Add fuzzing for wta

.gitignore

@@ -8,6 +8,12 @@ tools/wta/target*/
 tools/wta/*.excalidraw
 tools/wta/*.png
 
+# Cargo-fuzz artifacts (corpus, crashes, build output)
+tools/wta/fuzz/target/
+tools/wta/fuzz/corpus/
+tools/wta/fuzz/artifacts/
+tools/wta/fuzz/Cargo.lock
+
 # Claude Code local settings
 .claude/settings.local.json
 

build/pipelines/fuzz.yml

@@ -33,20 +33,61 @@
           buildEverything: true
           keepAllExpensiveBuildOutputs: false
 
+  - stage: BuildWtaFuzzer
+    displayName: WTA Rust Fuzzer Build
+    dependsOn: []
+    condition: succeeded()
+    jobs:
+      - job: BuildRustFuzzer
+        pool:
+          ${{ if eq(variables['System.CollectionId'], 'cb55739e-4afe-46a3-970f-1b49d8ee7564') }}:
+            name: SHINE-INT-L
+          ${{ else }}:
+            name: SHINE-OSS-L
+        steps:
+        - checkout: self
+        - bash: |
+            set -ex
+            msrustup toolchain install ms-nightly
+            cargo +ms-nightly install cargo-fuzz --locked
+          displayName: Install Rust nightly + cargo-fuzz
+        - bash: |
+            set -ex
+            cd tools/wta
+            cargo +ms-nightly fuzz build cmdline_builder \
+              --config .cargo/intelligent_terminal_feed.toml
+          displayName: Build WTA fuzz targets
+        - bash: |
+            set -ex
+            # cargo-fuzz outputs to tools/wta/fuzz/target/<triple>/release/
+            cp tools/wta/fuzz/target/x86_64-pc-windows-msvc/release/cmdline_builder.exe \
+               $(Build.ArtifactStagingDirectory)/WtaCmdlineFuzzer.exe
+          displayName: Stage fuzzer artifact
+        - task: PublishPipelineArtifact@1
+          displayName: Publish WTA fuzzer
+          inputs:
+            targetPath: $(Build.ArtifactStagingDirectory)/WtaCmdlineFuzzer.exe
+            artifactName: wta-fuzzer
+
   - stage: Submit
     displayName: Submit to OneFuzz
-    dependsOn: [Build]
+    dependsOn: [Build, BuildWtaFuzzer]
     condition: succeeded()
     jobs:
       - job:
         pool:
           vmImage: 'ubuntu-latest'
         steps:
         - task: DownloadPipelineArtifact@2
-          displayName: Download artifacts
+          displayName: Download C++ fuzzer artifacts
           inputs:
             artifactName: build-x64-Fuzzing
             downloadPath: $(Build.ArtifactStagingDirectory)
+        - task: DownloadPipelineArtifact@2
+          displayName: Download WTA fuzzer artifact
+          inputs:
+            artifactName: wta-fuzzer
+            downloadPath: $(Build.ArtifactStagingDirectory)
         - task: UsePythonVersion@0
           inputs:
             versionSpec: '3.x'
@@ -77,3 +118,9 @@
           env:
             target_exe_path: $(Build.ArtifactStagingDirectory)/ProtocolFuzzer.exe
             test_name: ProtocolServerParsing
+        - bash: |
+            onefuzz template libfuzzer basic --colocate_all_tasks --vm_count 1 --target_exe $target_exe_path --notification_config @./build/Fuzz/notifications-ado.json OpenConsole $test_name $(Build.SourceVersion) default
+          displayName: Submit OneFuzz Job — WtaCmdlineFuzzer
+          env:
+            target_exe_path: $(Build.ArtifactStagingDirectory)/WtaCmdlineFuzzer.exe
+            test_name: WtaCmdlineBuilder

tools/wta/Cargo.toml

@@ -8,6 +8,10 @@ description = "Windows Terminal Agent — ACP TUI client / MCP tool server"
 name = "wta"
 path = "src/main.rs"
 
+[lib]
+name = "wta"
+path = "src/lib.rs"
+
 [dependencies]
 agent-client-protocol = { version = "0.10", features = ["unstable_session_model"] }
 tokio = { version = "1", features = ["full"] }

tools/wta/fuzz/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "wta-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+arbitrary = { version = "1", features = ["derive"] }
+
+[dependencies.wta]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "cmdline_builder"
+path = "fuzz_targets/cmdline_builder.rs"
+doc = false

tools/wta/fuzz/fuzz_targets/cmdline_builder.rs

@@ -0,0 +1,55 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+// Fuzz target for WTA's commandline builder.
+//
+// This exercises build_wt_commandline with arbitrary (command, args) pairs
+// generated by the Arbitrary trait, looking for panics and correctness
+// violations in the quoting/escaping logic.
+
+#![no_main]
+
+use arbitrary::Arbitrary;
+use libfuzzer_sys::fuzz_target;
+use wta::build_wt_commandline;
+
+/// Structured fuzz input: a command string and a list of arguments.
+#[derive(Arbitrary, Debug)]
+struct FuzzInput {
+    command: String,
+    args: Vec<String>,
+}
+
+fuzz_target!(|input: FuzzInput| {
+    // Skip degenerate inputs that would make the test noisy
+    if input.command.is_empty() {
+        return;
+    }
+    if input.args.len() > 64 {
+        return;
+    }
+
+    let result = build_wt_commandline(&input.command, &input.args);
+
+    // Basic sanity checks — these catch escaping failures:
+
+    // 1. The result must start with the command
+    assert!(
+        result.starts_with(&input.command),
+        "Commandline doesn't start with command: {:?} -> {:?}",
+        input.command,
+        result
+    );
+
+    // 2. The result must not be empty if the command is non-empty
+    assert!(!result.is_empty());
+
+    // 3. No null bytes should appear (would truncate the commandline)
+    if !input.command.contains('\0') && !input.args.iter().any(|a| a.contains('\0')) {
+        assert!(
+            !result.contains('\0'),
+            "Null byte injected into commandline: {:?}",
+            result
+        );
+    }
+});

tools/wta/src/lib.rs

@@ -0,0 +1,12 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+// Library target for WTA — exposes functions needed by fuzz targets
+// and tests without pulling in the full binary's module tree.
+//
+// Only the pure-logic functions are re-exported here. Modules with
+// runtime dependencies (wt_channel, app, protocol) stay in main.rs.
+
+mod shell_fuzz;
+
+pub use shell_fuzz::build_wt_commandline;

tools/wta/src/shell/shell_manager.rs

@@ -7,6 +7,11 @@ use tokio::process::Command;
 
 use super::wt_channel::WtChannel;
 
+// Import the commandline builder from the shared fuzz-target module.
+#[path = "../shell_fuzz.rs"]
+mod shell_fuzz;
+use shell_fuzz::build_wt_commandline;
+
 /// Configuration for creating a new terminal.
 pub struct TerminalConfig {
     pub command: String,
@@ -115,19 +120,8 @@ impl ShellManager {
         let id = self.next_id();
         let wt = self.wt()?;
 
-        // Build the commandline string: "command arg1 arg2 ..."
-        let mut cmdline = config.command.clone();
-        for arg in &config.args {
-            cmdline.push(' ');
-            // Quote args containing spaces
-            if arg.contains(' ') {
-                cmdline.push('"');
-                cmdline.push_str(arg);
-                cmdline.push('"');
-            } else {
-                cmdline.push_str(arg);
-            }
-        }
+        // Build the commandline string for WT pane creation
+        let cmdline = build_wt_commandline(&config.command, &config.args);
 
         // Create a new tab in WT with the command
         let mut params = serde_json::Map::new();

tools/wta/src/shell_fuzz.rs

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+// Pure functions extracted from shell_manager for fuzzing.
+// This module is compiled into the library target only and has
+// no dependencies on the binary-specific module tree.
+
+/// Build a commandline string from a command and its arguments for WT pane
+/// creation. This is the string passed to `create_tab`'s `commandline` param.
+///
+/// # Security note
+///
+/// This function is a fuzz target — the quoting must be robust against
+/// agent-supplied strings containing shell metacharacters.
+pub fn build_wt_commandline(command: &str, args: &[String]) -> String {
+    let mut cmdline = command.to_string();
+    for arg in args {
+        cmdline.push(' ');
+        // Quote args containing spaces or double quotes
+        if arg.contains(' ') || arg.contains('"') {
+            cmdline.push('"');
+            // Escape embedded double quotes by doubling them
+            for ch in arg.chars() {
+                if ch == '"' {
+                    cmdline.push('"');
+                }
+                cmdline.push(ch);
+            }
+            cmdline.push('"');
+        } else {
+            cmdline.push_str(arg);
+        }
+    }
+    cmdline
+}