        let input = "PASS src/auth.test.ts\n\
+                      Test Suites: 1 passed, 1 total\n\
+                      Tests:       5 passed, 5 total\n\
+                      Snapshots:   0 total\n\
+                      Time:        2.341 s";
+        let result = filter_yarn_output(input);
+        assert!(result.contains("PASS src/auth.test.ts"));
+        assert!(result.contains("Tests:       5 passed, 5 total"));
+        assert!(result.contains("Time:        2.341 s"));
+    }
+
+    #[test]
+    fn test_filter_yarn_output_yn_prefix() {
+        // Input with YN0000-prefixed lines mixed with real output -> YN lines stripped
+        let input = "\u{27a4} YN0000: \u{2502} ESLint is enabled\n\
+                      \u{27a4} YN0000: \u{2502} Browserslist: loading config\n\
+                      Compiling TypeScript...\n\
+                      \u{27a4} YN0000: Done\n\
+                      Build succeeded with 0 errors";
+        let result = filter_yarn_output(input);
+        assert!(!result.contains("YN0000"));
+        assert!(result.contains("Compiling TypeScript..."));
+        assert!(result.contains("Build succeeded with 0 errors"));
+    }
+
+    #[test]
+    fn test_filter_yarn_output_resolution_steps() {
+        // Input with resolution/fetch/link progress -> stripped
+        let input = "Resolution step 1/3\n\
+                      Fetch step 2/3\n\
+                      Link step 3/3\n\
+                      All dependencies linked successfully";
+        let result = filter_yarn_output(input);
+        assert!(!result.contains("Resolution step"));
+        assert!(!result.contains("Fetch step"));
+        assert!(!result.contains("Link step"));
+        assert!(result.contains("All dependencies linked successfully"));
+    }
+
+    #[test]
+    fn test_filter_yarn_output_empty_after_filter() {
+        // Input with only boilerplate and empty lines -> returns "ok checkmark"
+        let input = "\u{27a4} YN0000: Done\n\
+                      \n\
+                      \n\
+                      Resolution step 1/1\n\
+                      ";
+        let result = filter_yarn_output(input);
+        assert_eq!(result, "ok \u{2713}");
+    }
+
+    #[test]
+    fn test_filter_yarn_output_classic_boilerplate() {
+        // Input with yarn classic patterns -> stripped
+        let input = "yarn run v1.22.19\n\
+                      info Visit https://yarnpkg.com/en/docs/cli/run\n\
+                      $ vitest run\n\
+                      PASS src/utils.test.ts\n\
+                      Tests: 3 passed\n\
+                      Done in 4.21s.";
+        let result = filter_yarn_output(input);
+        assert!(!result.contains("yarn run v1.22.19"));
+        assert!(!result.contains("info Visit"));
+        assert!(!result.contains("Done in 4.21s."));
+        assert!(result.contains("$ vitest run"));
+        assert!(result.contains("PASS src/utils.test.ts"));
+        assert!(result.contains("Tests: 3 passed"));
+    }
+
+    #[test]
+    fn test_filter_yarn_output_mixed() {
+        // Complex input mixing boilerplate + real output + empty lines
+        let input = "\u{27a4} YN0000: \u{2502} Resolution step\n\
+                      Resolution step 1/2\n\
+                      \n\
+                      yarn run v1.22.19\n\
+                      \n\
+                      \u{27a4} YN0000: \u{2502} @server/api (vitest)\n\
+                      \n\
+                      PASS src/api/auth.test.ts\n\
+                      PASS src/api/users.test.ts\n\
+                      \n\
+                      Test Suites: 2 passed, 2 total\n\
+                      Tests:       12 passed, 12 total\n\
+                      Snapshots:   0 total\n\
+                      Time:        3.891 s, estimated 5 s\n\
+                      \n\
+                      \u{27a4} YN0000: Done in 5s 123ms\n\
+                      Done in 5.12s.\n\
+                      info Visit https://yarnpkg.com/en/docs/cli/run";
+        let result = filter_yarn_output(input);
+        // Should NOT contain any boilerplate
+        assert!(!result.contains("YN0000"));
+        assert!(!result.contains("Resolution step"));
+        assert!(!result.contains("yarn run v1.22.19"));
+        assert!(!result.contains("Done in 5.12s."));
+        assert!(!result.contains("info Visit"));
+        // Should contain all real test output
+        assert!(result.contains("PASS src/api/auth.test.ts"));
+        assert!(result.contains("PASS src/api/users.test.ts"));
+        assert!(result.contains("Test Suites: 2 passed, 2 total"));
+        assert!(result.contains("Tests:       12 passed, 12 total"));
+        assert!(result.contains("Time:        3.891 s, estimated 5 s"));
+    }
+
+    #[test]
+    fn test_filter_yarn_output_token_savings() {
+        // Verify filter achieves measurable reduction on realistic mixed input
+        let input = "\u{27a4} YN0000: \u{2502} resolution starting\n\
+                      \u{27a4} YN0000: \u{2502} resolution completed\n\
+                      Resolution step 1/3\n\
+                      Fetch step 2/3\n\
+                      Link step 3/3\n\
+                      \n\
+                      \u{27a4} YN0000: \u{2502} @myorg/server (vitest run)\n\
+                      \n\
+                      yarn run v1.22.19\n\
+                      info Visit https://yarnpkg.com/en/docs/cli/run\n\
+                      \n\
+                      RUN  v1.2.0 src/\n\
+                      \n\
+                      PASS src/auth.test.ts (3 tests)\n\
+                      PASS src/users.test.ts (5 tests)\n\
+                      \n\
+                      Test Files  2 passed (2)\n\
+                      Tests       8 passed (8)\n\
+                      Duration    1.23s\n\
+                      \n\
+                      \u{27a4} YN0000: Done in 3s 456ms\n\
+                      Done in 3.46s.";
+        let output = filter_yarn_output(input);
+
+        let input_tokens = count_tokens(input);
+        let output_tokens = count_tokens(&output);
+
+        let savings = 100.0 - (output_tokens as f64 / input_tokens as f64 * 100.0);
+        assert!(
+            savings >= 40.0,
+            "Yarn filter: expected >=40% savings on mixed boilerplate, got {:.1}% (input={}, output={})",
+            savings,
+            input_tokens,
+            output_tokens
+        );
+    }
+
+    // --- Routing tests ---
+
+    #[test]
+    fn test_route_script_exact_matches() {
+        assert!(matches!(route_script("vitest"), Some(FilterRoute::Vitest)));
+        assert!(matches!(route_script("typecheck"), Some(FilterRoute::Tsc)));
+        assert!(matches!(route_script("tsc"), Some(FilterRoute::Tsc)));
+        assert!(matches!(
+            route_script("prettier"),
+            Some(FilterRoute::Prettier)
+        ));
+        assert!(matches!(
+            route_script("format"),
+            Some(FilterRoute::Prettier)
+        ));
+        assert!(matches!(route_script("lint"), Some(FilterRoute::Lint)));
+        assert!(matches!(
+            route_script("test"),
+            Some(FilterRoute::TestRunner)
+        ));
+    }
+
+    #[test]
+    fn test_route_script_unknown_returns_none() {
+        assert!(route_script("build").is_none());
+        assert!(route_script("dev").is_none());
+        assert!(route_script("start").is_none());
+        assert!(route_script("custom-script").is_none());
+        assert!(route_script("deploy").is_none());
+    }
+
+    #[test]
+    fn test_route_script_prefix_matching() {
+        // test: prefix routes to TestRunner
+        assert!(matches!(
+            route_script("test:unit"),
+            Some(FilterRoute::TestRunner)
+        ));
+        assert!(matches!(
+            route_script("test:integration"),
+            Some(FilterRoute::TestRunner)
+        ));
+        // lint: prefix routes to Lint
+        assert!(matches!(
+            route_script("lint:check"),
+            Some(FilterRoute::Lint)
+        ));
+        assert!(matches!(route_script("lint:ci"), Some(FilterRoute::Lint)));
+    }
+
+    #[test]
+    fn test_route_script_prefix_exclusions() {
+        // These should NOT route despite matching a prefix
+        assert!(route_script("test:e2e").is_none());
+        assert!(route_script("test:playwright").is_none());
+        assert!(route_script("test:cypress").is_none());
+        assert!(route_script("lint:fix").is_none());
+    }
+
+    // --- apply_filter integration tests ---
+
+    #[test]
+    fn test_apply_filter_vitest_produces_label_and_output() {
+        let vitest_text = " Test Files  2 passed (2)\n\
+                            Tests  13 passed (13)\n\
+                            Duration  1.23s";
+        let (filtered, label) =
+            apply_filter(FilterRoute::Vitest, vitest_text, "@server", "vitest", 0);
+        assert_eq!(label, "vitest (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Filter should produce non-empty output"
+        );
+    }
+
+    #[test]
+    fn test_apply_filter_tsc_produces_label_and_output() {
+        let tsc_text = "src/api.ts(10,5): error TS2322: Type 'string' is not assignable to type 'number'.\n\
+                         src/api.ts(20,5): error TS2345: Argument of type 'number' is not assignable.";
+        let (filtered, label) = apply_filter(FilterRoute::Tsc, tsc_text, "@server", "typecheck", 0);
+        assert_eq!(label, "tsc (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Filter should produce non-empty output"
+        );
+        // Filter groups by file and adds headers -- verify it processed the errors
+        assert!(
+            filtered.contains("TS2322") || filtered.contains("TypeScript"),
+            "Filter should contain structured tsc output"
+        );
+    }
+
+    #[test]
+    fn test_apply_filter_lint_produces_label_and_output() {
+        let lint_text = "src/utils.ts:10: warning - Unexpected any.\n\
+                          src/api.ts:20: error - Missing return type.";
+        let (filtered, label) = apply_filter(FilterRoute::Lint, lint_text, "@server", "lint", 0);
+        assert_eq!(label, "lint (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Filter should produce non-empty output"
+        );
+    }
+
+    #[test]
+    fn test_apply_filter_prettier_produces_label_and_output() {
+        let prettier_text = "Checking formatting...\n\
+                              src/utils.ts\n\
+                              src/api.ts\n\
+                              Code style issues found.";
+        let (filtered, label) = apply_filter(
+            FilterRoute::Prettier,
+            prettier_text,
+            "@server",
+            "prettier",
+            0,
+        );
+        assert_eq!(label, "prettier (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Filter should produce non-empty output"
+        );
+    }
+
+    #[test]
+    fn test_apply_filter_test_runner_produces_label_and_output() {
+        let jest_text = "PASS src/auth.test.ts\n\
+                          FAIL src/users.test.ts\n\
+                          Test Suites: 1 failed, 1 passed, 2 total\n\
+                          Tests:       1 failed, 5 passed, 6 total";
+        let (filtered, label) =
+            apply_filter(FilterRoute::TestRunner, jest_text, "@server", "test", 0);
+        assert_eq!(label, "test (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Filter should produce non-empty output"
+        );
+    }
+
+    #[test]
+    fn test_ok_checkmark_guard_skips_routing() {
+        // When filter_yarn_output returns "ok checkmark" (all boilerplate),
+        // routing should be skipped
+        let all_boilerplate = "\u{27a4} YN0000: Done\n\
+                                Resolution step 1/1";
+        let clean = filter_yarn_output(all_boilerplate);
+        assert_eq!(clean, "ok \u{2713}");
+        // In the run() flow, this would skip route_script entirely
+    }
+
+    #[test]
+    fn test_filter_then_route_integration() {
+        // Simulate full flow: yarn boilerplate + vitest text output
+        let yarn_vitest_output = "\u{27a4} YN0000: \u{2502} @server/api (vitest)\n\
+                                   Resolution step 1/1\n\
+                                   \n\
+                                   Test Files  1 passed (1)\n\
+                                   Tests  5 passed (5)\n\
+                                   Duration  450ms\n\
+                                   \n\
+                                   \u{27a4} YN0000: Done in 2s";
+        // Step 1: strip boilerplate
+        let clean = filter_yarn_output(yarn_vitest_output);
+        assert!(!clean.contains("YN0000"));
+        assert!(clean.contains("Test Files"));
+
+        // Step 2: route
+        let route = route_script("vitest");
+        assert!(matches!(route, Some(FilterRoute::Vitest)));
+
+        // Step 3: apply filter -- assert on label and non-empty output
+        let (filtered, label) = apply_filter(route.unwrap(), &clean, "@server", "vitest", 0);
+        assert_eq!(label, "vitest (via yarn workspace)");
+        assert!(
+            !filtered.is_empty(),
+            "Vitest filter should produce non-empty output from cleaned input"
+        );
+    }
+
+    // --- Early-exit on failure tests ---
+
+    #[test]
+    fn test_failed_command_should_not_route_to_filter() {
+        // Simulates what happens when yarn fails with "script not found"
+        // The error text passes through filter_yarn_output (it's not boilerplate)
+        // and then would be routed to tsc_cmd which returns misleading success
+        let yarn_error = "Usage Error: Couldn't find a script named \"typecheck\"";
+        let clean = filter_yarn_output(yarn_error);
+        // The error message survives boilerplate stripping (correct)
+        assert!(
+            clean.contains("Couldn't find a script"),
+            "Error message should survive boilerplate filtering"
+        );
+        assert_ne!(
+            clean, "ok \u{2713}",
+            "Error message should NOT become ok checkmark"
+        );
+        // This is why early-exit is needed: without it, this error text
+        // would be sent to tsc_cmd::filter_tsc_output which returns
+        // "TypeScript compilation completed" -- masking the error
+        let misled = tsc_cmd::filter_tsc_output(&clean);
+        assert!(
+            misled.contains("TypeScript compilation completed") || misled.contains("TypeScript"),
+            "Without early-exit, tsc filter masks yarn errors with success message"
+        );
+    }
+
+    #[test]
+    fn test_successful_command_still_routes_through_filters() {
+        // Simulate successful tsc output wrapped in yarn boilerplate
+        let yarn_tsc_output = "\u{27a4} YN0000: \u{2502} Starting tsc\n\
+                               src/api.ts(10,5): error TS2322: Type 'string' is not assignable to type 'number'.\n\
+                               src/api.ts(20,3): error TS2345: Argument of type 'number' is not assignable.\n\
+                               Found 2 errors in 1 file.\n\
+                               \u{27a4} YN0000: Done in 2s";
+        // Step 1: strip boilerplate
+        let clean = filter_yarn_output(yarn_tsc_output);
+        assert!(!clean.contains("YN0000"), "Boilerplate should be stripped");
+        assert!(
+            clean.contains("TS2322"),
+            "TSC errors should survive stripping"
+        );
+
+        // Step 2: route
+        let route = route_script("typecheck");
+        assert!(matches!(route, Some(FilterRoute::Tsc)));
+
+        // Step 3: apply filter (would only happen if command succeeded)
+        let (filtered, label) = apply_filter(route.unwrap(), &clean, "@server", "typecheck", 0);
+        assert_eq!(label, "tsc (via yarn workspace)");
+        assert!(
+            filtered.contains("TS2322"),
+            "TSC filter should preserve error codes"
+        );
+    }
+}